The Theory of Evolution.

The Theory of Evolution

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Definition Evolution is the slow , gradual change in a population of organisms over time. copyright cmassengale

Charles Darwin is credited with being the father of modern evolutionary theory, though he was not the first person to formulate ideas about how life on earth has changed over time. He was an unusual person to have on board ship in the 1830s. He could read and write well, and was skilled in the use of scientific principles used to gather data on the wide variety of plants and animals they would see during their several year survey of South America and areas of the South Pacific. On these voyages first began to think about how plants and animals had come to have the characteristics they had. For 20 years, Darwin studied nature, and the more he observed, the more convinced he became that the Biblical account of Genesis, which holds that all living things on Earth were created in their original state in the first days of creation, could not be true. Finally, in 1859, Darwin published his beliefs about life on Earth in The Origin of the Species. In this work, Darwin explains a theory about the development of life on Earth that comes to dominate natural science for the next 150 years. Darwin’s argument also became and remains one of the most controversial theories in history.

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HMS Beagle’s Voyage copyright cmassengale

Darwin- Charles Darwin first put forth the idea that living organisms on earth have changed or adapted over periods of millions of years. These changes are believed to have resulted from a process of random genetic mutations that ended up somehow benefiting an organism giving it an advantage over other members of the same species. (In MOST cases, mutations are harmful or even fatal to the organism.) This often resulted in the development of different forms of the same gene. Unique physical characteristics or abilities that allow an organism to survive in its environment are known as adaptations. Eventually, enough changes occurred that entirely new species of organisms developed. This process has been called speciation. Evolutionary scientists cite evidence of evolution in the fossil record, our growing knowledge of genetics, and in comparative observations of modern plants and animals.

Evolutionary theory is broken down into several major ideas:
Organisms have physical characteristics, adaptations, that allow them to survive in their environments. Variations occur within species. We have seen that in our study of genetics. We learned there are different forms of genes resulting from slight mutations over time. If one form of a gene or adaptation gives the organism a survival advantage over other members of the same species, that form of the trait will ultimately win out and be passed on to the offspring. This competition between organisms is known as natural selection: “survival of the fittest.” 4. Over time environmental conditions have changed. Organisms that were unable to adapt to the changes became extinct. 5. Over a period of millions of years, enough changes occur within certain species of organism that an entirely new species results. This is called speciation.

What variations can you observe in these animals?

The Goldenrod Crab Spider has two common color variations
The Goldenrod Crab Spider has two common color variations. How might this be explained by natural selection? The ancient Goldenrod spiders with white or yellow coloring had a survival advantage over those that were a different color in this particular environment. The yellow and white colored spiders survived better and produced more offspring with the yellow and white color trait.

This insect’s adaptation is shape and color. It is a leaf mimic.
Adaptations can be related to size, color, shape, or functionality of a particular body part. What are some of the adaptations for the organism shown here? This insect’s adaptation is shape and color. It is a leaf mimic.

What are some of the adaptations for the organism shown here?

Common Descent 6. Darwin proposed that organisms descended from common ancestors that gradually changed over time into entirely new organisms.

Believed evolutionary process of of horses, elephants, and whales.

It was Darwin’s belief that natural selection could not be “observed by humans” because it took place over such tremendous lengths of time-millions of years in some cases. However, modern examples of variation within populations of organisms of the same genus are used to demonstrate natural selection at work.

In our study of genetics we learned about selective breeding and genetic modification. Both involve humans manipulating breeding to produce desired outcomes. Selective breeding has resulted in the over 400 breeds of dogs we have on earth today. Most domesticated animals and food crops in our world today are a result of selective breeding. When nature “selects” which forms of traits will be passed on, it is referred to as natural selection. When humans manipulate this process and select which desired traits will be passed on, it is known as artificial selection. Artificial selection has resulted in new breeds of organisms, but not in entirely new species of organisms.

How does this process differ from natural selection?
These two animals are different breeds but the same species. What human-engineered process has resulted in the wide differences in these animals? How does this process differ from natural selection?

Commonly Identified Examples of Natural Selection
Darwin’s finches- During his exploration of the Galapagos Islands, Darwin observed that the beaks of the finches differed on many of the islands. Upon closer observation, Darwin concluded that the beak shapes had changed as a result of their surroundings, most importantly the source of food on each island for the finches. The beak shape on each island was the best shape for accessing the type of food finches ate on that island, but would not have been the best shape on one of the other islands. Darwin argued that as the sea level of the earth rose millions of years ago, populations of the original finches were trapped on small islands and became isolated from the other finches by stretches of ocean. Over millions of years, the form of the gene that best served the finches on each of the islands (based on the main food source for finches on each island) “won out” and that form of beak shape became the most common on that particular island.

The same thing appears to hold true in the tortoises living on the different islands of the Galapagos as well.

Peppered Moth- In Europe prior to the Industrial Revolution (1800’s), Peppered moths generally had a light, ashy color and blended well with the light colored bark of local oak trees. However, as more coal was burned in homes and factories throughout Europe, the trees became darkened with coal soot. The light colored moths stood out more and became easy prey for predatory birds. However, some of the moths had a different form of the gene for coloring and were darker. This form of the gene became favored in that forest. The darker form of the gene “won out” against the lighter form. Darwin called such a process Natural Selection. In other words, nature chose which genetic trait would be favored in a competition between different forms of the same gene.

How Isolation Can Lead to Biological Change
When a population of organisms becomes isolated from others of the same population, one form of a characteristic can become favored over others in this new or changed environment. The “favored” trait is the trait that gives the organism a survival advantage over organisms that do not have this form of a trait. Over time, the “favored” trait may become the trait that becomes the most prominent in the phenotype of the species. The other forms of the gene may disappear completely from that population of organisms.

Populations can become isolated by changes in geography, such as the development of impassable mountain ranges or changes in the water levels in a body of water. Isolation also resulted when continents separated. The Galapagos Islands, Australia, Tasmania, and Madagascar are famous for having species of plants and animals that are unlike any found elsewhere in the world. Remote “islands” like these and smaller islands are showcases for the effects of isolation on a population of organisms.

Lake Tanganyika Cichlids- This African lake is known for its many varieties of cichlids, a tropical fish very common in pet stores around the world. It is believed that all cichlids evolved from one species of cichlid that existed millions of years ago. Geological evidence suggests that during several points in the history of the lake, the water level decreased and a number of smaller lakes existed that were separated by shallow islands that had once been under water. Cichlids that were trapped in these smaller lakes are believed to have evolved and adapted based on the unique conditions of each lake. Forms of genes were favored in some lakes but not others. Eventually entirely new species of cichlids evolved in each of these smaller lakes. When the water levels rose and Lake Tanganyika returned to its previous size (millions of years later), the many new species of cichlids were now back in the same body of water, but still inhabited unique zones within the lake.

As the level of the lake dropped, the cichlids became “herded” into smaller sections of water that became isolated from the rest of the lake.

At its lowest level, populations of cichlids became completely isolated from other populations of cichlids. Certain physical traits or adaptations became favored in each new pool. These traits increased the survivability of the cichlids with those traits.

Did the isolation of different populations of cichlids result in the evolution of new physical traits that did not exist within the original cichlids population? Most scientists believe that all the varied forms of genes/traits seen in the several hundred species of African Cichlids were already present in the original population of cichlids.

