What makes us human?
Human Evolution
„ Upright posture, bipedalism
„ Advanced tool-making capability
„ Big brain, relative to body size, and small
canine teeth
„ Global dispersal
The history and geography of human
origins
„ Use of fire to modify environment
„ Language and ‘consciousness’ (self-
awareness)
„ Complex culture
Rosalind Harding, Rm 40.04 Henry Wellcome Building for Gene Function, Oxford
Primates: Life in the trees
lemur
„ A specialised form of primate:
Apes: evolution as a tree
gibbon gorilla chimp bonobo human orangutan
DNA analyses
(a) clarify relatedness
between species,
suggested by anatomy
(b) suggest a time scale
for tree
(c) specifically, a young
split time for humans
and chimps of 5-6
million years
What makes an
ape?
Monkeys: climb along tops of branches using hands & feet and tail to balance.
Apes: swing from branch to branch, & make more use of suspensory postures.
New genomic comparisons confirm
recent split <6.3 million years ago
15 Feb 2001
Hacia JG (2001)
Chimpanzee diversity: two species
1 Sept 2005
Pan troglodytes (common chimp)
Pan paniscus (bonobo)
29 June
2006
Our analysis also shows that human–chimpanzee speciation occurred less than 6.3 million years ago and probably more recently, conflicting with
some interpretations of ancient fossils. Most strikingly, chromosome X shows an extremely young genetic divergence time, close to the genome
minimum along nearly its entire length. These unexpected features would be explained if the human and chimpanzee lineages initially diverged,
then later exchanged genes before separating permanently.
Species divergence time: ~ 2-3 million years
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Chimpanzee diversity: several subspecies
Where and how did we become
different from other apes?
• Chimps are distributed across western and central Africa
• Subspecies can be distinguished by MtDNA and Y chromosome haplotypes,
and have different cultures of tool use and hunting behaviour
• Sub-species separation times: ~ 0.5 – 1 million years
Notwithstanding the DNA similarities, humans are quite a different animal
from their ape-like ancestors.
Gagneux, 2002, TIG 18:327-330
What can we learn from fossils?
gibbon gorilla
chimp bonobo human orangutan
First, they don’t fit on this
tree, most represent extinct
lineages.
Any missing links?
gibbon gorilla chimp bonobo human orangutan
Earliest hominid
Late Miocene hominid
from Chad reported in
2002.
Sahelanthropus
tchadensis
Hacia JG (2001)
Hominid/Hominin: any fossil
more closely related to extant
humans than to extant chimp
Hacia JG (2001)
Late
Miocene
ancestor
for
orangutan
Dated to 6-7 million yrs
ago.
This implies the humanchimp split must be older
than ~7 million!
Introducing the main family members:
The hominins
Moderns and Neanderthals
H. heidelbergensis
(archaic Homo)
Australopithecines
Early Homo sp.
H. ergaster
H. erectus (Asian)
Australopithecines and Homo habilis
Australopithecines
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Down from the trees
„ Lucy was bipedal, an adaptation for
travel across savannah woodlands and
grasslands
„ Big teeth, still not a big brain.
Sept 2006
Was there a big-brained ape ancestor?
„ Piltdown: the most famous fossil of all
Lucy
The hoax celebrated the idea that the
‘missing link’ was a big brained ape.
Lucy (Australopithecus afarensis)
compared with a modern human
Finds of australopithecines: completely
incompatible with Piltdown
Discovered in 1912 in Sussex
by Charles Dawson
Has hominin evolution been a
progression up from the Ape?
„ No
„ The theory of progression (by linear descent)
from an ape ancestor through missing links to
living modern humans, was dismissed by the
mid-twentieth century.
Fraud eventually dismissed by Le Gros Clark.
Australopithecine diversity: multiple
species (and sub-species)
„ Both gracile and robust forms (latter
sometimes called Paranthropus).
„ Evidence for sexual dimorphism within these
species
Proposed ‘missing links’ (early 1900s):
• ‘Java Man’ shown right including femur.
• Neanderthal phase
• A racial hierarchy of living humans
(Neanderthals linked with aboriginal
Tasmanians.)
