適者生存は自然淘汰の考え方を表す言葉だ。
Tekishaseizon wa shizentouta no kangaekata o arawasu kotoba da.
Survival of the fittest is a phrase that represents the idea of natural selection.
厳しい自然環境では、適者生存が求められる。
Kibishii shizenkankyou de wa, tekishaseizon ga motomerareru.
In harsh natural environments, survival of the fittest is necessary.