鸟为什么下蛋？
Why bird lay egg?
机制问题：蛋壳如何起到保护作用？
Mechanistic explanations for how an organism’s structures work.
发育问题：蛋壳是如何形成的？
Developmental explanations for changes in individuals, from DNA to their current form.
功能问题：蛋壳薄厚合适对鸟类有怎样的意义？
A species trait that solves a reproductive or survival problem in the current environment.
进化问题：蛋壳的厚度恰好合适是如何进化来的？
The history of the evolution of sequential changes in a species over many generations.
HOW?
以静态的观点问HOW，是机制问题
以动态的观点问HOW，是发育问题
WHY?
以静态的观点问WHY，是功能问题
以动态的观点为WHY，是进化问题