Piltdown Man challenged
this progression, so the
hoax was not without value.
‘Java Man’ (Pithecanthropus erectus) found by
Rene Dubois in 1891/2 Solo River, Trinil.
Is there a dispersal pattern for
Australopithecine diversity?
Australopithecus robustus
Australopithecus
afarensis (Lucy)
Australopithecus
africanus
Australopithecus boisei
‘Homo habilis’, makers of tools
„ Homo (Australopithecus?) habilis :
„Multiple species from East
African lake sites.
„Relationship to Chad
specimens?
„Dispersal to South Africa in
late Pliocene? These
Australopithecines are
regarded as a single species,
Australopithecus africanus.
Fossils are from cave sites.
„ Evidence for A. africanus
also in east Africa.
„ How does geographic range
compare with chimpanzees?
some, but not all, have slightly bigger
brains.
„ Originally, Oldowan tool industry was
associated with H. habilis but tools
could have made by other
australopithecines.
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What kept early hominin brains
small?
„ Constraint imposed by stresses on crania of
attachment of masticatory muscles. (Must have been
a rough and mainly vegetarian diet!)
„ Gracilization and associated increase in cranial size
in subsequent hominin evolution were facilitated by
inactivation of a gene encoding the predominant
myosin heavy chain (MYH)
„ MYH: active gene in chimps and orang-utan
„ MYH: inactive in humans, marked size reduction
in muscle fibres individually and muscles overall.
„ Molecular clock estimate for age of gene
inactivation: 2.4 ± 0.3 Myr
Early Homo species
Stedman et al. (2004) Nature 428: 415-418.
H. ergaster lived in Eurasia at same
time as in Africa
Striding out, standing tall,
and at last, a big brain
Brain size versus height
„ Dmanisi fossils date to
1.7 mya
„ Caucasus Mountains,
Republic of Georgia
(well north of the
tropics)
„ Associated Oldowan
tools
„ H. ergaster is the first
species of hominin
adapted for endurance
running.
„ Turkana boy (1.5 million years ago): the earliest
individual with estimated brain size (909cc)
significantly above primate allometry curve.
„ What species name was assigned?
„
Homo ergaster
The problem of mixing up fossils
sourced across time and space
Why leave Africa? The role of
Pleistocene climate change
Warm
Early H. erectus (Sangiran)
1.7 mya
Widespread
geographic distribution
between Africa, SW
Europe and SE Asia: a
Daka from Ethiopia (H. ergaster) single paleospecies?
is similar to early H. erectus
Asfaw et al. (2002) Nature 416:317-320
Later H. erectus (Peking
Man) 0.5-0.4 mya
Onset of Lower
Pleistocene glaciations
at ~2 million years ago
with formation of
permanent ice sheets
and sharp cooling.
Africa becomes drier.
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What is life in the Pleistocene like for
early Homo species?
Homo erectus did cross sea barriers
„ Hunting game as well
„ Archaeology on
as scavenging
„ Control of fire (must
have helped with life in
the chillier parts of
Europe)
„ Improving the tool kit
„ more elaborate
Acheulean stone
tools: e.g. handaxe
for butchering
„ Increasingly complex
social behaviour
Flores, dates to
840,000 years
ago.
„ Hobbits on Flores
date to as recently
as 20,000 yrs ago.
Hobbit on left compared with modern human
Two models for becoming human
Archaic Homo
„ Ancestor: Homo heidelbergensis
„ Middle Pleistocene climate: colder and more variable; long cold glacial
periods punctuated by short, warmer interglacials.
„ Migrations of many species (not just hominins) between Africa and
Eurasia during interglacials.
25,000 yrs ago:
no Neanderthals
Neanderthals
in Europe
~ 500,000 yrs ago
~ 200,000 yrs ago
Modern humans in
Africa
60,000 yrs ago:
modern humans
outside Africa
Becoming human:
developing language
Meanwhile, back in Africa, a different
kind of human had emerged
As Neanderthals
Archaeological evidence:
Music
Jewelry
More complex tools
Ritual (burial of dead with
flowers?)