In the ocean off the northeastern coast of the U. S
In the ocean off the northeastern coast of the U.S., the green crab has become a top predator of young mussels. In some areas, however, scientists found populations of mussels that were unaffected by the crabs. Upon closer examination, scientists discovered that the mussels in this area were able to chemically detect the crabs and in response develop a thicker shell that the crabs could not penetrate. Describe how this is an example of natural selection at work.

Does this change in the mussel population provide evidence of a species evolving a new physical characteristic to adjust to changes in the environment? NO. The form of the gene that resulted in thicker shells was already found in the mussel populations before the predatory crab showed up. However, it was not an advantage and was therefore not favored over the form of the gene that resulted in average shell thickness.

In this experiment, the size of a species of prey fish (guppy) varied depending upon which predator fish was found in the same pool. Larger guppy size became favored because it gave a survival advantage. Smaller guppy size became favored because it gave a survival advantage.

The Brown Anole Lizards of the Bahamas
In a reptilian version of "Survivor," lizards with longer legs ultimately get booted from islands by their short-legged opponents. Countering the widespread view of evolution as an eon-long process, evolutionary biologists discovered that when island lizards were exposed to a new predator, natural selection occurred in a six-month period, first favoring longer and then shorter hind legs. Brown Anoles(Anolis sagrei) lizards spend much of their time on the ground. But as previous studies have shown, when a ground-dwelling, predatory lizard is introduced, the anoles scamper up trees. They switch to an arboreal lifestyle to escape being eaten. Anoles’ long legs make them fast runners, giving them an advantage in a ground-based setting, but one where predators were few. Researchers led by Jonathan Losos of Harvard University studied brown anole populations on 12 small islands in the Bahamas. They introduced a larger, predatory lizard (Leiocephalus carinatus) to six of the islands, while keeping six other control islands predator-free.

The scientists counted, marked and measured lizards at the beginning of the study, after six months, and again after 12 months. After six months, the anole populations dropped by half or more on islands with predators. On predator islands, the anole survivors had longer legs than non-survivors Why do you think longer legs were favored on the islands with the predator lizard? Scientists suggest long legs were favored because longer-legged lizards were faster runners and were better able to elude capture by predators.

Tables turned, however, during the next six months
Tables turned, however, during the next six months. The surviving anoles on the islands with the predatory lizard became increasingly arboreal, spending much of their time in treetops. At the end of the six-month stint, measurements showed surviving anoles had shorter legs compared with non-survivors. (By the way, there was no significant difference in leg length between surviving and non-surviving anoles on the islands with no predators.) So, why do you think shorter Anole legs became favored on the islands with the predatory lizards?

Shorter limbs are better suited for navigating narrow tree branches, which the scientists figure helped the lizards evade becoming dinner. Did this experiment demonstrate the development of a new physical trait based on changes in environmental conditions? No. The short-legged trait already existed within the species. On the island without predators, there was no advantage to having short or long legs, so both traits were found within the Brown Anole population.

Practical Applications

Which of the leaf forms will be favored in this new ecosystem? Why?
A species of flowering plant found on a grassland has different variations of the gene for leaf size. It receives full sunlight all day. Over time the climate of the grassland changes. It receives more precipitation, allowing trees and eventually deciduous forest to grow. As the forest becomes more developed, less sunlight makes it through the canopy to the forest floor. Which of the leaf forms will be favored in this new ecosystem? Why? small medium The larger leaf will allow the plant to capture more sunlight, so it will be favored in the new environment.

Mosquito Control sprays an area with a pesticide to kill a species of mosquito living in that area. She notices later that some of the mosquitoes in the area did not die. A month later she comes back to spray the area again. This time she notices that even more of the mosquitoes survived. What is the most likely explanation for this?

Evolutionary theory does not argue that the form of the gen changed at that moment when the insects were sprayed. Rather, it suggests that a form of the gene resistant to the pesticide already existed within that particular species of insect. Up until the point that the insects were sprayed, there would have been no way of telling that the gene existed.

The New World Squirrel Monkey and an Old World Patas Monkey share many similar physical characteristics yet live on different sides of the world. How might a student of evolution explain this? Before the continents split, the two had a common ancestor. Once the continents moved apart, these diverged into new species.

How might the theory of evolution explain the differences between the red squirrel which lives primarily in the coniferous forests of North America and the grey squirrel which lives primarily in deciduous forests of North America? Red squirrels live in areas where there are more conifers. They blend in with the dead needles on the forest floor and with the bark with has red flakes. The gray squirrel and fox squirrels live in areas where the trunks and branches of trees are more grayish.

Mammoths and mastodons were both elephant-like animals that inhabited earth at the same time. Both became extinct about 10,000 years ago. How might evolutionary theory explain their extinction? There are different theories about why these animals became extinct. Some scientists believe they were hunted into extinction by humans who had developed better weapons. Others believe they were physically not adapted to the new environment that arose after the Ice Age.

Three different species of bear are found in North America
Three different species of bear are found in North America. How might evolutionary theory explain the differences in these species? Certain physical characteristics (like white fur) are favored more in the environments each species of bear is found in.

To a predator, the Scarlet King Snake is indistinguishable from the venomous Coral Snake. This is an example of a type of mimicry. How might evolutionary theory explain the development of the king snake?

Brevard, North Carolina has the only known population of white squirrels on earth (they are actually fox squirrels that have a white form of the gene for fur color.) These are NOT albino animals. Though the population is small compared to the normal colored fox squirrels. How can the continuation of this population be explained when “natural selection” would seem to make them easy targets for predators and therefore cause that form of the gene to become extinct? (Answer on next slide).

They are fed and protected by humans, and since they live in an urban area, there are few predators.

1. Credit for popularizing the theory of species evolution is generally given to
a. Gregor Mendel b. Charles Darwin c. Louis Pasteur d. Marie Curie 2. How was the first “modern” book on evolution, Origin of the Species, accepted by the general public? a. most people where very excited about it because it explained things they had not been able to understand before b. most people just laughed at the idea, but didn’t give it much thought c. the idea of evolution was considered scandalous by most people because of their religious beliefs d. Evolution started being taught in schools within a few years of the release of the book

3. From his observations of the different finch populations on the Galapagos, Darwin concluded a. that different shaped beaks had developed for no apparent reason b. that different shaped beaks had developed based on the particular food sources for finch on each island c. that the finches on all the islands eventually evolved so that all of them had the same beak shape d. that what he had originally thought were species of finches were actually an entirely different genus of birds that were similar to finches 4. The peppered moths of Europe are often cited by evolutionary scientists as examples of (micro)evolution, specifically that certain variations of a gene can become the more favored one if changes occur in an ecosystem. What change reportedly occurred within the peppered moth population? a. the genetic form for darker color became an advantage when the forests of Europe became darkened by coal soot. b. the lighter form of the color gene became favored in areas where the forests of Europe burned and everything turned to the color of ash c. both the lighter and darker form of the color gene were replaced by a greener color that helped the moths blend in more with the leaves of the forest d. all of the above

5. The wide variety of fish known as African cichlid is thought to demonstrate
a. evidence of a transitional species because the ancestors of cichlids were thought to be salamander-like amphibians b. how different variations of a species can evolve when populations of that species become isolated and have to adapt to different habitats c. evidence that over time different species of organisms become more and more alike d. all of the above 6. Which animal’s physical structure indicates it feeds on small worms and crustaceans it pulls from their burrows at low tide? a. b. c. d.

