Hominin Evolution

This may be a touchy subject, but I’m in the process of reviewing this material for a midterm later on this month. I need to ace this class. Let’s get on with it!

In relation to time, humans are new to the game coming in the last 100,000 years. That does seem long in comparison to the length of the societies that we’ve built, but in the case of geological time, that’s less than a second. The universe by physicists’ estimates is 15 billion years old (bya), with Earth forming around 4.4 bya, the first vestiges of life showing from 3.7 bya, and having the first primates appear around 85 million years ago. From there, the genus Homo flourished for a couple million years before being defeated completely and totally by Homo sapiens (us), leaving humans as the only Homo species left after 4 million years.

Geologic_Clock_with_events_and_periods.svg
We humans are really late to the party¬†as if God knew how much of a problem that we’d be.


Ardipithecus ramidus

Although not a member of Homo, (and its chimpanzee-like brain is a tell-tale sign) Ardi is special because it was the first recorded ape that could walk upright for brief periods of time. We know this because of Ardi’s mosaic pelvis. However, Ardi didn’t walk upright all the time, most likely because of the stress that places on its back and joints.

Australopithecus afarensis

Another non-Hominin, but also an important contender in the development of man. It could walk fully bipedal throughout its life!

787px-Australopithecusafarensis_reconstruction
Australopithecus afarensis

Homo erectus (1.9-100kYa)

Africa and Eurasia’s first hominin was tall at 6ft average and was beginning to develop larger brains that were capable of cognitive flexibility, tool construction, and hunting. Its teeth were changing to adapt to an omnivorous diet.

Homo heidelbergensis

Hominin brains just kept getting larger until…

Homo sapiens

Modern man or “wise man” as the Latin states have the largest and most complex brain on record for any hominin species or any species for that matter.

Selection Pressures for Humans

  1. We lived in large groups: this forms the basis of the Social-ecological hypothesis.
  2. Human babies were helpless for longer periods of time as compared to other animals: this led to alloparenting and the sexual division of labor.
  3. Larger brains were a costly tissue to feed: humans became omnivorous and ate meat to supplement their calorie intake as well as had smaller guts to expend less energy.

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