Essays on Science and SocietyGenome-Sequencing Anniversary

What Defines Us?

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Science  04 Feb 2011:
Vol. 331, Issue 6017, pp. 548
DOI: 10.1126/science.1203070

As a theologian, I am sometimes asked: What, then, does it mean to be human? If I ever knew the answer, I am becoming less clear all the time, thanks in part to discoveries related to the human genome. The irony is discomforting. As we gain precision, we seem to be losing conceptual clarity.

The “human” genome, it turns out, consists of sequences that are widely shared across the evolutionary tree. The microbes inside us, outnumbering our human cells ten to one, have their own genomes that interact with our DNA, contributing to our individual and species identity. Comparisons between the human genome and that of other primates, such as chimpanzees, suggest that the boundary of our much-vaunted human “uniqueness” is thin indeed. The sequence of a major portion of Neandertal DNA can now be compared with our own, and we are learning that Neandertals are hardly extinct, their DNA living on in many of us. Tantalizing discoveries now suggest that we once shared the planet with the newly discovered Denisova hominin, which appears to have interbred with some of our ancestors as recently as 40,000 years ago.

The Human Genome Project undermines cherished ideas about human uniqueness. But it also hints at a new vision of humanity. We are less clearly defined than we once thought, less set apart from the rest of life, but uniquely able to probe the data and ponder the questions. And, being humans, we let our discomfort give way to wonder. Who are we, and where will we go next?

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