Download Chapter 4 Modern Human Variation and Adaptation Historical Views

Chapter 4
Modern Human Variation and Adaptation
Historical Views of Human Variation 1
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As people encounter each other they look for ways to distinguish themselves. Skin color has been one of these ways as it is
so noticeable.
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By at least 1350 BCE (Before Common Era, new label), the Egyptians had classified humans based on skin color:
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Red for Egyptians
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Yellow for people from the East
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White for those of the North
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Black for those of the South
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Greeks saw all non-Greeks as barbarians. The barbarians could become Greek by taking on Greek culture.
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No indication the Greeks thought an innate basis for racial superiority

Hippocrates thought fertility/infertility of soil as causal
• The greater lusciousness of the tropics created a weaker, less warlike Asiatic
• The adversity of Greek soil resulted in character building
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Aristotle thought climate determined human variety
• The four humors: fire, water earth and air
• The Great Chain of Being
• All organisms aligned on the continuum from perfect form to lesser
• A fixed scale of nature, unchanging
Historical Views of Human Variation 2
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The lack of a rigid, racist hierarchy during the Greek (and Roman) era suggests that race is not innate, but constructed.
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This construction began during the European Age of Discovery and the later times of colonial domination by Europe
and the United States.
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With the Age of Discovery (post-Columbus) the issues of human diversity and what they mean expanded.
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Time of creation of nation-states
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New markets
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Europeans in contact with physically and culturally diverse populations at a pace much faster than during
Greek/Roman times
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The origin of race in Europe
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One explanation: There was a objective analysis of human diversity that validated the concept of European superiority
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Another explanation: The concept of European superiority was non-scientific, but based on social justification of
policies already in place with the expansion of the slave markets and colonialism.
Historical Views of Human Variation 3
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18th Century Naturalists and Race
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François Bernier was the first European to classify humans into races
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Decided that many morphological traits were needed
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No biological explanation was developed, based on Plato’s idea about ideal type (and forms)
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Linneaus (Karl von Linne)
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Binominal classification
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Homo sapiens (4 sub-species) and Homo troglodytes (apes)
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Homo sapiens europaeus, H. sapiens afer, H. sapiens asiaticus, H. sapiens americanus
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In a hierarchy from Europeans to Africans in context of perfection
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By the late 1700s, A German anatomist, Johann Blumenbach is often called reputedly the founder of modern physical
anthropology.
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Blumenbach introduced his typology of the Races of mankind
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Called five racial groups or human varieties: Causasoid (Europeans, “white race”); Mongoloids (Asians, “yellow
race”); Ethiopians (Africans, “black race”); Americans (Amerindians, “red race) and Malays (Polynesians, “brown
race”)
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He recognized that his classification system had limitations and overlaps. Even so, it was Blumenbach who coined the
term "Caucasian" to refer to Europeans
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He thought all other humans had devolved from the peoples of the originated in the Caucasus Mountains of Russia.
Historical Views of Human Variation 4
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For centuries, students of human variation searched for ‘scientific’ measures of racial differences.
One of the early researchers. Anders Retzius, introduced the idea of using the cephalic index (maximum breadth of
head/maximum length X 100).
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Terms for head shape:
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Doliocephalic heads are long and narrow
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Brachycephalic heads are broad
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Mesoscephalic are intermediate between these other two
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Head shape went out of fashion as an indicator of superiority when Northern Europeans and many African
populations were found to be similar in measurement.
The concept of biological determinism took hold by the mid-19th century
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In and of themselves these types of terms are merely descriptive, but they contributed to the idea of biological
determinism.
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Biological determinism links behaviors with physical traits

