Natural Selection

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.

Slide # 3 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”)

Old Theories of Evolution: Lamarck’s Theory of Use and Disuse Slide # 4 Old Theories of Evolution: Lamarck’s Theory of Use and Disuse 1801: Theory of Inheritance of Acquired Characteristics “Theory of inheritance of acquired characteristics” & “Use and disuse” If an organism changes in order to adapt to its environment, those changes are passed on to offspring. Said that changes in organisms occur to help an organism reach perfection. Problem: No organism is perfect Lamarck

Example of Lamarck’s Hypothesis Slide # 5 Example of Lamarck’s Hypothesis Example of Lamarck’s hypothesis: Male crab uses small front claw to ward off other males Because it has been used a lot, front claw becomes larger. Larger claw trait is passed on to offspring. Even though his hypothesis is flawed, he was the first to address the fact that organisms adapt to their environment

The Work of Lyell Influenced Darwin’s Ideas Slide # 6 The Work of Lyell Influenced Darwin’s Ideas Charles Lyell – English geologist 1830: On the Principles of Geology Natural forces & processes that shaped ancient Earth are the same forces acting on Earth today. Earth’s geologic features formed as a result of gradual processes. 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

The Work of Malthus Influenced Darwin’s Ideas Slide # 7 The Work of Malthus Influenced Darwin’s Ideas 1798: Thomas Malthus --Economist Essay on the Principle of Population Said that humans tend to have more offspring than nature can support Food production increased at a slower rate than population Darwin read Malthus’s essay after he returned from his voyage Darwin concluded that all organisms produce more offspring than the population can support Thomas Malthus

Charles Darwin: An Unlikely Evolutionist Slide # 8 Who was Charles Darwin? 1809: English naturalist Went on a 5 year voyage on the HMS Beagle as an unpaid scholar Collected plants & animals during journey Darwin did not set out to develop a theory of evolution Observations and specimens collected helped Darwin formulate his theory of evolution Charles Darwin

Route of Darwin’s 5 Year Trip Slide # 9 Route of Darwin’s 5 Year Trip Galapagos Islands Darwin spent a lot of time and collected a lot of specimens from the Galapagos Islands.

Darwin’s Observations Slide # 10 In Argentina, Darwin saw earthquakes raising the earth several feet Shells of marine animals found far inland & at great heights in Andes Mts Fossils of huge sloths & armadillo-like animals (both extinct) – similar to modern forms 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

Darwin’s Observations on the Galapagos Islands Slide # 11 Darwin’s Observations on the Galapagos Islands Fewer types of organisms on the islands Island species differ from mainland species & from island to island Finches on Galapagos resemble mainland finch, but there were more types on the islands

Darwin explained Evolution by Natural Selection Slide # 12 Darwin explained Evolution by Natural Selection 1859: Darwin published On the Origin of Species 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. Nature selects those individuals w/ favorable traits to leave more offspring that are better suited (FIT) for their environment. Published 25 years after Darwin wrote it!

Evidence that Supports Evolution: Fossil Record Slide # 13 Evidence that Supports Evolution: Fossil Record 1. Fossil: preserved remains (bones, teeth, shells) or evidence (imprint or footprint) of ancient organisms. Fossils found in sedimentary rock Younger sediments deposited on top of older sediments Older sediments contain older, simpler fossils Younger sediments contain younger, more complex fossils Fossils found in sediments of organisms that are extinct. Trilobites are extinct!

Slide # 14 Evidence that Supports Evolution: Geographic Distribution of Living Species Similar animals on each continent live in similar ecological conditions They were exposed to similar pressures of natural selection. Because of similar selection pressures, different animals ended up evolving similar characteristics Beaver NORTH AMERICA Beaver Muskrat Beaver and Muskrat Coypu Capybara Coypu and Capybara Muskrat SOUTH AMERICA Capybara Coypu

Evidence that Supports Evolution: Homologous Structures Slide # 15 Evidence that Supports Evolution: Homologous Structures 1. Homologous structures: similar structures but different functions Structures develop from same clump of embryonic cells 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. Homologous structures: forelimbs of vertebrates Pelvis & femur bones are vestigial in whales

Evidence that Supports Evolution: Similarities in Embryology Slide # 16 Evidence that Supports Evolution: Similarities in Embryology The embryos of vertebrates are very similar during early development. The same groups of embryonic cells develop in the same order and in similar patterns to produce tissues & organs. Common cells & tissues growing in similar ways produce homologous structures. Implies that common genes are involved. Embryos of vertebrates develop gill slits and tails.