In the beginning, there is the fertilized egg. Its form couldn't be simpler. But this will change. It's a piece of work to craft a creature from a single cell. By the time it enters the world, every living thing has experienced an odyssey of alteration. Change doesn't stop with hatching or birth. Growing up is also a story of transformation. A newborn kangaroo can grow over 50,000 times in weight. Some creatures do far more than simply grow up. They reinvent themselves. A fish can start life as a female but end up as a male. A bird can grow or shrink a brain area for song to suit the season. Polliwogs become frogs. Caterpillars turn into butterflies. We learn few more curious facts than these. But it's easy to lose sight of just how astonishing these changes are! And even weirder transformers live among us. Turn and face the strange. Meet the body changers. Hey, Emma, come here! Compared to the epic alteration of a caterpillar, our own changes may seem subtle. But there's no denying that kids change shape as they turn into grown-ups.The brain kicks off our own sexual transformations. Girls tend to get curvier from estrogen and other hormones. A child's body, and that of many other young creatures, changes shape when it reaches the age for reproduction.