The Argument: Flexible Heritage
In Chapter 10, Shenk mentions this idea of Lamarckism which was this hypothesis of Jean-Baptiste de Lamarck, a French biologist who believed that inheritance could also be used to inherit certain characteristics as well. (pg. 155-159) This is different than the whole idea of natural selection where the reason why, for example, a giraffe has a long neck is because that giraffes with that genetic mutation that causes them to have longer necks cause them to survive. This is an idea that is well established in many biology books, this idea of “survival of the fittest”. (Chapter 22 of Campbell) It is also a well-established major theme of biology of continuity and change with natural selection. However, with the discovery of epigenomes does the whole idea of genetic mutations get thrown out the window?
With the introduction of epigenomes we now know appearances can be altered without the DNA itself actually being altered. (pg. 159) Does that mean that maybe are whole idea of genetic mutation being the crux of changes in evolutionary behavior is rendered false? Since epigenomes are mostly decided by environmental factors, does that mean that most “mutations” or evolutionary characteristics are mostly environmentally caused, not just perchance?
Ellen Zhou (ellenzhou2006@gmail.com)
It is important to note that while appearances may change, DNA stays the same. Epigenomes affect the way DNA is expressed, but unlike mutations, the basic DNA code is still there. In the case of giraffes, special mutations like valves in the blood vessels of the neck, which exist to prevent blood from pooling in the head when giraffes bend down, are not switched on or off. Instead, they are always present, or else there would be a lot of dead giraffes.
ReplyDeleteWhile epigenetics explains why babies born in a famine are smaller, they do not replace evolution and mutation. Epigenetics do not alter the base DNA code, and instead change how it is expressed, usually during times of change. This allows organisms to have a degree of flexibility and in the short term, they are able to change and survive. While epigenetics is based on the environment, evolution is based on mutations and the passing down of them. Giraffes also use their necks to fight for a mate, which explains why their long necks stayed. If necks did not determine whether genes were passed down, giraffes could probably have evolved longer legs too.
Thus, epigenetics can have an effect on the degree to which a gene is expressed, but mutations can cause new genes to be present. Epigenetics can only have a small impact on the way animals are. The large amount of diversity in nature shows that genetics and evolution are the main causes, not epigenetics.