The Evolution of Humans

Learning Objective

·       To understand the process andtimeline of human evolution

Key Points

·       Humans began to evolve about sevenmillion years ago, and progressed through four stages of evolution. Researchshows that the first modern humans appeared 200,000 years ago.

·       Neanderthals were a separatespecies from humans. Although they had larger brain capacity and interbred withhumans, they eventually died out.

·       A number of theories examine therelationship between environmental conditions and human evolution.

·       The main human adaptations haveincluded bipedalism, larger brain size, and reduced sexual dimorphism.

Terms

aridityhypothesis

The theory that the savannah was expanding dueto increasingly arid conditions, which then drove hominin adaptation.

turnoverpulse hypothesis

The theory that extinctions due toenvironmental conditions hurt specialist species more than generalist ones,leading to greater evolution among specialists.

Red Queenhypothesis

The theory that species must constantly evolvein order to compete with co-evolving animals around them.

encephalization

An evolutionary increase in the complexityand/or size of the brain.

sexualdimorphism

Differences in size or appearance between thesexes of an animal species.

socialbrain hypothesis

The theory that improving cognitivecapabilities would allow hominins to influence local groups and controlresources.

Tobacatastrophe theory

The theory that there was a near-extinctionevent for early humans about 70,000 years ago.

savannah hypothesis

The theory that hominins were forced out ofthe trees they lived in and onto the expanding savannah; as they did so, theybegan walking upright on two feet.

hominids

A primate of the family Hominidae thatincludes humans and their fossil ancestors.

bipedal

Describing an animal that uses only two legsfor walking.