The concept that phenomena, including various aspects of behavior (e.g., intelligence, values, morals), are
governed by biological (genetic) factors.
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The inaccurate association of various behavioral attributes with certain biological traits, such as skin color.
By the mid-1800s, races were ranked on a scale based on skin color. The rank was from the sub-Saharan peoples at the
bottom to the NW Europeans at the top.
Historical Views of Human Variation 5
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After 1850, race was a constant source of debate.
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Many of our American heroes held deterministic (racist) views.
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Perhaps the iconic example of racial hierarchies is that published by Lewis H. Morgan, Ancient Society.
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In this book he outlines his views on technological, biological and cultural determinism.
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Want to read more? His book is posted at this website: http://www.marxists.org/reference/archive/morganlewis/ancient-society/
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As the founder of psychometry, Francis Galton (a cousin of Darwin) originated the eugenics approach to “race
improvement”.
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He began to study the variations in human intelligence.
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As a member of the Ethnological Society, he was greatly admired.
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Galton used an earlier statistician's idea called the law of the deviation from the average to develop a schema for classes
of human intelligence.
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He included dogs in his descriptions and suggested many races were of similar intelligence.
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This system was arbitrary, but was embraced as scientific.
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He expanded further to discuss the idea of dysgenesis where the less intelligent classes bred more offspring than
the more intelligent, upper classes.
Historical Views of Human Variation 6
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E. A. Hooton
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In 1926, wrote an article titled, Methods of racial analysis in which he outlined his ideas on race.
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"A great division of mankind, characterized as a group by the sharing of a certain combination of features, which have
been derived from their common descent, and constitute a vague physical background, usually more or less obscured
by individual variations, and realized best in a composite picture."
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Divided into large groups (primary groups) and secondary groups.
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Example: Mongoloid: Classic Mongoloid and Arctic Mongoloid
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Stanley Garn & his levels of races
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Wrote a book called Human Races in which he described several levels of races
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Geographical races: those which live in the same area but are distinctly different
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Local races: live in the same are but are different
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Micro races: those which share geography and culture but are still distinctly different
The Concept of Race 1
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All contemporary humans are members of the same polytypic species, Homo sapiens.
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A polytypic species is one composed of local populations that differ in the expression of one or more traits.
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Even within local populations, there’s a great deal of genotypic and phenotypic variation between individuals.
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What is race?
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Biological race: The idea that one or more physical traits distinguishes one group of humans from all the others.
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Often based on geography, nationality, genealogy, biology (sub-species), or some ‘flavor’
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Characteristics such as skin color are highly visible, and make it easy to group people into socially defined
categories
Social (Cultural) race: The cultural schema that result from the belief that races are biologically real
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While race is a term with biological connotations, it also has enormous social significance.
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There’s a widespread perception that physical traits are associated with cultural attributes.
The Concept of Race 2
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The term ethnicity was originally proposed in order to avoid the emotional baggage associated with the term race.
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The interchangeable use of the terms ‘ethnicity’ and ‘race’ are a product of the continued mistaken association of
phenotype and culture.
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Strictly speaking, ethnicity refers only to cultural factors.
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In its most common biological usage, the term race refers to geographically patterned phenotypic variation within a species.
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By the 17th century naturalists were classifying plants and animals and humans.
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But, even today there is no established criteria by which races of plants and animals are assessed.
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Prior to WWII, most studies of human variation focused on phenotypic variation between large, geographically defined
populations.
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After WWII, partly due to the Modern Synthesis, to genetics, and to a great extent to anthropologists shock over the Nazi
version of Social Darwinism the views began to change.
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Now evolutionary principles guide the research
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Now anthropology dispels the fixity of racial typologies.
The Concept of Race 3
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Biological race today
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Anthropologists recognize that humans are polytypic in that populations express
differences in some physical traits.
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Some of the differences are associated with geographic locations.
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Generally speaking, anthropology knows that race is not a real thing, genetically.
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Interesting work of R. C. Lewontin
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Lewontin determined that there is (as an average across traits) greatly more
diversity WITHIN a population as compared to BETWEEN populations.
However, we know that within populations there is great diversity of both
phenotypes and genotypes.
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There is no species type to which all members exactly conform.
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Locally is Mary Claire King (UW)
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Determined the close genetic similarity of humans and chimpanzees (99%), but
of course today we know it is more complex than this.
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Later moved on to breast cancer research
Figure 1: Percentage of human
genetic variation within and between
populations
The Concept of Race 4
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Typological model
