To create interstellar messages that have a realistic chance of being understood across interstellar distances, we need to identify some information shared by humans and extraterrestrials. We need to identify a foundation for establishing a universal language that will let us bridge the gap between our world and theirs, all without the convenience of face-to-face contact.

While it would be interesting to know that other civilizations possess sophisticated mathematics and that they understand some of the same chemical and physical processes of our shared universe that we do, if that were all we learned, wouldnt it be a bit anticlimactic? Even more interesting would be the discovery of insights unique to other civilizations. How then might we move beyond a discussion of physics and chemistry to discuss something about culture and individual behavioron their world or ours?

One topic that can help provide initial access to alien concepts of individual action, and even initial formulations of ethical and moral principles, is altruism. During the same forty years that SETI has developed as a science, so too have biological understandings of behaviors related to moralityin both humans and other animals. Particularly successful have been those scientists, often described under the umbrella term "sociobiologists," who have applied themselves to one of the greatest challenges faced by Charles Darwin: explaining how apparently self-sacrificial acts could have evolved, when these same acts seem to work against an individuals own reproductive success.

Darwin's theory of natural selection attempts to explain the evolution of complexity among terrestrial organisms. While Darwin was centrally interested in explaining the evolution of changes in the form and function of the body, he also attempted to explain the evolution of behavior. One behavior that posed a particular challenge to his theory of gradualistic change was altruism.

If in fact natural selection operates by the slow accumulation of characteristics that increase an individuals reproductive success, as Darwin claimed, how then could an evolutionist explain behaviors that appear to be self-sacrificial? There are times, for example, when an animal gives off a warning call upon sighting a dangerous predator. As a result, nearby animals of its own species may have increased reproductive fitness they might live another day to reproduce another night.

But what about the animal that gives the warning call? In many cases, it reduces its own chances of surviving by drawing attention to itself in the presence of a predator. How then could such self-sacrificial actions have evolved through natural selection? Wouldnt the altruists quickly die off, unable to pass on their altruistic tendencies to their offspring?

One answer, first formulated in the 1960s, is that such examples of self-sacrifice are altruistic only at a certain level. An action that may be self-sacrificial at the level of the individual might be adaptive, and one might even say selfish, at the level of the gene. Although drawing attention to oneself through a warning call increases an individual's chances of dying in the short run, it might also increase the chances that it will pass on some of the same genetic material that resides in its own body through the bodies of its close relatives, with whom it shares common ancestry, and thus common genes.

For example, my brother and I share fifty percent of our genes. My nephew and I share one-fourth of our genes. If in fact altruism is driven by my genes, then it makes sense even from a biological perspectiveto sacrifice my life for enough of my nieces and nephews. If I sacrifice my life for the lives of four of my brothers children, then at the level of my genes, Ive broken even. If I can save five or six of them, as far as my genes are concerned, its a done deal: I should sacrifice my own life to ensure that my nieces and nephews continue to live.

Of course, were all familiar with accounts of altruism that dont make sense from a purely genetic point of view: a person who gives her life to save only one nephew, or a distant cousin, or even a complete stranger. And indeed, sociobiologists have suggested mechanisms that help explain why we would care for others, even thought they are not kin.

But to return to the challenge of creating intelligible interstellar messages, theres a certain clarity in the genetic account of self-sacrifice that makes it a useful start for explaining our proclivity to care for others. We can describe the physical foundation for these actionsour genesin the same possibly universal language of chemistry that has been used for other interstellar messages. And we can describe when we would expect an individual to be altruistic through a few simple fractionsrepresenting the percentage of genes shared by the altruist and its beneficiary. With only some basic arithmetic, we can describe these fractions, an easy task if we have already established a complex universal language based on mathematics.

But as we will see in next weeks column, we are by no means limited to such a bare-bones description of altruism. Although genetic accounts of caring for others may provide a nice start for describing human behaviors, for anything approaching an adequate account of human altruism we need to draw upon alternative explanations of altruism, along with sophisticated new methods for designing interstellar messages.