Human Variation

Human Variation What is Variation?? The differences between people and populations. The differences among members of the same species.

Human Variation Polytypic: A polytypic species is composed of local populations that differ in the expression of one or more traits. Even within local populations there is a great deal of genotypic and phenotypic variation between individuals.

Human Variation Three questions anthropologists ask about human variation: 1. What is the pattern of variation within a population? 2. What is the pattern of variation between populations? Why?

Human Variation The Difference within a population: Differences in genotype and phenotype Allele frequencies Average height of a population

Human Variation The Differences Between Populations: Height differences Notable pattern of similarities and differences Geographic patterns?

Human Variation Why? What is the explanation for these patterns? Can we explain human biological variation in terms of genetics and evolution? Can we do so within a testable hypothesis?

Adaptive Significance of Human Variation Human variation is the result of adaptations to environmental conditions. Physiological response to the environment operates at two levels: Long-term evolutionary changes characterize all individuals within a population or species. Short-term, temporary physiological response is called acclimatization.

“Race” What is race? How do you define race?

Biological Determinism A European view that non-Europeans were “uncivilized,” and unintelligent. They associated physical characteristics that values, intelligence, values, and morals. Developed by Francis Galton, cousin of Charles Darwin.

Eugenics Flourished in the early 1900s (1900-1930s) “Race Improvement” through the forced sterilization of individuals of some groups and increased reproduction among others. Developed by Francis Galton.

The Concept of “Race” It’s simply a matter of variation within one species. The word “race” first appeared in the 1500s, with changing meanings. Has biological connotations but actually has social significance. “Ethnicity,” as a term, began to be used in the 1950s, to avoid the loaded term “race.” Ethnicity refers to cultural factors.

The Concept of “Race” Pre-WW2: “Race” categories only based on observable phenotypes. Today human variation is studied through allele frequencies. Variation between groups is actually much smaller than variation within groups. All humans are more alike than ANY other population of mammalian species.

“Race” and Physical Anthropology From visible phenotypic variation to the explanation of differences in allele frequencies What is the adaptive significance of such differences? Forensic anthropologists use expertise on ancestry to identify victims of war and crime.

Population Genetics The study of the frequency of alleles, genotypes, and phenotypes in populations from a microevolutionary perspective. A gene pool is the total complement of genes shared by the reproductive members of a population. Breeding isolates are populations that are isolated geographically and/or socially from other breeding groups.

Thermal Environments Mammals and birds have evolved complex physiological mechanisms to maintain a constant body temperature. Humans are found in a wide variety of thermal environments, ranging from 120° F to -60° F. Bergman’s Rule Allen’s Rule

Evolution of stature variation Bergman’s Rule: Body size tends to be greater in populations that live in cold environments. Allen’s Rule: In colder climates shorter limbs with increased mass-to-surface ratio are adaptive because they are more effective at preventing heat loss. Longer limbs are more adaptive in warmer climates because they allow for greater heat loss.

Ultraviolet Rays Ultraviolet Rays penetrate the skin and can eventually damage DNA within skin cells. The three major types of cells that can be affected are squamous cells, basal cells, and melanocytes. Affects chemical compounds that are essential for reproduction, DNA, folate, and Vitamin D

Ultraviolet Radiation Considering the cancer-causing effects of UV radiation from an evolutionary perspective: Early hominins lived in the tropics, where solar radiation is more intense than in temperate areas to the north and south. Early hominids spent their days outdoors. Early hominins didn’t wear clothing that would have protected them from the sun.

Evolution of skin pigmentation Lightly pigmented skin evolved three separate times, including with the Neandertals. Females in of a population have lighter skin than males of that same (biological) population. Females need more calcium/Vitamin D Males need higher folate levels to safeguard the production of sperm

Evolution of skin pigmentation Individuals with dark pigmentation need to spend more than 5X the amount of time in the sun as those with light pigmentation in order to make the same levels of vitamin D. Melanocytes: in people with very lightly pigmented skin often causes them to develop small spots of pigmentation (freckles).

http://www.ted.com/talks/nina_jablonski_breaks_the_illusion_of_skin_color.html

Polymorphisms Characteristics with different phenotypic expressions are called polymorphisms. A genetic trait is polymorphic if the locus that governs it has two or more alleles. Geneticists use polymorphisms as a tool to understand evolutionary processes in modern populations.

Polymorphisms at the DNA Level Molecular biologists have recently uncovered DNA variability in various regions of the genome. Scattered through the human genome are microsatellites, sites where DNA segments are repeated. Each person has a unique arrangement that defines their distinctive “DNA fingerprint.”

Human Biocultural Evolution Humans live in cultural environments that are continually modified by their activities. Evolutionary processes can be understood only within this cultural context.

Biocultural Evolution Mutual interactive evolution of human biology and culture. The idea that biology makes culture possible and that developing culture influences the direction of biological evolution Biology and culture have a symbiotic relationship This makes human evolution unique.

Human Biocultural Evolution Example: In the USA socioeconomic status plays a role in nutrition, whereas in some other areas of the world nutrition correlates with biological sex.

Biocultural Evolution One of the biggest changes in the past 10,000 = advent of agriculture. Preagricultural diet = very high in animal protein, high in complex carbs, but low in salts and lipids. Today it is the opposite: diets tend to be high in salts and lipids, low in complex carbs and calcium. Many of today’s diseases are related to this issue.

Agriculture Cereal grains and diary Overall human health actually declined with the advent of agriculture (ex: iron deficiency anemia first appears with the advent of agriculture). Clark Larsen “environmental catastrophe.” Jared Diamond “Worst mistake humans ever made.” BUT: the earth couldn’t support 7 billion humans without it.

Adaptive vs 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 “Feast or Famine Biology”

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 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 Brian 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

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

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 Most life cycle stages are marked by some type of biological transition similar to all other primates. Humans though, add a cultural layer to these changes…

Pregnancy, Birth and Infancy Cultural and social factor shape infant’s development in utero. Birth is dangerous event and often surrounded by ritual significance. How? “Underdeveloped” human infant brains adapted to developing in cultural enviornments.

Adolescence Puberty has very different meanings in different cultures. ex: a girl’s first period can be cause for a ritual celebration (Menopause can elevate a woman’s status in many non-western societies.) While men have biological markers during puberty as well, these are less apparent and so there are usually “coming of age” rituals and stories surrounding male adolescence.

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

Aging 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 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

Technology and 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??? YES! 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 The human species will continue to evolve (or become extinct)