Male nipples. Whale pelvic bones. Vestigial hind limbs in snakes. Evolution is full of features that look purposeful. But upon closer inspection, science tells us that they are actually by-products of development and shifting gene expression. New research suggests the human chin may be one such evolutionary spandrel, a term biologists use for a trait that emerges as a consequence of other changes rather than as a direct adaptation. For decades, scientists have assumed the human chin must serve..