Legacies of Human Evolutionary

1. Legacies of Human Evolutionary History: Effects on the Individual

2. Question: • Does the flexibility of human behavior pose problems for the species?

3. 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

4. Changing Contexts

5. Biocultural Evolution and the Life Course • Biological development occurs from embryo to old age • Cultural factors interact with genetically based characteristics

6. 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

7. 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

8. 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

9. 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

10. 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.

11. 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.

12. Comparison of Diet (Table 13-1)

13. Comparison of Diet

14. 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

15. 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

17. 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

18. 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

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

20. Variation in Growth Hormones

21. 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

22. 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

23. Life Cycle Stagesfor Various Animal Species

24. 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

25. Diameter of Birth Canal and Head Length and Breadth of Newborns

26. 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

27. Childhood • Humans have unusually long childhoods, which illustrates importance of learning for human adaptation • Humans might be unique in practice of provisioning for juveniles

28. Providing for Juveniles

29. Adolescence • Rapid growth seen during adolescent growth spurt unique among primates

30. Adulthood • Women in our evolutionary past likely experienced fewer menstrual cycles throughout life • Most were more often pregnant or nursing

31. 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

32. The Trend in Age at Menarche in Europe

33. 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

34. Life Spans (Table 13-4)

35. 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

36. Mitochondrial Theory • Free radicals produced by mitochondria diminish efficiency of cellular energy production • Ultimately leads to organ failure

37. Teleomere Hypothesis • Repeated sequences of DNA at end of chromosomes • Get shorter as organisms age • Ultimately, impairs healthy cell division

38. Changes in Life Expectancy Due to AIDS in Seven African Nations

39. 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

40. 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

41. 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.

42. 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.