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Evolution Part 1: Natural Selection

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1 Evolution Part 1: Natural Selection

2 The Father of Evolution Born in 1809, England Sailed on the HMS Beagle
Charles Darwin The Father of Evolution Born in 1809, England Sailed on the HMS Beagle During his voyage, he made observations that led him to his theory of evolution

3 This voyage lasted from 1831 to 1836.

4 Many of Darwin’s conclusions were based on observations of wildlife in the Galapagos Islands.
The Galapagos Islands lie 500 miles west of Ecuador in the Pacific Ocean, directly on the equator. “Galapagos” means turtle.

5 Galapagos finches Among other things, Darwin noticed there were several types of finches on these islands. In particular, Darwin observed something odd about the finches: they all looked like a bird he had seen on the South American continent.

6 The most distinct difference among finch species is their beaks, which are adapted for the specific diets available on the islands.

7 Once on the islands, the birds must have changed over the years.
Darwin hypothesized that some of the birds from South America migrated to the Galapagos. Once on the islands, the birds must have changed over the years. This would explain the numerous species of birds present.

8 This tree has how many major branches?
Warbler Finch Tree Finch Ground Finch Certhidea olivacea & C. Fusca Geospiza difficilis G. conirostris G. scandens Cacts Finch (nectar,eeds, blood) G. magnirostris Seed-eating Finch G. fuliginosa G. fortis Platyspiza crassitrostris C. heliobates Cactospiza pallida Woodpecker-like Finch Vegetarian Finch Insect-eating Finch Camarhynchus pauper C. psittacula C. pauper (seeds & insects) PHYLOGENETIC TREE: A diagram showing the evolutionary history of a species of an animal. The common ancestor is at the bottom. This tree has how many major branches? “Original” Finch

9 Darwin called the mechanism for evolution…
After returning from the Galapagos and studying all the different types of plants & animals he collected during the voyage, Darwin concluded that organisms change over time…. Darwin called this… evolution which means change in species over time Darwin called the mechanism for evolution… Natural Selection

10 Natural Selection a.k.a. Survival of the Fittest.
Those individuals that are better fit for their environment have a greater chance to survive and mate. Therefore, their genetic traits become more common or frequent over time. The genetic traits of less fit individuals become less common or frequent over time.

11 The recipe for Natural Selection

12 1. All species have genetic variation.
Every species is different, even within itself. Example: some beetles (of the same species) are green and some are brown

13 2. The environment presents challenges to survival.
There is a constant struggle for survival. Examples are: Natural disasters like droughts, fires, floods, etc. Competition for resources like food, space, or mates Other dangers like predation, disease, or parasitism Example: green beetles tend to get eaten by birds and survive to reproduce less often than brown beetles do. WHY would green beetles get eaten more often than brown beetles?

14 Individuals that are fit
Individuals that are fit* to their environment leave more offspring than those who aren’t. Example: The surviving brown beetles have brown baby beetles because this trait has a genetic basis. *Fit or fitness – does not mean “buff” beetles; more fit means they are better adapted or more likely to survive; they’re a good “fit” for their environment…

15 Therefore, characteristics of fit individuals increase in a population over time.
Conversely, over time, genes for less favored characteristics will become less common, but not eliminated (because they’re preserved in the heterozygotes) Example: The more advantageous trait, brown coloration, allows the beetle to have more offspring and becomes more common in the population. If this process continues, eventually almost all individuals in the population will be brown. (What would happen if a parasite prefers brown beetles, or if the environment was covered in green leaves?)

16 Therefore Darwin’s contributions:
Provided evidence that species evolve: In 1859, he proposed the theory of natural selection to explain evolution (survival of the fittest) - Over time, change within a population leads to the replacement of old species by new species as traits that are not selected for become less common. - Some evidence from fossils supports the theory that species on Earth have evolved from ancestral forms that are extinct. (species that have disappeared permanently.)

17 Evolution Part 2: Speciation and Hardy-Weinberg

18 What is a species? Or, why are these two owls different species, but these dogs aren’t? A species is one or more populations of individuals that can interbreed, producing fertile offspring. Speciation is the process by which new species are formed over time.

19 How does speciation occur?
Let’s begin with a simple example -- geographic isolation. This is when populations of individuals are geographically separated and prevented from mating with one another. This can be due to the formation of new mountains, canyons, rivers, or other landforms, for example.

20 How does speciation occur?
Over time, natural selection, acting on random mutations in the population, makes the DNA so different that the populations are no longer able to reproduce with each other Their chromosomes may not even match up. Once there is no gene flow between the populations, mutations start to accumulate differently in each population and the populations diverge into different species. This is called macroevolution – change on a grand scale including extinction and speciation.

21 Sometimes population ranges of different species overlap, but they still won’t interbreed. Here are some reasons why: Physical incompatibility For obvious reasons, crickets can’t mate with giraffes, for example. They just don’t have a common enough ancestor. Different mating schedules or locations For example, certain flowers and insects may prefer to mate at different times of day, may bloom at different times of the year, or may prefer different mating locations. So even if they are not geographically separated, they still won’t mate with someone with a different schedule. Behavior Animals, especially, are picky. Some have elaborate mating rituals or specific traits they look for in a mate. For example, in some spiders and mantises, if the rituals aren’t pleasing to the female, she will eat the male.

