Human Origins
Biology 4974/5974
D.F. Tomback
Biology 4974/5974
Evolution
Gibbons 2002
Gibbons 2002
Balter 2002
Balter 2002
Human Origins
Figures from Hall and Hallgrimson, 2014, Strickberger’s Evolution, 5 th ed. Jones
and Bartlett.
Our knowledge of the evolution of hominids from ancestral primates
becomes more detailed over time. Scientists are determining how
changes in genetics, anatomy, brain morphology, behavior produced
modern humans. They are also finding their migration paths.
Learning goals
Know and understand:
• Basic primate traits adapted to an arboreal lifestyle.
• The general timeframe of primate evolution leading to
modern humans.
• Early hominin fossils and species of genus Homo.
• Models for origin of Homo sapiens and replacement of
other Homo species.
• Findings from sequencing of Neanderthal and Denisovan
genome.
• Adaptations associated with human evolution and
societies.
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Human Origins
Biology 4974/5974
D.F. Tomback
Primate adaptations
Primates share a number of traits that were adaptations
for an arboreal lifestyle. Modified from Strickberger’s Evolution,
4th ed., Table 20-1:
• Independent mobility of the digits
 An opposable first digit in both hands and feet
• Replacement of claws by nails to support the digital pads
• Teeth and digestive tract adapted to an omnivorous diet
 A semierect posture that enables hand manipulation and
allows readiness for leaping
• Center of gravity close to hind legs
 Well-developed hand-eye coordination
 Binocular vision for depth perception
• Eyes all or partly encased by bony orbits for protection
• Reduction of the snout leading to shortening of the face
• Reduction in olfactory ability in diurnal species
 Compared to other mammals, a large and complex brain
Relationships of living primates (Box 25.1)
Class Mammalia, Order Primata
Suborder Strepsirrhines (lemurs, lorises)
Suborder Haplorhines (Old World monkeys,
New World monkeys, apes)
-Infraorder Platyrrhini (New World monkeys)
-Infraorder Catarrhini (Old World primates)
---Superfamily Cercopithecoidea (macaques,
baboons, langurs, colobines)
---Superfamily Hominoidea (apes, humans)
• Family Hylobatidae (gibbons, siamangs,
Fig. 25.2
orangutans)
• Family Hominidae (gorillas, chimps,
humans)
• Tribe Hominini (humans and their
close ancestors = hominins)
Nearest non-primate relative: colugos (Order Dermoptera).
Diverged in Cretaceous (Janečka et al. 2007).
The early fossil record: ape-human lineage
• 85 mya—Primates originated in the
late Cretaceous, Mesozoic Era.
• 35-40 mya—Suborder Haplorhines
appears, Eocene, Cenozoic Era.
• Separation into New and Old
World lineages.
• 29-35 mya—Hominoidea split from
Catarrhines.
• 8 mya—The gorilla-chimp-human
lineage split from ape lineage.
• ~7.5 mya—Last common ancestor
of humans and chimpanzees.
• 5-6.5 mya—Bipedal hominins.
• 2.5 mya—Genus Homo.
• 140,000 ya—Homo sapiens
• 30,000 ya—recent Homo sapiens
Fig. 25.1
Fig. 20-4 Hall and Ha
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Human Origins
Biology 4974/5974
D.F. Tomback
Early hominins
Hominin evolution: history of evolving
bipedalism, brainsize, and tool use.
• Orrorin tugenensis, Ardipithecus kadabba, 5 to 6.5
mya, bipedal but arboreal.
• Ardipithecus ramidus (Australopithecine), 4.3 to 4.5
mya, Ethiopia; Australopithecus boisei, large body
& teeth, ca. 2.5 to 4.5 mya. Australopithecus
afarensis, 3 to 3.9 mya, 3-4 ft tall, long arms, clear
bipedalism (tracks). Complete skeleton, “Lucy.”
East Africa. Fossil footprints at Laetoli, Tanzania.
