22.0 Introduction

1. The Descent of Man
1. Darwin Supported Idea of Human Evolution
1. Used arguments from anatomy, development and behavior
2. Evolved from now extinct ancestor of African apes
3. Fossil evidence weak then, stronger now fig 22.1

2. Human Evolution Still Controversial Topic

22.1 The evolutionary path to humans starts with the advent of primates

1. The Evolutionary Path to Apes
1. Archonta Were the Ancestors of the First Primates
1. Occurred around 65 million years ago
2. Nocturnal, large-eyed insectivorous mammals
3. Radiation gave rise to bats, tree shrews and primates

2. The Earliest Primates
1. Two improvements associated with primates
1. Grasping fingers and toes
1. First digit is usually opposable
2. Digits usually have nails, not claws

2. Binocular vision
1. Both eyes at front of face
2. Allows for precise judgement of distance

2. Characteristics possessed by other animals, but not together
3. Dentition began to change to support plant eating
4. Reduction in length of snout and number of teeth

3. The Evolution of Prosimians
1. Split of prosimians and anthropoids 40 million years ago
2. Prosimians were first primates
1. Lemurs, lorises and tarsiers are surviving examples fig 22.2
2. Have very large eyes, increased visual acuity
3. Are nocturnal animals

4. Origin of the Anthropoids
1. Higher primates include monkeys, apes and humans
2. Primates became dinural fed on fruits and leaves
3. Evolution favored many changes
1. Changes in eye design, color vision, adaptations to daytime foraging
2. Improved senses governed by expanded brain
3. Live in groups with complex social interactions
4. Long childhood associated with development of large brains

4. Identity of first anthropoid is still under contention
1. Includes Eosimias ("dawn ape") 45-million-year-old Chinese fossil
1. Known only from two jaw bones
2. Existed 25 million years after extinction of dinosaurs

2. Second candidate is 37-million-year-old Egyptian Catopithicus
1. Have found several skulls, jaws, teeth
2. Lemur-like, size of squirrel
3. Favored by current evidence

5. Evolved first in Africa, monkeys are direct descendants
6. New World monkeys
1. Some anthropoid apes migrated to South America, evolved in isolation
2. Are arboreal with flat-spreading noses
3. Many have grasping, prehensile tails fig 22.3a

7. Old World monkeys
1. Apes remaining in Africa split into two linages 25 million years ago
1. One gave rise to Old World monkeys
2. Other gave rise to hominids

2. Old World separated from New World monkeys for at least 30 million years
3. Include ground-dwelling and arboreal species
4. None have prehensile tails
5. Nostrils are close together, noses point downward
6. Some have toughened pads of skin for prolonged sitting fig 22.3b

2. How the Apes Evolved
1. Anthropoid Evolution
1. Include hominoids = apes + hominids
2. Living apes include gibbon, gorilla, chimpanzee fig 22.4
1. Have larger brains than monkeys, but lack tails
2. Generally larger size
3. Exhibit most adaptable behavior of all mammals, excluding humans
4. Becoming rare
5. Never existed in North or South America

2. The First Hominoid
1. Another controversial topic
2. In 1980s thought to be Ramapithecus
1. Late Miocene ape lived 5 to 10 million years ago
2. 8-million-year-old fossil jaw found in India in 1932
3. Fossils not found in Africa
4. More complete fossils found in 1981 showed closer relationship to orangutans

3. Best candidate now considered to be Proconsul
1. Earlier Miocene ape with characteristics of Old World monkeys
2. Lacks a tail, has apelike hands, feet and pelvis

4. Very few fossils from 5 to 10 million years ago exist
5. Difficult to identify first hominid ancestor

3. Which Ape Is Our Closest Relative
1. DNA studies explain ape evolution fig 22.8
2. Asian apes evolved first
1. Gibbons diverged 15 million years ago
2. Orangutans split off 10 million years ago

3. African Apes evolved between 6 and 10 million years ago
1. Closest living relatives to humans
2. African apes often placed in same taxonomic family as humans

4. Chimpanzees split from ape line 6 million years ago
5. Split between chimpanzees and humans very recent
1. Similar in 98.4% of nuclear DNA
2. Genetic difference comparable to sibling species of same genus
3. Human and chimpanzee hemoglobin differs in only one amino acid

6. Gorilla and human DNA differs by 2.3%
1. Reflects greater time since gorillas split off ape line 8 million years ago
2. Hominid ancestor diverged from line soon after apes