7. In the 18th century, the majority of peppered moths in pre-industrial Europe were light gray with dark spots. During the industrial revolution of the 19th century, wide use of coal covered much of the landscape in dark coal soot. During this time period, early scientists noted that the majority of peppered moths were now much darker. What was their explanation for this change in the peppered moth population? a. The moths became covered with coal soot b. The darker colored moths blended in better with the soot-covered bark on c. trees and were eaten less frequently by predators. c. The darker colored moths developed a bad taste that prevented birds from eating them.

8. Which statement describes a major difference between the birds shown in these images?
a. Their feathers are constructed of different materials b. Their beaks are specialized for the type of food they eat c. The bird on the end has young through live birth d. All of the above

9. Which of the following statements best describes the modern theory of evolution?
a. Physical traits are inherited from parents. Some of these traits provide the offspring with a survival advantage in its environment. b. Physical traits can change over long periods of time. If these changes provide the organism with a survival advantage, they can become permanent. c. Physical traits that do not give an organism a survival advantage can result in extinction. d. All of the above. 10. Physical characteristics that improve an organisms ability to survive in its environment are known as a. repercussions b. adaptations c. refractions d. apparatuses 11. Different forms of the same gene exist within species. Which statement best explains how these different forms are related to an organism’s ability to adapt to its environment? a. If one form of gene gives an organism a survival advantage over the other form, it will most likely become the most commonly expressed phenotype. b. Different forms of the same gene allow organisms to change color, size, or shape during a period of stress or danger c. Even if one form of the gene provides a survival advantage over another, the two will continue to be expressed in equal amounts in the population.

12. The Florida Marsh Hare, Snowshoe Hare, and the Desert Hare are very closely related. Over time, Desert Hares developed much larger ears than the other two species. Which statement most likely explains the difference in the size of the Desert Hare’s ears? a. Marsh and Snowshoe hares eat less so there is less energy available for ear growth b. Large ear size is an adaptation that improves survivability in the desert biome because the ears act as cooling mechanisms. c. Predators in the desert are much quieter, so larger ear size became a survival advantage Marsh Hare Desert Hare Snowshoe Hare

Pollenpeeper

The Fossil Record. Fossils are ancient imprints of organisms found in sedimentary rock. Scientists study this imprints and make a number of inferences about the organism. Some of these inferences are related to evolution. With regards to the fossils of animals, evolutionary scientists compare the bone structure of animals that appear later in the fossil record and with animals that still exist on earth today. Similarities in bone structure allow evolutionary scientists to infer which ancient animals may have been ancestors of later animal species.

Plant fossils do exist, but they are far less common than animal fossils. Why do you think this is?
Hard materials like bone or shells deteriorate more slowly and make better fossil imprints.

Determining the age of fossils is done in two primary ways: absolute dating and relative dating.
The sea urchin and sea anemone polyps on the right have been estimated at 65 million years ago. What can we infer about sea urchins and sea anemones from this data? That they have been around for millions of years.

Relative dating- the age of fossils is determined by the level of sedimentary earth in which they are found. Relative dating may allow researchers to estimate the age of a fossil by comparing it to others found in different levels. Which layer shows the oldest organisms?

Absolute dating- Absolute dating is a process where scientists measure the amount of residual radiation remaining in a fossil to determine its age. All living organisms contain traces of radioactive material. As organic material decays, it leaves behind traces of this radioactive material. All radioactive materials have what is called a half life. A half life is the number of years it takes for half of the original amount of the radiation to disappear. For example, the radioactive isotope Carbon 14 has a half life of 5730 years. The decay of Carbon 14 can be demonstrated in a graph or table format:

Practical Applications

13. Why are animal fossils far more common than plant fossils?
a. animals far outnumbered plants millions of years ago b. bone does not degrade even after millions of years c. hard structures like bone or shell degrade slower and make better fossil imprints d. all of the above 14. This starfish fossil has been estimated at 420 million years old. What can we infer from this? a. There were different species of organisms that looked a lot like starfish 400 million years ago b. Starfish became extinct, but then new species developed again millions of years later c. Starfish have been on earth for a very long time d. All of the above

15. Carbon 14 is a radioactive isotope that has a half-life of 5,730 years. A section of bone from a mammoth that is thought to have contained 8 grams of Carbon-14 when the mammoth died is tested using Carbon 14 technology. The remaining Carbon 14 is slightly less than 1 gram. How long ago did this mammoth live? a. About 5,000 years ago b. About 9,000 years ago c. About 18,000 years ago d. About 30,000 years ago

16. In the past several years, scientists have unearthed a number of fossil remains of giant crocodiles in areas of the Sahara Desert. What can we most likely infer from these fossils? a. Large crocodiles at one point in history were able to survive on land much the way tortoises are able to do today b. Central Africa experienced a massive flood millions of years ago that carried animal and plant remains far into the Sahara Desert c. The Sahara Desert was once a wet, swampy region. 17. In the natural world, what is the explanation for how new species arise? a. Two separate species, for instance a kangaroo and a koala bear mate to produce a new species b. Different forms of the same gene, mutations, and differences in environmental factors can cause one population to adapt in a different way than another. c. If an animal changes during its lifetime, for example a bird loses a wing in an accident, it may then go on to produce an entire species of one winged birds.

18. Many species of bacteria become resistant to antibiotics that used to destroy them. What is the best explanation for this? a. the bacteria are able to intentionally mutate to make themselves resistant to the antibiotic b. the bacteria evolve into an entirely new type of bacteria c. natural variations in the DNA of the bacteria have resulted in resistance in some. This trait is passed on to daughter bacteria. d. all of the above 19. Which is an adaptation that enables an animal to live in a cold environment? ability to hibernate ability to migrate c. thick fur and a layer of fat d. all of the above

20. Which statement best reflects a general principle of evolution?
a. All organisms will eventually change and adapt to their environments b. Organisms that are the “fittest” or best adapted to their environment will survive and reproduce c. Most organisms will intentionally mutate in order to adapt to their environment d. All of the above 21. Mrs. Sahr sprayed the dandelions in his yard with an organic weed killer. Most of the dandelions died, but a few were unaffected by the weed killer. How might this be explained using evolutionary theory? a. The spray was not mixed well, which means the concentration used on some plants was weak b. The surviving dandelions were able to adapt once they were sprayed and were able to repel the weed killer c. Variations within the dandelion population have resulted in some of them being immune to that type of weed killer.

22. A flounder’s shape and color pattern allow it to remain blended in with the bottom so it can ambush prey fish. This is an example of a mimicry adaptation b. camouflage adaptation c. protective coloration adaptation

23. The Arctic Fox changes from gray to white during the winter
23. The Arctic Fox changes from gray to white during the winter. How does this adaptation benefit the fox? a. It allows it to absorb more warmth from the sun in the middle of the Arctic winter b. It allows it to run faster because its winter coat is lighter than its summer coat c. It allows it to stalk its prey without being seen as easily d. All of the above

24. In terms of the theory of natural selection, why do African elephants have such large ears?
a. Elephants with the larger ears were able to find more food when food was scarce, so that trait was passed on over time. b. Elephants with larger ears were able to hear predators better, so that trait was passed on over time c. Elephants with larger ears were able to stay cooler during periods of extreme heat, so that trait was passed on over time. d. All of the above

a. The fish in each layer are completely different species
25. A scientist found a number of fossils of the same species of fish in Layer B. She dug deeper and found more fossils of fish in Layer A that were slightly different than those found in Layer B. What is the most likely explanation for the slight differences between the two sets of fossils? a. The fish in each layer are completely different species b. The fish is Layer B changed into the fish in Layer A. c. The fish in both layers were the same species that had adapted to slight changes in their environment.

