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10.2 - History of Life Life’s History History History of Life of Life Additional details about the evolution of multicellular organisms are illustrated in Figure 10.2-3. Marine organisms were the first to evolve, about 555 million • All life shares one common ancestor • Common ancestor – a species (usually extinct) from which a group enabling adaptive radiation to give to dinosaurs and mammals. Another mass extinction 65 million years ago removed the dinosaurs, again allowing (or all) of life isrise descended adaptive radiation of new species. Early hominids evolved 4 million years ago, from which modern humans appeared 130,000 years ago. • Groups of species share one common ancestor years ago, remaining in water until the transition to land 450 million years ago. A mass extinction 248 million years ago removed a large number of species, Jump to Adaptive Radiation Figure 10.2-3 This history of life timeline shows several important evolutionary milestone of life on Earth. Chapter 10 - Macroevolution 288 Biology 10.2 – History of Life Section continues History of Life Fossil Record • Fossil – the preserved traces or remains of living organisms from the past • Shows progressive change in organisms • Stasis – the periods of time in the fossil record that show limited change • Limitations of fossil record • Fossilization requires specific conditions • Organisms can appear suddenly in fossil record • Incomplete fossilization results in gaps in fossil record • Provide limited conclusions • Functions of structures • Prehistoric behavior • Fossil record supports theory of sequential evolutionary change • Older fossils located in older strata • Younger fossils located in younger strata • Ex) Sequential evolution of the coiled oyster *Simplified fossil record Biogeography • Biogeography – the study of the distribution of species, organisms, and ecosystems through geologic space and time • Earth’s land masses have moved over time • Fossils provide evidence of species that were present across Earth’s original land mass • Allopatric speciation occurred as land mass split • Ex) South American and African monkeys share common ancestor Biology 10.2 – History of Life History of Life Homologies • Homology – the similar features between different organisms resulting from common ancestry • Anatomical homology – a group of similar structures between different organisms resulting from common ancestry • Vestigial structures – structures which have lost all or most functionality through evolution • Ex) Pelvis in whale which lacks hind limbs • Convergent evolution • Creates similar structures/functions • Are not anatomical homologies • Molecular homology – similar stretches of genetic material between different organisms resulting from common ancestry • Ex) Shared genetic code indicates common ancestor • Organisms likely to be related have retained same stretches of DNA • Developmental homology – the similar features in the embryos of different organisms resulting from common ancestry • Hox genes – the sections of the genome that allow embryos to develop structures in the correct place • Similarities in development in different species indicate common ancestry Biology 10.2 – History of Life
