Human Origins and Evolution Chapter 24 PRIMATE FAMILY
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Human Origins and Evolution Chapter 24
PRIMATE FAMILY TREE 24. 1 Anatomical, molecular, and fossil evidence shows that the human lineage branches off the great apes tre Premonkeys Tamarins, titis, capuchins Baboons, mandrills, macques Primates are a monophyletic group of 400 species. All primates: Opposable thumbs, hands and feet for grasping, eyes on front of face, nails instead of claws,
APE FAMILY TREE Apes split off from Old World Monkeys and lost their tail. 2 groups of apes • Lesser apes: 14 species of gibbons, all in SE Asia • Great apes: orangutan, gorilla, chimps, and humans • Humans split from chimps 5 -7 mya
MOLECULAR ANALYSIS OF HUMAN AND CHIMPANZEE DNA 1 0 C diff in denaturation temperatures = 1% diff in DNA sequence Huge diff in appearance and behavior Due to gene regulation between 2 species
QUICK CHECK Did humans evolve from chimpanzees? Explain.
ANSWER No. Modern humans and modern chimps share a common ancestor. Changes have occurred along both lineages: from common ancestor to modern humans, and from the common ancestor to the modern chimps.
EARLIEST HOMININ (SAHELANTHROPUS TCHADENSIS) Hominin: all of the different species in the lineage leading to humans Earliest hominin: S. tchadensis about 7 million years old found in Chad in 2002 Chimp-sized brain with hominin-type brow ridges
LUCY (AUSTRALOPITHECUS AFARENSIS) Found in Ethiopia in 1974 Most complete hominin fossil 3. 2 million years old Fully bipedal
HOMININ LINEAGES At times, there were as many as 3 species living in Africa at the same time. 1 s t hominins to venture out of Africa: • Homo ergaster (aka Homo erectus) • 2 mya Homo neanderthalensis: • Descendent of Homo ergaster • Closely related to Homo sapiens • Thicker bodied than us with flatter head, and brains same size • 1 s t appeared in fossil record 600, 000 ya and disapperared 30, 000 ya
CRANIUM SIZE INCREASE • Body size increased • Tripling of brain and cranium (occurred after bipedalism)
ORIGINS 24. 2 Phylogenetic analysis of mt. DNA and the Y chromosome shows that our species arose in Africa. Multiregional Hypothesis: § modern H. sapiens derived from multiple H. ergaster populations that spread around the world 2 mya § Implies that modern traits evolved convergently in multiple populations Out-of-Africa Hypothesis: § modern H. sapiens arose from H. heidelbergensis (H. ergaster descendents) in Africa about 200, 000 years ago § Implies one evolutionary origin for modern traits
MITOCHONDRIAL DNA (MTDNA) Small circle of DNA (about 17, 000 base prs. long) Found in every mitochondrion Each cell has many mitochondrions Therefore, mt. DNA much more abundant than nuclear DNA Also easier to extract All your mt. DNA comes from mother’s egg, since sperm do not contribute mitochondria to zygote
VARIATION IN RESTRICTION SITES IN HUMAN POPULATIONS Using 12 diff restriction enzymes to cut mt. DNA from living people If restriction sequence was present, the enzyme would cut If sequence was mutated, the DNA would not be cut
PHYLOGENETIC TREE BASED ON RESTRICTION SITE VARIATION Study showed that modern humans arose relatively recently in Africa, and their most recent ancestor lived 200, 000 ya. The multiregional hypothesis is rejected. All non-Africans derive from within the African family tree.
SUPPORT FOR THE OUT-OF-AFRICA THEORY Modern humans arose from Africa 200, 000 ya: Out-of-Africa Hypothesis
NEANDERTHALS Neanderthals disappeared from Europe about 30, 000 ya when Homo sapiens (called Cro-Magnons) 1 s t appeared in Europe Did Cro-Magnons interbreed with H. neanderthals? If so, they would be our descendents.
THE EVIDENCE FOR AND AGAINST INTERBREEDING In sequencing entire Neanderthal genome: Our ancestors DID interbreed with Neanderthals 1 -4% of the genome of every non -African is Neanderthal-derived 2 possibilities for Discrepancy: • Neanderthal mt. DNA was lost through genetic drift 2. Female Neaderthals did not breed with our ancestors, but the males did
BECOMING BIPEDAL 24. 3 During the 5 -7 million years since the most recent common ancestor of humans and chimpanzees, our lineage acquired a number of distinctive features. Full bipedalism: 3. 5 mya Involved anatomical changes in: Skull Spine Legs feet
NEOTENY DNA of humans and chimps are 99% similar Attributed the differences between humans and chimps to gene regulation Neoteny: juvenilization: retention by adults of traits previously seen only in the young Humans are neotenous; exhibiting many traits as adults that chimps exhibit as juveniles • Hairless face • Small teeth • Flattened face • Hairless body • Large heads • Position of foramen magnum
BRAIN SIZE Humans have large brains for their body size. Possibilities: 1. Tool use 2. Social living…. coordination 3. Language
FOXP 2 The differences between humans and chimps lies in the 1% DNA differences. FOXP 2 gene: Encodes transcription factors that play a important role in development Mutation in this gene: Difficulty with speech and language
QUICK CHECK The FOXP 2 gene is sometimes called the “language gene”. Why is this name inaccurate?
ANSWER 1. The gene is expressed in many tissues, so its effects are not limited to language and speech. 2. Many genes are required for language, not just FOXP 2. 3. Also, its association with vocal communication in multiple species is striking.
HUMAN MIGRATORY ROUTES 24. 4 Human history has had an important impact on patt of genetic variation in our species. • Homo sapiens left Africa about 60 kya. There has been little chance for genetic differences to accumulate among geographically separated populations. • Humans have very little genetic variation; only about 1/1, 000 base pairs
HUMAN MIGRATORY ROUTES 85% of total genetic variation in humans occurs within a population (ie. Swedes) 8% between populations within races (I. e. in Caucasians between Swedes and Italians) 7% occurs between races
NATURAL SELECTION EXPLAINS HUMAN DIFFERENCES Heat-adapted Masai in Kenya Tall, slender body Dark skin, less entry of UV to produce Vitamin D, but lots of sunlight Cold-adapted Inuit in Greenland Short, squat body Light skin, more entry of UV to make Vitamin D in area of low sunlight
INFLUENCE OF CULTURE ON EVOLUTION 24. 5 Culture is a potent force for change in modern hu Inventions, such as clothing, have allowed our species to expand its geogr
CULTURAL INFLUENCE IN OTHER SPECIES Blue Tits learned to peck thru aluminum caps by watching other birds Meerkats teach their young to handle prey Chimps have learned to use tools to hunt insects.
LANGUAGE Chimps and bonobos are able to learn/use sign language to express words and simple sentences.
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