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Early concepts of race were categorized by types. These typological groupings are based on phenotypical traits (how a
person looks). A few set of researchers continue to use typological classifications:
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Forensic anthropologists must deal with the race concept because they are asked by law enforcement agencies to
identify an individual’s race from skeletal remains.
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Medical research often argues for the use of racial categories.
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Populational model
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Differs from typological classification as it defines groupings based on breeding populations, then by phenotypes.
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The problem today is that there are very few populations so isolated that they can be separated from other groups of
people.
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Clinal model
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The distribution of many “racial” traits are clinal in nature
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Cline: A gradual change in the frequency of genotypes and phenotypes from one geographical region to another.
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In humans, the expressions of some polymorphic traits exhibit a continuous distribution from one region to
another, and most of these traits are Mendelian. Examples:
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The distribution of the A and B alleles in the Old World provides a good example of a clinal distribution.
Old World distribution of skin color is another.
The Concept of Race 5
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Clinal model (continued)
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While the clinal model is closest to the actual human distribution it is not exact
because,
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Many traits are discontinuous.
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Many of the traits used to define race are influenced by several genes.
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Today, The reality or utility of race as a valid biological concept is debated by many
physical anthropologists because:
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There is more variability within populations than between and
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Racial typologies represent an arbitrary means of simplifying biological
complexity.
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Genetic distances (Source: O’Neill (2012). Models of classification. Retrieved from
http://anthro.palomar.edu/vary/vary_2.htm)
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Humans are 99.9% genetically identical, most similar of all species
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Chimpanzees are 2-3 times more diverse, orangutans 8-10 times more diverse
Racism
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Racism is based on the false belief that such factors as intellect and various cultural attributes are inherited along with
physical characteristics.
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Such beliefs commonly rest on the assumption that one’s own group is superior to other groups.
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Eugenics movements are good examples of racism
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It is political ideology that has maintained a racially stratified society, not biology
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Racism promotes: social oppression, racist views discourage the oppressed from questioning their social positions and
racism promotes the status quo.
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Racism has costs (for all of us): It prevents the contributions of individuals, aggravates social problems such as poverty,
society invests time and money to defend social and institutional barriers, undercuts diplomatic relationships, restricts
communication between groups, inhibits social change, and promotes disrespect for law enforcement and decreases
chance for peaceful solutions
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There is a fantastic website to visit, created by the AAA (American Anthropological Association) called Race: Are we so
different?
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Link: http://www.understandingrace.com/home.html
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Look over the various links and learn a lot!
Interpretations of Human Variation 1
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As physical traits such as skin color and hair type are polygenic, it is hard to measure the genetic influence on them
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As a result, modern anthropologists are shifting research to the study of differences in allele frequencies. Originally this
mean the studies were indirect as in the products of the genotypes (such as the ABO blood variants)
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Polymorphisms at the DNA level
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Human polymorphisms are loci with more than one allele.
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Polymorphisms can be expressed in the phenotype as the result of gene action (as in ABO), or they can exist solely at
the DNA level within non-coding regions
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Today can measure directly due to new techniques. Many of the techniques were the result of the work done on the
Human Genome Project (HGP).
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New data on what we call CNVs (copy number variants) shows great variation between humans
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Each person is so unique as to have their one CNV (DNA) fingerprint
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The discovery of microsatellites, (a type of CNV that only repeats a few times) helps to create a DNA fingerprint
Interpretations of Human Variation 2
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Polymorphisms at the DNA level (continued)
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SNPs (Single Nucleotide Polymorphisms) are small, infrequent changes in single nucleotide (read point mutations) that
help give a person a unique DNA pattern.
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SNPs seem to be located in the ‘noncoding’ regions of the DNA, such as in the introns.
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There seems to be more than 15 million variants found to date.
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More than 1000 persons have had their entire genomes sequenced.
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As a result the researchers have identified about 95% of common patterns of human variation. Also 50-100 gene
variants linked to diseases.
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Confirmed (again) that most of human variation is found in Africa, little is found outside of Africa.
Human Biocultural Evolution 1
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Humans live in cultural environments that are continually modified by their activities.
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Evolutionary processes can be understood only within this cultural context.
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One example of the biocultural model is SCA (sickle cell anemia)
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Impact of malaria: Estimate of 50 million new cases each year with at least 1 million deaths directly attributed to
malaria. It tends to kill the very young and very old
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Slash-and-burn agriculture is a traditional land-clearing practice involving the cutting and burning of trees and
vegetation. In many areas, fields are abandoned after a few years and clearing occurs elsewhere.
