Chapter 16

Legacies of Human Evolutionary History

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?

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.

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.

Life Cycle Stages forVarious Animal Species

Diameter of the Birth Canal of Adult Females and Head Length and Breadth of Newborns

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

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.

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.

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.

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.

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.

Onset of Puberty

Factors: Genetics Gestational experience Nutrition Disease Activity level Stress

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.

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.

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.

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.

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, 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?

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.