Help with Biology crossword puzzle. only need 4 more words?

Its about Mr.Darwin

7 letters clue=this drastic climate condition affected food on the galapagos for a long period of time.

13 letters clue= source of genetic variation occurs whenchromosomes sort out during meiosis

11 letters clue = natural geologic barrier that lead to the speciation of squirrels

15 letters clue=phenotype displayed in one of only two ways example right handed or left handed