With regards to the fossils of animals, evolutionary scientists compare the bone structure of animals that appear later in the fossil record and with animals that still exist on earth today. Similarities in bone structure allow evolutionary scientists to infer which ancient animals may have been ancestors of later animal species.

One commonly referred to comparison is the leg and foot of a modern horse to those of animals who are thought to be ancient horse ancestors.

Similarities in theorized camel ancestors.

Elephants….

The horse, camel, and elephant ancestry seems to make sense to many people, even some who are skeptical of evolution. Other fossils bone structure comparisons have resulted in ancestry models that are more difficult to accept. One of these is ancestry model for Orca (Killer Whales.)

According to one ancestry model, Orca is shown to have descended from a small, canine-like animal called mesonychids.

Pakicetus is argued to be the stage of Orca evolution where the ancestor first started spending time in water.

The Ambulocetus link is argued to be the point where the land ancestors of Orca started to become aquatic.

Dalanistes was fully aquatic and had finned appendages.

Rhodocetus lost its two hand appendages and had a tail fin.

Dorudon had front flippers.

From there, whales are thought to have diverged into baleen whales like the humpback and blue whale
and into toothed whales like dolphins, sperm whales, and Beluga whales (the Killer Whale is the largest member of the dolphin family.)

Once again, similarities in bone structure is what scientists used to build the partial ancestry of Orca.

Determining the Family Tree

Scientists build diagrams known as cladograms to represent their beliefs about how organisms have changed or evolved over time. For example: This cladogram demonstrates that the Jobaria is more closely related to the Camarasaurus than the Shunosaurus is because the split appears in more recent time. The top represents the most recent point in time. Each branching area represents a point of major evolutionary change, where one species begins to develop into two or more new species and eventually new phyla. The base represents the furthest point back in time.

a. Salamanders are more closely related to leopards than turtles are.
26. Based on this cladogram, which of the following statements is true? a. Salamanders are more closely related to leopards than turtles are. . Lampreys are more closely related to salamanders than they are to tuna . Salamanders are more closely related to leopards than lampreys are. . All of the above 27. Based on the cladogram, which of the following statements is true? a. the adaptation of hair is a much newer adaption than jaws b. one of the most ancient physical adaptations is a vertebral column c. amphibians have been around longer than reptiles d. all of the above

Transitional Species

Transitional species are ancient organisms that appear to demonstrate the point where one species of organism begins to change into another organism or even where one phylum of organism is changing into another. Evolutionary scientists believe that ancient amphibians, for example, evolved into the first reptiles, the first reptiles into mammals or birds, etc. Most current and perhaps most highly supported example of a transitional species is the recently discovered Tiktaalik roseae. Tiktaalik were an ancient animal that had characteristics that resembled the head of a crocodile and the body of a lobed fish.

Fish to amphibian to reptile?

Archaeopteryx- a transitional species in the evolutionary progression from small raptor dinosaurs to modern birds? Many scientists think so. Many don’t. One of the big questions is whether the archaeopteryx was a “feathered” dinosaur or a bird. There is a lot of division in the scientific world over the biological makeup of the archaeopteryx. Most scientists today agree Archaeopteryx was a bird, but they also believe is a transitional species between dinosaurs and birds.

Vestigial Structures Vestigial structures are structures such as a human’s wisdom teeth, and tail bone or an ostrich’s wings that no longer serve their original purpose in the organism. Most evolutionary scientists argue that all structures in an organism must have a function or must have had a function in earlier forms of the organism. The coccyx or “tail bone” is argued to be the vestigial remains of a tail. The human appendix has no known function.

All whales and dolphins have pelvis bones that are not attached to any other part of the skeleton and have no apparent function. It is argued that they are “left over” from the days when whale ancestors walked on four legs.

Homologous Structures-
Remember that the prefix homo means “same.” Homologous structures are similar structures such as a bones that appear in a number of different species of animals. For example, in the diagram below shows the basic structure of the limbs of several vertebrates. Notice that all the limbs, whether wings, legs, arms, or flippers are built upon the same basic structure (though not the same size.) The number of bones and the arrangement of bones is what is similar.

Homologous Structures

More Practical Applications

28. Evolutionary theorists often compare the bone structure of the appendages of different animals. What inference do they make from this type of comparison? a. that a similar bone structure (same number and arrangement) in these organisms suggests they had a common ancestor b. though the bones are arranged in the same way, the size differences suggest these organisms cannot have a common ancestor c. No scientific inference can be made from these comparisons

30. According to the fossil record, several hundred million years ago a class of arthropods called trilobites were abundant in the oceans. The fossils over 5,000 different species have been found. Today, there are no known living members of the trilobite class. What most likely happened to them? a. They were overharvested for food by ancient hunters b. They were not able to adapt to global changes and therefore became extinct c. They mutated into an entirely different species

They have gotten larger and developed a hump.
31. According to this evolutionary model for the ancestry of camels, what has happened to the camel over a period of 65 million years? They have gotten larger and developed a hump.

32. According to this chart, which statement is accurate?
African elephants descended from Mastodons whereas Asian Elephants descended from Mammoths. Asian and African Elephants descended from the same common ancestor as mammoths and mastodons (Primeelephas). Mastodons and mammoths were the same species of elephant that lived on different continents All elephants today descended from Mastodons. Mammoth Asian Elephant Primeelephas Mastodon African Elephant

Criticism of Evolution
Fossil evidence demonstrates similarities but by no means progression. What would you need to demonstrate evolutionary progression? Similar genes found across species does not automatically point to a common ancestor because the same gene in different organisms may do something entirely different. In the minds of many millions (billions?) of people, the characteristics of earth (both in the living and nonliving elements) is so enormously complex that it seems to them that the combination of “time” and “chance” could not explain it. Wide speculations are frequently made about fossils. Enormous gaps or missing links in the fossil chains. There is a lack of evidence related to transitional species. The Cambrian Explosion. Using modern scientific timelines, life on Earth was sparse and limited to microscopic bacteria and algae-like organisms for 3-1/2 billion years. But about 530 million years ago, fossil evidence demonstrates a possible explosion of life forms, including the major groups of animals we see today. The Cambrian Explosion does not rule out that significant changes have occurred in plants and animals, but it presents a problem for evolutionists because the number of new species appearing during a relatively short period of time cannot be explained by evolution which takes many more millions of years.

