A combination of adaptation and natural selection has produced some beautiful and elegant creatures. It also causes some animal body parts to be completely strange. Have sponges lost their brains? What’s so strange about the mantis shrimp’s seemingly telescopic eyes? Why do sheephead fish teeth look so weird? What made researchers think of origami when confronted with the mystery of salamander wings?
Yes, arachnid legs function “kind of like… tongue, nose and fingertips.” Of all the places where tentacles could grow, why would nature choose snakeheads? Skilled combatants claim that almost anything can be used as a weapon, but unlike aquatic salamanders, they may even draw a line across their ribs. Shoe stork is nothing if not an innovative hunter.
When mating season comes, male venomous platypuses don’t have to worry about being cuckolded for good reason. The proboscis monkey’s nose may strike one as plain, but the females of its species seem to appreciate it, and another of its appendages is — well, for now, let’s assume you’ve been warned. .
Although modern sponges are brainless animals, some scientists believe that this was not always the case. These marine invertebrates may once have had, if not true brains, something similar to them.
If so, why did the sponges dispose of their neurons? The answer from evolution is simple: if sponges have, indeed, “lost their nerves,” as BBC reporter Melissa Hogenboom puts it, it was because they didn’t need them and because the loss benefited the animals.
Frank Hirth of Kings College London believes that sponges have undergone an “evolved loss” of neural structures. This loss is similar, Hogenboom suggests, to the losses of organs in other animals, such as crustaceans, which, living in dark caves, lose the need for eyes and evolve away from having them.
The loss, if it occurred, would provide certain advantages. Without brains, sponges need a lot less energy, and, since sponges can passively acquire nutrients by filter-feeding, a nervous system wouldn’t be an asset to their survival. In fact, feeding a brain would be “a waste of energy,” Hirth says, and the maintenance of such an “energy demand” would be impossible for sponges, which “sit on the sea bed . . . just filtering food that comes along.”
The view that sponges once had something akin to brains and lost them remains controversial among scientists. Neuroscientist Leonid Moroz, of the University of Florida in St. Augustine, is one expert among others who believes that sponges never developed neurons, since such cells are unnecessary to sponges’ survival.
Hirth and Moroz presented their differences of opinion concerning the issue during a March 2015 meeting of the Royal Society in London. However, the matter remains unresolved. According to Angelika Stollewerk of Queen Mary University of London, at present, either Hirth or Moroz may be correct. Time—and evidence—may tell; until then, both of her colleagues’ views remain possibilities.
If Hirth’s view proves correct, though, one of the most bizarre animal body parts of all time would have to be the useless sponge brain that disappeared when the animal’s survival favored its simplification.