Adaptation and Exaptation Concepts

Study Notes

Adaptation has two meanings: a heritable trait enhancing survival/reproduction in a specific environment (maintained by natural selection for its current function), and the evolutionary process (natural selection) producing such traits.
A trait's current function doesn't necessitate its original evolutionary purpose for that function.
Example: Succulents storing water is an adaptation to arid environments.
The Jamaican bromeliad crab chemically engineers its pools for offspring benefits: removing decaying matter to maintain oxygen and adding snail shells for increased pH and calcium. These are adaptations demonstrated experimentally.

Exaptations are currently adaptive traits that originally evolved for different functions and were later co-opted for their current fitness-enhancing role.
Exaptation doesn't imply goal-oriented evolution, anticipation of future needs, or pre-determined uses. Natural selection only operates in the context of the current environment.
Example: Bird feathers – evolved before flight in theropod dinosaurs.

Criteria for demonstrating adaptive traits needs to be established.
Methods: quantifying selection, reciprocal transplants, and the comparative method.

"Darwinian demon": a hypothetical organism with perfect adaptation that maximises fitness in all areas.
Factors limiting perfect adaptation (and the absence of Darwinian demons): trade-offs, constraints imposed by development, genetic constraints, and environmental changes.