Darwin: a reluctant rebel Darwin and Evolution Darwin: a reluctant rebel 2006-2007

History of Evolutionary Thought Carolus Linnaeus (1707-1778) Taxonomist Binomial Nomenclature Agreed with the “fixity of species” theory

LaMarck Organisms adapted to their environments by acquiring traits change in their life time Disuse organisms lost parts because they did not use them — like the missing eyes & digestive system of the tapeworm Perfection with Use & Need the constant use of an organ leads that organ to increase in size — like the muscles of a blacksmith or the large ears of a night-flying bat transmit acquired characteristics to next generation Lamarck noted how well-adapted organisms were to their environments, and believed that fossils could be understood as less perfect forms which had perished in the struggle for increasing perfection. He explained adaptation as a result of change caused by environmental pressures.

LaMarckian vs. Darwinian view in reaching higher vegetation giraffes stretch their necks & transmits the acquired longer neck to offspring Darwin giraffes born with longer necks survive better & leave more offspring who inherit their long necks 

Charles Darwin 1809-1882 British naturalist Proposed the idea of evolution by natural selection Collected clear evidence to support his ideas What did Darwin say? What evidence supports Evolution by Natural Selection? What impact did Evolution have on biology?

Voyage of the HMS Beagle Invited to travel around the world 1831-1836 (22 years old!) makes many observations of nature main mission of the Beagle was to chart South American coastline After graduation Darwin was recommended to be the conversation companion to Captain Robert FitzRoy, preparing the survey ship Beagle for a voyage around the world. FitzRoy chose Darwin because of his education, his similar social class, and similar age as the captain. Darwin noted that the plants and animals of South America were very distinct from those of Europe Robert Fitzroy

Voyage of the HMS Beagle Stopped in Galapagos Islands 500 miles off coast of Ecuador The origin of the fauna of the Galapagos, 900 km west of the South American coast, especially puzzled Darwin. On further study after his voyage, Darwin noted that while most of the animal species on the Galapagos lived nowhere else, they resembled species living on the South American mainland. It seemed that the islands had been colonized by plants and animals from the mainland that had then diversified on the different islands

Galapagos Recent volcanic origin most of animal species on the Galápagos live nowhere else in world, but they resemble species living on South American mainland. 500 miles west of mainland

Unique species Show Campbell videos!!!

Darwin found… birds Finch? Sparrow? Woodpecker? Warbler? Collected many different birds on the Galapagos Islands. Thought he found very different kinds… Finch? Sparrow? Woodpecker? Warbler?

But Darwin found… a lot of finches Darwin was amazed to find out: All 14 species of birds were finches… But there is only one species of finch on the mainland! Large Ground Finch Finch? Sparrow? Woodpecker? Warbler? Small Ground Finch Finch? Sparrow? How did one species of finches become so many different species now? Warbler Finch Veg. Tree Finch Woodpecker? Warbler?

Tree Thinking Descendant species Ancestral species Large-seed eater? Large Ground Finch Small-seed eater? Small Ground Finch Darwin noted that the plants and animals of South America were very distinct from those of Europe. Organisms from temperate regions of South America were more similar to those from the tropics of South America than to those from temperate regions of Europe. Further, South American fossils more closely resembled modern species from that continent than those from Europe. Warbler? Warbler Finch Leaf-browser? Veg. Tree Finch

Correlation of species to food source Seed eaters Flower eaters Insect eaters Rapid speciation: new species filling new niches, because they inherited successful adaptations. Adaptive radiation

Correlation of species to food source More observations… Correlation of species to food source

Natural Selection gradual, non-random process by which biological traits become either more or less common in a population mechanism that drives evolution Evolution = change in a species over many gnerations (long period of time)/ accumulation of adaptations There is variation in traits. Caused by mutations in DNA Caused by inheritance of dominant/recessive alleles = different phenotypes Only organisms that are “best fit” for the environment survive, reproduce, and pass on their traits to offspring.

Natural Selection: 4 steps Natural Variation exists in nature Competition - Organisms struggle for survival: more organisms are produced than the environment can support Survival of the fittest: Only the best adapted survives. Adaptations are important Organisms change over time in response to the environment: organisms change but they have a common descent – they have common ancestors

Adaptations: inherited characteristics that allow individuals to “do better” in their environment. Adaptations increase their chance of survival and reproduction

Artificial selection This is not just a process of the past… It is all around us today

Selective breeding

Natural Selection vs. Artificial Selection Artificial Selection: nature provides variation, and humans select variations that we find useful (domestic animals and crops) Natural Selection: the environment is the selective force. Only those organisms that are well adapted will survive in the wild.

Sexual Selection