Israeli Researchers Find Brain Size Related to Animal Extinctions

There was a direct correlation between an animal’s brain size and the mass extinction of large animals over the past tens of thousands of years, according to researchers at Tel Aviv University, and the University of Naples. Extinct species had, on average, much smaller brains than species that survived the numerous different eras of Earth’s history from the Ice Age to the rise of Man.

This should come as no surprise to anyone who ever learned about the dinosaurs. They were known for having really small brains. For example, the tyrannosaurus rex, the king of the dinosaurs, was one of the largest animals that ever existed on the face of Planet Earth. And yet its brain was the size of a peanut.

Many smaller animals, however, have brains that are much larger in a ratio to their total body sizes than human brains have.

The researchers link the size of the brain in relation to the body size of each species to intelligence, concluding that a large brain, which indicates – in comparison to different species of animals – relatively high intelligence, helped the extant species adapt to changing conditions and cope with human activities such as hunting, which has been a major cause of extinction.

Humans – Homo sapiens – may have survived for this very reason. There were many other forms of man from Homo erectus to Neanderthals. The human race may have survived for all of these years because its intelligence allowed it to build the things needed to survive in changing environments and to understand that it was necessary to migrate when severe changes in weather occurred. Other forms of the Homo Genus may have died out because they were not able to learn to adapt to their environments and did not spread out more over the Earth.

The study was led by doctoral student Jacob Dembitzer of the University of Naples in Italy, Prof. Shai Meiri of Tel Aviv University’s School of Zoology and the Steinhardt Museum of Natural History, and Prof. Pasquale Raia and doctoral student Silvia Castiglione of the University of Naples. The study was published in the journal Scientific Reports.

The researchers explain that the last Ice Age was characterized by the widespread extinction of large and giant animals on all continents on earth (except Antarctica). Among these were, in America, giant ground sloths weighing 4 tons, a giant armadillo weighing a ton, and mastodons; in Australia the marsupial diprotodon weighing a ton, giant kangaroos, and a marsupial ‘lion’; and in Eurasia giant deer, woolly rhinoceros, mammoth, and giant elephants weighing up to 11 tons,.

Other large animals, however, such as elephants, rhinos, and hippos, survived this extinction event and exist to this day. The researchers also note that in some places, the extinction was particularly widespread; in Australia, the red and grey kangaroos are today the largest native animals, and in South America the largest survivors are the guanaco and vicuña (similar to the llama, which is a domesticated animal), and the tapir while many of the species weighing half a ton or more have become extinct.

The researchers collected data from the paleontological literature on 50 extinct species of mammal from all continents, weighing from 11 kg (an extinct giant echidna) up to 11 tons (the straight-tusked elephant, which was also found in the land of Israel), and compared the size of their cranial cavity to that of 291 evolutionarily close mammal species that survived and exist today, weighing from 1.4 kg (the platypus) up to 4 tons (the African elephant). They fed the data into statistical models that included the weighting of body size and phylogeny between different species.

Prof. Meiri said, “We found that the surviving animals had brains 53% larger, on average than evolutionarily closely related, extinct species of a similar body size. 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.”