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Human cultural adaptations affected the ecology of other organisms like the mosquito and malaria parasite,
also causing genetic change in the human population. allele was probably low.
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Prior to the development of horticulture in Africa, the frequency of the sickle cell. In fact, one estimate is it
appeared between 1,250-2,100 years ago.
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Sickle cell trait (being heterozygote) was an evolutionary advantage initially with the increase of malaria. Because
some HbA homozygotes are lost to malaria and HbS homozygotes usually die, this is often called a balanced
polymorphism
Human Biocultural Evolution 2
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Lactose tolerance
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Another example of the biocultural model is lactose tolerance (also called lactase persistence) is the ability to produce
lactase after the age of 5 years is a dominant trait.
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There appears to be co-evolution between cattle and humans. A lower incidence of lactose tolerance in some
human populations can be tied to:
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A cultural environment with a strong emphasis on pastoralism
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A recent history of consumption of fresh milk
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The mutation was lactase persistence in areas where it became an advantage:
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Lactose intolerance is high in most African and Asian populations and tends to be low in European populations.
There is a lower prevalence in Africa in populations that have a history of dairy farming.
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In the cattle cultures
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May be an advantage in areas where vitamin D production is lower (further away from equator), but latest data
suggest lactose tolerance (in Europe) developed in more southern parts of Europe first.
Map of Lactose Tolerance
Population Genetics 1
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Population genetics is the study of the frequency of alleles, genotypes, and phenotypes in populations from a
microevolutionary perspective.
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A population is a group of interbreeding individuals (breeding group) and is marked by a degree of genetic relatedness
and shares a common gene pool.
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In every generation, the genes (alleles) are mixed by recombination and rejoined through mating.
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Factors that determine mate choice are geographical, ecological, and social.
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Breeding isolates are populations that are isolated from other breeding groups.
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Human population segments within the species are defined as groups with degrees of endogamy (mating
within the group).
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FYI: The risk of cousin marriages is much lower than first thought. Read more here
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FYI: To increase your fitness, marry your 2nd or 3rd cousin
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Today there are greatly accelerated rates of exogamy (marrying/mating outside the group).
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Population Genetics 2
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Population genetics research is based on the Hardy-Weinberg Equilibrium equation (theory)
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The mathematical relationship expressing— under ideal conditions—the predicted distribution of alleles in populations.
HW is central theorem of population genetics.
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It is a math formula that starts from the idea of no evolution (null hypothesis) and says allele frequencies between
generations will be unchanging.
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If they change, evolution has occurred and then the math tries to figure out the various contributions of the forces
of evolution to the changed frequencies.
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Factors that act to change allele frequencies
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New variation (i.e., mutation)
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Redistributed variation (i.e., gene flow or genetic drift)
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Selection of “advantageous” allele combinations that promote reproductive success (i.e., natural selection).
Adaptive Significance 1
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Human variation is the result of adaptations to environmental conditions.
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There are actually three major ways to adapt to an environment:
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Genetically
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Culturally
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Physiologically (all organisms have mechanisms to respond to stress and to reestablish homeostasis)
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Stress, in a physiological context, is any factor that acts to disrupt homeostasis.
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The body responses to any factor that threatens its ability to maintain homeostasis. Homeostasis is a condition of
balance, or stability, within a biological system, maintained by the interaction of physiological mechanisms that
compensate for changes (both external and internal).
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Physiological adaptations can be short-term , long-term or permanent (called acclimatization) depending on the
duration of the environmental change and when it occurs; sweating is an example of this
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Developmental acclimatization is physiological adaptation that is permanent; chest shape to accommodate high altitude
is an example of this
Adaptive Significance 2
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What are the factors that create differences in skin color?
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Skin color is produced by melanin, hemoglobin and carotene
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Melanin is a pigment produced in the skin.
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All people have about the same number of melanocytes. The primary difference in skin color is in the amount of
melanin produced by the melanocytes
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The pigment melanin is responsible for the majority of variation in lightness and darkness in skin color.
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There are two types: eumelanin (dark or brown) and pheomelanin (light or red brown)
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Hemoglobin is another pigment affecting skin color which gives oxygenated blood cells their red color.
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Carotene provides a yellow to orange factor.
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Thickness of the outer skin layers also alters appearance
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Age and sex can create differences in skin color.
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Solar radiation, (ultraviolet rays) vitamin D, and skin color
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Ultraviolet Rays penetrate the skin and can eventually damage DNA within skin cells.
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The three major types of cells that can be affected are squamous cells, basal cells, and melanocytes (where melanin is
made). See diagram on page 83.
Adaptive Significance 3
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Solar radiation, Vitamin D and skin color (continued)

