Legacies of Human Evolutionary

History: Effects on the Individual

Question:

Does the flexibility of human behavior pose problems for the species?

Evolved Biology and Contemporary Lifestyles—

Is there a Mismatch?

Some aspects of modern human lives are disconnected from our evolved biology

In past 10,000 years, pace of cultural change has accelerated, changing the context of human evolution

Changing Contexts

Biocultural Evolution and the Life Course

Biological development occurs from embryo to old age

Cultural factors interact with genetically based characteristics

Human Growth and Development Today and

in the PastHuman growth continues through late teens or early 20s

Three major spurts are typical, including first two trimesters in utero, first four years and the adolescent growth spurt

Adolescent Growth Spurt

Pronounced increase in growth rate at puberty, compared to fairly steady level maintained since about four years

Western teenagers typically grow around 4 inches per year

Followed by decline in rate of growth until adult stature is achieved by late teens

Human Brain Growth

25% of its adult size at birth

50% at six months

75% at 2.5 years

90% at 2 years

95% at 10 years

Human Brain Growth

Such a small amount of growth before birth is unusual for primates and mammals

Selective advantages of such an underdeveloped brain

Exit through narrow pelvis modified for bipedalismBrain develops in stimulating, cultural context

Nutritional Requirements for Growth

Nutrients needed for growth, development, and body maintenance include: proteins, carbohydrates, fats, vitamins and minerals.

The amount we need of these nutrients coevolved with foods available to humans throughout evolutionary history.

Deficiencies during pregnancy can last a new child’s lifetime

The specific pattern of amino acids required in human nutrition (essential amino acids) reflects an ancestral diet high in animal protein.

Essential Amino Acids

The 9 (of 22) amino acids that must be obtained from the food we eat because they are not synthesized in the body in sufficient amounts.

Comparison of Diet (Table 13-1)

Total dietary energy (%)

PreagriculturalDiet

ContemporaryDiet

RecentlyRecommended

Protein 33 12 12

Carbohydrate 46 46 58

Fat 21 42 30

Alcohol ~0 (7–10) —

Cholesterol (mg) 520 300–500 300

Comparison of Diet

Total dietary energy (%)

PreagriculturalDiet

ContemporaryDiet

RecentlyRecommended

Fiber (g) 100–150 19.7 30–60

Sodium (mg) 690 2,300–6,900 1,000–3,300

Calcium (mg) 1,500–2,000 740 800–1,500

Ascorbic acid (mg)

440 90 60

Preagricultural Diet Prior to 10,000 years ago

Typically high in animal protein, low in fats, particularly saturated fats

High in complex carbohydrates (including fiber), low in salt, and high in calcium

Human health declined in most parts of the world, beginning about 10,000 years ago

“Epidemological transition” marked by rise of malnutrition, drop in life expectancy

Once adaptive, now maladaptive

Ability to store fat, an advantage when food availability often alternated between abundance and scarcity

“Feast or famine” biology incompatible with context of constant feast

80% of new cases of type 2 diabetes appearing between now and 2025 will be in developing nations

Type 2 diabetes, linked to poor diet and inadequate exercise, occurring in children as young as 4

“Epidemiologoical collision” in countries where malnutrition and infectious diseases collide with obesity

Other Factors Influencing Growth and Development: Genes and Environment

Genetics – set the underlying limitations and potentials for growth and development

Environmental factors can influence growth and development, but an individual can not exceed their genetic potential.

Epigenome-Instructions that determine how genes are expressed in a cell

Epigenetics-Changes in phenotype that are not related to changes in underlying DNA and that may result from the interaction between the genotype and the environment

Other Factors Influencing Growth and Development: Genes and Environment

Hormones – produced by endocrine glands

Growth hormone has an impact on almost every cell in the body.Cortisol, elevated during stress, suppresses normal immune function during high levels

Endocrine Glands

Glands responsible for secretion of hormones into the bloodstream, i.e. pituitary, thyroid, and adrenal glands, ovaries and testes

Variation in Growth Hormones

The Human Life Cycle1. Prenatal begins with conception and ends with

birth.

2. Infancy is period of nursing.

3. Childhood, or juvenile phase, is period from weaning to sexual maturity (puberty in humans.)

4. Adolescence is from puberty to the end of growth.

5. Adulthood is the completion of growth.

6. Menopause beginning one full year after the last menstrual cycle

Life History Theory

Typical developmental patterns shaped by natural selection

Entire life course thought of as a series of trade-offs among various life history traits

Life Cycle Stagesfor Various Animal Species

Pregnancy, Birth and Infancy

Cultural and social factor shape infant’s development in utero

Birth is dangerous event and often surrounded by ritual significance

“Underdeveloped” human infant brains adapted to developing in cultural environments

Diameter of Birth Canal and Head Length and Breadth of Newborns

Nursing

Most anthropologists suggest three to four years of nursing was the norm for humans in our evolutionary past

Agriculture produced more options for supplemental foods and could quicken weaning

Nursing can act as birth control

Childhood

Humans have unusually long childhoods, which illustrates importance of learning for human adaptation

Humans might be unique in practice of provisioning for juveniles

Providing for Juveniles

Percent Who Survive

Weaning Adolescence

Lion 28 15

Baboon 45 33

Macaque 42 13

Chimpanzee 48 38

Human Populations

!Kung 80 58

Yanomamo 73 50

Paleoindian 86 50

Adolescence

Rapid growth seen during adolescent growth spurt unique among primates

Adulthood

Women in our evolutionary past likely experienced fewer menstrual cycles throughout life

Most were more often pregnant or nursing

Menopause

Advantages“programmed” to live 12 to 15 years beyond birth of last child since human parenting involves years of post-partum careGrandmother hypothesis

Women freed to provide high-quality care to grandchildren

The Trend in Age at Menarche in Europe

Aging and Longevity

Attitude towards old age is culturally determined

Top 5 causes of death in the US are heart disease, cancer, stroke, accidents, and chronic obstructive lung disease (no longer in this order)

Senescence, the process of physiological decline in all systems of the body occurring toward the end of the life course

The decline is gradual throughout adulthood

Life Spans (Table 13-4)

OrganismApproximate 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

Pleiotropic Genes

Genes that have more than one effect.

Genes that have different effects at different times in the life cycle.

May help to explain evolutionary reasons for aging, but do not explain the causes of senescence

Mitochondrial Theory

Free radicals produced by mitochondria diminish efficiency of cellular energy production

Ultimately leads to organ failure

Teleomere Hypothesis

Repeated sequences of DNA at end of chromosomes

Get shorter as organisms age

Ultimately, impairs healthy cell division

Changes in Life Expectancy Due to AIDS

in Seven African Nations

Effects of Technology on the Brain

Our brains coevolved with technology and language development

Contemporary technological change may be much more rapid than evolution can keep up with

But, brains may be developmentally modified by using new technologies

Are We Still Evolving?

Socioeconomic and political concerns have powerful effect on our species today

Anthropologists can not predict whether humans will eventually become a different species or become extinct

There is little doubt that the human species will continue to evolve or become extinct

Why It Matters

The “small but healthy hypothesis” states that small adult stature under circumstances of low resource availability is adaptive in that small adults would need fewer resources and would fare better under chronically stressful conditions.

Why It Matters Anthropological and evolutionary

perspectives reveal that small body size also means small organs, less ability to perform work, and lower reproductive success.

Even if a baby whose mother was malnourished during pregnancy is well nourished from birth on, the child’s growth, health, and, for females, future pregnancies appear to be compromised.

This has clear implications for public health efforts that attempt to provide adequate nutritional support to pregnant women.