Kin selection and reciprocity are two important evolutionary theories:

kin selection -> I'll help you because your related to me thus by helping you I'm really helping my own genes to multiply, I don't expect to get any direct benefit.
reciprocity -> I'll scratch your back if you scratch mine, I expect to get a direct benefit from you later as repayment for me helping you now I don't care if your related to me or not.

They apply in different cases/social structures in family groups kin selection is a better explanation but in looser groups reciprocity might be more important.

A character that responds to the environment is said to be phenotypically plastic.

- When plasticity is adaptive, it is a facultative adaptation
- Learning is a facultative adaptation.
- Skin tanning is another
- Response to cold, heat, altitude, & disease

But I dont understand what puzzle it is? :/