7. Common ancestor of hominids more like chimpanzee than gorilla

4. Comparing Apes to Hominids
1. Common ancestor of apes and hominids was an arboreal climber
2. Differences between evolving apes and hominids associated with locomotion
1. Hominids became bipedal, walked upright
2. Apes evolved knuckle-walking

3. Bipedal hominids distinct in skeletal anatomy fig 22.5
1. Vertebral column more curved than ape's
2. Spinal cord exits from bottom not back of skull
3. Pelvis is broader, more bowl-shaped
4. Hip, knee and foot have altered proportions

4. Human body weight carried on lower limbs
1. Comprise 32 to 38% of body's weight
2. Lower limbs are longer than upper limbs
3. Upper limbs comprise 7 to 9% of body weight

5. African ape body weight carried by upper and lower limbs
1. Upper limbs longer, comprise 14 to 16% of body weight
2. Lower limbs are shorter account for 18% of body weight

3. The Origins of Bipedalism
1. Bipedalism Was Key Event in Evolution of Hominids
1. Evolved as ancestors left dense forests for open grasslands, woodlands fig 22.6
2. Two schools of thought
1. First says brain enlarged first, bipedalism followed
1. Intelligence necessary to make decision to walk upright
2. Move out of forests to grassland

2. Second says bipedalism a precursor to enlarged brains
1. Bipedalism freed forelimbs to manufacture and use tools
2. Favored subsequent evolution of bigger brains

3. Debate settled with fossils found in Africa
1. Bipedalism extended back 4 million years ago
2. Brain expansion did not appear until 2 million years ago

4. Evidence for bipedalism includes series of footprints from Laetoli, East Africa
1. Two individuals walked side-by-side for 27 meters fig 22.7
2. Footprints preserved in 3.7-million-year-old volcanic ash
3. Impression shows strong heel strike, deep indentation by big toe
4. Big toe not splayed out to side like monkey or ape

2. Why Bipedalism Evolved Is Still Matter of Controversy
1. Tool-making unlikely, no tools appear until 2.5 million years ago
2. Alternative ideas
1. Upright walking faster, uses less energy
2. Upright posture permits picking fruit from trees, seeing over grasses
3. Posture reduces body surface exposed to sun's rays
4. Upright stance aids wading of aquatic hominids
5. Frees forelimbs of males to carry food back to females, encourages pair-bonding

3. None of ideas are universally accepted
4. Origin of bipedalism still a mystery fig 22.6

22.2 The first hominids to evolve were australopithicines

1. An Evolutionary Tree with Many Branches
1. Two Major Groups of Hominids
1. Three to seven species in genus Homo
2. Seven species of smaller-brained Australopithicus

2. The Discovery of Australopithecus
1. Dart discovered first hominid fossil in 1924 in South Africa
1. Fossil skull of a five-year old individual
2. Jaw was rounded not pointed like ape
3. Vertical position of foramen magnum suggested walking upright

2. Fossil now dated at 2.8 millions years old
3. Named Australopithecus africanus
4. Fossil dating now done via single-crystal laser-fusion dating
1. Laser beam melts feldspar crystal , released argon gas
2. Amount of gas released reveals age of rock and nearby fossils
3. Less than 1% margin of error

3. Other Kinds of Australopithecus
1. robustus fossil discovered in 1938 in South Africa
1. Stockier build
2. Massive teeth and jaws

2. boisei fossil discovered by Mary Leakey in 1959 in east Africa
1. Even more stockily built
2. Almost 2 million years old
3. Massive bony ridge on crest of skull to anchor jaw muscles

3. Johanson discovered oldest prehuman hominid fossil in 1974 fig 22.9
1. Nicknamed "Lucy"
1. 40% complete, 3 million years old
2. Given scientific name A. afarensis (found in the Afar Desert)
3. Shape of pelvis reveal sex and that she walked upright
4. Head more similar to ape and brain chimpanzee-sized

2. Over 300 specimens subsequently found
1. Skulls are obviously apelike, strong projecting face
2. Brain size averages 430 cc, about the size of an orange

4. Three additional kinds of australopithicines reported
1. Two massively boned ancestors of A. boisei include A. aethiopicus and A. bahrelghazali
2. Fragmentary evidence of very ancient A. anamensis
3. Indicate that this genus is very diverse

4. Early Australopithecines Were Bipedal
1. Numerous fossils clearly indicate bipedalism
2. Other physical characteristics
1. Weighed about 18 kilograms, were about 1 meter tall
2. Dentition hominid
3. Brains the size of apes fig 22.10
1. Apes brains 500 cc or less
2. Homo brains 600 cc
3. Modern Homo sapiens brains average 1350 cc

