The tenth anniversary of the human genome has been marked by some striking new genetic insights into human evolution and diversity. Do these new discoveries have any significance for the dialogue between science and religion in general, or for our sense of human uniqueness in particular?
The publication of the Neanderthal genome sequence in May 2010 set the pace. Not surprisingly -- given that our last common ancestor with the chimpanzee was around 5 to 6 million years ago, compared to a mere half a million years for our last common ancestor with the Neanderthal -- it turns out that we are genetically far closer to the Neanderthals than to the apes. In all, only seventy-eight changes in the genetic letters ('nucleotides') that would change the amino acid sequence of particular proteins were found in the Neanderthal DNA that were the same as the chimpanzee sequence but different in the human. Amongst other differences, 111 duplications of small DNA segments were found in the Neanderthal but not human sequence. Genetically we are closely related twigs on the great evolutionary bush of life.
But we knew that already. More surprising for many was the provocative finding that non-African humans are genetically closer to Neanderthals than African humans. In fact, the European and Asian genomes that were sequenced appear to contain one to four percent DNA of Neanderthal origin, and the gene flow that occurred appears to have been almost entirely from Neanderthal to human, rather than vice versa. How come? The most likely scenario is that there were a few instances of sexual reproduction between Neanderthals and human individuals belonging to the population that is thought to have emigrated out of Africa to populate the world sometime after seventy thousand years ago, explaining why the Neanderthal DNA sequences are not found in African genomes. The contribution of the Neanderthal genome has remained in European and Asian populations ever since.
To put this in perspective, most of our genes are very similar anyway to those found in Neanderthals and chimpanzees, and to other mammals like mice. We all share a "how-to-build-a-mammal" instruction manual, and the relatively minor genetic differences between us (minor relative to those we share in common) are the icing on the cake, as it were, that make us a human rather than a mouse, a chimp or a Neanderthal.
The year 2010 saw yet another twig appear on the hominin branch of the evolutionary bush, this time one even closer to the Neanderthals than our own. This story begins with the discovery by a Russian team of a sliver of finger bone from a remote Siberian cave in the Altai Mountains, known as the Denisova Cave. The team stored it away, thinking it was from one of the Neanderthals that frequented the cave between thirty thousand and forty-eight thousand years ago. But when DNA extracted from the bone was eventually sequenced, the results -- published just before Christmas -- revealed a population distinct from both humans and Neanderthals.
The finger appears to belong to a novel hominin population that shared a last common ancestor with Neanderthals more recently than humans, and overall is genetically closer to Neanderthals than to humans. It is too early to say whether the so-called 'Denisovans' represent a separate species and fossil data will be required to clarify that question. But what the results do suggest is that Melanesians -- the inhabitants of Papua New Guinea and islands northeast of Australia -- have inherited as much as one-twentieth of their DNA from the 'Denisovans', indicating that some limited inter-breeding took place between these ancient populations. Most fascinating of all is the idea that multiple hominin lineages were coexisting in Europe and Asia, along with modern humans, as recently as twenty-thousand to forty-thousand years ago.
Do these findings have any particular theological significance? It is difficult to know why this should be the case. In the Judeo-Christian tradition humankind uniquely is made "in the image of God". The suite of capabilities that emerged during human evolution is necessary but not sufficient to do justice to this much discussed theological insight. Our particular genetic instruction manual generates large frontal lobes, advanced cognitive abilities, rationality, language, consciousness and the ability to choose between right and wrong. It is this suite that gives us the ability to pray, worship and engage in communal religious practices.
But the idea of being made "in the image of God" is not encompassed simply within a static list of such human qualities. Theologians have drawn attention to the dynamic, relational aspects of the concept. It is humanity-in-relation-to-God, together with God-given responsibilities to humans in relationship with each other, that are thought to be more central to the idea. When did such spiritual capabilities and responsibilities first come into being? It is really difficult to know, but the answer certainly seems more rooted in God's intentions and purposes for humankind than in genetic change per se. Students can spend a long time being trained in the finer points of drama, but the play only gets off the ground when the actors are finally given their lines.
It seems quite likely that more twigs will continue to appear on the hominin branch of the bush of life as genomics continues to extend its reach. Such discoveries as such do not appear to raise any new theological questions. But other 2010 discoveries did highlight two genomic insights that do have relevance for religious views of human identity. The first insight comes from further Genome Wide Association studies that continue to subvert any lingering commitments to genetic determinism, for example the idea that there are genes "for" a particular human trait. The second insight comes from the finding that we are all more genetically different from each other than we realized even a few years ago. Genetics is underlining the uniqueness of each human individual. By the end of 2011 it is estimated that more than 30,000 human genomes will have been sequenced. Watch this space. Theological reflections on these findings will be the topic for Part 2.