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 Past Human 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 bipedalism Brain 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 (%) Preagricultural Diet Contemporary Recently Recommended Protein 33 12 Carbohydrate 46 58 Fat 21 42 30 Alcohol ~0 (7–10) — Cholesterol (mg) 520 300–500 300

Total dietary energy (%) Comparison of Diet Total dietary energy (%) Preagricultural Diet Contemporary Recently Recommended 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 Cycle Prenatal begins with conception and ends with birth. Infancy is period of nursing. Childhood, or juvenile phase, is period from weaning to sexual maturity (puberty in humans.) Adolescence is from puberty to the end of growth. Adulthood is the completion of growth. 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 Stages for 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

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 care Grandmother 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

Approximate Maximum Life Span (in years) Life Spans (Table 13-4) 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

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.