8. In order for evolution to work, there would have had to have been a time when the first life form, a single celled organism, appeared. This organism would have had to become alive through a process known as spontaneous generation. That is, exactly the right elements would have had to, by chance, join together to form amino acids (the basic building block of life.) These amino acids would then, by chance, have to somehow link together into the enormously complex configuration that is RNA or DNA. Then, a number of these RNA/DNA molecules would have had to have, by chance again, somehow hooked up with other RNA/DNA molecules to form a gene. This gene would then have to, by chance , hook up with all the other genes that form to make one chromosome of a single celled organism. Then, this chromosome would also have had to have somehow, by chance, combined with a variety of other chromosomes that would all be needed to make just one single celled organism. Spontaneous Generation theorists believe that all the elements needed for life were present in the ocean billions of years ago, and that a violent burst of energy (from lightening perhaps) forced these elements to combine into the ingredients form life mentioned above. The Spontaneous Generation theory continues to lose support in the scientific world, and there are very few other scientific theories regarding the “first cell” that are considered credible by large numbers of scientists. Many scientists, even those who support the theory of evolution, have concluded that the chance of a living cell generating from non-living components is impossible. 9. New technology has found that the information about certain fossils found in the past was wrong.

So we have seen some very different beliefs about evolution and natural selection.
Which, if any, of Darwin’s ideas might be supported by modern scientific observation and exploration? What evidence did Darwin say could prove evolution? What are some of the problems with the theory of evolution? Do you think our modern understanding of genetics supports, refutes, or has no effect on the theory of evolution? How might the beliefs of a scientist (or any person for that matter) affect his or her interpretation of data or material? If there are so many legitimate arguments against the theory of evolution, why does it continue to be included in school texts and treated by so many science documentaries as though it were fact rather than theory? The other day, I was watching a dinosaur documentary with my daughter. A small reptile that lived (according to the documentary) many millions of years ago scurried across the screen. Scientists believe this reptile had hair, so the narrator of the documentary said, “[This animal] was a link between reptiles and mammals. What is scientifically wrong about this statement?

More Evidence That Life Started in Space Friday , March 14, 2008
Nobody knows how life on Earth began, but the primordial soup likely got a lot of its ingredients from space. Scientists have discovered concentrations of amino acids in two meteorites that are more than 10 times higher than levels previously measured in other similar meteorites. Amino acids are organic molecules that form the backbone of proteins, which in turn build many of the structures and drive many of the chemical reactions inside living cells. The production of proteins is believed to constitute one of the first steps in the emergence of life. Meanwhile, meteorites found on Earth are typically chunks of material created in the solar system's youth. So the finding suggests that the early solar system was far richer in the organic building blocks of life than scientists had thought. The researchers speculate that rocks from space may have spiked Earth's primordial broth. It's an argument that's been made before. In fact, the hypothesis of "panspermia" has been around for more than a century. But the prevalence of amino acids strengthens the reasoning. Scientists already knew amino acids could have formed in some environments on the early Earth, but the presence of these compounds in certain meteorites has led many researchers to look to space as a source. The meteorites used for the study were collected in Antarctica in 1992 and 1995 and held in the meteorite collection at the NASA Johnson Space Center in Houston. Researchers took small samples from three rare CR chondrites, which date from the time of the solar system's formation. The rocks likely came from an asteroid that was long ago shattered. "The amino acids probably formed within the parent body before it broke up," said Conel Alexander of the Department of Terrestrial Magnetism at the Carnegie Institution. "For instance, ammonia and other chemical precursors from the solar nebula, or even the interstellar medium, could have combined in the presence of water to make the amino acids. "Then, after the break up, some of the fragments could have showered down onto the Earth and the other terrestrial planets," he added. "These same precursors are likely to have been present in other primitive bodies, such as comets, that were also raining material onto the early Earth.“ The study will be detailed in the journal Meteoritics and Planetary Science.

Study: Common Ancestor of All Apes Walked Upright
Wednesday, October 10, 2007 By Charles Q. Choi The ancestors of humanity are often depicted as knuckle-draggers, making humans seem unusual in our family tree as "upright apes." Controversial research now suggests the ancestors of humans and the other great apes might have actually walked upright too, making knuckle-walking chimpanzees and gorillas the exceptions and not the rule. In other words, "the other great apes we see now, such as chimps or gorillas or orangutans, might have descended from human-like ancestors," researcher Aaron Filler, a Harvard-trained evolutionary biologist and medical director at Cedars-Sinai Institute for Spinal Disorders in Los Angeles, told LiveScience. Filler analyzed how the spine was assembled in more than 250 living and extinct mammalian species, with some bones dating up to 220 million years old. He discovered a series of changes that suggest walking upright — and not with our knuckles — might actually have been the norm for the ancestors of today's great apes. In most creatures with a backbone, the body is separated roughly in half by a tissue structure that runs in front of the spinal canal. This "horizontal septum" divides the body into a dorsal part (corresponding to the back side of humans), and a ventral part (or the front half). A strange birth defect in what may have been the first direct human ancestor led this septum to cross behind the spinal cord in the lumbar or lower back region — an odd configuration more typical of invertebrates. This would have made horizontal stances inefficient. "Any mammal with this set of changes would only be comfortable standing upright," Filler said. "I would envision this malformed young 'hominiform' — the first true ancestral human — as standing upright from a young age," he added, while the rest of the mutant's family and species continued to walk around "on all fours." This change to an upright posture could have occurred "very abruptly, with just a few shifts in 'homeotic' genes, or ones responsible for how the body plan is laid out," Filler said. The earliest known bipedal apes — those walking on two legs — were thought to date back as far as some 6 million years or so. Now Filler's new findings suggest the earliest upright ape known so far was the extinct hominoid, Morotopithecus bishopi, which lived in Uganda more than 21 million years ago. "Humanity can be redefined as having its origin with Morotopithecus," Filler said. He detailed his findings online Oct. 10 in the journal PLoS ONE. This research pushes back the date for the origins of bipedalism roughly 15 million years, to before the last common ancestor of humans, chimps, gorillas and orangutans, as well as lesser apes such as gibbons. The results match up with recent findings that suggest upright walking might have started before humanity's ancestors even left the trees. "If you look at baby siamangs, which are a kind of gibbon, you'll see them walk bipedally on their own," Filler said. "It's just their natural way of walking. They never knuckle-walk." If bipedalism did evolve 21 million years ago, it more likely evolved to walk in trees than on the ground, said University of Chicago evolutionary anthropologist Russell Tuttle. "Twenty-one million years ago, there were a lot of trees around," he said. Besides Morotopithecus, fossil vertebrae suggest three other upright ape species precede the 6-million-year mark, Filler added. "So you have this fossil evidence for bipedalism, and you have apes such as gibbons," he said. "Perhaps humans represent the primitive condition, and knuckle walkers such as chimps and gorillas are modified." The ancestors of chimps and gorillas might have evolved knuckle-walking as a speedier mode of travel, Filler suggested. If bipedalism did come first, that means gorillas and chimpanzees might have evolved knuckle-walking independently of each other. Future analysis of the genes of those apes could show they came across knuckle-walking in different ways, supporting Filler's ideas. "I am getting the feeling that a revolution in our thinking about the origins of bipedality is now under way," said evolutionary anthropologist Robin Crompton at the University of Liverpool in England.

