Chapter 19

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

PowerPoint Lectures forBiology: Concepts and Connections, Fifth Edition – Campbell, Reece, Taylor, and Simon

Lectures by Chris Romero

Chapter 19Chapter 19

Human Evolution


How Are We Related to Neanderthals?

• Neanderthals were an evolutionarily recent human relative that lived in Europe until about 30,000-40,000 years ago

• Neanderthals lived alongside Cro-Magnons, direct ancestors of present-day Europeans

• Did the two groups interbreed so that vestiges of Neanderthals survive in modern humans?

• Analysis of DNA isolated from Neanderthal bones has shown that Neanderthals were a distinct species from modern humans


PRIMATE DIVERSITY

19.1 The human story begins with our primate heritage

• The mammalian order Primates includes the lemurs, tarsiers, monkeys, and apes

• Primates had evolved as small arboreal mammals by 65 million years ago

– Most living primates are arboreal

– Humans retain in their bodies many traits that evolved with our arboreal relatives


• Primate features include

– Limber joints

– Grasping hands and feet with flexible, sensitive digits

– A short snout

– Forward-pointing eyes that enhance depth perception

• The squirrel-sized slender loris illustrates a number of primate features


• The lorises, lemurs, and pottos make up the oldest group on the primate phylogenetic tree

– All live in tropical forests, and all are threatened by habitat destruction

• Tarsiers, the second branch, are small, nocturnal tree-dwellers living in Southeast Asia

– Tarsiers are more closely related to anthropoids than to the loris-potto group

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• The anthropoid group includes monkeys and apes

– Humans are members of the ape group (hominoids)

– Anthropoid features include

• Larger brain relative to body size

• More reliance on eyesight

• Opposable thumb

– Anthropoids began diverging from other primates about 50 million years ago


• Monkeys do not constitute a monophyletic group

– New World monkeys are found in Central and South America

• All are arboreal

• Nostrils are wide open and far apart

• Many have a prehensile tail

– Old World monkeys

• Lack a prehensile tail

• Nostrils open downward


• Monkeys differ from most apes in having forelimbs about equal in length to hind limbs

• Old World monkeys and apes diverged about 20-25 million years ago

• The human ancestry probably diverged from an ancestor shared with chimpanzees between 5 and 7 million years ago


19.2 Hominoids include humans and four other groups of apes

• Hominoids include gibbons, orangutans, gorillas, chimpanzees (and bonobos), and humans

– Are chiefly vegetarians

– Lack tails

– Have longer forelimbs than hind limbs

– Have relatively large brains

– Apart from humans, have a limited geographical range in the tropics


• Gibbons are the only entirely arboreal apes

– Found in Southeast Asia

– Only nonhuman monogamous ape

• The orangutan is a shy, solitary species

– Largest living arboreal animal

– Lives in rain forests of Sumatra and Borneo


• The gorilla is the largest ape

– Found only in African rain forests

– Usually live in groups of up to 20 individuals

– Spend nearly all their time on the ground

• Chimpanzees and bonobos spend a quarter of their time on the ground

– Knuckle walkers, like the gorilla

– Inhabit tropical Africa


Video: Gibbons Brachiating

Video: Chimp Agonistic Behavior

Video: Chimp Cracking Nut


• Many aspects of chimpanzee behavior resemble human behavior

– Make and use tools

– Raid other social groups of their species

– Can learn human sign language

– Seem to be self-aware

• Gorillas and chimpanzees are more closely related to humans than to other apes

– Chimpanzees are our closest living relatives, sharing more than 99% of our genes


HOMINID EVOLUTION

19.3 The human branch of the primate tree is only a few million years old

• Paleoanthropology studies human origins and evolution

• Humans and chimpanzees diverged from a common ancestor 5 to 7 million years ago


• A number of derived characters distinguish humans from other hominoids

– Bipedal

– Shorter jaws

– Larger brain

– Capable of language and complex thought

– Manufacture and use complex tools

– Long-term pair-bonding between mates

– Longer period of parental care


• Hominids are extinct members of the human branch of the evolutionary tree

– Oldest hominid: 7 to 6 million years ago

– Australopiths: Between 4 and 2 million years ago

• Do not represent a monophyletic group

• Some overlapped with the genus Homo

– At times, several hominid species coexisted; all but our own are extinct

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19.4 Upright posture evolved well before an enlarged brain in hominids

