Size and scale during development and regeneration.

One of the most fascinating questions in developmental biology—and dare I say it, in biology in general—is how different organs acquire and maintain their species-specific size during development, homeostasis and regeneration. Biologists (and more recently physicists and mathematicians) have been addressing this topic for centuries, from Aristotle's description of avian development through D'Arcy Thompson's introduction of the role of mechanical forces early last century, to the complex gene networks that are currently being unraveled. The core questions have been refined over the years, but their essence can be summarized as follows: