Almost from the beginning of our knowledge of genetics, it’s been asked, “Can the way we (humans) live change our genetics?” These days this is much the same as asking if culture can change the genome. It’s actually a relatively old question.

The question got its biggest boost from one who is now a boogeyman for biology, Jean-Baptiste Lamarck (1744-1829). Lamarckism is the idea that an organism can pass on to its offspring characteristics that it acquired during its lifetime. This is sometimes called Lamarckian inheritance or soft inheritance and was a popular idea until Darwin, Mendel, and modern genetics put various nails into the Lamarckian coffin. (Lamarckian ideas, zombie like, resurfaced very politically as Lysenkoism for a while in Soviet Russia.) The mechanics of genes, DNA, and reproduction as we now understand them rule out the ‘genetic codification’ (ad hoc, as it were,) of such fleeting characteristics as appeared in an individual. This is also interpreted to mean that cultural influences, say, whether you drank a lot of milk or not, are not part of the genetic patterns.

This view of the ‘inheritance of short term characteristics’ has been changing. (Short term here probably means a few thousand years, although that is very much open to further research.) I mentioned drinking milk on purpose, because studies of people with what is called lactose intolerance (those who do not digest raw milk properly) find them to have a different genetic pattern (and gene expression) than those without. This genetic difference has been associated with being either a ‘hunter-gatherer’ or ‘farmer-shepherd,’ which are aspects of cultural behavior that influence whether much milk is drunk or not. A genetic structure for lactose tolerance has been found prevalent among northern (European) peoples and among some African tribes – all known for their culture of raising animals for meat and milk.

Somewhere in the relatively recent human history, within the last 20,000 years or so, the genome in some people adapted to the lifelong drinking of raw milk. Previously, raw milk was available only at the mother’s breast for a relatively short duration, so the genetic expression shut down the ability to digest raw milk after a few years of life. The adaptation removed that ‘shut down signal.’ What were the mechanics for this change?

That’s an ongoing question in biology, as the lid is being pried off the mystery box of epigenetics. Epigenetics is the study of changes in appearance (phenotype) or gene expression caused by mechanisms other than changes in the structure of DNA. This is to say epigenetics deals with changes in genetic expression during the lifetime of an individual, or possibly even some generations, but that is, in general not hereditable (doesn’t become incorporated in the DNA).

In broad view, epigenetics is the result of a vastly complex interplay of genetic coding (DNA, RNA) and the development of proteins (proteomics). For example, epigenetics studies how it is that a pluripotent stem cell (a cell with the ability to become almost any other kind of cell), is turned into a specific kind of cell (heart cell, muscle cell, skin cell etc.). It’s clear that once a cell is differentiated, its epigenetic background (sometimes called the epigenome) continues until the organism dies. A heart cell stays a heart cell. If, however, the interplay between epigenome and genome somehow results in a change in the DNA sequence, and that DNA sequence is found at meiosis (the formation of zygotes: sperm and egg), then a form of Lamarckian inheritance may take place. This outcome is controversial, but transgenerational epigenetics has been reported in about 100 cases, and is becoming an intense area of study.

If there is such a thing as culture affecting the genome, then the probable route is through epigenetics.

This brings me to a recent article in the New York Times (March 2, 2010), Human Culture: An Evolutionary Force which opens to the wide audience of that high profile media outlet a small portion of the ongoing discussion among biologists about the (possible) role of culture in changing human genetics and human evolution.

For the most part, the article states the broad outlines of culture affecting evolution. Its focus is several examples where it seems that cultural preferences have become expressed in the genome – lactose tolerance being a principle example. A couple of other examples are given, usually with speculation about how this may have come about through evolutionary selection, and finishing with a statement to the effect that “we don’t know much.” Here’s a sample…

Though the genome scans certainly suggest that many human genes have been shaped by cultural forces, the tests for selection are purely statistical, being based on measures of whether a gene has become more common. To verify that a gene has indeed been under selection, biologists need to perform other tests, like comparing the selected and unselected forms of the gene to see how they differ.

Dr. Stoneking and his colleagues have done this with three genes that score high in statistical tests of selection. One of the genes they looked at, called the EDAR gene, is known to be involved in controlling the growth of hair. A variant form of the EDAR gene is very common in East Asians and Native Americans, and is probably the reason that these populations have thicker hair than Europeans or Africans.

Still, it is not obvious why this variant of the EDAR gene was favored. Possibly thicker hair was in itself an advantage, retaining heat in Siberian climates. Or the trait could have become common through sexual selection, because people found it attractive in their partners.

A third possibility comes from the fact that the gene works by activating a gene regulator that controls the immune system as well as hair growth. So the gene could have been favored because it conferred protection against some disease, with thicker hair being swept along as a side effect. Or all three factors could have been at work. “It’s one of the cases we know most about, and yet there’s a lot we don’t know,” Dr. Stoneking said.

[Source: New York Times]

Of course, this is a newspaper article, not a book. It can’t and shouldn’t try to cover everything, and this is a very big issue. Still, the degree to which our culture may be affecting our genes; the pace of change, the mechanisms involved – has the potential for huge impact on humanity – especially in the light of genetic modification techniques. So my caveat – a big HOWEVER – is that describing a slice of this story without any reference to other important slices is something of a disservice to the readers and certainly to the biologists. It’s hard to imagine a background piece such as this one not making any references to the Lamarckian controversies or to epigenetics.

It also has a problem with equating evolution and genetics. Though related, they are two different things. Genetics are the mechanisms involved in cell reproduction and procreation. Evolution is the cumulative effect of evolutionary dynamics over a considerable period of time on the outcomes of genetics.

For culture to be an evolutionary force, it first has to find expression through the genes. As I already mentioned, that this is happening and how it happens is not at all settled. Furthermore, not all changes to the genes have any impact on evolution, one way or another. Some changes are evolutionarily useful, those are probably retained. Some are not, and are generally lost from the gene pool (eventually the carriers die out). The interplay between changes in genetics and the forces of evolution (survival of the fittest, selective adaptation) is extremely complex, and biologists are very much in the process of discovering the pathways and relationships. How this happens, at a molecular level, is one of the biggest questions in modern biology. How long evolution takes is a corollary issue. How culture may, or may not, change evolution is, at this point, highly speculative. The article should say so.