Real-Time Evolution Seen Among Darwin's Galapagos Finches
Friday , July 14, 2006 By Sara Goudarzi For the first time, scientists have observed in real-time evolutionary changes in one species driven by competition for resources from another. In a mere two decades, one of Charles Darwin's finch species, Geospiza fortis, reduced its beak size to better equip itself to consume small-sized seeds, scientists report in the July 14 issue of the journal Science. The finch once had its own kingdom on the Galapagos island of Daphne Major. It had its pick of seeds to eat. But the arrival of another species of finch about 20 years ago, and additional food competition from a drought on the island in 2003, changed everything. "When there is a severe drought on a small island, natural selection occurs," said study co-author Peter Grant of Princeton University. The new, larger species ate the larger and harder seeds on the island, food that the biggest members of the native finch clan normally ate. "The recent immigrant species had almost eaten the supply of food themselves, so they almost went extinct," Grant said. "The resident species, the species that was there before the new species arrived, underwent a large shift toward small size in beaks." Typically, the small members of the species can't crack the larger seeds. But with the depletion of the larger seeds, the small-beaked population, which could reach the smaller feed and needed less food to meet its daily energy needs, had a better survival rate. This type of evolutionary change is known as character displacement. "It's a very important one in studies of evolution, because it shows that species interact for food and undergo evolutionary change, which minimizes further evolution," Grant said. "It has not been possible to observe the whole process from start to finish in nature." Copyright © 2006 Imaginova Corp. All Rights Reserved. This material may not be published, broadcast, rewritten or redistributed.

Experts: Missing Link in Bird Evolution Found
Friday , June 16, 2006 Dozens of fossils of an ancient loon-like creature that some say is the missing link in bird evolution have been discovered in northwest China. The remains of 40 of the nearly modern amphibious birds, so well-preserved that some even have their feathers, were found in Gansu province, researchers report in Friday's issue of the journal Science. Previously only a single leg of the creature, known as Gansus yumenensis, had been found. "Gansus is a missing link in bird evolution," said Matt Lamanna of the Carnegie Museum of Natural History in Pittsburgh. "Most of the ancestors of birds from the age of dinosaurs are members of groups that died out and left no modern descendants. But Gansus led to modern birds, so it's a link between primitive birds and those we see today," Lamanna, a co-leader of the research team, said in a telephone interview. It was about the size of a modern pigeon, but similar to loons or diving ducks, he explained, and one of the fossils even has skin preserved between the toes, showing that it had webbed feet. "We were lucky far beyond our expectations" in finding these fossils, Hai-lu You of the Chinese Academy of Geological Sciences said at a briefing Thursday. "A world lost for more than 100 million years was being revealed to us," he said. Previously there was a gap between ancient and modern species of birds, and "Gansus fits perfectly into this gap," added Jerald D. Harris of Dixie State College in Utah. "Gansus is the oldest example of the nearly modern birds that branched off of the trunk of the family tree that began with the famous proto-bird Archaeopteryx," said Peter Dodson of the University of Pennsylvania, a co-author of the paper along with Lamanna, You and others. The remains were dated to about 110 million years ago, making them the oldest for the group Ornithurae, which includes all modern birds and their closest extinct relatives. Previously, the oldest known fossils from this group were from about 99 million years ago. The fact that Gansus was aquatic indicates that modern birds may have evolved from animals that originated in aquatic environments, the researchers said. "Our new specimens are extremely well preserved, with some even including feathers," Lamanna said. "Because these fossils are in such good condition, they've enabled us to reconstruct the appearance and relationships of Gansus with a high degree of precision. They provide new and important insight into the evolutionary transformation of carnivorous dinosaurs into the birds we know today." The remains were found in an ancient lake bed near the town of Changma. Researchers split open slabs of mudstone to find them. It was like turning the pages of a book, Lamanna said. "We went to Changma hoping that we'd discover one, maybe two, fragments of fossil birds," he said. "Instead, we found dozens, including some almost complete skeletons with soft tissues. We were successful beyond our wildest dreams." The new fossil material "is remarkable for its excellent preservation and establishes that Gansus is an early member of the Ornithurae. ... The new fossils demonstrate that Gansus clearly is a bird that spent much of its life looking for food in water," commented Hans-Dieter Sues, associate director for research and collections at the Smithsonian's National Museum of Natural History. Gansus is an additional "link in a long chain of intermediate forms between Archaeopteryx, the oldest known bird from the late Jurassic, and modern birds," said Sues, who was not part of Lamanna's research team.

Asteroid Impacts May Have Boosted Evolution
Tuesday , December 18, 2007 By Dave Mosher Space rocks are blamed for a lot of rough times on Earth, from the die-off of most marine animals some 250 million years ago to the disappearance of the dinosaurs 65 million years in the past. A new theory, however, suggests that catastrophic meteorite impacts are linked to an explosion in biodiversity about 470 million years ago, during the Ordovician Period. Within a few million years, the number of trilobite species and scores of other creatures on Earth jumped at least three to four times. Birger Schmitz, a geologist at the University of Lund in Sweden who worked for more than 10 years to help gather evidence backing up the claim, is the first to admit that his group's findings are hard to swallow. "It seems completely at odds with anyone's expectations," Schmitz said, "but you have to remember, for example, that it was at first difficult for many scientists to accept asteroid explanations for the disappearance of the dinosaurs." Schmitz and his colleagues detail their findings in the Dec. 16 advance issue of the journal Nature Geoscience. Smackdown Just before the jolt to Ordovician life, Schmitz said two massive bodies in the asteroid belt between Mars and Jupiter slammed into one another, littering the solar system with rocks ranging in size from comparable to Manhattan Island down to microscopic bits of dust. "Even today, more than 20 percent of the meteorites we see came from this breakup event," Schmitz said. That makes the L-chondrite meteorites, as they're known, the most common kind to rain down on Earth. Such extraterrestrial rocks contain a unique form of radioactive chromium, so Schmitz and his team were able to figure out precisely when, how much and how often the cosmic debris slammed into Earth. "We saw a sudden jump in meteorite material around the time of increased biodiversity," Schmitz said — greater than 100 times more material, in fact. "That's a major event, and an incredible coincidence that I don't think we should ignore," he told LiveScience.com. Schmitz cautioned that while the two events line up in an uncanny way, there is still a lot of work left to do to connect the increased meteorite impacts to inflating biodiversity. "It took us about 15 years to accumulate data for this finding, and it's something that isn't just a computer model or simulation. It's real, tactile evidence," he said of the work, which included slowly acid-dissolving almost a ton of rock collected from around the world to sift out bits of chromium. The scientists compared their meteorite record to layers of fossilized plants and animals, determining that the cosmic smashup happened shortly before the biodiversity boost. "I expect that it will take us another 15 years of playing in the dirt to get there, to find Ordovician impact craters and beds associated with this breakup," he said. Pushing their luck Schmitz isn't certain exactly how pummeling the planet with rocks could cause life to thrive, but he thinks it has something to do with creating new nooks and crannies for life to adapt to in its new environment. "Before the breakup you had primitive animals adapted to rough conditions, so you could say they were prepared for the storm," Schmitz said. Schmitz also explained that evolution is very much "give-and-take," as radiating into new species requires a figurative kick in the shins. "If you push an ecosystem too hard, you'll destroy it," he said. "But for the organisms living on Earth at the time, [the environment] pushed them to adapt and fill new niches. It's like at the university: I tell my students all the time that if we don't push you, you don't evolve." Whether or not the cosmic smashup ultimately caused life on Earth to thrive 470 million years ago, the connection between events in space and life on Earth is intriguing, Schmitz said. "There's much more to be learned how the history of Earth and its life is related to the universe," he said. "We're only in the beginning of exploring that connection." Copyright © 2007 Imaginova Corp. All Rights Reserved. This material may not be published, broadcast, rewritten or redistributed.

