Anthropology 7 Human Evolution Winter 2003
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Why aren’t organisms perfect (optimal)? Constraints on adaptation.
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Finch beak depth & beak width are controlled by same genes: pleiotropy Dog front and back leg length controlled by same genes Can’t select for more of one without more of the other.
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Annonia purpurea Gomphothere. 2. Evolutionary disequilibrium, or “lag”.
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Means loss of variation in smaller populations And populations can diverge by chance Genetic disorders can be common in certain populations because of founder effects (presence in a small group of founders).
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Imagine fitness landscape is like topographic map Population can be at local peak Population can ’ t reach global peak without dropping into valley Selection avoids valleys Population will not always reach global peak.
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The evolution of eyes illustrates local optima. COMPOUND EYES eyes Appos:aon superposition CAMERA-TYPE EYES d land C ephah lens Mirror Debris Near ptnholes cup c-ye-s Mere Ph ororeception.
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Example: Laws of physics limit how large animals can be Mass increases with the cube of body dimensions Strength of bones and muscle increases only with the square of body dimensions → Selection can’t create animals beyond a certain size.