Life, evolution, is about reproduction, how effectively we get into each other's jeans, so to speak. As individuals, we may be independent most of the time, but we can't make a new individual alone. To do that we must conjugate our genome with someone else's, and getting into their jeans is how we do that.
Or is it?
Perhaps we've been making a big evolutionary mistake
Maybe what is as important is how we and other species get into each other's genes. Organisms--all of us--are collections of large numbers of cells descended from a single starting cell (the fertilized egg). We tend to view ourselves as having one genome, and in that sense being a unitary, biological whole. Evolutionary theory is about how collections of such wholes, the fertilized eggs of a population in a generation, change over time.
But increasing evidence shows several important facts. First, each time a cell divides into two 'daughter' cells, mutations occur, and these are then transmitted to the next generation of daughter cells. And, at the molecular level, the division of one cell into two, even forgetting mutations, is never exactly equal. One gets more of one protein than the other, the other gets more mRNAs and so on. You are a huge collection of cells with such a branching history of variation from a single fertilized egg cell.
But our life is not just what happens to that set of cells. Instead, as evidence is now showing more clearly, we are colonized by countless other cells--bacteria and other micro-organisms--and they, too, divide on and in us, accumulating mutations along the way. And, more importantly, we are unable to live without them, nor they without us. The simple classical and perhaps clearest example is our intestinal flora, that is responsible for vital aspects of our digestion and hence our survival.
A burgeoning area of investigation called microbiomics (every field needs a sexy label, of course), the study of the many different microbes that inhabit various parts of our bodies, is off and running. This work is finding a wealth of relationships between us and others, so much so that researchers are suggesting that our genome can't in fact be fully understood on its own, but rather must be thought of as just one part of a larger genome that also includes the genes of all our colonizers. Or from the microbes' perspective, their own and their host's genomes.
Many different common chronic diseases that for several decades have been thought to be due to wear-and-tear of long life and modern lifestyles, are being shown to involve genes involved in aspects of our immune systems. So in both regard to disease and to the microbiome of normal variation, our traits may be more 'infectious' than we had thought. The term 'infection' implies the old idea that we're normally bug-free unless we are sick. Instead, perhaps we are sick if we are bug-free!
Going further: what, after all, is an organism? What is evolution about?
Maybe our entire concept of organism and its traits is biologically
badly mistaken. Perhaps metazoans really are often, or largely, a
colony of cells with one genome plus adherent colonies of cells with
other genomes. Neither can do without the other. They've evolved
jointly. Aberration in either can cause cell death. When it's of the
'organism' we give it different name from when it's just of one of the
We might call this 'coevolution' and perhaps it could lead to
substantial rethinking about what we are, or what species are, or their
evolution. Or how we use our notion of organism to dichotomize
vis-à-vis the 'environment', when basically they are more unitary? The ultimate in co-operation.
Again, as with sex, we may have been misled by Noah's ark, Linnaeus,
and Darwin into life science based on organism, when that is only one
aspect of how things are organized. The idea that Nature is composed of a series of distinct species, a legacy of classical thinking up to the present, is actually a large subject with much that is interesting and perhaps truly profound to think about. We'll discuss it in a subsequent post.
Meanwhile, the idea of meddling in, or the responsibility to keep out of, or delve into, each others' genes is not just something for Levi Strauss to consider.