Why dark skin color?
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Skin color and vitamin D overproduction (rejected with additional research)
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Those stressors are still under consideration:
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Skin cancer (Ultraviolet light and cancer) rates
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Skin cancer rates are higher in white skinned populations
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More skin cancer in Texas than in Massachusetts
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Most often in post-reproductive segments of population
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Sunburn
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Infection due to the blistering from skin damage is a factor
Sunburn interferes with the ability to sweat
Folate (The damage to folic acid from solar radiation) was proposed by John Eaton (reported in Jablonski and
Chapin article)
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Folate deficiency alters the sperm and leads to male sterility
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Developing fetuses can be harmed (spina bifida)
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
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Adaptive Significance 4
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Solar radiation, Vitamin D and skin color (continued more)
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Why light skin color?
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Stressor: Areas of low levels of ultraviolet radiation away from equatorial regions have decreased risk. But the risk
of rickets rises
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Hypotheses:
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Vitamin D hypothesis: It is widely accepted that the evolution of light skin is related to the synthesis of
vitamin D from the sun and stimulation of chemical compounds caused by ultraviolet radiation.
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Lack of vitamin D leads to rickets
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There are several studies of darker-skinned, recent migrants to northern clines who suffer from rickets.
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Cold adaptation (dark skinned WWII soldiers are greater risk than light skinned) but debated at this time
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Camouflage or protective coloration hypothesis. Europe is snowy today and was very snowy during glacial
times
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In Asia, the same cold-related phenomena exist as is Europe, but northern Asia is drier and less cloudy.
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Actually, many north Asians are lighter than people from southern Europe.
Source: Skelton, R. (1997). Anthropology 360 lecture: Human variation. Retrieved from
http://www.anthro.umt.edu/notes/360
Adaptive Significance 5
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Thermal Environment (Hot and Cold) (continued)
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Body size and proportions also are also factors.
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Bergmann’s Rule considers the relationship of body mass or volume to surface area:
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In mammalian species ,body size tends to be greater in populations that live in
colder climates.
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As mass increases the relative amount of surface area decreases proportionately.
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Because heat is lost at the surface, it follows that increased mass allows for
greater heat retention and reduced heat loss
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Allen’s Rule considers shape of the body, especially appendages
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In colder climates, shorter appendages, with increased mass-to-surface ratios, are
adaptive because they’re more effective at preventing heat loss.
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Conversely, longer appendages, with increased surface area relative to mass, are more adaptive in warmer
climates because they promote heat loss.
Adaptive Significance 6
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Thermal Environment (Hot and Cold)
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Mammals and birds have evolved complex physiological mechanisms to maintain a constant body temperature.
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Our ancestors evolved in a warm to hot environment as our adaptations to heat demonstrate. Today, humans are found
in a wide variety of thermal environments, ranging from 120° F to -60° F.
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Response to heat
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We have sweat glands spread over our bodies (average 1.6 million!)
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Body hair in humans is the same number as in chimps and gorillas, but the size is smaller .
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Another mechanism is the ability for vasodilatation and vasoconstriction
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Vasodilatation is the expansion of blood vessels, permitting increased blood flow to the skin.
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Vasodilatation permits warming of the skin, and facilitates radiation of warmth in order to cool the skin.
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Vasodilatation is an involuntary response to warm temperatures, various drugs, and even emotional states
(blushing).
Adaptive Significance 7
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Thermal Environment (Hot and Cold) (continued)
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Response to cold