• Footprints left by Australopithecus afarensis indicate that hominids have been bipedal for at least 3.5 million years

• An important clue to bipedalism is the spinal cord exit at the base of the skull, allowing an upright position

• "Lucy," a fossil dating back 3.24 million years, indicates that A. afarensis was small brained, small in stature, and bipedal

• Whatever the selective pressure for bipedalism, it evolved before an enlarged brain

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Lucy, a 3.24-million-year-old skeleton


19.5 Larger brains and reduced sexual dimorphism mark the evolution of Homo

• Homo habilis (about 2.4 million years ago)

– Had a larger skull and used tools

• Homo ergaster (about 1.9 to 1.6 million years ago)

– Had a larger brain than H. habilis

– Used more sophisticated tools

– Showed less size difference between sexes


• Sexual dimorphism may offer some clues to the social system of extinct hominids

– Less dramatic in species that exhibit pair-bonding

– May be associated with long-term parental care by both parents

• Homo erectus was the first hominid to migrate out of Africa, eventually as far as Indonesia


19.6 When and where did modern Homo sapiens arise?

• Homo sapiens evolved in Africa and later migrated to Asia and Europe in one or more waves

• Earliest H. sapiens fossils from Ethiopia support molecular evidence about human origins

– Europeans and Asians share a more recent common ancestor than H. neanderthalensis

– Many African lineages represent early branches on the human family tree


• Mitochondrial DNA and Y-chromosome analyses support divergence from a common African ancestor who lived 100,000-150,000 years ago

• Recently found 18,000-year-old H. floresiensis fossil represents a previously unknown hominid species

• The rapid expansion of humans may have been related to their creativity and increased cognition

– Evidence of sophisticated thought in 77,000-year-old art


CONNECTION

19.7 Human skin colors reflect adaptations to varying amounts of sunlight

• Dark skin color protects against UV-induced loss of folate, necessary for fetal development

• Why aren't all humans dark skinned?

– UV radiation catalyzes vitamin D synthesis

– Dark-skinned humans evolving in equatorial Africa received sufficient UV radiation

– Loss of pigmentation allowed humans migrating to northern latitudes to receive sufficient UV


CONNECTION

19.8 A genetic difference helped humans start speaking

• Language and complex, abstract communication permit the creation of human cultures

• A mutation in the FOXP2 gene has been linked to human language ability

– Likely arose within the last 100,000 years, matching emergence of Homo sapiens


OUR CULTURAL HISTORY AND ITS CONSEQUENCES

19.9 Culture gives humans enormous power to change the environment

• Human culture is the accumulated knowledge, customs, arts, beliefs, and other products socially transmitted over generations

– Evolutionary basis: growth in brain size and complexity during childhood, allowing children to learn from the experiences of earlier generations


• Culture has made Homo sapiens a unique force in the history of life on Earth

– We can change the environment to meet our needs at a faster rate than biological evolution

– We have been able to transcend our physical limitations at the expense of other species and the environment


19.10 Scavenging, gathering, and hunting were the earliest human endeavors

• Scavenging, gathering, and hunting

– Were how the earliest hominids lived

– Continued to be the way of life for australopiths and species of Homo

– Were the norm for Homo sapiens during most of the last 100,000 years

– Continue today in some societies


• Toolmaking

– Led to hunting becoming a major source of food

– Allowed humans to profoundly affect other species

• Origins of agriculture

– Communal activities

– Divided labor

– Semipermanent residences


19.11 Agriculture was a major development in human history

• Agriculture developed in Africa, Eurasia, and the Americas about 10,000 to 15,000 years ago

– Began in the Fertile Crescent of the Middle East

– Patterns of overuse and changes in climate turned the Fertile Crescent into the desert of today

• Farming was the first step in Homo sapiens becoming the dominant species on Earth


19.12 Development of complex tools affects human culture and the world

• The Industrial Revolution that began in the 1700s initiated a change to energy-intensive, large-scale machine production

• More food production and medical advances led to a rapidly growing human population

• The speed of technological change outpaces biological change, jeopardizing many species and perhaps ourselves

Chapter 19

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