22 Natural selection acts on individuals; Evolution (the change) is measured in populations.
Microevolution is defined as the change in allele frequencies* in a population over generations. *Frequency – how often something occurs expressed as a decimal; for example, if something occurs 50 out of 100 times, it has a frequency of 0.5

23 Hardy-Weinberg In 1908, 2 scientists independently came up with a mathematical way to measure if a population is evolving by measuring changes in allele frequencies. The equation assumes the following conditions: Very large population No migration No net mutations Random mating No natural selection (if the above are occurring the population is most likely NOT going to evolve)

24 What causes genetic change in a population?
Those conditions are never fully met. Therefore, the 4 main factors that cause change of allele frequencies in a population are: Natural selection Genetic drift Gene flow Mutation Of these, only natural selection adapts a population to its environment, and we’ve already talked about it. The other three may be good or bad for a population or it may be neither good nor bad for it.

25 Genetic Drift Genetic drift is change in allele frequency due to sampling error (chance) This factor is more pronounced when the population is smaller than when the population is bigger. Two examples: Bottleneck effect – occurs when a population is drastically reduced in size due to a natural disaster such as hurricane or disease, and many alleles are lost completely while others are over or under represented from what they were in the large population; ex) cheetahs; population is at risk due to a lack of genetic variability Founder effect – occurs when a few individuals from a large population found (start) a new, isolated population ; ex) insects blown from the mainland to an island; humans moving from one continent to another and marrying within their own isolated community, such as the Amish in the U.S.

26 Gene flow Another word for gene flow is migration. Gene flow is when the allele frequency of a population is altered by individuals moving into (or out of) a population.

27 Mutation As we have studied in past units, a mutation is a change in your DNA. This is the other factor that can change allele frequencies. A flower population with only blue alleles can sometimes produce a red flower due to mutation. That changes the allele frequency. In general, only things you were born with can be inherited. Things that change your appearance but are not genetic, such as tattoos or ear gauges, cannot be inherited. Even most mutations in your DNA cannot be inherited by your offspring. Think about why. What’s the big exception?

28 Evolution Part 3: Evidence of Evolution

29 Scientific Evidence of Evolution includes:
Fossil Record Biogeography Homologies

30 Fossil Record Calcium must be replaced by harder minerals
In order for fossils to form: Calcium must be replaced by harder minerals Burial must occur by sedimentation Sediment includes particles in swamps, mud, ocean floors, tar pits, etc. Fossils are how we know that extinct animals used to live here on Earth.

31 Equus, the modern horse, evolved from the dog-sized Hyracotherium
Equus, the modern horse, evolved from the dog-sized Hyracotherium. Notice it evolved from a four-toed front foot to the one-toed front foot of the modern horse. Gradualism says that this happened gradually over millions of years. The evolution of the horse is an example of gradualism.

32 Evidence for both theories is observed in the fossil record.
Punctuated Equilibrium says that these species existed in long periods of stasis interrupted by relatively brief periods of genetic instability that produced changes. This overall change still happened over millions of years. Evidence for both theories is observed in the fossil record.

33 Biogeography Is the study of the geographic distribution of species and fossils. It is used to test predictions about the nature, age, and location of certain fossils. . What first suggested evolution to Darwin. Species tend to be more closely related to other species from the same area than to other species with the same way of life but living in different areas. Explains/reflects both homology and analogy

34 Homologies Characteristics that are shared by related species because they have been inherited in some way from a common ancestor. There are 3 main categories of homologies: Anatomical (as opposed to analogies; vestigial structures) Biochemical Developmental .

35 Anatomical Homologies
Homologous structures have the same underlying structure, but may have evolved different functions. . For example, the bones on the front fins of a whale are homologous to the bones in a human arm and both are homologous to the bones in a chimpanzee arm.

36 Anatomical Homologies
Divergent Evolution: formation of new species from an existing species adapting to new environments. - Homologies are evident

37 Divergent evolution example
All canines have long legs, walk on their toes, have bushy tails, non-retractable claws, and a dew claw on the front feet. These and other shared characteristics are due to the fact that they all come from a common ancestor. Different populations diverged at different points and created all these species. Sometimes called adaptive radiation. Often occurs when niches become available due to a catastrophic event that has led to the extinction of other animals.

38 Anatomical Analogies ANALOGOUS STRUCTURES are similar in function but not in origin or structure Spines/thorns serve a similar function…what? Left: American cactus (spines are modified leaves) Right: African euphorb (thorns are modified branches/stems) Therefore, different structure and origin Often result from convergent evolution; organisms evolve similar features independently, often because they live in similar habitats. These similarities are NOT due to having a common ancestor. Sometimes called parallel evolution.

39 Anatomical Analogies Convergent Evolution: process by which unrelated species become similar as they adapt to similar environments.

40 Convergent evolution example
Sharks, dolphins, tuna, penguins have streamlined bodies, and fins. These similarities are NOT because they have a common ancestor. Sharks are cartilaginous fish, dolphins are mammals, tuna are bony fish, and penguins are birds. They share similarities because they both adapted to the same marine environment and predatory lifestyle.

41 Vestigial Structures Vestigial structures are structures that no longer serve a useful purpose and/or are much less important than they used to be. Examples include: whale pelvis, claws on a boa’s belly tailbone pinky toes appendix human canines wisdom teeth goose bumps muscles to move human ears & make hair stand on end

42 Biochemical Homologies comparing genes to show relationships.
Idea is that closely related organisms have more similar genes / proteins than distantly related organisms. For example, fish, chimpanzees, and humans all have hemoglobin. You would expect the human hemoglobin to be more similar to the chimpanzee hemoglobin than to the fish hemoglobin since the chimp and the human are more closely related.

43 Developmental Homologies
Embryology is the study of organisms in their earliest stage of development. Traces similarities in development. For example, all chordate embryos have pharyngeal gill slits and post-anal tails. That’s part of the definition of being a chordate.

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