• Australopithecus africanus “Taung child”, 2.5 to 3
mya. Large, thickly enameled teeth, human
proportions, adult weight 40-70 lbs, brain 450 cc.
South Africa.
• Paranthropus robustus, ~2 mya, large teeth, large
jaw, sagittal crest, heavier body (80 lbs), brain 550
cc. South Africa.
Fig. 25.5
Gibbons (2002)
Lucy reconstruction
The fossil record: Homo
The genus Homo first appeared in late Pliocene, 2.5 mya
in east Africa. Larger brain, smaller molars.
• Homo rudolfensis, 1.8 to 2.4 mya, and Homo habilis, 1.6 to
2 mya, east Africa. 5.6 ft tall, cranium 750 cc; (Oldowan
tools) climbing trees, hunting, scavenging small animals.
• Homo ergaster, 1.6 mya, 5.6 ft, lean body, brain ca. 7501100cc; fire, tool use (Acheulean tools), hunting (large
animals?), scavenging.
• Homo erectus, 50,000 y to 1.5 mya, 5.5 ft tall, thick skull,
heavy brow ridge, small teeth, cranium 750-1200 cc; fire,
tool use (Acheulean), scavenging, hunting (large
animals?). Widespread: Africa, China, Europe, SE Asia.
Great variation.
• Homo heidelbergensis, 0.2 to <1.0 mya., brain ca. 1200 cc,
anatomy between H. erectus and H. sapiens.
Controversial: descended from H. ergaster and not H.
erectus?
Recent Hominins
Considered descendants of Homo heidelbergensis:
• Homo neanderthalensis, 24,000 to ~200,000 ya, brain
>1350 cc; large face, large nasal chamber, Mousterian
tools, hunted big game, ceremonies, ritual burials.
Europe, Middle East.
• Homo “Denisovan,” 30,000 to 200,000 ya from Denisova
Cave in Siberia, Russia. (More closely related to
Neanderthals).
• Homo sapiens (anatomically modern), 35,000 to 200,000
ya, brain 1350 cc, African origin, Mousterian tools, hunted
big game.
• Homo sapiens sapiens (Cro-Magnon man), 35,000 to
present. High skull vault, reduced brow ridges, flatter,
smaller face. Aurignacian stone tool culture, hunters,
increasing technological innovation.
Note the number of recent Hominins that lived at the
same time.
Note: three
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Human Origins
Biology 4974/5974
D.F. Tomback
Controversial species: “Hobbits”
Homo floresiensis (Endbox 25.2)
• Skeletons discovered only on Flores, Indonesian island:
“…lost world of small archaic humans, who hunted dwarf
elephants and Komodo dragons on an Indonesian island
as recently as 18,000 years ago”.
• Skull like Homo erectus, but with only 380 cc capacity;
3.3 ft tall, skeletal height of Lucy (australopithecine).
• Large feet, “the Hobbit”.
• Examination of wrist morphology indicates more primitive
than Neanderthal or Homo sapiens (Tocheri et al. 2007).
• Small, relict population of Homo erectus, which migrated
out of Africa before modern humans?
• Dwarfism or other interpretation is congenital
malformation: microcephaly.
The evolution of Homo sapiens
Models for the origin of modern
humans and wide-spread
replacement of Homo erectus:
• 1. Multiple-origin or “candelabra”
model: Simultaneous evolution of
ancestor into parallel Homo sapiens
forms.
• 2. Single origin, “out of Africa” model:
Homo sapiens originated in Africa and
dispersed out to colonize other areas
and replaced H. erectus (see Vigilant
et al. 1991). Mt-DNA, y chromosome,
autosomal genes support single origin.
• 3. A new model becoming clear: “Out
of Africa” but with evidence of
hybridization with Neanderthal in
Europeans and Asians. Evidence for
hybridization with Denisovans for first
migration out of Africa.
Fig. 25.8
Noonan, J. P., et al. 2006.
