Usually it's a bad idea for an anthropologist to start talking about fish biology, but this paper struck me as interesting:
Alternative life histories shape brain gene expression profiles in males of the same population
Nadia Aubin-Horth et al.
Atlantic salmon (Salmo salar) undergo spectacular marine migrations before homing to spawn in natal rivers. However, males that grow fastest early in life can adopt an alternative 'sneaker' tactic by maturing earlier at greatly reduced size without leaving freshwater. While the ultimate evolutionary causes have been well studied, virtually nothing is known about the molecular bases of this developmental plasticity. We investigate the nature and extent of coordinated molecular changes that accompany such a fundamental transformation by comparing the brain transcription profiles of wild mature sneaker males to age-matched immature males (future large anadromous males) and immature females. Of the ca. 3000 genes surveyed, 15% are differentially expressed in the brains of the two male types. These genes are involved in a wide range of processes, including growth, reproduction and neural plasticity. Interestingly, despite the potential for wide variation in gene expression profiles among individuals sampled in nature, consistent patterns of gene expression were found for individuals of the same reproductive tactic. Notably, gene expression patterns in immature males were different both from immature females and sneakers, indicating that delayed maturation and sea migration by immature males, the 'default' life cycle, may actually result from an active inhibition of development into a sneaker.
Very interesting that the "normal" behavior appears to be maintained by the suppression of genes that result in the "sneaker" phenotype. It suggests that behavioral variants may arise by new duplications or mutations, spread somewhat as stable strategies, and complete a selective sweep when ways are found to down-regulate them in accordance with environmental conditions where the strategy is maladaptive.
The other thing is the vast scope of expression differences. Here, of course, there are fairly radically different phenotypes -- probably more so than in any mammal. But if expression differences are more potentially malleable than, say, coding sequences, we may find pretty wide differences in humans as well. This study was just about the brain, not other tissues. The brain is a hugely complex system in its own right, and there is perhaps as much evolutionary potential there as the rest of the body combined.
Aubin-Horth N, Landry CR, Letcher BH, Hofmann HA. 2005. Alternative life histories shape brain gene expression profiles in males of the same population. Proc Roy Acad Lond B 272:1655-1662. Abstract