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The Evolution of Humans

The Evolution of Humans. The Beginning. Human evolution began approximately 60 million years ago with the earliest primates Ancestral Primate Mammals with long snouts, sharp teeth and large eyes Most likely lived in trees, feeding mostly on insects. The Beginning cont….

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The Evolution of Humans

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  1. The Evolution of Humans

  2. The Beginning • Human evolution began approximately 60 million years ago with the earliest primates • Ancestral Primate • Mammals with long snouts, sharp teeth and large eyes • Most likely lived in trees, feeding mostly on insects

  3. The Beginning cont… • Over time they developed 3 distinct traits • More flattened molars suited for a plant diet • Grasping hands and feet with opposable first digits • Forward-directed eyes that binocular vision and depth-perception • Over the next 20 to 30 million years these mammals evolved into prosimians and anthropoid organisms

  4. PROSIMIANS • The living members of this group include lemurs – which are currently found in Madagascar. • They have: • long faces, some digits and claws, and some have nails • mobile toes, but not-opposable

  5. LEMUR

  6. ANTHROPOIDS • Present-day monkeys, apes and humans • Almost all are diurnal and feed mainly on fruits and leaves • Evolved large brains for processing information • Live in complex social groups and have prolonged care for young • As Gondwanaland (a super continent made up of South America, Africa, India, Australia, and Antarctica) separated to S. America and Africa two groups of monkeys evolved: • New World Monkeys (South America - evolved in isolation) • Old World Monkeys

  7. NEW WORLD MONKEYS • Ex. Spider monkeys • Long grasping tails • Flat noses • Live in trees

  8. OLD WORLD MONKEYS • Ex. Baboon, Rhesus monkey • Lacked long grasping tails • Protruding noses

  9. HOMINOIDS • Includes the apes and the humans • Apes include: gibbon, orangutan, gorilla and chimpanzee • All lack tails • Most are ground dwelling • Longer front limb and larger brains relative to body size

  10. Hominoid Ancestor • During the Miocene period (25 mya), the weather began to change. • The continents were drifting into their present location, and as a result the weather became dryer and colder • This changed the tropical forest into more of a grassland habitat

  11. Hominoid Ancestor Cont… • During this time, apes became abundant • Among the Miocene apes, the members of the dryopithecus are of particular interest – they are thought to be a possible hominoid ancestor • The bones of their feet indicate they walked on the ground (they still walked on all fours) using the knuckles of their hands to support their weight (like today’s apes)

  12. DRYOPITHECUS

  13. HOMONIDS • Just when humans split from apes is not known, but the common belief is that it occurred approximately 6 million years ago • A cooling trend is increasing grasslands • We do not know what first homonids were like, but assume they came out of the trees into the grassland, and began to walk upright (bipedal) to help them survive • Spot predators and prey over tall grasses • Free hands to perform other functions

  14. Hypothetical phylogenetic tree of hominoids

  15. AUSTRALOPITHECINES (Southern Apeman) • 3.5-4 mya • 4-5 feet in height • Bipedal • Non-opposability of big toe • Small brain • Many species of Australopithecines: • afarensis (Lucy) • africanus • robustus • Relationship is in dispute!!

  16. A. afarensis and A. africanus • Most primitive • Smallest brain • Large canine teeth • Protruding face • Limb features show erect walking

  17. A. robustus • Larger • More varied diet (vegetarian)

  18. Possible Explanation??

  19. Homo habilis • Appeared more than 2 mya (fossils) • Humans evolved in Africa • Larger brain size (30% greater than A. africanus) • Males larger than females

  20. Homo erectus • 1.6 mya • Shape of skull indicates intellect, memory and language • Improved tools • Fossils found primarily in Africa, but also Asia • Smaller teeth • Larger brain • May have evolved into two or three species of early humans

  21. Homo neaderthalensis • Neanderthals • 250,000 to 30,000 years ago • Named after Neanderthal Valley, Germany • Brain was larger than today’s human brain • Advanced tools, made blades, cave drawings • Buried with flowers and tools • May have been capable of complex speech

  22. Homo sapiens • 100,000 years ago to present • Large brain size • Forehead that rises sharply • Eyebrow ridges that are very small • A prominent chin • More sophisticated tools • Some scientists consider Homo neanderthalensis to be a subspecies of Homo sapiens, rather than a species unto itself.

  23. Monogenesis Hypothesis • Proposes that H. sapiens evolved only in Africa and the migrated to other continents • Displaced the Neanderthal and other descendants of earlier H. erectus populations • Regional genetic differences in humans evolved with the past 80,000 to 100,000 years, since H. sapiens left Africa • Supported by molecular evidence (DNA)

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