Pre-adaptation
Under preadaptation , Präadaption or predisposition ( synonyms for pre-adaptation is understood to mean) in both the Evolution - and in the developmental biology , the presence of either mutation incidental or originally created for a different adaptive purpose features that with a change in environmental conditions prove to be a selection advantage. To put it simply, they represent an evolutionary adaptation before the onset of selection pressure .
The evolutionary biologist Lorenzen explains how this phenomenon comes about as follows: In many genotypes there are potencies which, as in the cases listed, are only realized through adequate environmental stimuli. On the other hand, even minor genotypic changes can produce quite dramatic effects under certain conditions.
An obvious example of pre-adaptation are the flying membranes of the Borneo flying frog Rhacophorus pardalis . They have skins between the toes and in the elbow joint. As they flee, they drop from trees and sail to the ground. The flight membranes are homologous to the webbed frogs of other frogs. Since these were already designed as an adaptation to life in the water, they represent an advance adaptation to gliding.
A pre-adaptation can also exist because many features can have a double or multiple function. One example is the evolution of feathers and wings in birds . This did not necessarily have to be coordinated in parallel. Feathers were already present in dinosaurs before the development of bird flight and were used for thermal insulation. Recent fossil finds reveal a number of intermediate stages from simple to complex feathers in clearly ground-dwelling dinosaurs. With the evolution of the wing, they could then also be used for flying.
The pre-adaptation has found an additional molecular genetic basis through the discovery of alternative splicing as well as introns and exons . Alternative splicing, in particular, is a prime example of multiple functions and enables the rapid development of new proteins without changing the primary DNA code by recombining already "tried and tested" DNA code sections. If one takes into account that - in humans, for example - well over 90 percent of the DNA does not code directly for proteins, it becomes clear what amount of genetic information is available which, in principle, can be activated for the development of new features by even small changes in the DNA in the area of gene regulation . This peculiarity of the eukaryotes can be regarded as an essential cause for the variety of forms of this group of living beings.
Individual evidence
- ↑ S. Lorenzen: The importance of synergetic models for understanding macroevolution. In: Eclogae Geologicae Helvetiae. 81, No. 3, 1988, pp. 927-933.