Where does Physiological variation come from? January 19, 2005

Why do we all look different?

Yali’s question: diversity. Humans come in many forms: –Body shape –Colors –Lifestyles

How to explain diversity? Avoid flawed labels like “civilized,” “barbaric,” “savage,” “primitive.” Diamond: History followed different courses in different places because of environment, not biology, genetics or intelligence.

Evolution Simplest definition: change over time. Nature and Culture What does it mean to be human biologically?

Evolution What does it mean to be a theory? Other important theories: –Gravity –Earth revolves around Sun Do you believe in evolution?

Evolution part I: Natural Selection Evolution: Change over time Microevolution: change in gene (allele) frequencies in a population over time Macroevolution: change of species over time (speciation)

Natural Selection Change in gene (allele) frequency as a result of: –Differential fertility –Differential mortality

Example No. 1: Guppies Continuous variation: –Color –Spots

Example No. 1: Guppies Colorful fish: Enjoy differential fertility Suffer differential mortality

Example No. 2: Peppered Moth Pre-industrial revolution: –Most moths are light colored.

Example No. 2: Peppered Moth Post-industrial revolution: –Majority of moths are very dark.

Example No. 2: Peppered Moth Explanation: –Change in environment (soot discolored tree trunks) caused a change in mortality among moths which changed the gene (allele) frequency affecting coloration.

Darwin’s Three Postulates: Variation exists. Variation is heritable. There is a struggle for existence. Conclusion: “Descent with modification” aka Natural Selection

Survival of the Fittest? “Struggle for existence DOES NOT MEAN survival of the fittest!

What Darwin Didn’t Know: How traits are inherited and why. Where new variation comes from.

Genetics Gregor Mendel –

Inside the Nucleus of a Cell: Chromosomes –23 pairs (46 total) make up 1 gene Body Cells –Diploid (contain 2 copies of each chromosome) Sex Cells –Haploid (only 1 copy of each)

DNA Introns –No function –Vast majority of DNA Exons –Code for functions –Minority of DNA

Inheritance Parent Generation: homozygous F1 Generation: heterozygous Genotype: allele combination

Phenotype Observable characteristic controlled by: Genotype Environment

Why do we all look different?

Back to Yahi’s Question Over many thousands of years, human bodies have evolved into different shapes, sizes and colors to adapt to different environments.

BUT...

Environment does not determine phenotype! Environment cannot cause a feature to appear that is not in the genotype. Culture is also necessary for people to adapt to any environment.

Key Terms: Allele-half of a gene pair, each half comes from one parent. Genotype-genetic code for any particular trait, contains 2 alleles. Phenotype-expressed trait based on genotype and environment. Adaptation-change that is advantageous for survival in a given environment. Heritability-ability of traits to be passed from parents to subsequent generations.