Human Evolution The fossil record is incomplete but provides evidence to the events in human evolution DNA analysis provides additional information Species with common DNA sequences are more likely to have arisen from a common ancestor

Homo sapiens “The wise human” Probably first appeared about 200,000 years ago 60 million years ago an ancestral rodentlike insect eater flourished Chapter opener

Aegyptopithecus 30-40 million years ago (MYA) Monkeylike animal, size of a cat Found in tropical forests of Africa, tree dweller Social Possible ancestors of gibbons, apes, and humans

Dryopithecus 22-32 MYA Oak ape Found in SW and central Europe One of first hominoids Ancestor to apes and humans Lived in trees but could walk Size of a 7 year old, small brains, and pointed snout Figure 16.1

Hominin Ancestor to humans Fossils from 4-19 MYA scarce 6 MYA hominin line broke off from apes At least three candidates for first hominin Ardipithecus kadabba (from Ethiopia) Sahelanthropus tchadensis (from Chad) Orrorin tugenensis (from Kenya)

Figure 16.2

Australopithecus 2-4 MYA Bipedal, not a tree dweller Several species Flat skull bases Stood 4 to 5 feet tall Humanlike teeth Brain size of a gorilla’s Hunter-gatherer lifestyle

Australopithecus 4.1 MYA A. anamensis 3.6 MYA A. afarensis (Lucy) - Larger brain, more humanlike skull - Less prominent face 2.5 MYA A. garhi - Hunted and butchered meat - 4.5 feet tall, long arms like ape - Small cranium, large teeth, apelike face - Fossils from Afar region

A. afarensis “Lucy” Figure 16.3

Homo habilis 2.3 MYA Humanlike cave-dweller Cared intensely for young First to use tools extensively (habilis means handy) Coexisted with and was followed by Homo erectus

Table 16.1

Homo erectus 1 MYA Shallow forehead, massive brow ridges, brain about 1/3 the size of modern humans Angled skull-base, possible speech Social, cooperative, used fire Male-female pairs Found in China, Java, Africa, Europe, and SE Asia Pockets may have persisted until about 35,000 years ago Figure 16.4

Homo sapiens idaltu Lived about 156,000 years ago Physically similar to modern humans Probably resembled an Australian aborigine Figure 16.5

Homo neanderthalensis Split from the human lineage about 516,000 years ago Lived all over Europe Reconstructions of skeletons indicates major differences from us - Larger brains; prominent brow arches - Muscular jaws; distinct spacing of teeth - Large, barrel-shaped chest

Homo neanderthalensis Neanderthals coexisted with the lighter-weight, finer-boned Cro-Magnons from 30,000-40,000 years ago Cro-Magnons had signs of cultures, including: - Communal graves, jewelry, and intricate cave art For reasons unknown, by 28,000 years ago Neanderthals disappeared

Modern Humans Cave art from about 14,000 years ago indicates that by that time our ancestors had achieved milestones in cultural evolution - Fine hand coordination; use of symbols A preserved man, frozen in ice from about 5,200 years ago, is genetically like us - Ötzi, the Ice Man

Molecular Evolution The study of evolution through comparison of: - DNA and protein sequences - Chromosome banding - Genome structure Mutations occur in DNA over time Comparing two DNA sequences - Fewer changes indicate closer relation and more recent divergence - More changes, more ancient divergence

Comparing Chimps and Humans We have more in common with chimpanzees than any other animal DNA hybridization and protein comparisons reveal that chimps and humans share 98.7% of their gene-encoding proteins Comparison of insertions and deletions (indels) suggests that our similarity is only about 96.6%!

What Makes Us Human Traits defining “humanness” may be rare Keratin gene - Affects hair coverage - Expressed in chimps and gorillas - Nonsense mutation in humans Speech – FOXP2 gene Hemoglobin genes - Humans switch from embryonic to fetal versions of hemoglobin - Longer fetal period, increased brain growth

What Makes Us Different Underlying difference that makes us humans may be in gene expression not the genome sequence Our genome is like that of the pufferfish, minus many of the DNA repeats and introns Overall, the human genome has a more complex organization of the same basic parts than simpler animals - Contains many more duplicated genes

Ancient DNA DNA has been isolated from a few well preserved fossils - 17 million-year-old magnolia leaf in amber - 4-5 million-year-old insects in amber Researchers at Penn State University have sequenced nearly all of the mammoth genome from specimens that were flash-frozen at high altitudes

Comparing Chromosomes Karyotypes among great apes differ mostly by inversions Karyotypes between apes and more primitive primates differ predominantly by translocations All mammals share identical X-chromosome banding Synteny is the correspondence of gene order preserved between two species

Table 16.2

More Genetic Markers Mitochondrial DNA (mtDNA) - Used to trace maternal lineage - Lack of DNA repair in mitochondria leads to a faster mutation rate Y chromosome - Sons inherit it from their fathers - Used to trace male lineage

Mitochondrial “Eve” mtDNA sequences of indigenous peoples worldwide were compared to determine the common ancestral mtDNA sequence Hypothesized ancestral woman lived approximately 170,000-200,000 years ago in Africa This is remarkably close to the date of the Homo sapiens idaltu fossils

Populating the New World People spread across Eurasia and elsewhere by 40,000 years ago, and lastly through Siberia During the last Ice Age (23,000 to 18,000 years ago), people entered the Americas by crossing the Bering Strait from Siberia Today, Native Americans carry a very distinctive genetic nametag: Five mtDNA and two Y chromosome haplogroups

Populating the New World By 14,000 years ago, Native Americans had arrived inland - Genetic evidence also suggests that some populations died out The earliest Eskimos came from a different migration than the one that was ancestral to Native Americans and modern Eskimos - The left no present-day descendants

Figure 16.18