Evolution and the History of Life MLK Fall 2005 M.Elizabethwww.marric.us/teaching
Chapter 8.1 Change Over Time –Differences Among Organisms –Do Species Change Over Time –Evidence of Evolution: The Fossil Record Fossils Reading the Fossil Record Gaps in the Fossil Record Vestigial Structures –Case Study: Evolution of the Whale –Evidence of Evolution: Comparing Organisms Comparing Skeletal Structures Comparing DNA from Different Species Comparing Embryonic Structures
Changes Over Time Differences between species relate to adaptations. Adaptations – a hereditary characteristic (attribute) that helps an organism survive and reproduce in its environment. –Physical adaptations are heredity. Which means that the organism has no choice about the characteristics. – Emotional, cultural, and behavioral adaptations are choices that humans can make.
Its all about Species What is a Species? –A population of organisms that can mate with one another produces fertile offspring. Example: Horses, Donkeys, and Mules –Breeding a male donkey to a female horse results in a mule; –Breeding a male horse to a female donkey produces a hinny + = Sterile Mule Horses and Donkeys are separate species
Do Species Change Over Time The Earth is very old – 4.6 Billion Years The Earth was formed approx. 4.6 bya –The oldest rock is 3.5 Billion years Fossil evidence suggests that species have changed over time because younger fossils are different, yet similar to older fossils.
Evolution Evolution is the process by which populations of organisms acquire and pass on unique traits from generation to generation, affecting the overall makeup of the population and potentially leading to new species.
Four distinct mechanisms generate evolution (change in allelic frequency in populations over time): 1. mutation 2. gene flow 3. genetic drift 4. selection (natural and artificial)
Gene flow = movement of alleles from one population to another, which may change the allele frequencies Gene flow can happen in several ways; in reality, usually a combination of them –individuals leave a population, taking their alleles with them –individuals join a population, introducing new alleles (or more copies of ones already present) –individuals in the population mate with outsiders, but the offspring stay in the population this introduces new alleles (or additional copies of ones already present), because half of the offspring's alleles are from the outsider
Gene flow essentially moves alleles between populations –this tends to make neighboring populations similar to each other –because they exchange alleles and individuals in each have ancestors from the other –gene flow can take a mutation in one population and spread it throughout the world
Gene Flow the more migration or interbreeding occurs between two population, the more rapidly they become similar gene flow is important because it explains how a species like humans can be essentially the same all around the world
Genetic Drift Genetic drift = change in allele frequencies due to chance how it works –in any random process, like flipping a coin, we can predict the odds of any given outcome, but we can't predict which specific outcome will occur in any given case Genetic Drift has a greater effect on smaller populations than larger populations.
In large populations, drift will not have much effect just as when you flip a coin 1000 times, you expect to get fairly close to 500 heads but the smaller the population, the more this random sampling error will change allele frequencies every generation just as when you flip a coin only 4 times, you are not surprised at all to get 75% heads, or even 100% heads
Geologic Time Notations ya – Years Ago mya – Million of years ago bya – Billion years ago Precambrian Paleozoic ERA Mesozoic ERACenozoic ERA
Era word roots Geologist use the clues in some of these words. For example: – zoic refers to animal life – paleo means ancient –meso means middle, –ceno means recent. So the relative order of the three youngest eras, first Paleoozoic, then Mesozoic, then Cenoozoic, is straightforward.
Evidence of Evolution: The Fossil Record Fossils Reading the Fossil Record Gaps in the Fossil Record Vestigial Structures
Fossils Are found in the earths crust – the very uppermost part of the earth that is exposed to the surface or lying immediately below the oceans.
The Best Crust for Fossils Sedimentary Rocks are the best crust for fossil formations; Example: The Grand Canyon. Strata = Layers of sediment so its called sedimentary rock
What are Fossils Fossils are the mineralized remains of animals or plants or other traces such as footprints. All of the fossils and their placement in rock formations and sedimentary layers (strata) is known as the fossil record. The study of fossils is called paleontology.
Law of Superposition:Youngest on Top An undeformed sedimentary rock layer is older than the layers above it and younger than the layers below it A B C D
Law of Superposition A B C D In terms of Relative Age Rock Layer B must be younger than Rock Layer A but Rock Layer B is older than Rock Layers C and D.
Once the order of formation is known, a RELATIVE AGE can be determined for each rock layer http://pubs.usgs.gov/gip/fossils/
Gaps in the Fossil Record Occur because specific conditions are needed for fossils to form Organisms with hard body parts (skeletons) are more likely to form fossils than organisms with soft body parts. Basic to this is the organisms cannot be eaten before fossilization –Find shells and bones Fossils form best without oxygen – why peat bogs and tar pits have great fossils. Burial by sediments reduce oxygen exposure. Freezing also allows fossil formation – Mammoth that Japanese scientists are trying to clone from DNA extracted from frozen Mammoth fossil. Fossils once formed must not be destroyed.
Sea shells embedded in marine rock near Santa Cruz Ammonites near Redding
Vestigial Structures Mammals are warm blooded vertebrates Vestigial structures are organs that have no apparent function. Examples: –Human appendix – narrow tube attached to the large intestines –Chimpanzee, gorilla, and orangutan appendix is functional and used to help digest tough plant material
Whale evolution (terrestrial to aquatic in ~ 8 Myr) 8 million years total
PBS Whale Evolution PBS Whale Evolution http://www.pbs.org/wgbh/evolution/library/03/4/l_034_05.html One structural remnant (remaining part) of this evolutionary process are hind limb bones. These bones are called vestigial structures.
