Evolution and Natural Selection. Chapters 1.4-1.6, Bush. Introduction to Natural Selection. History of Evolutionary Thought Theory of Natural Selection Examples of Natural Selection. Introduction to Natural Selection. History of Evolutionary Thought Theory of Natural Selection
Chapters 1.4-1.6, Bush
“I have called this principle, by which each slight variation, if useful, is preserved, by the term Natural Selection.”
(The Origin of Species)
Natural Selection is a “Theory” in the same way that we consider gravity or Einstein’s relativity to be a theory
1) Variation in traits
Drought causes collapse of food supply, survival plummets
High mortality in smaller individuals, strong selection for large birds that can crack large, tough seeds
Larger individuals may have higher fitness
(i.e., produce more offspring) than smaller
Fishing industry produces selection that favours smaller cod and can produce a decrease in average body size.
The average members of the population may
have higher fitness than the extremes.
Babies of intermediate
birth weight have higher
survivorship than very
small and very large babies
Natural selection could favour both extremes
over the intermediate types
In the finch, Pyrenestes ostrinus
both very large and very small bills are beneficial for eating large and small
"nothing inbiology makes sense except in the light of evolution"
-Theodosius Dobzhansky (1900-1975)