Stage two Natural selection: -directional change relative to - - PowerPoint PPT Presentation

Stage two

Natural selection:

• directional change relative to environmental context
• acts on variation produced and redistributed by mutations,

recombination, drift, and migration

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Anthropology example of natural selection

Sickle-cell anemia: genetically inherited blood disease Mutated hemoglobin collapses red blood cells into sickles leading to anemia and death Normal dominant allele = HbA Mutated recessive allele = HbS

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Anthropology example

Expect: selection against HbS (sickle-cell allele) Instead: 30% some regional populations are carriers

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Anthropology example

Correlation between: regions malarial pressure and high frequencies of the HbS allele Malaria: deadly parasitic infection spread by mosquitoes

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Regions of note Mediterranean, Arabian peninsula, Southeast Asia, W. Africa Biocultural evolution example

• slash-and-burn agriculture: mosquito breeding areas near humans

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Anthropology example

In regions where malaria is present: Malaria acts as a selective agent favoring heterozygotes Malaria kills homozygotes for the normal allele pair Anemia kills homozygotes for the recessive allele pair Heterozygotes (carriers) are more fit Natural selection increases the frequency of HbS allele in West African populations

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Classifying biology

Question: Which is the most similar?

• classify by looking at evolutionary relationships

Answer: croc and pigeon

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Macroevolution

Macroevolution: larger scale change over geologic time Classification: categorize organisms to understand evolutionary relationships Kingdom: Animalia Phyla: Chordata Class: Mammalia Order: Primate Family: Hominidae Genus: Homo Species: sapiens

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Homologies

Homologous traits: similarities due to common descent E.g., birds, bats, mice, crocs all have four limbs Contrast with analogies: similarities due to common function

Two types of homologies

Ancestral traits: traits that have been inherited from a remote ancestor

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Two types of homologies

Ancestral traits: traits that have been inherited from a remote ancestor Derived traits: have been modified from the ancestral condition

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Schools of classification

Evolutionary systematics

• constructs phylogenetic trees:
• hypothesizes about ancestor-descendant relationships
• time dimension

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Schools of classification

Cladistics

• use shared derived traits to identify new species

Clades: lineages sharing a common ancestor

• Anthropologists mostly use cladistics