3. Fossils found only in Africa

2. The Root of the Hominid Tree
1. The Oldest Known Hominid
1. Near complete skeleton discovered in 1994
1. Clearly bipedal, forward foramen magnum
2. Most ancient specimen yet found, 4.4 million years old
3. More apelike than australopithicines

2. Assigned new genus Ardipithecus ramidus fig 22.11

2. The First Australopithicine
1. Hominid fossils 4.2 million years old found in Kenya in 1995
1. Include partial tibia with bipedal characteristics
2. Assigned to genus Australopithicus less apelike than Ardipithecus
3. Fossils are intermediate in may ways

2. Species named Australopithicus anamensis
3. Additional fragmentary specimens found
1. Slightly built individuals
2. First members of genus, ancestral to A. afarensis

3. Differing Views of the Hominid Family Tree
1. Traditional approach pictures progression in linear sequence
1. Seven species of australopithicines not related in linear manner
2. Relationships resembles a bush rather than a single stem

2. A cladistic approach
1. Array organisms to portray ancestral relationships fig 22.12
2. Evolutionary relationships characterized by innovations
3. Individuals grouped into "clades"
1. Individuals in a group share characteristic inherited from common ancestor
2. Innovation unseen in more ancient ancestors

3. Lumpers and splitters
1. Lumpers focus on common elements in different fossils
1. Lumps together fossils that share key characteristics
2. Differences attributed to diversity within group
3. Lumper hominid phylogenetic tree, three species fig 22.13a

2. Splitters focus on differences between groups
1. Assign fossils with different characteristics into different species
2. Splitter phylogenetic tree, seven species fig 22.13b
3. Utilizes more of the available data
4. Human paleontologists accept as more accurate approach

22.3 The genus Homo evolved in Africa

1. African Origin: Early Homo
1. First Humans Evolved 2 Million Years Ago
1. Ancestor though to be A. africanus
2. Numerous fossils of Homo discovered within last 30 years
3. New fossils discovered yearly, evolutionary picture changes

2. Homo habilis
1. Stone tools and hominid bones found near A. boisei site in 1960s
2. Skull had brain volume of 680 cc
3. Specimen called Homo habilis
4. Partial skeletons found in 1986
1. Individuals small in stature
2. Arms longer than legs, australopithicine in appearance

3. Homo rudolfensis
1. Fossil skull discovered by Richard Leakey in 1972
1. 1.6 million years old, clearly human in characteristics
2. Brain volume 750 cc
3. Clearly human, not australopithicine

2. Some anthropologists considered it a large male of H. habilis fig 22.14

4. Homo ergaster
1. Some early Homo fossils do not fit into either species fig 22.15
1. Larger brains than H. rudolfensis
2. Skeletons less australopithicine, more modern in size and proportion
3. Have small cheek teeth like modern humans

2. Placed in third species of early Homo

5. How Diverse Was Early Homo?
1. Very few specimens found
1. Debate if they are all H. habilis or three separate species
2. More researchers accepting three species designation

2. Indicates Homo underwent early adaptive radiation
1. rudolfensis most ancient, then H. habilis
2. ergaster most recent, ancestor to later species of Homo

3. Great diversity stresses complexity of early evolution of Homo
1. Human evolution not simple linear process
2. Follows examples of other mammals, bush with diverse branches

2. Out of Africa: Homo erectus
1. Homo erectus Is Clearly a Human
1. Next fossil to appear after early Homo species fig 22.16
2. Many specimens examined
1. Skeleton from neck down substantially more human
2. Brain much larger
3. First specimens found outside of Africa

2. Java Man
1. Interest in finding "missing link" between apes and humans in 1860s
1. Dubois intrigued by orangutans from Borneo and Java
2. Sought fossil evidence

2. Dubois found fossil skull cap and thigh bone in 1891
1. Long, straight legs, excellent walker
2. Very large, 1,000 cubic centimeter brain
3. Judged to be 500,000 years old

3. Now accepted as clearly human
4. Numerous skeletons subsequently found

3. Peking man
1. Skulls discovered in China in 1920s
2. Also found crude tools and ashes from campfires
1. Casts made and sent to laboratories
2. Originals lost to World War II
3. Few additional specimens found

3. Cranial capacity of 1043 cc

4. Homo erectus
1. Include Java man and Peking man
2. Comparison to H. habilis
1. Taller, larger brain, walked erect
2. Skull has prominent brow ridges, rounded jaw
3. Shape of skull interior suggestibility to talk

