Human evolutionary history

Humans show similarities with ‘apes’ (gibbons, orang, gorilla, chimps)

• shared derived traits: large brain, no tail, more upright posture

other Old World monkeys ‘apes’ and humans

increased brain sizeloss of tail

upright posture

Human evolutionary history

Which are closer: gorilla & chimps or humans & chimps?

• are traits shared derived versus convergent / lost?

human

similarities inteeth, skull, genitals

gorilla

?chimps

human

knucklewalkingmorphology

gorilla chimps

Human evolutionary history

Molecular data suggests chimps and human are close relatives

human

similarities inteeth, skull, genitals

gorilla

chimps

human

knucklewalkingmorphology

gorilla chimps

DNA similarities

common ancestor~5 million yrs ago

Human evolutionary history

Humans’ closest living relatives are chimpanzees

• shared derived traits: morphological: skull, teeth, genitals behavioral: hunting, tool use, social behaviors

other Old Worldmonkeys chimps

increased brain sizeloss of tail

upright posture

gibbons

skull elongationloss of some hair

brow ridge

orang gorilla human

similarities in teeth,skull, genitals

many unique traits

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Figure 19.3

Mill

ions

of y

ears

ago

Australopithecusanamensis

Ardipithecusramidus

Ardipithecusramidus kadabba

Orrorin tugenesis

Australopithecusafarensis

Australopithecusafricanus

Australopithecusrobustus

Australopithecusboisei

Homoergaster

Homohabilis

Homoerectus

Homoneanderthalensis

Homosapiens

?

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• The earliest hominids were a diverse group– Various species of Australopithecus date

from about 4 to 1 million years ago– Our own species, Homo sapiens, is the

only hominid that has not become extinct

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• Australopithecines had relatively small brains – This indicates that

bipedalism preceded the evolution of the enlarged brain

– Bipedalism is a basic human trait

19.4 Upright posture evolved well before our enlarged brain

Figure 19.4

A brief history of human brains Neandertals - large brains 200,000 years ago Modern homo sapiens (and their brains) evolved ~

100,000 years ago in africa Most toolmaking came tens of thousands of years later Agriculture and the rapid growth of human

populations came 90,000 years later

Evolution

Evolution of mind The mind evolved just like the rest of the

body. The principle is clear, but the details are

highly contentious What might have been a driving force for

human minds?

Evolution

Evolution

The Mating MindGeoffrey Miller

Why do we have big brains?

Evolution of the brain Brain is expensive

brain energy use as a percent of resting body usage most vertebrates: 2 to 8% apes and some monkeys: 13% Humans: 20%

Evolution requires you to pay your way as you go;

no investment for 50,000 years in the future What was the brain used for in the mean time?

Forms of Darwinian Selection

Natural selection "nature red in tooth and claw" competition for food and for staying alive

Sexual selection Competition for mates

Sexual Selection Female mate selection

asymmetry of costs lead to male display and female selection

male birds generally have the plumage male humans have orgasm relatively easily, females less

easily Females are choosing

but also male selection in humans - why? hidden estrous requires multiple copulations male investment in childrearing?? or just ongoing courtship

The Handicap Principle Handicap’s provide useful signalsthat

the male is fit Handicaps in human

Aside: the immorality of handcap Sexual selection causes runaway "fads"

peacock's feathers

Advertising fitness Fitness

Genetic quality Health and nutrition

Sports what do you win? - status

Conspicuous consumption Conspicuous generosity

not kinship or reciprocal altruism

Theory of mind