Human lineage Cheat Sheet by Anais_Pe

Distin­ction between early hominins and modern humans through bipedal locomo­tion, brain size, slowed develo­pment, dental morphology and cultural adapta­tions.

Fossil record consists of partial cranium, partial mandibles, some teeth, part of a femur and lower arm bones.

Brain size = much smaller than modern human, closer to ape size. Face also = very flat with large brow ridge.

Mixture of primitive and derived dental traits e.g. canine sharpens itself on the first premolar like in chimps.

Postcr­anial skeletal evidence for locomotion suggests bipedalism in Ardipi­thecus e.g. pelvis, feet and hands.
- Feet show mixture of modern ape and human morpho­logy: opposable toe like apes, but other 4 toes adapted to bipedalism.
- Pelvis shows shorter + broader ilium than in chimps. Lower part of pelvis = more ape-like.

So in conclu­sion, most likely bipedal but perhaps also transi­tional? Gait would have been different to that of modern humans.

Chimp pelvis (quadr­upedal) = much taller and slimmer.

Stepping involves rotation of torso, facili­tated by torque (twisting force). Torso is kept from tipping by abductor muscles attached to the ilium.

Bipedalism requires knees to be close to centre of the body (i.e. curve inwards), so femur slants downwards and inwards.

Arboreal hominins faced with enviro­nmental changes and retreat of forests. More grasslands with some trees and shrubs. Bipedalism as a means of escaping fast-r­unning predators.

Bipedalism could have altern­atively evolved in an arboreal setting before being used terres­tri­ally. Morphology of teeth in early hominins show arboreal diet to support this. This also expands the savannah mosaic hypothesis as it suggests the possib­ility for a semi-a­rboreal lifestyle - this matches evidence of transi­tional bipeda­lism.

Keeping cool
(Wheeler)

Heat stress becomes more important as tree cover retreats and enviro­nment becomes more exposed. Standing upright reduces this stress.
Doesn't fit evidence regarding bipedalism evolving in semi-a­rboreal hominins, but could have been a factor in mosaic enviro­nments?

Turkana Boy excavated by Leakey.

Morpho­logical evidence for H. erectus' ability to run for long distances and throw objects with high accuracy.

Longer neck and torque to counteract the twisting of the torso generated when running. Other morpho­logical features present also = consistent with modern human adapta­tions to long-d­istance running.

Overall = mixture of primitive and derived traits.

Java Pithec­ant­hropus erectus
~1.3 mya

The first human ancestors excavated outside of Europe. Then classified as Pithec­ant­hropus erectus ("erect monkey­-ma­n"), these remains were ultimately attributed to H. erectus. Initially however the S. pekinensis remains were classified under the Pithec­ant­hropus genus as associ­ations were made between the two.

Recent v. archaic H. erectus

Pithec­ant­hropus = much older than Sinant­hropus. Multiple species evolving simult­ane­ously in different climactic condit­ions? Divergent evolution between the two, possibly caused by meteor in sea of China.

Temper­atures begin to cool down c. 75kya

Long + low skull with rounded bulge at back.

Very thick leg bones, scapulae had more muscles attach­ments, wider rib cage... Overall very sturdy and strong, slightly shorter than modern humans on average.

Animal remains often dominated by one or two species - e.g. Mauran in France with remains of bison and aurochs. This non-random sample suggests cooper­ative and organised hunting strate­gies.

Pigment is collected, crushed and made into crayons which have been shown to be usable on skin (so could have been used for body markin­gs?). Markings could have been symbolic, ritual­istic or even medicinal. Evidence of ocre use in Los Aviones, Spain, in shells used as recept­acles.