Adaptive Evolution In Mammals And Birds Is Much Faster Than We Thought


Stephen Luntz

Stephen has a science degree with a major in physics, an arts degree with majors in English Literature and History and Philosophy of Science and a Graduate Diploma in Science Communication.

Freelance Writer

spotted hyenas

A study of 15 species of mammals and birds has found consistently higher rates of evolution than expected, but of these spotted hyenas, shown here have the greatest fuel for evolution, at least among the Tanzanian population that has been studied in great detail. Image Credit: Maureen Lunn Uploaded by Mariomassone, CC BY 2.0

A novel method to estimate the genetic variations underlying natural selection has produced a surprising answer. In the species studied, additive genetic variance is up to four times higher than anticipated, suggesting a proportionally faster rate of evolution.

However, there's a lot the study didn't answer, and the authors say its implications could be either good or bad news for species survival depending on whether the measured rate is a response to human interference or not.


Genetic differences between individuals of the same species are known as “evolution's fuel”. However, measuring them is a challenge – we can easily study the diversity of a particular trait, such as fur color or wingspan, but predicting which traits will prove important to survival is much harder. If we focus on a few characteristics, something different could be evolving unobserved.

A large international team set out to evade this problem by looking at variations in the number of offspring within a species. Doing this from scratch would be an immense operation, but they drew on existing long-term studies of 19 wild populations of 15 species of mammals and birds, and reported their analysis in the journal Science

The work relies on the recognition that what matters for natural selection is the capacity to produce descendants. Specific traits are just a way to achieve that – so to explore diversity, one should look at how many offspring each individual produced.

First author Dr Timothée Bonnet of the Australian National University acknowledged the measure isn't perfect. “An individual could have a lot of babies but those babies are crap,” he told IFLScience. The number of grandchildren or great-grandchildren might be more meaningful.


Nevertheless, Bonnet believes the team's measure of looking only at a single generation is probably, “relatively immune” to distortion from those who choose quantity over quality in reproduction.

Moreover, the research was already demanding enough. “To perform this study, we needed to know when each individual was born, who they mated with, when they had babies, and when they died,” Bonnet said in a statement

Individually, the projects are immense tasks, running an average of 30 years and “Providing the team with an incredible 2.6 million hours of field data” combined, Bonnet said. On top of all that, the paper's authors then needed to find ways to control for non-genetic factors like social learning in species that raise young partially collectively.

Unsurprisingly, different species have different rates of evolution. The fastest of the 15 proved to be Tanzanian spotted hyenas, whose rate of evolution was around four times previous estimates. Others were slower, but still double what was expected. No clear patterns were observed as to which species are evolving faster, unsurprising given the small sample.


We know how fast animals have evolved over millions of years, Bonnet told IFLScience. “These rates are quite slow, but this is a smoothed out version of evolution. The fossil record is very sparse, we may only find a specimen every few hundred thousand years. If evolution is driven in one direction for a while and then in another we will miss that.”

All the studies available were on birds and mammals – no one has invested the time required to trace the ancestry of reptile or insect populations in such detail. Bonnet told IFLScience; “It's very hard to tell without more studies,” whether other branches of life would have the same levels of variation, and therefore the similar responses to natural selection. However, he added; “There is no reasons known why things might be different [among other animals]”.

It's possible to interpret the results as good news. The faster animals can evolve, the better their chances of surviving what the next century – almost certainly the most challenging in 65 million years – will throw at them.

Unfortunately, Bonnet told IFLScience, there is a much more pessimistic possibility: that the animals studied are already struggling with changing conditions in the Anthropocene, and their rates of evolution have accelerated in response. If so, previous estimates may actually have accurate assessments of baseline evolution, but things have already changed for most life on Earth, indicating even greater dangers of extinction.


“It's not telling us anything about the future,” Bonnet said. For that, more research will be needed.


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  • animals