Collectively, the examples of animal biology we have described establish something quite remarkable about animal adaptation: the responses of organisms faced with demanding or threatening environmental conditions can be influenced by the nature of those conditions, such that they can generate adaptations that are appropriate to the threat. This is in contrast to what for decades has been assumed to be the sole mechanism; variations in phenotype being generated by random genetic mutation. It now seems, therefore, that there are both random and non-random ways to produce the phenotypic variations that natural selection can act upon, causing adaptation and evolution. As understanding of how genes work emerged from the 1950s onwards it became difficult to conceive a mechanism by which genetics could accept information from the environment; the action of genes appeared well and truly one-directional. Political concerns may also have affected serious consideration of direct environmental influence on phenotype because the idea can be misinterpreted and wrongly applied, for example with regard to intelligence. “Nature not nurture” became a dogma in evolutionary biology.
Image credit: Hans Etholen https://pixabay.com/users/hve56-19607712/
In the early 21st century a measurable shift in thinking occurred. Research publications concerning extension of the evolutionary synthesis increased steeply after publication of Dr Mary Jane West-Eberhard’s book, “Developmental Plasticity and Evolution”1 in 2003, and as, concurrently, new techniques in molecular genetics research became available, enabling new understanding of epigenetic phenomena. The examples described here were selected to illustrate what has been added to evolutionary knowledge, and the consequent relaxation of restraints historically demanded by the MES.
It is not that the MES is being rejected; its mechanism remains largely correct and its evolutionary influence very important. However, the known mechanisms and consequent possibilities of evolution are expanding substantially, not least by advances in understanding of the molecular mechanisms of adaptation. Epigenetics is one example of this, another is processes of phenotypic alteration caused by changes in the combinations in which multiple genes are expressed rather than by mutational changes to the genes themselves2.
”It is not that the MES is being rejected, however … ”
Adaptation and evolution being responsive to the environment presents new possibilities to ecology and evolutionary biology, it may mean that living things have more capability to counter environmental threat than was previously believed. At a time when life on Earth faces extreme threat from environmental change, that may be a source of hope.
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References
- West-Eberhard. Mary Jane. Developmental Plasticity and Evolution. Oxford University Press, 2003 [↩]
- Gerhart, J., and M. Kirschner. ‘The Theory of Facilitated Variation’. Proceedings of the National Academy of Sciences 104, no. Supplement 1 (15 May 2007): 8582–89. https://doi.org/10.1073/pnas.0701035104 [↩]