The Tempered Gene

( First of two parts )

I cannot help it. It has become automatic. Every time I see graveyards that are pimpled by uneven expressions of remembrance from the leaning wooden crosses to the palatial mausoleums, this statement flashes in my mind like the stock market ticker tape: "What I cannot see is the difference between the bones of Alexander the Great and that of his slave."

I took note of that statement I had read when I was about 13. I do not remember who said it and where it came from but I think she/he would be very interested to know that even beyond the level of bones, genetic science has now revealed that all humans are at least 99.9 percent genetically the same. In poetry, "death" is always the great leveler. But with this new discovery in genetics, as far as graveyards are concerned, I think they should also have some sort of a "double helix" sculpture to represent our genes at the entrances to remind us that even in life, biologically speaking, it is really mostly a level-playing field for humans.

We are all at least 99.9 percent genetically similar. What does this mean in terms of our genetic links with other species? What does this say about the common ancestor of modern-day humans? If we humans are almost perfectly, genetically indistinguishable from each other, is "race" now a meaningless concept? Does this mean that "nurture," i.e., the environment, the experience of culture and civilization that shape us, is what mostly makes us unique from each other?

In order to begin to understand those questions and try to come up with possible answers, we have to first define what a gene is. Genes are a set of DNA molecules which instruct the cells to make amino acids, the proteins considered to be the building blocks of life. At the nucleus of each cell in our bodies, are found two sets of chromosomes that we inherited from each of our parents. Parceled out into the 24 chromosomes, are the three billion base pairs of DNA that make up the human genome. A gene is the sequence of DNA molecules made up of four nucleotide bases, namely, adenine (A), thymine (T), cystosine (C) and guanine (G). A always pairs with T and C always with G. If it helps, try to imagine the human body made up of basically only four colored dots: red, blue, green and yellow where red always paired with blue and green with yellow. Three billion of these colored dot-pairs are in the 24 chromosomes in the nucleus of each cell of your body. The only cells that do not contain the complete set of chromosome are the egg cell, because it only contains the mother’s chromosomes, the sperm cell because it contains only the father’s chromosomes, and the red blood cells because these do not have nuclei.

In this year’s January issue of Nature celebrating the 50th anniversary of J.D. Watson and F. Crick’s determination of the molecular structure of DNA, Svante Pääbo of the Max Planck Institute for Evolutionary Anthropology, wrote an article: "The Mosaic that is our Genome." It made use of studies that pointed to possible answers to our linkages with other species as well as to the birthing place of our modern-day human ancestry. Evolutionary science has so far stood on firm ground with regard to our descent from the great apes. The new insight provided by Pääbo’s article stemmed from evidence that showed that humans are genetically closer to the African great apes – the chimpanzees (around 1.2 percent difference with humans), bonobos and gorillas – than they are to the orangutans in Asia. Now that scientists are able to examine molecular data, former data from older paleontological methods that estimated our divergence from the chimpanzees 30 million years ago have now been narrowed to only about four to six million years ago. What does this mean for us? Well, this homes us in on a timeframe within which genes are altered and branch off to make another genus or species. In other words, it tells you how much time it took, at least in the case of chimpanzees and humans, for a certain magnitude of genetic differences to arise to dictate whether a primate offspring will swing on trees and eat al fresco as first nature, or walk erect as a biped and have moments holding a menu while having uniformed members of one’s own species as servers. Data were further used and compared with that of variations within the species belonging to the great apes and they revealed that we humans have less genetic differences with our fellow humans than the chimpanzees have with their own kind. In other words, if the differences between the genes of the same species could account for a particular trait, the great apes would have more leeway than humans.

Another study cited by Pääbo, I found most revealing and interesting. This involved variations in the gene sequences along the chromosome that are structured in blocks called "haplotypes." When 928 haplotype blocks from living humans in Asia, Africa and Europe were studied, compared and analyzed for differences, it seemed to show that within the human gene pool, the most variation is found in Africa, but outside Africa, are only "subsets" of the variation found within Africa. Evidence for this was acquired tracing both mitochondrial DNA from the mother and Y chromosome from the father and both found their geographical origin in Africa. Another study, this time in Sweden by Ulf Gyllensten of the University of Uppsala tracing only mitochondrial DNA from the mother, also supports this "Out of Africa" theory that we modern-day humans all came from an African Eve.

So we humans are far more deeply alike than we thought or we were made to believe in human history by those who used "race" to hitch their claimed superiority to something unalterable in Nature such as biology. It turns out that so far studies give us evidence that all of us humans alive today, if made to go back to our genetic history, would all find our origin in sub-Saharan Africa, before the exodus of populations to Europe and Asia began about 50,000 years ago. (To be concluded)