Natural Selection in Penguins - a tutorial
illustrating how natural selection occurs
OF NATURAL SELECTION
- All natural populations have the
reproductive capacity to exceed the resources that sustain them, however they
cannot increase in size indefinitely without running out of food, living space
and other resources
In other words: more young are
born than can survive - remember the Grants found this to be true in the
Because more young are born
than can survive to reproductive age - you can infer that members of a
population must compete for the available resources
- Individuals of a population
differ in the details of their form, function and behavior (remember the
slight variations in beak depth and width among the finches). Most of this
variation is heritable - passed from parents to offspring - the Grant's found
a strong genetic component in beak width and depth.
- Some forms of heritable
traits are more adaptive (suited to the environment) than others in
the competition for resources.
For example: some finch beaks are better at cracking large seeds and some
are better at cracking small seeds.
From this you can infer that because the more adaptive (better suited)
traits promote survival and reproduction (=success) - they must increase
in frequency over the generations, and the less adaptive traits
must decrease in frequency or disappear.
- In essence, natural selection
is the physical and biological environment acting as a sorter of individuals
- choosing which individuals possess the best adaptations for their current
conditions. Therefore, a population will change over time. If the
environment will switch again - over time - to reflect those changes. Natural
selection is a highly localized event - because environments vary from region
Finally, a species cannont perceive or anticipate its needs for particular
adaptations. Species (populations) are limited to using the adaptations that
they were born with - just like the lone survivor with the suitcase. Once
you survey the situation, you can't switch suitcases in mid-disaster.