Though Charles Darwin sometimes referred to higher and lower animals, his theory replaced the great chain of being with a branching bush of life. In Darwin's version of evolution, fish aren't any less evolved than we are.
Some fish probably evolved intelligent behavior because they lived in complicated environments where it benefited them, said University of Neuchatel biologist Redouan Bshary. "Fish brain structure is more primitive than that of mammals, but they've still had 400 million years to evolve something with it," he said. "There's no a priori reason why fish should remain stupid."
One of the researchers most responsible for revealing the minds of fish is Victoria Braithwaite, whom I first met at dinner during a recent visit to Pennsylvania State University, where she is a professor of biology. I made the regrettable choice of ordering the salmon, which is, I now realize, one of the smarter fish.
Braithwaite is the author of the 2010 book Do Fish Feel Pain?, to which her answer is a definite yes.
She started out studying salmon, trying to figure out how they navigate. She realized nobody had really looked at the cognitive abilities of wild fish.
So she and a colleague started putting fish into mazes to see what they could do.
"We were flabbergasted by what they were able to achieve," she said. Several strategies emerged. Species at home in ponds noted small landmarks such as plants and rocks. Those used to streams ignored these, since such small objects are likely to be swept down current.
Many fish know left from right. Some species turn their right side to new objects, she said, thus sending the information into the left hemisphere, showing how parts of their brains are specialized. When encountering familiar objects, they look with their left eyes and process with their right brains.
