In trying to understand why some animals have evolved to be better at learning than others, Dr. Tadeusz Kawecki, an evolutionary biologist at the University of Fribourg, finds that
one reason for the difference is that being smart can be bad for an animal’s health.

His studies found that the very act of learning takes a toll: forming neuron connections may cause harmful side effects. It is also possible that genes that allow learning to develop faster and last longer may cause other problems, like choosing the wrong food.