How Did Humans Evolve?

• Some Early Primate Adaptations for Life in Trees Were Inherited by Humans

• The Oldest Hominid Fossils Are from Africa

• The Earliest Australopithecines Could Stand and Walk Upright

• Several Species of Australopithecus Emerged in Africa

• The Genus Homo Diverged from the Australopithecines 2.5 Million Years Ago

• The Evolution of Homo Was Accompanied by Advances in Tool Technology

• Neanderthals Had Large Brains and Excellent Tools

• Modern Humans Emerged Only 150,000 Years Ago

• Several Waves of Hominids Emigrated from Africa

• The Evolutionary Origin of Large Brains May Be Related to Meat Consumption

• The Evolutionary Origin of Human Behavior Is Highly Speculative

• The Cultural Evolution of Humans Now Far Outpaces Biological Evolution

Primates

• Primates include tarsiers, lemurs, monkeys, apes, and humans– Figure 17-12, p. 332 illustrates representative

primates…

Early Primates Were Adapted for Life in Trees

• Some of these adaptations were inherited by humans– Large, forward-facing eyes with overlapping

fields of view (allowed accurate depth perception)

– Color vision– Grasping hands– Enlarged brain (facilitated hand-eye

coordination and complex social interactions)

The Oldest Hominid Fossils Are from Africa

• Hominids include humans and extinct humanlike primates

• The oldest known hominid fossils are between 6 and 7 million years old

The Oldest Hominid Fossils Are from Africa

• Sahelanthropus tchadensis lived more than 6 million years ago– Exhibits human-like and ape-like

characteristics– See Figure 17-13, p. 333…

The Oldest Hominid Fossils Are from Africa

• Ardipithecus ramidus and Orrorin tugenensis lived between 4 million and 6 million years ago

• Knowledge of these earliest hominids is limited - few specimens have been found

The Oldest Hominid Fossils Are from Africa

• The first well-known hominid line, the australopithecines, arose about 4 million years ago– See Figure 17-14, p. 334…

The Australopithecines

• The earliest australopithecines possessed knee joints that permitted bipedal (upright, two-legged) locomotion– 4 million year old fossilized footprints confirm

that early australopithecines sometimes walked upright

The Australopithecines

• An upright stance was significant in the evolution of hominids because it freed their hands from use in walking

The Australopithecines

• Several species of Australopithecus have been identified from fossils

• Australopithecus anamensis

• Australopithecus afarensis – believed to have given rise to:– A. africanus– A. robustus – A. boisei

• All australopithecines were extinct by 1.2 million years ago

The Genus Homo

• The genus Homo diverged from the australopithecine line 2.5 million years ago

• See Figure 17-14, p. 334 for a possible evolutionary tree for humans…

The Genus Homo

• Homo habilis appeared 2.5 million years ago– Bodies and brains were larger than

australopithicenes– Retained apelike long arms and short legs

The Genus Homo

• Homo ergaster appeared 2 million years ago– Limb proportions were more like those of

modern humans

The Genus Homo

• Homo ergaster is believed by many to be the common ancestor of:– H. erectus (first hominid species to leave

Africa approximately 1.8 million years ago)

– H. heidelbergensis• Some migrated to Europe and gave rise to

H. neanderthalensis• Those remaining in Africa gave rise to H.

sapiens (modern man)

Advances in Tool Technology

• Hominid evolution is closely tied to the development of tools

• Homo habilis produced fairly crude chopping tools that were unchipped on one end to hold in the hand– See Figure 17-15(a), p. 336 to observe an

example of a hand axe…

Homo habilis

Copyright © 2005 Pearson Prentice Hall, Inc.

Advances in Tool Technology

• Homo ergaster produced finer tools that were typically sharp all the way around the stone– Some of these may have been tied to spears– See Figure 17-15(b), p. 336 to observe

examples of H. ergaster tools…

Homo ergaster

Advances in Tool Technology

• Homo neanderthalensis produced exceptionally fine tools with extremely sharp edges made by flaking off tiny bits of stone – See Figure 17-15(c), p. 336 to observe

examples of H. neanderthalensis tools…

Homo neanderthalensis

The Neanderthals

• Neanderthals lived in Europe from 150,000 to 30,000 years ago

• They were heavily muscled, had brains slightly larger than modern humans, walked fully erect, and constructed finely crafted stone tools

The Neanderthals

• Neanderthals were once believed to be a variety of H. sapiens; however, molecular evidence indicates that Neanderthals are a separate species

Modern Humans

• Homo sapiens appeared in Africa about 150,000 years ago

• European and Middle Eastern H. sapiens appeared about 90,000 years ago and were known as Cro-Magnons

Cro-Magnons

• Cro-Magnons had domed heads, smooth brows, and prominent chins

• 30,000-year-old Cro-Magnon artifacts include:– Bone flutes– Ivory sculptures– Evidence of elaborate burial ceremonies

• See Figure 17-16, p. 337…

Cro-Magnons

• Unlike their predecessors, Cro-Magnons created remarkable cave paintings that made use of sophisticated artistic techniques

• See Figure 17-17, p. 337…

Cro-Magnons and Neanderthals Lived Side by Side

• Cro-Magnons coexisted with Neanderthals in Europe and the Middle East for as many as 50,000 years

• It is not known why the Neanderthals became extinct

Several Waves of Hominids Emigrated from Africa

• Two hypotheses have been proposed for the evolution of Homo sapiens– “African replacement” hypothesis– “Multiregional origin” hypothesis

“African Replacement” Hypothesis

• Members of the genus Homo made repeated long-distance migrations out of Africa beginning 1.8 million years ago

• H. sapiens emerged from Africa about 150,000 years ago and spread across the Near East, Europe, and Asia

“African Replacement” Hypothesis

• The dispersing H. sapiens populations replaced all other hominids

• See Figure 17-18(a), p. 339…

African Replacement Hypothesis

The spread of Homoerectus began at least1.8 million years ago

Homo sapiens' expansionbegan around 100,000years ago

“Multiregional Origin” Hypothesis

• H. erectus emerged from Africa 1.8 million years ago and spread across the Near East, Europe, and Asia

• Continued migrations and interbreeding occurred among widespread H. erectus populations

“Multiregional Origin” Hypothesis

• Regional populations of H. erectus evolved into H. sapiens

• See Figure 17-18(b), p. 339…

Regional populationsof Homo erectus evolved intoHomo sapiens whileintermingling withone another

Multiregional Hypothesis

The Evolutionary Origin of Large Brains

• Highly developed brains may have evolved in response to increasingly complex social interactions, such as the cooperative hunting of large game

The Evolutionary Origin of Large Brains

• If the distribution of this group-hunted meat was best accomplished by individuals with large brains, then natural selection may have favored such individuals

The Cultural Evolution of Humans

• Human evolution has come to be dominated by cultural evolution, the transmission of learned behaviors from generation to generation

The Cultural Evolution of Humans

• The evolutionary success of humans is the result of cultural evolution and a series of technological revolutions– The development of tools– The agricultural revolution– The industrial revolution

The Cultural Evolution of Humans

• Human cultural evolution and the accompanying increases in human population have resulted in humans becoming an important agent of natural selection with respect to other life forms

The Cultural Evolution of Humans

• In the words of Stephen Jay Gould, “We may not be suited for our role as stewards of life’s continuity on Earth, but here we are”