Cite as:

Justin K. Werfel and Yaneer Bar-Yam, The evolution of reproductive restraint through social communication, PNAS 101: 11019-11024 (2004).


The evolution of altruistic behavior through group selection is generally viewed as possible in theory but unlikely in reality, because individual selection favoring selfish strategies should act more rapidly than group selection favoring cooperation. Here we demonstrate the evolution of altruism, in the form of conditional reproductive restraint based on an explicitly social mechanism, modulated by intrapopulation communication comprising signal and evolved response, in a spatially distributed predatory/parasitic/pathogenic model system. The predatory species consistently comes to exploit a signal implying overcrowding, individuals constraining their reproduction in response, with a corresponding increase in equilibrium reproduction rate in the absence of signal. This signaled restraint arises in a robust way for a range of model spatial systems; it outcompetes non-signal-based restraint and is not vulnerable to subversion by noncooperating variants. In these systems, communication is used to evaluate population density and regulate reproduction accordingly, consistent with central ideas of Wynne-Edwards [Wynne-Edwards, V. C. (1962) Animal Dispersion in Relation to Social Behavior (Hafner, New York)], whose claims about the evolutionary importance of group selection helped ignite decades of controversy. This quantitative simulation model shows how the key evolutionary transition from solitary living to sociality can occur. The process described here of cooperation evolving through communication may also help to explain other major evolutionary transitions such as intercellular communication leading to multicellular organisms.

Press Release

Altruism enables survival - new insight on evolution

Why do individuals co-operate when they could benefit by being selfish? Since the ancient Greeks, scientists and philosophers have tried to understand altruism. 

A new model for the origin and evolution of altruism and social communication was published today in the Proceedings of the National Academy of Sciences. This groundbreaking research can help scientists examine the dangers of overexploiting resources and extinction, which are very real problems in today's world. It also answers an ongoing controversy in evolutionary biology by demonstrating that avoiding extinction requires social cooperation and altruism that seems counter to the competition between organisms described by Darwin. 

The model, proposed by researchers at the New England Complex Systems Institute Justin Werfel and Yaneer Bar-Yam, examined the evolution of reproductive restraint through social communication, and showed that selfish individuals introduced to an altruistic population always ended up being driven to extinction. 

"We developed a model, similar to real life, where communication and reproduction are linked among creatures to ensure survival when resources are limited."

"Specifically, when an individual is surrounded on all sides by others, with no possible room to reproduce, it sends out a chemical, auditory or tactile signal that causes others to temporarily change their reproductive rate. 

"The way these simulated individuals consistently evolve, under a wide range of conditions, is to restrict their reproduction when they get the signal. Those surrounded aren't reproducing; the ones showing restraint don't know about the crowding firsthand, but are acting altruistically (giving up immediate benefit to themselves) through this explicitly social mechanism."

It has long been known that anthropological studies have shown that people will communicate about their condition and reduce their population growth when resources are threatened.

Professor Bar-Yam makes an analogy to what has happened with the world human population in recent years: "When the human population explosion threatened to overwhelm the world, the word went out and many efforts were made to reduce population growth. Today the world population is still growing but not nearly as fast as it was expected to grow when the population explosion was described in the 1970s."

"The dangers of overexploiting resources and extinction are real problems today. Recognizing what would make people act to preserve their environment is a crucial issue today." Bar-Yam continues. "This issue is intimately linked to basic research questions in understanding altruistic and selfish behavior."

The key element of this new model is how a population can spread over an area. The researchers showed that the ability to spread locally leads exploiters to cause their own extinction in the face of limited resources in that local area. Under the same conditions, the altruists survived by collectively limiting their population growth to match the locally available resources. This leads to the altruists winning the evolutionary competition, and the species surviving. 

According to Werfel, "What is intriguing is that organisms in this model learn to signal each other when the resources are depleted, then they reduce their reproduction to avoid extinction.

"The ability to signal and communicate the need to change behavior in the face of low resources is a property of many organisms, even single celled organisms signal each other chemically to change their reproduction. The paper published in PNAS has model organisms that do exactly that. They signal each other when resources become depleted, reduce their reproduction when they receive the signal, and when resources increase, they increase their reproduction."

According to Prof. Bar-Yam, "What is particularly remarkable is that selfish organisms cannot successfully invade and overtake the population. This has long been the bugaboo of other theories." According to their paper, the reason for this is that a selfish individual will have offspring that are selfish, and they will tend to be clustered in an area that has few resources. The limited resources that these selfish individuals have cause their extinction.