Legacies of Human Evolutionary History

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Chapter 16

• Legacies of Human Evolutionary History

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Chapter Outline

• 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?

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Humans

• 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.

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Biocultural Evolution and the Life Cycle

• 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.

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Life Cycle Stages forVarious Animal Species
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Diameter of the Birth Canal of Adult Females and
Head Length and Breadth of Newborns
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Life Spans
Organism Approximate Maximum Life Span (in years)
Bristlecone pine 5,000
Tortoise 170
Human 120
Blue whale 80
Indian elephant 70
Gorilla 39
Domestic dog 34
Rabbit 13
Rat 5
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Behavioral Ecology

• 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.

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Primate Life Phases

• 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.

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Brain Growth

• 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.

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Five Basic Nutrients

• 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.

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Evolution of Nutritional Requirements

• 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.

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Onset of Puberty

• Factors
• Genetics
• Gestational experience
• Nutrition
• Disease
• Activity level
• Stress

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Theories Nonreproductive Period in Human Females

• 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.

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Overpopulation

• 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.

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Impact on Biodiversity

• 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.

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Impact on Biodiversity

• 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.

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Acceleration of the Evolutionary Process

• Human-invented antibiotics are one example of how
  humans have accelerated the evolutionary process
  in other organisms.
• HIV-AIDS, dengue hemorrhagic fever, Legionnaires
  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.

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Is There Any Good News?

• 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.

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Are We Still Evolving?

• We are still evolving, but we dont 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.