Origins of Human Nervous System Found in Sea Sponges
Wednesday, June 06, 2007 By Ker Than That natural bath sponge you use to scrub-a-dub-dub your body might not have a nervous system, but its cells possess many of the genes needed to make one. The surprising discovery, detailed in June 6 issue of the open-access journal PLoS ONE, suggests the evolutionary origins of the nervous system are much older than scientists previously thought. The study found that sponges contain about 25 genes that are very similar to human genes found in the synapses of nerve cells. Synapses are bulb-like connections neurons use to communicate; in humans and many other animals, they play a crucial role in learning and memory. Genes are specific DNA sequences that carry instructions for when, where and how much a certain protein a cell should make. Synapse-like interactions "Sponges are the first animals to branch off compared to the rest of animals. They don't have nervous systems, yet we found they have many of the genes that are used in the synapse of modern humans," said Todd Oakley, an evolutionary biologist at the University of California, Santa Barbara (UCSB), who was involved in the study. Even more surprisingly, the proteins made by the sponge genes were found to interact with one another in ways similar to proteins in human synapses. "Not only do they have [human synapse genes], they also have this signature that they may be functioning in a similar way in the absence of a nervous system, as they do in the presence of one," Oakley told LiveScience. The function of the sponge genes are not clear, but their human counterparts combine to form complex protein "machines" important for synaptic communication, Oakley said. The team's research was made possible by the recent sequencing of the sponge genome, which has yet to be published but is available online. In addition to lacking nervous systems, sponges also don't have internal organs or muscles. Sponges are filter-feeders: They spend most of their lives anchored to sediment or rock. Feeding and the excreting wastes are done with the aid of flowing water. May I borrow that gene? Scientists think the first true neurons and synapses first appeared on Earth more than 600 million years ago in organisms called cnidarians, which today include the hydra, sea anemone and jellyfish. "While sponges do show evidence that their cells can communicate with each other, the nervous system is much more efficient," Oakley said. The researchers speculate that the sponge genes were recycled over evolutionary time, with small modifications, to create the nervous systems of later animals. "Evolution can take these ‘off-the-shelf' components and put them together in new and interesting ways," said study leader Kenneth Kosik, a UCSB neuroscientist. Other genes would also have had to evolve or to have been co-opted to create complex nervous systems, such as our own. Scientists think an estimated 77 to 1,000 genes are important for human synaptic communication, Oakley said. Copyright © 2007 Imaginova Corp. All Rights Reserved. This material may not be published, broadcast, rewritten or redistributed.

Study: Shark Fins, Human Arms Formed by Same Genes
Thursday , July 27, 2006 ADVERTISEMENT The triangular shark fin that sends frightened swimmers scrambling to shore is made using the same genes that help form the arms and legs of humans, a new study reports. Researchers found that about a dozen genes that help give rise to a shark's median fins — those that run along its back and belly — also determine where paired side fins will form on its body. These genes are known to play important roles in the development of paired limbs in humans and other land animals. The genes come from an ancient ancestor shared by sharks and humans. "It shows that this genetic program for building limbs has its origins in the median fin structures of very early vertebrates," or animals with backbones, study leader Martin Cohn of the University of Florida told LiveScience. The study, detailed in the July 27 issue of the journal Nature, also found that the genes are vital for the formation of the ribbon-like fins on the back of lampreys, a primitive jawless fish that does not have paired side fins. Sharks and lampreys belong to groups of fish that diverged many millions of years ago, so the new finding suggests genes important for the development of fins, and eventually limbs, were in place long before the different kinds of fishes evolved and went their separate ways. Copyright © 2006 Imaginova Corp. All Rights Reserved. This material may not be published, broadcast, rewritten or redistributed.

Human Ears Evolved From Ancient Fish Gills
Friday , January 20, 2006 By Bjorn Carey Your ability to hear relies on a structure that got its start as a gill opening in fish, a new study reveals. Humans and other land animals have special bones in their ears that are crucial to hearing. Ancient fish used similar structures to breathe underwater. Scientists had thought the evolutionary change occurred after animals had established themselves on land, but a new look at an old fossil suggests ear development was set in motion before any creatures crawled out of the water. The transition Researchers examined the ear bones of a close cousin of the first land animals, a 370-million-year-old fossil fish called Panderichthys. They compared these structures to those of another lobe-finned fish and to an early land animal and determined that Panderichthys displays a transitional form. In the other fish, Eusthenopteron, a small bone called the hyomandibula developed a kink and obstructed the gill opening, called a spiracle. However, in early land animals such as the tetrapod Acanthostega, this bone has receded, creating a larger cavity in what is now part of the middle ear in humans and other animals. Missing link The new examination of the Panderichthys fossil provides scientists with a critical "missing link" between fish gill openings and ears. "In Panderichthys, it is much more like in tetrapods, where there is no longer such a 'kink' and the spiracle has widened and opened up," study co-author Martin Brazeau of Uppsala University in Sweden told LiveScience. "[The hyomandibula] is quite a bit shorter, but still fairly rod-like, like in Eusthenopteron. It's like a combination of fish and tetrapods." However, it's unclear if early tetrapods used these structures to hear. Panderichthys most likely used its spiracles for ventilation of either water or air. Early tetrapods probably passed air through the opening. Scientists would need preserved soft tissue to say for sure. "That's the question that we're starting to investigate, whether early tetrapods used it for some ventilation function as well," Brazeau said. Whether it was for the exhalation of water or air, it's not really clear. We can infer that it's quite expanded and improved from fish." This research is detailed in the Jan. 19 issue of the journal Nature. Copyright © 2006 Imaginova Corp. All Rights Reserved. This material may not be published, broadcast, rewritten or redistributed.

Sharks' Electrical Sense Related to Human Genes
Wednesday, February 08, 2006 By Ker Than The same genes that give sharks their sixth sense and allow them to detect electrical signals are also responsible for the development of head and facial features in humans, a new study suggests. The finding supports the idea that the early sea creatures which eventually evolved into humans could also sense electricity before they emerged onto land. The finding is detailed in the current issue of the journal Evolution & Development. Sixth sense Sharks have a network of special cells that can detect electricity, called electroreceptors, in their heads. They use them for hunting and navigation. This sense is so developed that sharks can find fish hiding under sand by honing in on the weak electrical signals emitted by their twitching muscles. The researchers examined embryos of the lesser spotted catshark. Using molecular tests, they found two independent genetic markers of neural crest cells in the sharks' electroreceptors. Neural crest cells are embryonic cells that pinch off early in development to form a variety of structures. In humans, these cells contribute to the formation of facial bones and teeth, among other things. The finding suggests that neural crest cells migrate from the sharks' brains to various regions of the head, where they develop into electroreceptors. Glenn Northcutt, a neuroscientist at the University of California, San Diego, who was not involved in the study, said the finding was interesting, but that more studies are needed before a direct link between neural crest cells and electroreceptors can be established. "It still requires a definitive experiment, where the developing neural crest cells are marked with dye, the embryo develops and the dye clearly shows up in the electroreceptors," Northcutt said. In the new study, the researchers found snippets of genetic material associated with neural crest cells in the electroreceptors. They did not dye the neural crest cells and trace their development. Our electrical ancestors Scientists think that all primitive animals with backbones, including the early ancestors of humans, could sense electricity. As they evolved, mammals, reptiles, birds and most fish lost the ability. Today, only sharks and a few other marine species, such as sturgeons and lampreys, can sense electricity. "Our fishy ancestors had the anatomy for it," said study team member James Albert, a biologist from the University of Louisiana. The ability to sense electrical signals is useful in aquatic environments because water is so conductive. On land, however, the sense is useless. "Air doesn't conduct electricity as well," Albert said. "When it happens, it's called a lightning bolt and you don't need special receptors to sense it." The development of the electroreceptors is believed to mirror the development of the lateral line, a sense organ in fish that allows them to detect motion in surrounding water. Similar processes are thought also to be involved in the development of the inner ear, the organs which help humans keep their balance. The electroreceptors are also believed to behind many sharks' ability to detect changes in the Earth's magnetic field. Other studies indicate that, like sailors, sharks can also navigate by celestial cues. Scientists think that these two abilities are what allow some sharks to swim straight lines across vast distances of featureless ocean. One recent study found that a great white shark, nicknamed Nicole, swam nearly 7,000 miles between South Africa and Australia in just under 100 days. Copyright © 2006 Imaginova Corp. All Rights Reserved. This material may not be published, broadcast, rewritten or redistributed.