These imply language
ability
Anatomy is also
compatible with speech
production
„ Modern humans
„ Modern at 200,000 years ago
„ Modern by what criteria?
„
anatomy
„ Did modern humans emerge as the lucky survivors of a
population bottleneck?
„
„
No
What have we learnt from genetics since mitochondrial
Eve?
„ Genetic evidence for modern human language ability – Fox P2
(Review: Holden, C. 2004 Science 303:1316-1319)
„ While Neanderthals were becoming one kind of human,
moderns became another
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Out of Africa: diversity among early
modern Homo sapiens
(a) Skhul 5, Israel,
90,000 Yrs
(b) Cro-Magnon 1,
France, 23-27
KYrs
(c) Kow Swamp,
robust Aboriginal
Australian, 9-13
KYrs
Shared features:
Cranial vault
height high and
domed, brow
ridges lighter or
absent, chin
present
What happened when modern
humans met Neanderthals?
„ They lived in neighbouring valleys for thousands of years on the
western edge of Europe.
„ Divergence time not so great to suggest reproductive isolation
through speciation, but what about mating preference?
„ Genetic evidence from ancient mtDNA for population structure
suggests gene flow, if any, was restricted.
The Lapedo child
shares features of
both Moderns and
Neanderthals:
evidence for
admixture?
Dispersal of Moderns out of Africa
„ Into Middle East by 90,000 years ago, and then retreat.
(Neanderthal distribution expands)
„ Archaeological analysis of an emerged reef terrace on the Red
Sea coast of Eritrea dated to ~125Kyr ago indicate that early
humans exploited marine shore-line food resources. No fossils,
but behaviour is associated with moderns. (Walter et al. 2000
Nature 405:65-69.)
„ Reach Australia by 60,000 years ago, apparently via south
Asian coastal route.
„ 40,000 years ago: substantial presence of moderns in Europe
and Asia (little evidence in archaeological record at earlier
dates)
„ Was there a bottleneck in dispersal out of Africa? Implicated by
genetic data.
„ Note that this bottleneck is not associated with speciation,
only with modest structure between sub-Saharan and other
human populations.
Modern humans outlive Neanderthals
„ Caspari R and Lee S-H (2004) Older age becomes common late in
human evolution. PNAS 101(30): 10895-10900
„ Data: ratio of older to younger adults in hominid dental samples from
successive time periods
„ Assess age by degree of molar wear
„ Assess longevity from ratio of older to younger individuals (O:Y)
Results
Old
37
Early & Middle Pleistocene Homo 42
Young O:Y ratio
316
0.12
166
0.25
Neanderthals
96
24
Australopithecines
Early Upper Palaeolithic
European Moderns
37
50
0.39
2.08
Conclusion: increase in longevity during hominid evolution, but most
dramatically for modern humans
Modern human art: implications for
‘theory of mind’ ?
End of the ice ages: emergence of
racial features as we now know them
„ Into the LGM: Modern human populations contract in
size and geographic range
„
Populations of Neanderthals in Europe and Hobbits on
Flores go extinct.
„ Out of LGM: Ice retreats, sea levels rise, new range
expansions. New populations re-organise themselves
across the landscape
„ Continuities of morphological type
„ Art at ~70,000 yrs
ago in Africa
„ Art at ~30,000 yrs
ago in Europe: the
Paeolithic revolution
„
„
currently identified as racial variation
emerge in association with location
Kennewick Man,
8410 +/- 60 B.P.
Washing State,
USA
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What makes us human? A final review
„ Upright posture, bipedalism (adapted for endurance running, not
sprinting)
„ Tool-making capability, which becomes increasingly more
advanced.
Big brain, relative to body size, and small canine teeth
Global dispersal with only modest genetic differences
Use of fire to modify environment
Language and ‘consciousness’ (self-awareness)
Culture, combining
„ Transmission of information (memes) by copying, teaching,
and learning, with
„ Presentation of information to communicate an expression of
‘self’
„ Cultural expression as Art
„
„
„
„
„
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