Reproduction has long been considered the key moment of evolution but new research suggests that social isolation can be just as vital.
Animals including primates, but also toads, ants and beetles, genes are expressed differently depending on the environment they are experiencing.
In a study by Dr Nathan Bailey at the University of St Andrews in Scotland, and Dr Allen Moore at the University of Georgia in the US, noted how social interactions were important for evolutionary research.
But, they reasoned, if parent-offspring bonding, competition for resources, and courtship and mating rituals were important, then isolation must require equal attention too.
"The environment an animal experiences can influence which genes it expresses, when, and how much, so conditions of social isolation might cause expression of different traits," said Dr Bailey.
"This in turn could affect responses to natural selection in terms of survival and reproduction, which has evolutionary consequences. For some species, it might even mean that temporary social isolation is favourable."
As an example, the invasive cane toad species in Australia often ventures off alone to explore new territory.
However, this isolation gives it an extraordinarily strong attraction to members of the opposite sex when it returns to the social environment – the toad becomes an exciting hunk, essentially.
Because this boosts the likelihood of successful mating, it is necessary for the species to thrive as it expands into new regions.
In a similar fashion, a species of European ant is known to become reclusive when it is poisoned – ensuring that its nestmates do not get infected.
"Traits expressed during social interactions might exist because they've been shaped by selection, but at the same time, social interactions themselves represent a type of environment that can select and shape how individuals behave," said Dr Bailey.
Social interactions are therefore a dual quality, a trait in themselves but also an environment, the researchers said.
They propose a measurement called the "index of social isolation" which would allow scientists to compare an animal's perfect amount of isolation with how much time alone it is having.
The researchers plan to measure the optimal balance of interaction and isolation by testing individuals to find which results in the best survival and reproduction levels.
By comparing this ideal to real-world observations, the researchers hope to figure out whether animals are more or less isolated than they should be.
This would ultimately lead to more effective conservation strategies, reintroduction models, and breeding programs.
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"To understand how short-term social isolation experienced by individual animals translates into trans-generational evolutionary impacts for a larger population, we need a number, something measurable that we can compare across different species and contexts," said Dr Bailey.
"After all, isolation that has negative effects for one species could in fact be beneficial for another."
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