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Human Origins
Biology 4974/5974
D.F. Tomback
Revelations from genome sequencing of
Neanderthals and Denisovans
First Neanderthal DNA extracted and
sequenced (Noonan 2006)
• Discovered the pigmentation gene
mc1r from bones of two Neanderthals.
• Results in red hair and pale skin.
• Concluded that some Neanderthals
had light coloration.
• Previous workers found the FOXP2
speech gene, indicating the potential
for language abilities.
Culotta, 2007
Hybridization revealed from sequencing
• Complete draft nuclear genome sequence of Neanderthal
compared to H. sapiens (Green et al. 2010)
• 1% to 4% of European and Asian nuclear DNA, but not
African, is distinctly Neanderthal.
• Early modern humans interbred very rarely with
Neanderthals 50,000 to 80,000 years ago, after leaving
Africa.
• Some gene sequences in H. sapiens are derived, where
Neanderthals carry the ancestral form. These merit
study.
• One allele shared with Neanderthals RUNX2 causes
delayed closure of cranial sutures and a bell-shaped rib
cage, protruding frontal bones—all Neanderthal traits.
Hybridization, continued
Homo “Denisovan” genome sequenced.
• Denisovans and Neanderthals split about 200,000 ya.
• Evidence for hybridization with Melanesians and original
Australians: 3% Denisovan DNA; Han Chinese have
traces of Denisovan DNA. (Ramussen et al. 2011).
E.g., Introgression of immune system HLA alleles into H. sapiens from
hybridization with Neanderthals and Denisovans (Abi-Rached et al.
2011): “On migrating out of Africa, modern humans encountered archaic
humans…who had immune systems better adapted to local pathogens.”
Rasmussen et al. 2011
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Human Origins
Biology 4974/5974
D.F. Tomback
Adaptations associated with Hominin evolution
Bipedalism: Early adaptation.
• Made long distance foraging possible, freeing arms to
carry food, use weapons and tools.
• Easier to see predators.
• Increased reproductive success by enabling females and
young to remain at a home base, while male brought food.
Increased dependence on meat:
• Highly nutritious and can feed a group.
• May have led to cooperation for hunting and increased
social cohesion.
• This led to learning about the environment.
Adaptations
Other adaptations:
• Increased cranial capacity from about 500 cc in Australopithecus to
1350 cc in Homo sapiens.
• Change in skull morphology, increasing capacity between first and
recent Homo sapiens (higher vault).
• Language ability, requiring both morphological and neurological
changes (tongue, soft palate, larynx).
• Societies based on kin selection and reciprocal altruism.
• These may have led to moral values, such as fairness and justice.
Balter 2002
Rapid expansion of the human brain: Was this fueled
by the nutritional impact of cooking food?
• Human brains require a lot of
energy.
• The first humans consumed
meat.
• This saved energy by shrinking
digestive tracts.
• Cooking partly digests food and
allows more calories to be
assimilated.
• Less energy required to chew
and digest cooked food.
• Rapid benefits, smaller jaws and
teeth. Bigger brains.
• Need earlier evidence for fire,
but some claim evidence goes
back 1.9 million years.
Gibbons, A. (2007)
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Human Origins
Biology 4974/5974
D.F. Tomback
Study questions
• Name five adaptations associated with an arboreal lifestyle that
paved the way for hominin evolution.
• When did primates first appear in the fossil record?
• Identify: Ardipithecus ramidus, Australopithecus afarensis, Homo
erectus, Homo floresiensis, Homo neanderthalensis, the
Denisovans. Which were believed descended from Homo erectus?
From Homo heidelbergensis?
• When did the genus Homo first appear?
• What are the models for the replacement of Homo erectus by Homo
sapiens? Which is now favored?
• When Homo sapiens evolved, what other homini were living?
• When did the earliest Homo sapiens appear? When did Homo
sapiens sapiens appear?
• What is the evidence for hybridization involving Neaderthals,
Denisovans, and Homo sapiens? Was some of this hybridization
adaptive potentially adaptive?
• What roles did bipedalism, meat, cooking food, and language
acquisition play in the evolution of hominids?
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