Nothing is biology makes sense except in the light of evolution.Theodosius Dobzhansky.
Nothing in evolution makes sense except in the light of genetics.William Rice.
Nothing in genetics makes sense except in the light of epistasis and pleiotropy.Bjørn Østman.
More statements of this nature could be added under Dobzhansky's and next to Rice's, and similarly more under Rice's. It would be a whole tree of nothing makes sense's. Please feel free to contribute your own.
This was prompted by two articles on epistasis and pleiotropy in Nature Education. Excellent reads:
Epistasis: Gene Interaction and Phenotype Effects by Ilona Miko in Nature Education 1(1).
Pleiotropy: One Gene Can Affect Multiple Traits by Ingrid Lobo in Nature Education 1(1).