Evolution, 4th Edition

■■Humans evolved from arboreal, social primate

ancestors with binocular vision, grasping hands,

and cognitive abilities associated with social life—

features that were important foundations for

later human evolution.

■■Important evolutionary changes in the evolu-

tion of the human body include adaptations for

bipedality, opposable thumbs, alteration of the

vocal tract, a higher reproductive rate, a higher

metabolic rate, and a longer childhood. The

most important change is our very large brain,

with its unparalleled cognitive abilities.

■■Hominins are the lineage that includes humans

and that diverged from chimpanzees about 7

Mya. Fossil hominins show that humans origi-

nated in Africa. Fossils of species in the genus

Homo date from about 3 Mya. H. erectus was the

first hominin to leave Africa, and spread through

Europe and Asia. About 600 Kya, a second wave

left Africa and gave rise to Neanderthals and

Denisovans. Finally, Homo sapiens spread out

of Africa 60 Kya, hybridized and acquired genes

from Neanderthals and Denisovans, and spread

across the entire Earth by 12 Kya.

■■Human populations do not show much diver-

gence across the genome: among Africans, East

Asians, and Europeans, only 12 percent of the

total genetic variation is caused by differences

in allele frequencies among populations. Some

of those differences, however, are responsible

for variation in skin color, metabolism, and other

traits that adapt humans to different environ-

ments. Many traits show continuous ranges of

variation, and the concept of discrete races does

not apply to the human species.

■■Two distinctly human traits are our enormous

brain and our use of language. A larger brain

was likely selected for by ecological factors and

by social interactions in groups. Our high meta-

bolic rate supports both the brain’s huge energy

consumption and our high rate of reproduction.

Speech is enabled by both the large brain and a

modified vocal tract.

■■Other ape species, especially chimpanzee and

bonobo, make and use tools in the wild, and can

learn and use elements of language in captivity.

This suggests that the common ancestor of hu-

mans and African apes had rudimentary capaci-

ties for language, tool making, and reasoning.

■■Culture enabled humans to occupy more differ-

ent environments, over a broader geographic

area, and to use a greater variety of food and

other resources than any other species. Agri-

culture began about 11 Kya. It had profound

impacts on our diet, social organization, and

population growth; the prevalence of diseases;

and the fates of countless other species. The

changes caused by agriculture altered the

course of human evolution, as shown by several

genetic adaptations to diet and changed condi-

tions that came with agricultural societies.

■■Natural selection and evolution are ongoing

in human populations, even in industrialized

societies. Height and cholesterol level are two

of the many traits that affect fitness and that are

heritable. Many traits are mismatched to our

agricultural diet, which has been widespread for

only several hundred generations, and to other

aspects of modern life.

■■Culture is a pronounced human feature that has

enabled our species to inhabit and dominate

almost all of Earth. Cultural traits change in ways

that have some similarities to genetic evolution,

but there are also important differences be-

tween cultural and genetic evolution. The most

important is horizontal transmission: by imitation

and learning, a cultural trait can spread across a

population (and today, even the entire globe)

within a single generation.

TERMS AND CONCEPTS

biased transmission

cultural evolution

meme

Neanderthal

social brain

hypothesis

SUGGESTIONS FOR FURTHER READING

An introduction to almost all aspects of human

evolution is Basics in Human Evolution, ed-

ited by M. P. Muehlenbein (Academic Press,

London, 2015), with contributions by 48 au-

thors. The Story of the Human Body: Evolu-

tion, Health, and Disease, by D. E. Lieberman

(Vintage Books, NY, 2014), is an outstand-

ing treatment of the topics indicated by its

title. Genetic and genomic aspects of human

evolution are comprehensively treated in the

textbook Human Evolutionary Genetics by M.

Jobling and colleagues (Garland Science, NY,

SUMMARY

21_EVOL4E_CH21.indd 569 3/22/17 1:51 PM