Over the past tens of thousands of years, large animals with larger brains (in relation to the size of their body) were less likely to go extinct, according to a new Tel Aviv University and University of Naples in Italy collaborative study.
Size does matter
The research, published in the journal Scientific Reports, concluded that a large brain meant relatively high intelligence, thus helping species to adapt. Without the ability to adapt and avoid hunters, species are known to go extinct.
The scientists collected data from the paleontological literature on 50 extinct species of mammals from all continents, weighing from 11 kg. (an extinct giant echidna) up to 11 tons (the straight-tusked elephant, which was also found in Israel).
They compared the size of their cranial cavity to those of 291 evolutionarily close mammal species that survived and exist today, weighing from 1.4 kg. (the platypus) up to four tons (the African elephant). The data was entered into statistical models that included the weighting of body size and phylogeny between various species.
Why is a large brain important?
“We know that most of the extinctions were of large animals, and yet it is not clear what distinguishes the large extant species from those that went extinct," said doctoral student Jacob Dembitzer of the University of Naples. "We hypothesized that behavioral flexibility, made possible by a large brain in relation to body size, gave the surviving species an evolutionary advantage – it has allowed them to adapt to the changes that have taken place over the last tens of thousands of years, including climate change and the appearance of humans.
"Previous studies have shown that many species, especially large ones, went extinct due to over-hunting by humans that have entered their habitats," Dembitzer said. "In this study, we tested our hypothesis for mammals over a period of about 120,000 years – from the time the last Ice Age began, and the time that modern man began to spread all over the world with lethal weapons, to 500 years before our time.
"This hypothesis even helps us explain the large number of extinctions in South America and Australia, since the large mammals living on these continents had relatively small brains.” he said.
“We found that the surviving animals had brains 53% larger on average than evolutionarily closely related, extinct species of a similar body size," said Prof. Shai Meiri. "We hypothesize that mammals with larger brains have been able to adapt their behavior and cope better with the changing conditions – mainly human hunting and possibly climate changes that occurred during that period – compared to mammals with relatively small brains.”
The researchers offered giant ground sloths weighing four tons and a giant armadillo weighing a ton as some examples of large animals with smaller brains affected by widespread extinction during the Ice Age. In contrast, elephants, rhinos and hippos survived this period.