Finding a sexual partner is a complex business for humans. At its simplest, it requires two willing participants to be present at the same place at the same time. And unsurprisingly, humans have developed sophisticated social skills to coordinate their movements for just this purpose (as have many organisms).
But what if the participants have no social skills and so are unable to coordinate in this way? How do participants lacking social skills ever mate? That’s an important question, and not just for humans with poor social skills. Indeed, many simple organisms reproduce sexually but do not seem to have the social skills to coordinate their movements.
This conundrum is called the social coordination problem, and sociologists have long puzzled over how socially challenged species survive.
Today we get an answer thanks to the work of Chris Marriott at the University of Washington in Seattle and Jobran Chebib at the University of Zürich in Switzerland. These guys have created a computer model that simulates the interaction between organisms, their genes and the environment in which they exist.
This model shows how individuals without social skills can still mate successfully and provides a unique insight into the way social skills can eventually evolve in these kinds of populations.
A key part of the new model is its ability to simulate the interaction between the genetic make-up of a population of individuals and their environment. And it does this in a clever way.
In the new model, the “environment” consists of a network of nodes connected at random. An individual can explore this world by jumping from one node to the next using the links between them.
Individuals top up energy at each node but use it as they move. The net gain or loss of energy each day determines if the creature lives or dies.
At the same time, an individual with enough energy can indulge in sex with another creature that happens to be at the same location, provided that this one also has sufficient energy. This results in the birth of a new creature with characteristics of both parents. Individuals that do not have sex can also reproduce asexually.
The way individuals choose their routes is important. Each creature does this using information encoded in its “genome”: a long sequence of potential routes through the environment from one location to another.
At a specific location, the individual searches its genome for routes associated with that position. It then chooses the route that maximizes its future resources, and this determines where it moves next.
That has important consequences for an emerging population. Marriott and Chebib begin by releasing a single individual into this environment. It obviously cannot have sex and so reproduces asexually, producing another individual with the same genome.
Since both individuals have the same genome, they move through the environment in the same way, producing other individuals with the same genome or having sex to produce individuals with similar genomes.
After many generations, the result is a group of individuals with similar genomes which move through the environment in the same way. In other words, a herd.
This leads to a breeding pattern called assortative mating, where individuals mate with similar others rather than random partners. That’s a simple consequence of being part of a herd with similar behavior patterns.
Individuals also tend to return to their birthplaces, because this information is automatically encoded in their genomes. That’s how natal philopatry emerges.
All this is in stark contrast to populations of individuals with different genomes that are dropped into the environment at random. These individuals tend to die, because they only meet other individuals by complete chance. So sexual reproduction is rare.
And when it does occur, it tends to create individuals with similar genomes that end up producing herds and indulging in assortative mating and natal philopatry in exactly the same way as the less diverse populations.
The extraordinary thing is that all these behaviors emerge from the interaction between the individuals’ genetic make-up and their environment. There are no social skills involved at all.
“We find three kinds of social organization that help solve this social coordination problem (herding, assortative mating, and natal philopatry) emerge in populations of simulated agents with no social mechanisms available to support these organizations,” say Marriott and Chebib.
That’s fascinating work and not just because it shows how mating can occur between individuals with no social skills. Marriott and Chebib speculate that the emergence of these mating behaviours provides an environment in which social coordination skills can eventually evolve. “We conclude that the non-social origins of these social organizations around sexual reproduction may provide the environment for the development of social solutions to the same and different problems,” they say.
Many creatures learn social skills from other individuals or come under social pressure of one kind or another to behave in a specific way. But nobody has ever been sure how these skills have emerged because of the chicken-and-egg nature of the problem: you can’t learn social skills unless you’re part of a group, and you can’t be part of a group unless you have social skills.
Marriott and Chebib have found a way through this paradox based on the connection between genes and environment. There next step? To see whether real social coordination skills evolve in the populations they produce. We’ll be watching!
Ref: arxiv.org/abs/1504.06781 : Finding a Mate With No Social Skills