Chapter 11 NATURAL SELECTION AND ADAPTATION
An adaptation is a characteristic that enhances the survival or reproduction of organisms that have it.
The members of the population become better suited to some feature of their environment through change
in a characteristic that affects their survival or reproduction.
ADAPTATIONS IN ACTION: SOME EXAMPLES
1. Philodendron and other aroids produce two kinds of leaves adapted to different environments: small
leaves for the dark forest floor and growth toward the dark looking for a tree trunk to climb, and large
leaves with long petioles to catch sunlight in the upper regions of the forest canopy.
2. Pseudocopulatory pollination in orchids. Several species of orchids have modified flower parts to
look somewhat like a female insect, and the flower emits a scent that mimics the attractive sex
pheromone of a female, bee, fly or thynnine wasp depending on the orchid species. The flower is
pollinated in the process of copulation; the insect does not derive any benefit from this activity.
3. The skull bones of most terrestrial vertebrates are rigidly attached to one another, but in snakes, they
are loosely joined. They swallow their prey by drawing it into a gullet with recurved teeth mounted
on a number of freely moving bones that act as levers and fulcrums, operated by complex muscles.
4. Australian arboreal weaver ants construct nests of living leaves by the intricately coordinated action
of numerous workers, groups of which draw together the edges of leaves by grasping one leaf in their
mandible while clinging to one anther.
THE NATURE OF NATURAL SELECTION
Most adaptations are complex and appear to be constructed to perform a certain function, e.g. growth,
feeding, pollination, etc.
The process of natural selection is random and mindless.
Those with variations that enhance survival and reproduction replace those less suited who
reproduce to a lesser extent.
Adaptive biological processes appear to have goals but there is no conscious anticipation of the future in
cells.
The future cannot cause material events in the present.
This apparent purpose is caused by the operation of a program coded or prearranged information residing
in DNA sequences, that controls a process.
DEFINITIONS OF NATURAL SELECTION
Survival is a prerequisite for reproduction.
Fitness is often defined as reproductive success.