3. Traditionally considered direct ancestor of modern humans
4. Honor now reserved for H. ergaster

5. Homo Migrates Out of Africa
1. H. erectus fossil found in Africa in 1976
1. Supports African origins of H. erectus
2. 1.5 million years old

2. Spread through Africa, migrated to Asia and Europe within 1 million years

6. The Success of Homo erectus
1. Developed social structure
1. Lived in tribes of 20 to 50 individuals
2. Inhabited caves, built crude, wooden shelters
3. Hunted and butchered large animals, cooked with fire

2. Species survived for over 1 million years
1. Disappeared in Africa and Europe 500,000 years ago
2. Lasted longer in Asia, until 250,000 years ago

22.4 Modern humans evolved quite recently

1. The Last Stage of Hominid Evolution
1. Three Species of Modern Humans
1. H. heidelbergensis, H. neanderthalensis, H. sapiens fig 22.18
2. Other researchers consider them as just one species, H. sapiens

2. Homo neanderthalensis
1. New species arrived in Europe from Africa 130,000 years ago, H. erectus becoming rare
2. neanderthalensis fossils found in Europe in 1856
1. neanderthalensis originated in Africa
1. Branched from ancestral line 500,000 years ago
2. Mitochondrial DNA is different than mDNA from modern humans

3. Physical characteristics of neanderthals
1. Short, stocky, powerfully built individuals
2. Massive skulls, heavy bony brow ridges
3. Brains larger than modern humans

4. Social characteristics
1. Made diverse tools,
2. Common by 70, 000 years ago in Europe and Asia
3. Cared for sick and injured, attention given to the dead
4. Symbolic thinking of modern humans

3. Homo heidelbergensis
1. Neanderthals not direct ancestors of H. sapiens
1. Based on great age and degree of specialization
2. Evolved from H. heidelbergensis

2. Fragmentary fossil evidence
1. Oldest fossil from Ethiopia 600,000 years old
2. Contemporary of H. erectus in Africa

3. Advanced anatomical features
1. Has bony keel running along midline of skull
2. Thick ridge over eye sockets, large brain
3. Forehead and nasal bones like H. sapiens

4. Homo sapiens
1. Oldest fossil from Ethiopia, 130,000 years old
1. Only surviving species of Homo
2. Only surviving hominid

2. Best evidence in skeletons found in Israel
1. Dated at 90,000 to 100,000 years old
2. Modern appearance, high, short brain cases
3. Vertical foreheads, slight brow ridges
4. Cranial capacity of 1550 cc

3. No fossils outside of Africa and Middle East older than 40,000 years
1. Implies H. sapiens evolved in Africa, migrated to Europe and Asia
2. Called the Out-of-Africa model
3. Other view is the Multiregional model, human races evolved independently

2. Out of Africa ^_ Again?
1. The Mitochondrial DNA Controversy
1. Evolution of human races originated from one H. sapiens ancestor in Africa
1. DNA in mitochondria transmitted only by females
2. Trace versions of the mitochondrial gene back through history
3. "Mitochondrial Eve" theory no longer accepted
4. Data different depending on how it is entered in the computer model
5. Greatest number of mutations in modern Africans
6. Greatest number of mutations should occur in oldest DNA
7. Consistent with oldest humans originating in Africa

2. H. sapiens evolved from H. erectus in Africa and remigrated to rest of world fig 22.19

2. A Clearer Picture from Nuclear DNA
1. Examine highly variable marker segments of nuclear DNA
2. Analyzed CD4 gene on chromosome 12 in populations all over the world
1. 24 different versions of the two CD4 segments found
2. 21 versions found in Africa
3. Three versions found in Europeans
4. Two versions found in Asians and Americans

3. Indicates chromosome 12 has existed in Africans longer than non-Africans
4. Strongly supports Out-of Africa origin of humans

3. The Emergence of Modern Humans
1. Cro-Magnons
1. Replaced European Neanderthals about 34,000 years ago
1. Came first from Africa, replaced Neanderthals in Middle East by 40,000 years ago
2. Spread across Europe, possibly interbreeding with Neanderthals

2. Characteristics of Cro-Magnons
1. Used sophisticated tools
2. Had complex social organization
3. May have been first humans with fully modern language capabilities
4. Responsible for elaborate cave paintings of herd animals fig 22.20

3. Modern humans spread into North America via Siberia 13,000 years ago

2. Homo sapiens Are Unique
1. Evolution marked by continual increase in brain size
2. Use symbolic language, transmit accumulation of experience to next generation
3. Have experienced cultural evolution