Chapter 5 (4thed) / Chapter 3 (3rded) What Can Evolutionary Theory Tell Us About Human Variation?

Applying Evolutionary Theory (Micro vs. Macroevolution

Microevolution

Researchers focus on short-term evolutionary changes in a species over a few generations.

Macroevolution

Researchers examine long-term evolutionary changes, sometimes over millions of years, including the origins of new species.

Modern Evolutionary Synthesis

Also known as neo-Darwinism

Developed in the 1930s and 1940s to combine

Darwin's concept of natural selection

Mendel's ideas about heredity

Modern Evolutionary Synthesis

Helped undermine the 19th century anthropological concept of "biological race"(i.e. Social Darwinism)

Recognizes that all human beings are a single species

Uses neo-Darwinism to examine human biological variation

Modern Evolutionary Synthesis (Species Concepts)

1) Biological

2) Phylogenic

3) Phenetic

Species Concepts

Neo-Darwinians defined a species in terms of populations of organisms

1) Biological Species Concept

Species are reproductively isolated from other species

Species cannot produce fertile offspring if interbred with other species

Species often occupy a specific niche in nature

(This is the most common concept one is taught)

Phylogenetic Species Concept

Developed out of issues with the biological species concept

Hybridization between presumed species has been documented

Identifies species based on a set of unique morphological or genetic features that distinguish members from other, related species

This species concept is used by some paleoanthropologists

3) Phenetic Fossil Species Concept

Users first calculate morphological differences between living species

Assumption is that similar degrees of morphological difference can be used to distinguish species in the fossil record

Allows fossils to be sorted that are in a continuously changing lineage

Genetics and Populations

Gene pool consists of all the genes in all members of a species, or in a population of a species.

Gene frequency refers to how often variants of a specific gene (i.e., alleles) occur within a population.

Genetics and Populations

Polymorphous indicates that most alleles have a range of different forms.

Polymorphic alleles account for most genetic variation. (i.e. Alleles for red, brown, blue)

Private polymorphisms are found in some but not all members of a population. (e.g. allele variations for 'red hair')

Population geneticists use statistical analysis to study short-term evolutionary change in large populations.

Genetics, Populations, and "Race"

Human populations across the world may appear phenotypically different.

Clines display gradually shifting geographic variations in a phenotypic trait across populations.

"Race" is a biologically meaningless concept because human populations share basically the same range of genotypic variation.

Race is a sociocultural and historical constructthat shape

The "Truth" about Race

Older concepts of "race" emphasized phenotypic (appearance) variation.

Newer concepts of "race" examine genotypicvariation.

Some see this as the molecularization of racism.

(NatGeo collection of DNA info from populations or using clines as the basis for 'race')

Genetics, Populations, and "Race"

The molecularization of "race" is reflected in

Political discussions, such as the controversial book The Bell Curve

Efforts by politically and economically marginalized groups to enhance their standing

Medical treatments based on supposed "racial" differences

Efforts to trace one's ancestry

Microevolution and Human Variation

Phenotypic variation between human populations

Does not reflect different alleles for different populations

Involves differences in the proportions of the same alleles common to all humans

Gene flow refers to exchange of genes between two or more populations with overlapping gene pools

Microevolution and Human Variation

Gene drift represents random changes in gene frequencies from one generation to another due to

Disaster

Disease

Migration

Founder effect is a kind of genetic drift where small subgroup of a larger population becomes isolated.

Unrepresentative proportions of alleles can result.

Microevolution and Gene Flow

The Four "Processes" of Evolution:

Changes in gene frequencies among human populations are related to:

1) Natural selection

2) Mutation

3) Gene flow

4) Genetic drift

Adaptation and Human Variation

Modern geneticists have discovered the importance of gene interaction.

Pleiotropy arises when one gene contributes to multiple phenotypic features.

Polygeny refers to when multiple genes interact to produce a single phenotypic feature

Adaptation and Skin Color Variation

Skin color is an adaptive response shaped by natural selection to variation in ultraviolet radiation across the globe.

Similar skin colors evolved independently by human populations in similar environments.

Adaptation and Skin Color Variation

Skin color variation reflects two opposing clines of skin pigmentation.

Skin color varies from dark to light as one moves from the equator to the poles.

Protects against sun damage

Reduces the risk of skin cancer

Skin color varies from light to dark as one moves from the poles to the equator.

Favors vitamin D production

Promotes healthy bone development

Intelligence and Human Variation

There is no single way to define or measure human intelligence.

Variations in IQ scores

Reflect differences in social class and education

Are not related to "races" defined by superficial phenotypic traits such as skin color

Models of Macroevolution

Macroevolution deals with geological time and both the extinction of old species and the origin of new species.

Evidence for macroevolutionary processes includes

Close study of fossils

Comparative anatomy of living organisms

Major models of macroevolution are

Phyletic gradualism

Punctuated equilibria

Models of Phyletic Gradualism

Dominant approach until ~25 years ago

Macroevolution represents a uniform process of microevolution over time.

Speciation results from the slow, gradual transformation of a species over time, known as anagensis .

Species boundaries are arbitrary.

Fossil record shows no sharp breaks between old and new species.

Can We Predict the Future of Human Evolution?

As with all living beings, humans are concerned with survival and reproduction in a changing world

The development of culture means that humans are also concerned with leading meaningful lives

Humans are subject to evolutionary processes but culture allows a range of adaptive responses

Question #1 (Primate Evolution)

In your chapter reading, you were introduced to patterns that exist in primate evolution across time. What are 4 evolutionary trends that primates have had since they broke away from the rest of the mammalian class according to LeGros Clark? What is believed to have contributed to these trends from scientists? Provide examples, when possible, to support your arguments.