A theory might invoke dominant and recessive genes to explain how brown-haired parents ended up with a red-headed child, or use gravity to shed light on the parabolic trajectory of a baseball.

一个理论可能会引入显性和隐性基因来解释为什么棕色头发的父母 会生出红色头发的小孩，或者运用重力来阐释棒球的抛物线轨迹。