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Where does Physiological variation come from?
January 19, 2005
Why do we all look different?
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 – 1822-1884
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.