Evidence of Evolution: Comparing Organisms Comparing Skeletal Structures Comparing DNA from Different Species Comparing Embryonic Structures
Comparing Skeletal Structures Homo logous Structures –Having similar origins and anatom ical patterns –Examples – bird wings, human arms, whale flippers, bat wings, cat legs.
Analogous Structures Analogous structures do the same thing – similar function, but different anatomy. –Wings (butterfly external skeleton, bat internal skeleton Analogous structures: wing of an insect, bird, bat and pterosaur
Comparing DNA from Different Species The actual molecular characteristics of DNA is measured and compared to other organisms. There are four different nucleotides in DNA (Adenine, Guanine, Cytosine, and Thymine). Gene sequencing – sections of DNA are sequenced for the order of nucleotide bases (ATCG or ATGC or ACTG, etc).
What We've Learned So Far By the Numbers: What Does the Draft Human Genome Sequence Tell Us? The human genome contains 3164.7 million chemical nucleotide bases (A, C, T, and G). The average gene consists of 3000 bases, but sizes vary greatly, with the largest known human gene being dystrophin at 2.4 million bases. The total number of genes is estimated at 30,000 much lower than previous estimates of 80,000 to 140,000. Almost all (99.9%) nucleotide bases are exactly the same in all people. The functions are unknown for over 50% of discovered genes.
Crime Solving: The COmbined DNA Index System, CODIS, blends computer and DNA technologies into a tool for fighting violent crime.
Comparing Embryonic Structures Ontogeny: Development of the Individual from conception to death. Phylogeny: Development of the Species. Vertebrate organisms (those having a backbone) have similar stages of life as an embryo
Chapter 8.2 How Does Evolution Occur Charles Darwin –Darwins Excellent Adventure –Darwins Finches –Darwin Does Some Thinking –Darwin Learned from Farmers and Animal and Plant Breeders –Darwin Learned from Geologists –Darwin Learned from the Work of Thomas Malthaus –Natural Selection –More Evidence of Evolution (DNA Mutation)
Darwins Excellent Adventure HMS Beagle – Galapagos Island Travels Galapagos Islands are part of the country of Ecuador though the islands are about 1,000 kilometers west of the continent of South America in the Pacific Ocean. There are 19 volcanic islands with a land area of 8,000 km 2 in an area of the Pacific Ocean over 60,000 km 2 About Darwin http://www.aboutdarwin.com/timeline/time_01.html
Diversity Darwin saw finches that were very different from each other as he traveled to the various islands of the Galapagos. Because of their physiological differences (beak shapes), the finches had very different diets
The diversity of life… Although there is unity in life there is also a great deal of diversity! Estimates of Diversity: ~1.7 million cataloged species 50,000 vertebrates 260,000 species of plants 750,000 species of insects Total diversity 5-30 million species !
Darwin Does Some Thinking Darwin wonders how did the finches become so different. He thought maybe there was a storm that separated the original population resulting in geographic isolation (one of the ways that speciation can occur)
Darwin Learned from Farmers and Animal and Plant Breeders Darwin was very familiar with artificial selection or better known as selective breeding. Certain traits are determined by the breeder to be favorable. If only those organisms with the favorable traits are breed then the trait will occur more often in the population. By isolated certain individuals the differences can grow.
Darwin Learned from Geologists Darwin learned from Charles Lyell that the Earth was formed over a long period of time by natural process. This idea of geologic time (really really long time ago) helped Darwin to more seriously consider natural processes for changing populations.
Darwin Learned from Thomas Malthus Thomas Malthus was an economist. Malthus reasoned that humans have the potential to reproduce beyond the capacity of their food supply. Malthus recognized that there are some limitations to human population growth: –War (for animals it is predation-predators) –Disease –Starvation
Competition Because there are some limitations to growth, Darwin thought that those survivors must be better equipped (adapted) to their environment allowing them to out-compete other individuals. The offspring of the successful competitors have the same traits so are also more likely to survive in the same kind of environment.
Natural Selection Darwin theorized that evolution occurs through a process he called natural selection 1.Overproduction – Each species produces more offspring that will naturally survive. 2.Genetic Variation – individuals will be slightly different from one another. 3.Survival Struggle – competition for resources Abiotic and Biotic factors 4.Successful Reproduction – fitness (Survival of the fittest)
More Evidence of Evolution Darwin did not know what the mechanism was for how parents passed their traits to their offspring. Gregory Mendel (1822-1884) the Catholic monk studied traits in sweet peas. With Mendel's work and biochemistry we now know that the mechanism is meiosis involving DNA that is subject to mutation.
Mutation Changes to the heredity material- DNA, deoxyribonucleic acid – result in a changed genotype. Some changes that occur are not observed because the change did not significantly affect a function. Changes that affect function result in a different phenotype (what things look or function like).
Types of Mutation Changes can occur by single nucleotide substitutions Insertions or deletions of longer sequences of nucleotides (the components that make up deoxyribonucleic acid Chromosome alterations – which can be seen with a microscope.
Asking and Answering How? and Why? How and why questions are usually answered using a hypothetical- deductive (H-D) approach. –hypothesize –predict –test! - experiments (field + lab) Hypothesis vs. Theory
Evolution is just a theory Scientific theories are factual statements about Nature. Good theories are logically supported and are demonstrated by the results from multiple tests.
Evolution is about the Origins of Life The Theory of Evolution mostly describes how change occurred after complex life arose.
"Nature red in tooth and claw" Evolution says nothing about which traits will evolve; only that they will change.
"Survival of the Fittest" Cultural and ethical decisions of who is fittest and should survive are not Natures Laws. The term is used in business but with a different definition of fittest This is different from…..when fitness involves reproduction and those organisms that reproduce have demonstrated fitness.