9/11/14 Cont. of Chapter 3 ● What did Darwin see? ○ many South American animals are endemic to South America ○ only live there ○ Darwin collected fossils of their ancestors in the Cenozoic Patagonian ○ Evolutionary convergence: pattern in which dependence of distant relatives grow to resemble each other; similar ways of life, have experienced similar natural selection ○ Galapagos islands ■ volcanic archipelago 600 miles off coast of Ecuador ■ oceanic on Cocos hot spot, never connected to mainland ○ populated by castaways, blown or rafted from mainland South America ■ large and small islands, diverse habitats, separated by straits of varying widths ○ contemporary biographic theory explained why each region has a distinctive set of inhabitants ■ local geologic, climatic, and environmental conditions influence organisms living there ■ regions with similar rocks and climate ought to have similar organisms ○ But Galapagos, though volcanic and arid like Cape Verdes, have entirely different inhabitants ○ 550 plant species on Galapagos ○ 250 are endemic (known nowhere else) ○ Dispersal: spread in space ○ Passive dispersal: hitchhickers, windblown seeds ○ Dominant “trees”: ■ composite: sunflowers, daisys, marigolds, dandelions, “weeds” in highlands ■ cactus in arid coastal region ○ Fauna is dominated by reptiles ■ better at passive dispersal than mammals ■ other lizards feed on cactus ○ Large grazing herbivore: galapagos tortoise (overgrown cousin of small tortoise) ■ descendent of small West Indies tortoise ○ Only terrestrial birds ■ 13 species, many confined to one island ■ descended from one ancestral emigrant from South America ○ Many feeding habits, reflected in shape of beak ○ Evolutionary divergence ■ descendants of one ancestor developed different adaptations and became less similar ○ Evolutionary convergence ○ Adaptive radiations: adapted many different ways of life ○ Endemism: encouraging divergence; some species can only be on one island ● Galapagos finches ○ geographic isolation + natural selection = new species ○ insects and land snails show similar phenomena ● Darwin ○ married, settled down, wrote his biography ● Thomas Robert Malthus 1798 ○ argued against utopian proposals ● Malthusian inequity = natural selection ○ reproductive capacity always exceeds the carrying capacity of the habitat, for every species ○ Darwin didn’t publish theory until 1858 ● Alfred Russell Wallace ○ Founder of modern biogeography > tropical ornithology ○ first to recognize Wallace’s Line ○ 1855: evolution happens ■ new species are derived from previously existing species ● 1859 Origin of Species ○ What is Origin of Species? ■ by descent with modification ■ all life forms are related ○ Strengths of Darwinism ■ natural selection ○ Compilied evidence from biology and geology ● Natural Selection ○ mortality is high ■ only the fittest survive ○ as a result of natural selection ■ evolution produces adaptation ■ giraffe’s neck ■ demonstrated by numerous experiments and field observations ● Principle of Homology ○ Geoges Cuvier, Sir Richard Owen ○ Large groups of animals share common body plan ○ homologous structures are inherited are the common ancestor ■ i.e. forelimb bones of vertebrates ● Homology ○ similarity due to common ancestry ○ Homologous ■ built from same parts ■ evidence for common ancestry ● Analogous ○ invested independently in two animals ○ built from different parts ○ same function ○ not inherited from common ancestor ○