Enter with a friend of similar fitness and ability .

和一位健康状况、跑步水平相似的朋友一起参加。

The difficulty is in assigning what darwin called ' fitness ' to a particular genetic feature .

难点在于将达尔文所谓的“适应性”设定为某种特定的遗传特征。

The greater fitness variance among males creates greater pressure for men to compete with each other for mates .

这种更大的适合度差异使得雄性在相互竞争交配权时肩负更大的压力。

The same is true for your mental fitness .

对你的心理健康来说也是如此。

Small changes can add up to better fitness .

小小的改变也能让我们更健康。