Press Release: Theory predicts the uneven distribution of genetic diversity within species

THE EVOLUTION OF REPRODUCTIVE RESTRAIN THROUGH SOCIAL COMMUNICATION

J. K. Werfel and Y. Bar-Yam, PNAS 101, pp. 11019-11024, 2004. PDF file Press release

A news article about this work is below.

MORE TALK, LESS SEX BREEDS SUCCESS FOR SPECIES' SURVIVAL

From http://www.thehollandsentinel.net/stories/072704/lif_072704034.shtml
and http://www.fox11az.com/scitech/sci/stories/KMSB-20040720-dnbp-surviving.bde0f0f.html

TOM SIEGFRIED

In a battle for survival, you'd probably bet on the strong silent type. But maybe you should put your money where the mouths are.

In the long run, sensitive talkers have an advantage over active aggressors. That's because more talking can mean fewer offspring. And contrary to common understanding, reproductive restraint might be a better way to evolve.

It's one of those odd nuances of evolution seemingly straightforward logic turns out not to be so logical. Life is complicated, and in the real world of dog-eat-dog or predator-eat-prey the "be fruitful and multiply" approach is not always a sound strategy.

On the one hand, reproducing is the key to passing your genes down to future generations, which is what evolution is supposed to be all about. But the so-called "selfish gene" idea doesn't tell the whole story. If predators proliferate uncontrollably, there won't be enough prey around to eat. So the predators will go extinct.

There must be some other trick to being the species that survives. And a new computer simulation suggests that the trick is learning how to talk.

Talking in the general sense of communicating, or sensing signals, is the secret to evolutionary success, say Justin Werfel of MIT and Yaneer Bar-Yam of Harvard University. Communication permits cooperation, and by cooperating individuals can avoid the pitfalls of unbridled greed.

Bacteria, for example, emit chemical signals allowing members of a colony to adopt strategies that benefit the group. More elaborate intercellular signaling was essential for many-celled organisms to evolve. And more sophisticated communication drives social cooperation in advanced animals, including humans.

Among communication's many benefits is enforcing restraint on reproduction when resources are in short supply, Bar-Yam and Werfel assert in a new paper, published online in the Proceedings of the National Academy of Sciences. Using a fairly simple computer simulation (analyzed with some fairly complicated math), the scientists show how sensitive talkers succeed in the cyberspace equivalent of life in the jungle.

In the simulation, predators and prey occupy squares on a grid. As the simulation runs, the grid is repeatedly updated. Prey reproduce at a constant rate to occupy more squares; predators reproduce and spread to new squares as well, eating any prey that they encounter.

At each update step, some of the predators undergo "mutations" that alter their reproduction rate. These mutations create new genetic strains of predators with more or less propensity to multiply. At first, the strain of predators that reproduce more rapidly appears to be winning the battle to conquer the grid. But in the long run, those strains eat too much of the prey. "Eventually, resources are exhausted and the strain goes extinct," the scientists point out.

Strains that reproduce more slowly survive longer, since the prey reproduce fast enough to keep those predators supplied with food.

Now, if a predator's rate of reproducing and spreading depends only on its genes, it takes a long time for the species to respond to changes in the prey population. But when a predator has communication skills say, the ability to sense the presence of neighbors it can respond to changing circumstances more rapidly. In the grid game, predators sensitive to such "crowding" signals reduce their reproduction rate when surrounded by other predators on adjacent squares. Simulations show that those sensitive predators win the game in the end. And if sensitive predators invade an established community of noncommunicators, sooner or later those with sensing skill will prevail. Communication ability therefore seems to offer an evolutionary advantage.

This result might explain an old evolutionary mystery: Why do animals ever cooperate? In day-to-day life, the battle for survival is among individual organisms. It really does seem like the stronger and selfish ones should be the winners. If you're looking out for the welfare of others instead of yourself, you're likely to be a loser. And your selfish genes will go nowhere.

However, as the late Stephen Jay Gould emphasized, evolution really works on multiple levels. The battle for survival is not restricted to organisms or their genes, but to groups and species as well. So cooperation can sometimes be a useful ability for the greater good of the community.

Under certain circumstances, strains of predators who respond to signals can cooperate, and therefore outcompete the strains that can't. And in the early history of life, mutations must have on occasion conferred the ability to respond to signals. "If a single, rare mutation can toggle the presence or absence of that ability," say the scientists, "then a simpler, noncommunication population will tend to give way over time to a responsive one, bringing about full-fledged social communication in the population."

Any strain of cheaters showing up later refusing to go along with the group and reproducing at will soon goes extinct, further simulations show.

So for those who think that evolution teaches the supremacy of selfishness, it would be good to remember that natural selection is not as simplistic as it sounds. And that it's wrong to think that only the strong survive.
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