Natural Selection

True or False 1.Evolution is a theory about the origin of life. False 2. Organisms are always getting better through evolution 3. Natural selection involves organisms trying to adapt False – no perfect organism False ~ results from genetic variation 4. Evolutionary theory is invalid because it is incomplete and cannot give a total explanation for the biodiversity we see around us. False ~ All scientific theories are works in progress. As new evidence is discovered, theories are revised or even disproven Source: Slide # 2

Important Vocabulary 1. Species: A group of organisms whose individuals can breed together to produce fertile offspring. 2. Population: A localized group of individuals belonging to the same species. 3. Evolution: A slow change in a population over time. 4. Adaptation: any structural or physiological change that gives an organism an advantage in the environment. Examples: structural = stingers, thorns, camouflage physiological = being heterozygous for sickle cell anemia (protection against malaria), endotherms maintain constant body temp & can live in colder climates than amphibians and reptiles Slide # 3

Charles Darwin : His Journey and Observations

Charles Darwin explained how Natural Selection could cause a population to adapt and change over time. (note he states- a “population” will change -not an “individual”) Slide # 5

Slide # 6 Route of Darwin’s 5 Year Trip Darwin spent a lot of time and collected a lot of specimens from the Galapagos Islands. Galapagos Islands

Charles Darwin: An Unlikely Evolutionist 1.Who was Charles Darwin? a.1809: English naturalist b.Went on a 5 year voyage on the HMS Beagle as an unpaid scholar  Collected plants & animals during journey c.Darwin did not set out to develop a theory of evolution d.Observations and specimens collected helped Darwin formulate his theory of evolution Charles Darwin Slide # 7

Darwin’s Observations 1.In Argentina, Darwin saw earthquakes raising the earth several feet 2.Shells of marine animals found far inland & at great heights in Andes Mts 3.Fossils of huge sloths & armadillo-like animals (both extinct) – similar to modern forms 4.Animals on Galapagos were similar but not same as those on mainland S. America & Antarctica Galapagos penguin 14 inches tall 5 lbs Eat small fish & sardines Nests in burrows Chinstrap penguin 28 inches tall 9-14 pounds Eat small fish & krill Build nests out of small stones Slide # 8

Darwin’s Observations on the Galapagos Islands 1.Fewer types of organisms on the islands 2.Island species differ from mainland species & from island to island 3.Finches on Galapagos resemble mainland finch, but there were more types on the islands Slide # 9

Ideas that Shaped Darwin’s Thinking

The Work of Lyell Influenced Darwin’s Ideas 1.Charles Lyell – English geologist a.1830: On the Principles of Geology b.Natural forces & processes that shaped ancient Earth are the same forces acting on Earth today. EX: Rain erodes mountains & molten rock pushes up to create new ones. a.Earth’s geologic features formed as a result of gradual processes. b.Must take millions of years to change geography 2. Darwin read Lyell’s work while on his voyage & agreed with Lyell’s conclusions Charles Lyell Slide # 11

The Work of Malthus Influenced Darwin’s Ideas : Thomas Malthus --Economist a.Essay on the Principle of Population b.Said that plants and animals tend to have more offspring than nature can support c.Food production increase at a slower rate than population 2.Darwin read Malthus’s essay after he returned from his voyage 3.Darwin concluded that all organisms produce more offspring than the population can support Thomas Malthus Slide # 12

Old Theories of Evolution: Lamarck’s Theory of Use and Disuse : Theory of Inheritance of Acquired Characteristics a.“Theory of inheritance of acquired characteristics” & “Use and disuse” b.If an organism changes in order to adapt to its environment, those changes are passed on to offspring. (We now know that organisms cannot change or adapt to their environment) a.Said that changes in organisms occur to help an organism reach perfection. Problem: No organism is perfect Lamarck Slide # 13 Zoologist; came up with the word invertebrate. Most scientists thought these creatures were too lowly to study

Example of Lamarck’s Hypothesis Even though his hypothesis is flawed, he was the first to address the fact that organisms adapt to their environment Slide # 14 Example of Lamarck’s hypothesis: 1.Male crab uses small front claw to ward off other males 2.Because it has been used a lot, front claw becomes larger. 3.Larger claw trait is passed on to offspring.

Darwin explained Evolution by Natural Selection : Darwin published On the Origin of Species a.Proposed that natural selection was the mechanism for evolution. Individuals vary in one or more traits & there can be slight differences in their ability to survive & reproduce. b.Nature selects those individuals w/ favorable traits to leave more offspring that are better suited (FIT) for their environment. Slide # 15 Published 25 years after Darwin wrote it!

The Evidence that Darwin used to Develop the Theory

Evidence that Supports Evolution: Fossil Record 1. Fossil: preserved remains (bones, teeth, shells) or evidence (imprint or footprint) of ancient organisms. a.Fossils found in sedimentary rock b.Younger sediments deposited on top of older sediments c.Older sediments contain older, simpler fossils d.Younger sediments contain younger, more complex fossils 2.Fossils found in sediments of organisms that are extinct. Slide # 17 Trilobites are extinct!

1. Biogeography: the geographical distribution of species in relation to geography and other species 2. Influenced by continental drift Evidence that Supports Evolution: Geographic Distribution of Living Species Flying squirrels and sugar gliders look similar, but are only found on their respective continents. Similarities in appearance are due to development under similar selection pressures.

Evidence that Supports Evolution: Homologous Structures 1. Homologous structures: similar structures but different functions a.Structures develop from same clump of embryonic cells b.Provides evidence that four-limbed vertebrates descended from a common ancestor. 2. Vestigial structures: structures or organs that are reduced in size; do not seem to serve a useful function 3. Homologous & vestigial structures imply that common genes are involved. Slide # 19 Homologous structures: forelimbs of vertebrates Pelvis & femur bones are vestigial in whales

Evidence that Supports Evolution: Similarities in Embryology 1.The embryos of vertebrates are very similar during early development. ** All vertebrate embryos have: 1.) Notochord, 2.) dorsal hollow nerve cord, 3.) pharyngeal slits, and 4.) post-anal tail 2. The same groups of embryonic cells develop in the same order and in similar patterns to produce tissues & organs. 3. Common cells & tissues growing in similar ways produce homologous structures. 4. Implies that common genes are involved. Slide # 20

Post Darwin: DNA Evidence Supports Evolution We can compare amino acid sequences to which are most closely related We can compare DNA sequences to which are most closely related Why didn’t Darwin use DNA evidence in developing his theory? It had not yet been discovered!