We use heat, clothing and shelter as cultural adaptations

Our bodies carry a fat layer as insulation
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Increasing the metabolic rate, shivering and even wrapping oneself into a ball are adaptations

Vasoconstriction is the narrowing of blood vessels to reduce blood flow to the skin.
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Vasoconstriction is an involuntary response to cold and reduces heat loss at the skin’s surface.
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With reduction of blood flow comes the risk of damage to tissues (frostbite)
High Altitude
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High Altitude Stresses
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Hypoxia: Oxygen starvation or hypoxia is more common in high altitudes due to the relationship of barometric
pressure and altitude causing oxygen content to be less concentrated
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Other Stresses: Ultraviolet radiation is greater at high altitudes. Thinner air also causes considerable heat loss, and
conditions are extremely dry.
Adaptive Significance 8
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High Altitude (continued)
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Physiologic Responses
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Physiologic Responses to Hypoxia
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The body reacts to high altitude immediately, including increase in respiration and red blood cell production.
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Possible hyperventilation, loss of appetite, and weight loss and memory loss can also occur.
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Most changes are temporary.
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Physical Growth in High-Altitude Populations
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Chest dimensions and lung volume are greater at all ages in high-latitude Peruvian populations.
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People are also shorter, related to delayed maturation. The changes are a direct result of hypoxic stress, rather
than genetics.
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Increased chest growth is a functional adaptation to hypoxia, but smaller body size is not
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Glucose use is more efficient among the Quecha of the Andes.
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In Tibet alteration in the blood flow of the placental may be way to avoid loss of fetuses.
Adaptive Significance 9
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Infectious diseases
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Caused by invading organisms such as bacteria, viruses, or fungi.
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Throughout human evolution, infectious disease has exerted selective pressures on populations and influenced the
frequency of alleles that affect the immune response.
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Until about 10,000 to 12,000 years ago, humans lived in small nomadic hunting and gathering groups.
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With the advent of settled living and close proximity to animals, opportunities for humans to contract disease increased
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Some terms:

Microorganisms responsible for infectious disease are known as pathogens
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Agents that serve to transmit disease from one carrier to another are called vectors. Mosquitoes are vectors for
malaria just as fleas are vectors for bubonic plague.
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Term meaning continuously present in a population is endemic

A pandemic is an extensive outbreak of disease affecting large numbers of persons over a wide area.

A disease that is transmitted to humans through contact with nonhuman animals is called a zoonotic disease.
Zoonoses and Human Infectious Disease
Adaptive Significance 10
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Impact of infectious disease
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Infectious diseases were less common among hunter-gatherers because of group mobility, low population density; lack
of domestic animals; and small population size
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When people settled down they were in more contact with the zoonoses and issues of sanitation arose.
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Before the 20th century, infectious disease was the number one limiting factor to human populations.
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Since the 1940s, the use of antibiotics has reduced mortality resulting from infectious disease.
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In the late 1960s, the surgeon general declared the war against infectious disease won.
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Between 1980 and 1992 deaths from infectious disease increased by 58%.
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Increases in the prevalence of infectious disease may be due to overuse of antibiotics.
Continuing Impact of Infectious Diseases 1
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The continuing impact of infectious disease
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Humans and pathogens exert selective pressures on each other, creating a dynamic relationship between disease
organisms and their hosts.
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Microorganisms evolve
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A pathogen must not be so virulent as to kill its host too quickly
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Just as disease exerts selective pressures on host populations to adapt, microorganisms evolve and adapt to various
pressures exerted on them by their hosts.
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Emerging (and reemerging infectious diseases)
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HIV

HIV provides the best-documented example of evolution and adaptation in a pathogen.

SIV (simian) has shared a long evolutionary history with a number of African primate species, but is deadly to
Asian primates

In the sooty manabey, HIV-2 and SIV are nearly identical
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How did it transmit? Bush meat is a likely explanation.
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Mixture of 2 different primate SIVs

As to HIV-1, it likely evolved from a chimp version of SIV
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For humans, AIDS/HIV is a zoonotic disease.
Continuing Impact of Infectious Diseases 2
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Emerging (and reemerging infectious diseases) (continued0
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SARS (Severe Acute Respiratory Syndrome)

2003 an attack in China
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Contact with domesticate and/or wild animals in the markets
o
H1N1, a form of swine influenza, re-emerged in 2009

A variant of this flu was responsible for the 1981 pandemic

H1N1 inflected 50 million Americans, and killed was between 8000-18000
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Ebola virus rampaged through Uganda in 2012
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This disease has no cure
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Mortality rates range from 50-90%
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For modern infectious diseases:
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Infectious diseases will become more prominent with global warming
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Drug resistant pathogens represent an emerging threat
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