Evolutionary biologists are looking at how organisms have adapted to their environments before they made any change of mind and heart to the hierarchy of things. It turns out, brain size may be an important factor in predicting the long term success of a species. The bigger the head, relative to the rest of the body, the greated the chance an animal has of surviving through time.
The conclusion was reached by biologist Eric Abelson at Stanford University, studying the correlation between brain size and evolutionary success. Scientists know that when the body size grows, so does the brain, so when they plotted brain size against body size, they got a consistent curve.
Abelson observed that there are some animals that have bigger or smaller brains than the curve would predict. The bigger brain to body size ratio typically indicates an intelligent animal. According to Emma Marris of Nature who described what Abelson did next:
Abelson looked at the sizes of such deviations from the curve and their relationships to the fates of two groups of mammalian species - ‘palaeo' and ‘modern'. The palaeo group contained 229 species in the order Carnivora from the last 40 million years, about half of which are already extinct. The modern group contained 147 species of North American mammals across 6 orders. Analysis of each group produced similar results: species that weighed less than 10 kilograms and had big brains for their body size were less likely to have gone extinct or be placed on the International Union for Conservation of Nature red list for endangered species.
For species larger than about 10 kilograms, the advantage of having a large brain seems to be swamped by the disadvantage of being big. Large species tend to reproduce later in life, have fewer offspring, require more resources and larger territories, and catch the attention of humans, either as food or as predators. Hunting pressure or reductions in available space can hit them particularly hard.
But for smaller mammals, such as rodents, the future may belong to the big-brained. Animals with larger brains relative to their body size have been shown to be more likely to thrive when introduced to new places, and Abelson's work suggests that they would outperform their dimmer peers when it comes to adapting to changes at home as well. This behavioural flexibility of the brainy could tide them over until the slower process of genetic change is able to catch up to a changed environment, Abelson says. "If the climate cools significantly I may not be able to adapt anatomically in my lifetime, but if I was sufficiently flexible I could build a warmer house."
Larger brained animals may be less likely to go extinct in a changing world because they are more adaptable and flexible when it comes to adjusting their behavior when conditions change.
Check out Marris's account of the study in Nature.