For many,
evolution boils down to a simple phrase: survival of the fittest. Within a population, individuals differ in their ability to survive and reproduce, and the winners in this competition form the next generation.
"Wherever we look, the results are unequal across populations," says Matthew Zipple, an evolutionary biologist at Cornell University. "In natural populations, there is a huge amount of variation in starting position in terms of the environment and the genetics of the individual."
Biologists usually focus on the genetic and environmental causes of this variation, but sometimes organisms just get lucky.
A male ram vying for a female's attention may encounter a rival who accidentally slips on a wobbly rock and falls. A
bird feeding chicks may accidentally stumble upon food before others.
Such lucky accidents, which humans can neither predict nor control, may at least partially explain why some individuals succeed and others fail. This led him to ask, "What is the role of luck and what is the role of competition in causing such inequalities in life?""
Answering this question is not easy because the potential ingredients for an individual's success - genes, environment, and luck - vary widely among natural populations. So Zipple and his colleagues approached the question creatively.
"We wanted to know what if we created a society where everyone starts out with the same genetics, has access to the same resources in the same environment at an early age," says Zipple. "When these people grow into adults, do they look different? Do we see inequality develop?".
Creating a society of equal mice
The team created this society using about a hundred genetically identical mice. Groups of 26 two-week-old mice and their mothers were placed in enclosures that mimicked their natural habitat but had "resource zones" with food and shelter available to all. The team followed the mice for 46 days, measuring their behavior and various aspects of fitness, such as weight.
That said, there was one important variable. In this strain of mice, males compete with each other for territory and access to food, while females do not. "We have a very useful system in which one sex experiences very strong competition and the other sex does not," says Zipple. "If the genetics and the environment are the same, what remains are "these really micro-contingents."
An individual male mouse may accidentally win a fight with his twin for food, this happy accident will help him become larger than his twin, allowing him to win the next fight.
As the researchers describe in the paper, these randomnesses matter much more to males than to females, suggesting that competition reinforces the importance of luck.
As for males, "they start dividing pretty early on into really high quality and low quality, or males that get access to resources and males that are deprived of resources," said Michael Sheehan, a biologist at Cornell University and senior author of the study. "We don't see this pattern observed among females. They stay at about the same level all the time."
The importance of luck
"Researchers don't know exactly what random events steer male mice down different paths. But the study demonstrates how competition raises the stakes of luck early in life," said Robin Snyder, a theoretical ecologist at Case Western Reserve University who was not involved in the study.
It's hard to say exactly what these results mean outside the context of this experiment. But for Snyder, who studies how random events affect the reproductive success of organisms, this study was an addition to a growing body of work in the field.
"We've found that even if there's something special about you, something lasting - you're particularly energetic or you have great genes - it's a necessary but not sufficient trait to be exceptionally successful," she says. "You also have to be lucky."
Might be true for humans
Social scientists sometimes point out that people who succeed early tend to continue to succeed. Of course, early success may be due to factors such as talent or merit. But research shows that luck can be an important factor, too.
"There are people who start out with the same genetics, the same, whatever you want to call it, talent, the same access to resources, but they end up with very different outcomes in adulthood," Zipple says.
He said it has implications for the study of evolution and should encourage biologists to consider non-genetic reasons for an individual's success, especially in highly competitive environments.