The decoded genome is only a first step to understanding the variety of human life, writes Robert Foley.
Scientific achievements come in many forms. Some, such as Darwin's theory of evolution, represented a major new insight into the working of the natural world and changed the way people think. Some, such as Watson and Crick's discovery of the structure of DNA, solved major problems that baffled contemporaries. Others, such as the sequencing of the human genome, which has just been announced, are rather different. While it is an astounding technical and organisational piece of work, we know nothing now that we did not know yesterday about the fundamental workings of the human being. As a scientific event, therefore, it means more for what lies ahead than for what we have learned. In that sense, the Human Genome Project is not the end, but the beginning.
This is especially the case for biological anthropology, that branch of anthropology and the sciences that is concerned with human evolution and diversity. Anthropologists have a long history of putting the human body under the microscope, trying to extract every bit of information possible, and using this to reconstruct our evolutionary history or to understand the process of adaptation. Genetics is a key part of this work, and with the human genome mapped and sequenced, we will have a better understanding of how human genes are constructed.
However, the key to the past successes of anthropology have lain in looking at patterns of variation - how does one person differ from another, what do two populations have in common, and so on. Only with the comparative perspective offered by the study of human diversity can we make any claims to have increased our understanding. The publication of the book of human genes is therefore only the first step on a very long road. In effect this is one sequence, and yet every one of the 6 billion people on this earth will have a different sequence. These differences will be very small, but they can also be very significant, giving rise to why some people are tall, others short, some have blue eyes, some brown, why some are prone to cancer, and so on. For the anthropologist, the real interest is in uncovering the variation, and so sequencing the human genome simply provides a better reference point from which we can start to explore the evolutionary, functional and indeed just random patterns of variation.
Much of that work is already under way. Molecular genetics has already had a major impact on anthropology, revealing how little genetic variation there is, how recent the origin of our species is, and locating those origins in Africa. But if the Human Genome Project is just a reference point, for the anthropologist the important question to ask is, "a reference point for what?".
Undoubtedly, more and more molecular genetic variation will be revealed, but this is still very much the beginning of the questions that anthropologists will be interested in pursuing.
The key point is the recognition that genetic diversity is just one level of variation in humans. It is a fundamental and important one, but it is still only one. Genes code for proteins and control development, each of which can represent another level of variation. This is what biologists refer to as phenotypic variation - the way we vary in shape and size and behaviour, the things we can actually see and observe in people.
This variation is the result of the influence of both genes and environment, and the interaction between the two. Human diversity is therefore something that occurs at many levels, from the genetic to the cultural. To uncover the range of human genetic diversity is only one part of the story. What anthropologists will be interested in is how genetic variation relates to other ways in which humans vary - their body shape and size, their patterns of demography, their health and subsistence, and their history as seen in archaeology and languages. For example, it could be that in some areas we may find lots of genetic variation, but little phenotypic variation, or vice versa. Tackling how that sort of pattern can arise will be the challenge to anthropology over the next decade - how evolution, ecology, behaviour and history have shaped the patterns of genes we see today, rather than thinking that the answer lies in the genes themselves, seen in isolation. It is the integration of these levels that will provide the Darwin or Watson and Crick type of scientific achievement.
Robert Foley is reader in evolutionary anthropology and director of the Duckworth Laboratory, department of biological anthropology, University of Cambridge.