Adaptations human eye is a good example, so is grand canyon
Fish have a spherical gradient lens
Before Darwin, there was no scientific explanation for the fact that organisms are
well adapted to their circumstances
William Paley the eye is designed for seeing and where there is design in the natural world, there
has to be a designer
Darwin’s Theory of Adaptation –Natural Selection:
The ability of a population to expand is infinite but the ability of any environment to support
populations is always finite. “The struggle for resources”Darwin (The struggle for existence)
Organisms within a population vary, and this variation affects the ability of individuals to survive
and reproduce.(variation in fitness)
The variation is transmitted from parents to offspring. (inheritance of variation)
The supply of food was not sufficient to feed the whole population
Beak depth varied among the birds on the island, and this variation affected the bird’s survival.
The average beak depth was greater than the average beak depth in the same population before
The parents and offspring has similar beak depth Selection preserves the status quo when the most common type is the best
Evolutionary theory predicts that, over tie, selection will increase the beak depth until costs of the
larger beak size exceeds the benefits.
Equilibrium produced by stabilizing selection
Populations do not remain static over the long run unless selection is operating.
Evolution need not always lead to change in the same direction.
Species are populations of varied individuals that may or may not change through
Before Darwin, people thought of species as unchanging categories (like a triangle).
Ernest Mayrcalled this essentialism.
According to Darwins theory a species is a dynamic population of individuals.
Both stasis and change result from natural selection and need explanation. Stasis is not the natural
state of species.
Individual Selection Adaptation results from the competition among individuals not
between entire populations or species.
Benefits are for the individual. May or may not benefit the population or species. Example is that
almost all organisms produce more offspring than are necessary to maintain the species. From the
species view the extra 8/10 just waste food.
Fecundity the ability to produce offspring. The evolution of complex Adaptations:
Why small variations are important:
Continuous variation gradient – human’s heights
Darwin said that this is essential for the evolution of complex adaptations, didn’t think discontinuous
Discontinuous variation no intermediates achondropl