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Chapter 16
Legacies of Human
Evolutionary History
Chapter Outline
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Evolution of Human Behavior and the
Life Course
Biocultural Evolution and the Life Cycle
Human Impact on the Planet and Other
Life Forms
Overpopulation
Is There Any Good News?
Are We Still Evolving?
Humans
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Human biology is the result of millions of
years of evolution.
 Human beings are unique because we are
the product of biocultural evolution.
 Humans can live in a variety of climates have
a varied diet, and respond to the environment
both behaviorally and physically.
 The legacies of human evolution impacts the
individual, society, and the planet.
Biocultural Evolution and the
Life Cycle
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Anthropologists use life history theory to
answer questions about nonhuman primate
and human growth and development.
 The premise of life history theory:
– An organism has a limited amount of energy for
investment in its life course.
– There is a continual tradeoff in energy investment
among life history traits, and natural selection
shapes these tradeoffs.
Life Cycle Stages for
Various Animal Species
Diameter of the Birth Canal of Adult
Females and Head Length and Breadth
of Newborns
Life Spans
Organism
Bristlecone pine
Tortoise
Approximate Maximum
Life Span (in years)
5,000
170
Human
Blue whale
Indian elephant
Gorilla
Domestic dog
Rabbit
Rat
120
80
70
39
34
13
5
Behavioral Ecology
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Examines human social behavior in an
evolutionary framework.
 Reproductive efforts are a series of trade-offs
in time, energy, and resources invested in
mating and parenting.
 This paradigm argues
– males increase reproductive success by
maximizing the number of mates they have
– females maximize reproductive success by finding
a mate that will supply resources to her and her
children.
Primate Life Phases
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Most have four distinct phases: gestation,
infancy, juvenile, and adult.
 Monkeys, apes, and humans have added the
subadult phase.
 Only humans have a postreproductive phase
for females that follows menopause.
 Humans are unique among primates in that
our life cycle stages are marked by biological
and culturally determined social changes.
Brain Growth
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The pattern of human brain growth is unusual among
primates and other mammals:
– At birth the brain is about 25 % of its adult size.
– Six months after birth it has doubled in size and
reached 50% of its adult size.
– By age 5, the brain has reached 90% of its adult
size.
– By age 10 the brain is at 95% of its adult size.
Five Basic Nutrients
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Proteins are the major structural
components.
Carbohydrates are an important source of
energy.
Lipids include fats and oils.
Vitamins speed up the chemical reactions
necessary for running the body.
Minerals contribute to normal functioning and
health.
Evolution of Nutritional
Requirements
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Nutritional needs evolved according to the foods
available to our evolutionary ancestors.
We inherited the ability to digest animal protein from
our mammalian forebears.
Early primates evolved the ability to digest plants.
Our ape-like ancestors were fruit-eaters and passed
on their ability to process fruit to us.
Onset of Puberty
Factors:
 Genetics
 Gestational experience
 Nutrition
 Disease
 Activity level
 Stress
Theories: Nonreproductive
Period in Human Females
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Child-rearing theory - Women are "programmed" to
live 12 to 15 years beyond the birth of their last child.
Grandmother Theory - Women can provide
resources to their grandchildren if their own children
are independent.
Nonselection Theory - Menopause is an artifact of
the extension of the life span.
Overpopulation
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Currently human population increases
at an annual rate of 1.8% worldwide.
10 k.y.a., only about 5 million people
inhabited the Earth. There were about
500 million by the year 1650.
It is unlikely that world resources can
keep up with the current rate of
population expansion.
Impact on Biodiversity
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There have been at least 15 mass extinctions
in the past 570 m.y.
 Overhunting has been implicated in the
extinctions of many mammals near the end of
the Pleistocene.
 Humans were responsible for the recent
extinction of the moa, numerous species of
lemurs, and many bird and mammal species.
 Humans are responsible for the reduction of
the habitats of elephants, pandas, rhinos,
tigers, and gorillas.
Impact on Biodiversity
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Humans destroy about one football field-sized
area of rainforest every second.
 This seriously contributes to the loss of
biodiversity.
 Biodiversity is central to the ecology of this
planet, and many potentially beneficial
compounds may never be discovered if
biodiversity continues to decline.
Acceleration of the
Evolutionary Process
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Human-invented antibiotics are one example
of how humans have accelerated the
evolutionary process in other organisms.
 HIV-AIDS, dengue hemorrhagic fever,
Legionnaire’s disease, Lyme disease, and
drug-resistant strains of bacteria are
examples of the impact of human behavior on
the evolution of infectious diseases.
 Overuse of DDT has rendered it virtually
useless in fighting mosquito-borne malaria.
Is There Any Good News?
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The rate of growth of human populations has
slowed somewhat.
 Decreases in family sizes may result in
improvements in the environment.
 International efforts to preserve primate
populations have increased.
 Developing and developed countries are
beginning to discuss ways to reduce global
poverty.
Are We Still Evolving?
We are still evolving, but we don’t know if we
will become a different species in the future.
 Extinction is the ultimate fate of almost every
other species on Earth and it is likely we will
go extinct at some point also.
 Since humans are constantly exposed to new
environments and diseases, and children
continue to die due to limited medical care
and malnutrition, gene frequencies continue
to change.
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