Earlier Evolutionary Explosion May Have Preceded Cambrian
Monday , January 07, 2008 By Dave Mosher Complex life on Earth may have blossomed during two "explosions," not one, a new study suggests. Earth's biggest species diversification occurred 542 million years ago, during what's called the Cambrian explosion. But a similar and rapid burst in evolution occurred 33 million years prior, researchers now think. They've dubbed the event the Avalon explosion. “It now appears that at the dawn of the macroscopic life, between 575 and 520 million years ago, there was not one, but at least two major episodes of abrupt morphological expansion," said Shuhai Xiao, a paleontologist at Virginia Tech. The new study, detailed in the Jan. 4 issue of the journal Science, examines life during Ediacaran Period on Earth, between 635 million years and 542 million years ago. The authors compared 200 different species to reveal that their body types — and richness of diversity — appeared at around the same time. Despite the first boost in diversity, however, the Ediacaran creatures all but vanished before the Cambrian explosion that followed. "The Avalon explosion represents an independent, failed experiment with an evolutionary pattern similar to that of the Cambrian explosion," the authors said. Copyright © 2008 Imaginova Corp. All Rights Reserved. This material may not be published, broadcast, rewritten or redistributed.

New Research Suggests Simple Approach to Beginning of Life
Monday , June 12, 2006 By Michael Schirber Somewhere on Earth, close to 4 billion years ago, a set of molecular reactions flipped a switch and became life. Scientists try to imagine this animating event by simplifying the processes that characterize living things. New research suggests the simplification needs to go further. All currently known organisms rely on DNA to replicate and proteins to run cellular machinery, but these large molecules — intricate weaves of thousands of atoms — are not likely to have been around for the first organisms to use. "Life could have started up from the small molecules that nature provided," says Robert Shapiro, a chemist from New York University. Shapiro and others insist that the first life forms were self-contained chemistry experiments that grew, reproduced and even evolved without needing the complicated molecules that define biology as we now know it. Primordial soup An often-told origin-of-life story is that complex biological compounds assembled by chance out of an organic broth on the early Earth's surface. This pre-biotic synthesis culminated in one of these bio-molecules being able to make copies of itself. The first support for this idea of life arising out of the primordial soup came from the famous 1953 experiment by Stanley Miller and Harold Urey, in which they generated amino acids — the building blocks of proteins — by applying sparks to a test tube of hydrogen, methane, ammonia and water. If amino acids could come together out of raw ingredients, then bigger, more complex molecules could presumably form given enough time. Biologists have devised various scenarios in which this assemblage could have taken place — in tidal pools, near underwater volcanic vents, on the surface of clay sediments or even in outer space. But were the first complex molecules proteins or DNA, or something else? Biologists face a chicken-and-egg problem, because proteins are needed to replicate DNA, but DNA is necessary to carry the instructions for the building of proteins. Many researchers, therefore, think that RNA — a cousin of DNA — may have been the first complex molecule on which life was based. RNA carries genetic information like DNA, but it can also direct chemical reactions as proteins do. Metabolism first Shapiro, however, thinks this so-called "RNA world," which many biologists believe existed before DNA arose, is still too complex to be the origin of life. Information-carrying molecules like RNA are sequences of molecular "bits." The primordial soup would be full of things that would terminate these sequences before they grew long enough to be useful, Shapiro says. "In the very beginning, you couldn't have genetic material that could copy itself unless you had chemists back then doing it for you," Shapiro told LiveScience.

Instead of complex molecules, life started with small molecules interacting through a closed cycle of reactions, Shapiro argues in the June issue of the Quarterly Review of Biology. These reactions would produce compounds that would feed back into the cycle, creating an ever-growing reaction network. All the interrelated chemistry might be contained in simple membranes, or what physicist Freeman Dyson calls "garbage bags." These might divide just as cells do, with each new bag carrying the chemicals to restart — or replicate — the original cycle. In this way, "genetic" information could be passed down. Moreover, the system could evolve by creating more complicated molecules that would perform the reactions better than the small molecules. "The system would learn to make slightly larger molecules," Shapiro says. This origin of life based on small molecules is sometimes called "metabolism first" (to contrast it with the "genes first" RNA world). To answer critics who say that small-molecule chemistry is not organized enough to produce life, Shapiro introduces the concept of an energetically favorable "driver reaction" that would act as a constant engine to run the various cycles. Driving the first step in evolution A possible candidate for Shapiro's driver reaction might have been recently discovered in an undersea microbe, Methanosarcina acetivorans, which eats carbon monoxide and expels methane and acetate (related to vinegar). Biologist James Ferry and geochemist Christopher House from Penn State University found that this primitive organism can get energy from a reaction between acetate and the mineral iron sulfide. Compared to other energy-harnessing processes that require dozens of proteins, this acetate-based reaction runs with the help of just two very simple proteins. The researchers propose in this month's issue of Molecular Biology and Evolution that this stripped-down geochemical cycle was what the first organisms used to power their growth. "This cycle is where all evolution emanated from," Ferry says. "It is the father of all life." Shapiro is skeptical: Something had to form the two proteins. But he thinks this discovery might point in the right direction. "We have to let nature instruct us," he says. Life's Big Questions When? The oldest known fossils, called stromatolites, are about 3.5 billion years old. Although the theory is debated, these colonial structures appear to have been formed by photosynthesizing cyanobacteria (blue-green algae). Simpler organisms likely came earlier. Where? The main competing theories are "hot start" vs. "cold start." The former holds that the first life fed off the sulfur-based chemistry near a hot volcanic vent, while the latter contends that temperatures had to be cooler to permit stable bio-molecules. What? Genetic analysis shows that hyperthermophiles sit near the root of the tree of life, implying an ancient origin. But this does not mean these hot-loving microbes were the first to breathe life; they may simply have survived meteorite impacts that wiped out everything else on the primordial Earth. What's more certain is that the first organisms were anaerobic, as there was little oxygen in our planet's early atmosphere. Copyright © 2006 Imaginova Corp. All Rights Reserved. This material may not be published, broadcast, rewritten or redistributed.

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The Theory of Evolution.

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Presentation on theme: "The Theory of Evolution."— Presentation transcript:

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