Monday, May 06, 2013

Social learning and the complexity of evolution


from de Wall 2013: (A) A whale whacks the water surface with its tail... Allen et al. show that this behaviour was spread through social learning. (B) Van de Waal et al. report that vervet monkeys acquire food preferences from their mothers...The monkeys do not touch the previously distasteful blue corn, even though in this phase of testing, both colours are palatable.
CREDIT: (A) JENNIFER ALLEN AND THE OCEAN ALLIANCE; (B) ERICA VAN DE WAAL
Two rather stunning papers in Science emphasis and illustrate the importance of social learning - with a commentary article here. In our Evolution and the Complexity Principle Brian Josephson and I mentioned birdsong as an example of non-human non-genetic cultural evolution, but here they give examples from whales and monkeys.

In fact the idea that cultural learning within animals was important can be traced back in the scientific literature to Kinji Imanishi (the ref given is 1973 but he began studying Japanese macaques in 1948), but this suggestion was "but so far ahead of its time that few Western scientists paid attention"

The whales paper shows how using "lobtail feeding" (an additional refinement to bubble feeding) spread through a population of humpback whales over a period of 27 years. By applying Network Based Diffusion Analysis to nearly 74,000 observations they find that social learning is almost certainly the key factor - the techniques used are quite elegant and you can also see a representation of the social network of the 653 individual whales that were sighted over 20 times (although of course this only shows the times when they were seen together so it is an under-representation of total interactions).

I find the monkeys paper a bit less interesting if only becasue you can do experiements on monkeys so the approach is less elegant and more direct.  Basically they show that once monkeys had learned that one colored food tasted bitter their descendants and other group members also avoided these foods. In the words of the summary:
Groups first learned to avoid the bitter-tasting alternative of two foods. Presentations of these options untreated months later revealed that all new infants naïve to the foods adopted maternal preferences. Males who migrated between groups where the alternative food was eaten switched to the new local norm. Such powerful effects of social learning represent a more potent force than hitherto recognized in shaping group differences among wild animals
Taken together though these papers underline the basic message that the simplistic nostrums of Dawkins on evolution are untenable.  (His "memes" nonsense doesn't explain this either, as Simon Conway Morris famously observed the idea of memes is hilariously simplistic. Talk about a "Lobtail Feeding Meme" or a "Colored Food Avoidance Meme" misses the point).

Another aspect of the greater and more interesting complexity of real evolutionary mechnanisms is shown in a Nature paper called Extensive transcriptional heterogeneity revealed by isoform profiling
This shows that the transcription of DNA by RNA is by no means as simple as has been supposed.  Indeed there is 
"[an] extensive layer of isoform diversity previously hidden among overlapping RNA molecules. Variation in transcript boundaries seems to be the rule rather than the exception, even within a single population of yeast cells. Over 26 major transcript isoforms per protein-coding gene were expressed in yeast. Hundreds of short coding RNAs and truncated versions of proteins are concomitantly encoded by alternative transcript isoforms, increasing protein diversity. In addition, approximately 70% of genes express alternative isoforms that vary in post-transcriptional regulatory elements, and tandem genes frequently produce overlapping or even bicistronic transcripts."
All much more interesting, and much more complex, than people think. Fascinating!


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