5 Reading: Precursor to Civilization
The Evolution of Humans
Human evolution is an ongoing and complex process that began seven million years ago.
LEARNING OBJECTIVES
To understand the process and timeline of human evolution
KEY TAKEAWAYS
Key Points
- Humans began to evolve about seven million years ago, and progressed through four stages of evolution. Research shows that the first modern humans appeared 200,000 years ago.
- Neanderthals were a separate species from humans. Although they had larger brain capacity and interbred with humans, they eventually died out.
- A number of theories examine the relationship between environmental conditions and human evolution.
- The main human adaptations have included bipedalism, larger brain size, and reduced sexual dimorphism.
Key Terms
- sexual dimorphism: Differences in size or appearance between the sexes of an animal species.
- encephalization: An evolutionary increase in the complexity and/or size of the brain.
- Red Queen hypothesis: The theory that species must constantly evolve in order to compete with co-evolving animals around them.
- turnover pulse hypothesis: The theory that extinctions due to environmental conditions hurt specialist species more than generalist ones, leading to greater evolution among specialists.
- savannah hypothesis: The theory that hominins were forced out of the trees they lived in and onto the expanding savannah; as they did so, they began walking upright on two feet.
- Toba catastrophe theory: The theory that there was a near-extinction event for early humans about 70,000 years ago.
- social brain hypothesis: The theory that improving cognitive capabilities would allow hominins to influence local groups and control resources.
- aridity hypothesis: The theory that the savannah was expanding due to increasingly arid conditions, which then drove hominin adaptation.
- hominids: A primate of the family Hominidae that includes humans and their fossil ancestors.
- bipedal: Describing an animal that uses only two legs for walking.
Human evolution began with primates. Primate development diverged from other mammals about 85 million years ago. Various divergences among apes, gibbons, orangutans occurred during this period, with Homini (including early humans and chimpanzees) separating from Gorillini (gorillas) about 8 millions years ago. Humans and chimps then separated about 7.5 million years ago.
Generally, it is believed that hominids first evolved in Africa and then migrated to other areas. There were four main stages of human evolution. The first, between four and seven million years ago, consisted of the proto hominins Sahelanthropus, Orrorin and Ardipithecus. These humans may have been bipedal, meaning they walked upright on two legs. The second stage, around four million years ago, was marked by the appearance of Australopithecus, and the third, around 2.7 million years ago, featured Paranthropus.
The fourth stage features the genus Homo, which existed between 1.8 and 2