Charles Darwin's book On the Origin of Species, published in 1859, made a number of bold claims about the nature of evolution, including the assumption that animal species with greater diversity in their lineage would also produce more subspecies.
This assumption is not as obvious as you might think at first glance. Only a couple of years ago this hypothesis was found to be true for birds. Now, researchers from the University of Cambridge in the UK have shown that Darwin was right on this issue and for mammals: mammalian subspecies are indeed important from an evolutionary point of view, and perhaps more important than previously thought.
In addition to being an important contribution to our understanding of evolution in general, the findings may also be helpful in ongoing conservation efforts – helping experts figure out which animals need to be protected to ensure their survival.
“My research on the relationship between species and subspecies diversity shows that subspecies play a critical role in long-term evolutionary dynamics and in the further evolution of species,” says anthropologist Laura van Holstein.
Darwin actually called them 'species', but the idea is the same – groups within a species with their own traits and breeding ranges. For example, there are three subspecies of the northern giraffe and 45 subspecies of the red fox.
However, humans do not have a subspecies.
To test Darwin's hypothesis, van Holstein examined a huge database of animal classification, analyzing the collected knowledge about mammalian species and subspecies to find patterns.
The data showed that diversification between species and between subspecies was associated, as Darwin suggested, but there was more – subspecies tend to form, diversify, and increase in different ways depending on the habitat (for example, land or sea).
The results show that the correlation between species diversity and subspecies diversity is strongest in non-terrestrial mammals – those that live in the sea or spend a lot of time in the air – and thus are less exposed to physical boundaries such as mountains.
The researchers say that in animals such as bats and dolphins, it would be better to view the subspecies as the beginning of a new species rather than an evolution of an old one.
Another question posed by the researchers was whether there was any connection between the subspecies and the possible creation of a whole new species.
“The answer was yes,” says van Holstein. “But evolution is not determined by the same factors in all groups, and for the first time we know why because we looked at the strength of the relationship between species diversity and subspecies diversity.”
Habitat discoveries of the subspecies are especially important when it comes to conservation, because the habitat of so many animals is threatened by climate change and human activities, and these findings indicate that our actions do have an impact on the evolutionary process.
“Evolutionary models can now use these results to predict how human activities, such as deforestation, will affect evolution in the future, disrupting the habitat of species,” says van Holstein.
'Exposure to animals will vary depending on how it affects their locomotion or distance from humans. Animal subspecies are generally ignored, but they play a key role in the long-term dynamics of future evolution. '
The research was published in Proceedings of the Royal Society B.
