ASIM'S WEBWORLD View: Main School Main AP Biology Chapter Guides RELATED LINKS Review Questions and Answers		AP BIOLOGY: Chapter Twenty-Three Outline INTRODUCTION Darwin Supported Idea of Human Evolution Evolved from now extinct ancestor of African apes Used arguments from anatomy, development and behavior Fossil evidence weak then, stronger now fig 23.1 Idea Very Controversial Humanity a result of evolution not Divine creation Clashes between religious community and education THE EVOLUTION OF PRIMATES Tree Shrews Were the Ancestors of the First Primates The Earliest Primates Occurred 40 million years ago Two improvements associated with primates Grasping fingers and toes Binocular vision Characteristics possessed by other animals, but not together Prosimians were first primates Lemurs are surviving examples fig 23.2 Are nocturnal animals Monkeys: Day-Active Primates Primates became dinural about 36 million years ago Replaced prosimians rapidly Daytime hunting favored improvements in vision Improved senses governed by expanded brain Development of an opposable thumb Live in groups with complex social interactions Long childhood associated with development of large brains Evolved first in Central Africa Some migrated to South America, evolved in isolation Only New World monkeys have grasping, prehensile tails Apes: The Path to Humanity Apes evolved independently from monkeys 25 million years ago fig 23.3 Have larger brains than monkeys Large size, but lack tails Exhibit most adaptable behavior of all mammals, excluding humans Hominids: humans and their direct ancestors Hominoids: hominids plus apes No know apes ever found in North America DNA studies explain ape evolution fig 23.4 Gibbons diverged 10 million years ago Split between hominids and gorillas/chimpanzees 5 million years ago Human and chimpanzee DNA differ in only 1.27% of nucleotide sequences EVOLUTIONARY ORIGINS OF HUMANS Hominids New group of apes evolved on savannas 15 million years ago fig 23.5 Two critical steps on path to human evolution Bipedalism Larger brains The Discovery of Australopithecus Dart discovered first hominid fossil in 1924 Jaw was rounded not pointed like ape Brain case larger than any ape of its size Fossil now dated at 2.8 millions years old Named Australopithecus africanus An Evolutionary Tree with Many Branches A. robustus fossil discovered in 1938 Stockier build Massive teeth and jaws A. boisei fossil discovered by Mary Leakey in 1959 More stockily built Massive bony ridge on crest of skull to anchor jaw muscles Almost 2 million years old Fourth kind of australopithecine fossil discovered in 1989 Australopithecines are direct human ancestors Structure of feet and pelvis supports walking upright Large brains, teeth more human than apelike fig 23.6 Lucy: The Oldest Hominid Johanson discovered oldest prehuman hominid fossil in 1974 fig 23.7 40% complete, 3 million years old, scientific name A. afarensis Walked upright, head and brain more similar to ape More primitive specie, A. ramidus, discovered in 1994 fig 23.8 Resembles chimpanzees May represent root of human evolutionary tree Genus Australopithecus immediately ancestral to genus Homo fig 23.9 THE FIRST HUMANS Second Version Replaced Earliest Human Ancestors fig 23.10 African Origin: Homo habilis Fossil skull discovered by Richard Leakey in 1972 Brain volume much larger than australopithecines 1.6 million years old, clearly human in characteristics Eventually became extinct Out of Africa: Homo erectus Many fossils with same characteristics verify H. erectus as true human Java man Dubois found fossils in 1891 Long, straight legs, excellent walker Very large, 1,000 cubic centimeter brain Judged to be 500,000 years old Now accepted as clearly human Peking man Skulls discovered in China in 1920's fig 23.11 Also found crude tools and ashes from campfires The Success of Homo erectus Include Java man and Peking man Comparison to H. habilis Taller, larger brain, walked erect Skull has prominent brow ridges, rounded jaw Shape of skull interior suggest capability of speech Older fossil found in Africa in 1976, supports African origins 1.5 million years old Spread through Africa, migrated to Asia and Europe within 1 million years Developed social structure Lived in tribes of 20 to 50 individuals Inhabited caves, built crude, wooden shelters Hunted and butchered large animals, cooked with fire Species survived for over 1 million years Disappeared in Africa and Europe 500,000 years ago Lasted longer in Asia, until 250,000 years ago H. erectus differs from modern humans in brain size MODERN HUMANS Homo sapiens Species first appeared 500,000 years ago Has persisted only half as long as H. erectus thus far Out of Africa - Again Controversy regarding evolution of human races Some support races evolved independently in various areas Mitochondrial DNA supports that all races descended from one ancestor in Africa DNA in mitochondria transmitted only by females Trace versions of the mitochondrial gene back through history Greatest number of mutations should occur in oldest DNA Greatest number of mutations in modern Africans Thus oldest humans originated in Africa fig 23.12 H. sapiens evolved from H. erectus in Africa and remigrated to rest of world fig 23.13 Neanderthal man H. sapiens fossils found in Europe in 1856 Short, stocky, powerfully built individuals Massive skulls, heavy bony brow ridges Made diverse tools, cared for sick and injured Social and psychological characteristics of modern humans Common by 70, 000 years ago in Europe and Asia Cro-Magnon man First appeared in Europe 34,000 years ago Coexisted with and eventually replaced Neanderthals 40,000 years ago Used more sophisticated tools Had more complex social organization May have been first humans with fully modern language capabilities Responsible for elaborate cave paintings of herd animals fig 23.14 Modern humans spread into North America via Siberia 13,000 years ago Homo sapiens Are Unique