It’s no secret that a mouse stops growing before it becomes the size of a whale. But the physiological and genetic mechanisms that control how fast—and how big—an animal grows have largely remained a mystery. A study of fruit flies, however, is shedding some new light on how animals regulate body size, and may also help explain why certain cancer tumors grow out of control.
Two largely independent processes determine how big an animal gets. The first controls how fast an animal grows and depends on insulin or similar hormones to cue cells to grow and divide. The second regulates the timing of maturation or, in insects, metamorphosis (the process by which a caterpillar turns into a butterfly). In fruit flies, for instance, two hormones influence the timing of metamorphosis. One is ecdysone, known as the molting hormone because elevated levels can prompt an insect to shed an old skin or undergo other changes. The other is juvenile hormone (JH), which stops growth and initiates metamorphosis when levels drop.
Read the full, original story: Why Spiders Don’t Grow to Horrific Size
