The phenotype and evolution (more on defining evolution)

In the previous post I made it clear that I was defining evolution in terms of changes in phenotype.  This is an important point, as many only consider changes in gene frequency to be evidence of evolution.  As an example, in a recent article in the scientist (http://www.the-scientist.com//?articles.view/articleNo/35317/title/Humans-Under-Pressure/) the author writes: “Although the team did not find any actual changes in gene frequencies—the gold standard for demonstrating evolution has taken place . . .”.  This would seem to imply that it is genetic change, rather than phenotypic change, that is the important sign that evolution has occurred.  There is a logical fallacy here: While a change in allele frequency necessarily means that evolution has occurred, the opposite is not the case.  Documentation that evolution has occurred does not necessarily mean that allele frequencies have changed.

To see this, consider the change in stature of the Japanese people since 1870 (figure modified from http://www.dh.aist.go.jp/en/research/centered/anthropometry/).  Since 1870 there has been a secular change in the stature of the Japanese from roughly 5 feet tall in 1880 to the modern height in 1980 of roughly 5 feet 5 inches  (that is averaging men and women).  It is safe to say that little if any of this change in stature is due to a change in allele frequency.  The rather obvious conclusion is that this change in stature is due to a change in diet from a largely starch (rice) based diet in the 1800’s to a modern diet rich in proteins and vegetables.  The best data on this are shown in the dietary changes since the end of world war 2 (from www8.cao.go.jp/syokuiku/data/eng_pamph/pdf/pamph3.pdf). 

Height of Japanese over time Japanese diet

The question is, is this evolution?  Recognize that the heights given in the graph are adult heights, thus, I can reasonably argue that these are adult phenotypes, that will be subject to at most minor changes within individuals.  In short these are not developmental changes.  Thus, we see the population getting larger due to the birth of individuals that will grow to be tall, and the death of older Japanese that were shorter.  This fulfills my definition of evolution, and as a consequence it seems to me we must call it evolution.  Note that if you do not accept my definition, it is also evolution under Futuyma’s definition.  That is it is a lasting change in mean phenotype that transcends the life of an individual.

The temptation is to say that this is “simply” a change in environment.  However, it is better considered a change in the cultural milieux.  Changes in diet are due to the changes in the behavior of individuals, which is learned, and culturally transmitted.  In short, it is heritable.  From this it should be clear that the evolution, that is changes in the distribution of the phenotype, need not be supported by genetic changes.  Anything that can contribute to secular changes in the phenotypic distribution can support evolutionary change.  (Note, I was going to say the resemblance between parent and offspring, but with culture such simple statements are fraught with peril –see Boyd and Richerson’s books http://www.amazon.com/Not-Genes-Alone-Transformed-Evolution/dp/0226712125/ref=sr_1_1?ie=UTF8&qid=1367256338&sr=8-1&keywords=boyd+Richerson)

Much more complicated, in my mind is whether secular changes in phenotype due to secular changes in the environment count for evolution.  I know of no clear examples of this, so a hypothetical example will have to suffice.  It is known that snakes grow larger in warm environments, thus, it is reasonable to imagine that the average size of garter snakes will increase as a result of global warming.  This change could involve simply changes in the environment (mean temperature), and nevertheless would satisfy both my definition, and Futuyma’s definition of evolution.  It seems to me that if it satisfies the definition of evolution we must consider it to be evolution.  I will say I am not fully happy with this, but well, it is what it is.

Addendum:  As evolutionary biologists we often find ourselves fighting the fight of evolution vs creation.  I think that this has the effect of Balkanizing our thinking.  This is particularly true of our thinking of what is and isn’t evolution.  I am purposely writing this blog to be read by evolutionary biology professionals, and as such trying to push my thinking to the logical ends, whether or not it makes it difficult to hash over stale arguments about whether or not Jesus petted dinosaurs (by the way:  Assuming he kept chickens, and given we know that birds are Saurischians, yes, he probably did pet dinosaurs).

One Response to “The phenotype and evolution (more on defining evolution)”

  1. It´s very interesting. In Spain there was a change in stature after the Civil War and the next years. The society was poor and the food and sanity very bad. In this time the stature was similar, without changes. Since 1975, when Spain was open to the world, the society was grown up in quality of life (can eat proteins) and stature in parallel. It´s curious, but i don´t know wich is the porcentage of evolution or diet. In a short space of time maybe only diet, but what happen if we use the data of 200, 500 or 1000 years ago. Thanks for the information i will still reading your studies from Spain.

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