A group of researchers has found that our choice of diet has had an effect on our genomes. Specifically, they’ve found that individuals from groups with traditionally high-starch diets have more copies of the gene for Salivary Amylase, the enzyme which breaks down starches in our mouths and stomachs, as compared to those with low-starch diets. This is fascinating news because it is the beginning of an answer to the question: towards what are we evolving? What are the selective pressures acting on our genes to produce further iterations of our species’ existence? In general, this is an extremely difficult question to answer, if not impossible.
There are some examples of human intervention into evolution; our efforts at breeding plants and animals have yielded several well known successes (including the development of a transparent frog, see below) and we also use evolution to design molecules with specific properties (ref. 1). These, however, are examples where many generations can be generated rapidly and only those individuals with desired traits are allowed produce offspring.
Fitness is the term that is generally used to quantify how likely an individual is to be reproductively successful, and is thus a most relevant concept in determining the direction in which evolution is nudging us. When the environmental variables and set of possbile behaviors are simple, it is possible to make predictions concerning fitness. For instance, a salt marsh is an environment in which organisms are subject to varying levels of salinity. It is a fair bet that after continued but not overwhelming exposure to increased levels of salt, an initially non-salt-tolerant plant will become salt tolerant. This is the case because the individuals with some salt tolerance are presumably more fit than others, and their offspring will retain that advantage.
When one tries to analyze what makes a human being fit, however, there are several obstacles. First, the set of circumstances we’re adapting to are quite complex, meaking it no minor task to pick out which elements might be most important. Second, we define what constitutes fitness through our influence on social structure. Third, even if we’re somehow genetically most-fit, we can choose to thwart evolution by not having any children. One might think that the rich constitute a good candidate for the title of most-fit, but they certainly do not reproduce the most. If anything, the group with the highest reproductive success is the poor.
Even if we believe that Darwinian evolution is the dominant force in defining how we will change over the coming epochs, we must admit that it plays some roll. In attempting to understand the future of our species, and how to act in our own best interests, we must acknowledge the forces at work in shaping our selves. Darwinism is clearly important for analyzing broad trends, such as in the research presented above. However, the fast-and-faster acting influence of cultural evolution which currently influences every aspect of our lives, will undoubtedly be of paramount importance to understanding humanity as well. Our challenge is now to understand how the effects of cultural evolution will play out, feeding back on our biology.
1. Farinas ET, Bulter T, Arnold FH. (2001) Directed enzyme evolution. Curr Opin Biotechnol. 12(6):545-51
2. Perry GH, Dominy NJ, Claw KG, Lee AS, Fiegler H, Redon R, Werner J, Villanea FA, Mountain JL, Misra R, Carter NP, Lee C, Stone AC. (2007) Diet and the evolution of human amylase gene copy number variation. Nat Genet. 39(10):1256-60.