The Origin of Biological Novelty

The word "novelty" can obscure important distinctions. A new gene is not the same thing as a new protein function. A new function is not necessarily the same thing as a new anatomical structure. And the origin of a structure is not the same question as the later ecological success of organisms possessing it.

New genes can arise through duplication and modification of older genes, rearrangement of genetic material, and in some cases from sequences that were previously noncoding. Existing proteins can acquire altered functions, while regulatory and developmental changes can produce new phenotypes from existing components.

These processes show that biological novelty is not restricted to simple changes in the frequency of pre-existing traits.

Comparative genomics has identified numerous gene families produced by duplication and divergence. Experimental work demonstrates functional changes in proteins. Research on de novo gene birth provides evidence that some protein-coding genes have arisen from ancestrally noncoding sequence. Evolutionary developmental biology documents extensive reuse and modification of conserved developmental systems.

Reconstructing the origin of very young genes can be difficult, and the origin of ancient genes and structures is generally more difficult still. Absence of recognizable homology does not by itself prove de novo origin. Different kinds of novelty therefore require different forms of evidence.

How frequently do different mechanisms generate genuinely new biological functions? How do molecular novelties become integrated into larger cellular and developmental systems?