EARLY HOMINID EVOLUTION:

http://www.wsu.edu/gened/learn-modules/top_longfor/timeline/

01_notes_definitions.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

http://www.wsu.edu/gened/learn-modules/top_longfor/timeline/

01_notes_definitions.html

Three million years ago was a critical period in the development of the hominid species,

and ultimately, of human beings

• 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

• most important characteristic of the genus Homo is larger brain size compared to other hominids

• the association of cultural artifacts and tools

Members of the Genus Homo

H. rudolfensis Homo habilis Heidelbergensis Neandertalensis

• two current theories1. 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/homo-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

– for about 70,000 years, Neanderthals roamed Earth with modern Homo sapiens

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 life-supporting tasks

• Homo floresienses (95,000 to 13,000 years ago)

– 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/little-people-flor

es.html (11:42)

H. floresiensis compared to modern human

• Homo sapiens (sapiens) (200,000 years ago to present)– hunting – elaborate tools– cave art– symbolic artifacts– ceremonial practice