Transcript EARLY HOMININ EVOLUTION:

EARLY HOMINID EVOLUTION:
http://www.wsu.edu/gened/learnmodules/top_longfor/timeline/01_notes_defin
itions.html
• Sahelanthropus tchadensis
(7 mya)
– fossils of six and perhaps as
many as nine individuals
– oldest hominid
– may have been the time
(before or after?) when the
hominids are thought to
have diverged from
chimpanzees
• often referred to as the
“great divergence”
• Orrorin Tugenensis (6 mya)
– means “original man” in Tugen
– represented by only a few fragments of
bone
• thirteen fossils belonging to at least five
individuals
– may be a direct line of descent to
modern humans
• if correct, then all of the australopithecine
species would represent a different
branch of hominids, rather than human
ancestors
• the human line would presumably stretch
from an as yet undiscovered species at the
point of divergence through Orrorin
tugenensis, and from thence through
several as yet undiscovered species to the
earliest Homo species
• Ardipithecus ramidus
(4.4 million years ago)
– much more widely
accepted by the
scientific community as
a hominid than previous
species
– lacks almost all of the
advanced
specializations of
modern chimps such as
knuckle-walking and
brachiation
– may have walked
upright
• Australopithecus anamensis (4.2 to 3.9
million years ago)
– direct evidence of bi-pedalism somewhat earlier
than 4 million years ago
– these early hominids had developed upright
walking prior to the disappearance of woodlands
and forests in eastern Africa
– thickened enamel on teeth suggesting a diet of
hard-to-chew foods is also a trait characteristic of
all later hominids
Three million years ago was a critical period
in the development of the hominid species,
and ultimately, of human beings
http://www.wsu.edu/gened/learnmodules/top_longfor/timeline/01_notes_defin
itions.html
• Australopithecus afarensis (3.6
to 2.9 mya)
– “Lucy”
• Finding Lucy (4:33)
– fragments of 320 individuals of
have been discovered
– the earliest species for which we
have reliable brain and body size
estimates, thanks to a rich fossil
record for the species
– probably inhabited the savannas
and open woodlands where they
likely found fruits, seeds, and
roots
• knee and pelvic bone structure of were very humanlike,
leaving no doubt that A. afarensis walked upright
• Fossil evidence of bipedalism (3:06)
• Latoli footprints (3:20)
"Lucy" in comparison with a modern
human female
• Kenyanthropus platyops (3.5 to
3.3 million years ago)
– small ear holes and advanced
traits like a relatively flat face and
small molars
– may put it in the direct line to
modern humans
• humans may have emerged from a
completely different line descending
from O. tugenensis and/or K.
platyops, as the Leakeys believe
– many anthropologists will
continue to withhold judgement
on its validity and significance
• Australopithecus africanus (3 to 2 million
years ago)
– pelvis is more human than apelike
– shape of the jaw is like that of humans, and the
size of the canine teeth is further reduced
compared to afarensis
• Paranthropus aethiopicus, robustus and boisei
(2.7 to 1.4 million years ago)
– evolved “along side” early human species
and undoubtedly interacted with them
– not regarded as being in the ancestral line to
modern humans
• small brained (400-550 cc)
compared to human species
• “chewing” specialization in
contrast to our ancestors, that
evolved as omnivores with a taste
for meat
massive grinding teeth and jaws
Members of the Genus Homo
• most important characteristic of the genus
Homo is larger brain size compared to other
hominids
H. rudolfensis
Homo habilis
Heidelbergensis Neandertalensis
• the association of cultural artifacts and tools
• two current theories
1. Parallel Evolution Theory
•
several dispersed populations of Homo
evolved into Homo sapiens at roughly the
same time
2. Radiation theory
•
modern human beings arose in Africa about
200,000 years ago and migrated out of Africa
•
•
called the “Out of Africa” theory
more recent theory based on genetic
evidence
• Homo rudolfensis (2.3 to 1.9 million years ago)
– oldest, fairly complete human skull yet discovered
– mix of characteristics makes this individual a good
candidate for a transitional species between the
australopithecines and the genus Homo
• Homo habilis (2.3 to 1.6 million years ago)
– "handy man", was so called because of evidence
of tools found with its remains
– the bulge of Broca's area, essential for speech, is
visible in one H. habilis brain cast, indicating that
the species may have been capable of
rudimentary speech
• Homo ergaster (2 million to
1.5 mya)
– the most complete skeleton on
any early hominid species
– male 11 to 13 years of age
– first Homo species to have
roughly the same body
proportions as modern
humans
• Homo erectus (1.8 to 0.3 million years ago)
– the most long-lived species in the genus Homo
– may have been the first
to leave Africa
• remains are dispersed
across three continents
– larger brained individuals exhibit a 50% increase
in brain size over earlier hominids
Individual specimens of Homo erectus vary widely but trends are visible over
time. These artist's reconstructions of three faces from skulls show variations
over a period of about a million years
• probably the first species to use and control
fire
• decrease in sexual dimorphism
• a mutation slowed down the growth of the
fetal brain
– this also slowed our whole maturation process
– modern humans have the longest juvenile stage
of any life form
• Homo heidelbergensis (600,000 to 200,000
years ago)
– more robust and muscular than modern humans
– evidence that it hunted and butchered the large
mammals of the period—elk, bison, horses,
rhinos, and even mammoths
– at least estimated 28 individuals
• 5,000 bones found
• Homo neanderthalensis (250,000 to 30,000
years ago)
– scientists long believed they were a closely related
sub-species of modern humans and for a time
classified as Homo sapiens neandertalensis
– modern human DNA differed more than expected
from the Neanderthal DNA
– http://www.pbs.org/wgbh/nova/teachers/evolution/ho
)
mo-sapiens-vs-neanderthals.html (4:58
– average Neanderthal brain was slightly larger than
that of modern humans, but this is probably
correlated with larger body size in gender
– arm and leg bones are approximately twice as
thick as ours, suggesting both their immense
strength and the rugged conditions of their
existence
The left arm is completely
withered from an early
injury or disease. The fact
that the individual with an
injury this severe survived
into a relatively advanced
age implies the existence
of a complex social life in
which other group
members would have
shared food and other lifesupporting tasks
– for about 70,000 years, Neanderthals roamed
Earth with modern Homo sapiens
• Homo floresienses (95,000 to 13,000 years ago)
H. floresiensis compared to modern human
– the Little People of Flores
– has been described as one of the most spectacular
discoveries in paleoanthropology in half a century—
and the most extreme human ever discovered
– scientists theorize that a group of H. erectus somehow
found their way across this barrier and colonized the
island. Over time, the usual “island effects” by which
large animals tend to become smaller and small ones
larger affected this isolated population
– may be dwarf sub-species of Homo erectus
– http://www.pbs.org/wgbh/nova/evolution/littlepeople-flores.html (11:42)
• Homo sapiens (sapiens) (200,000 years ago to
present)
– hunting
– elaborate tools
– cave art
– symbolic artifacts
– ceremonial practice