A large population of butterflies lives in southeastern Asia. About half have spots and half don’t. In 1995, a rare viral illness was introduced to the population, and there was no cure. More spotted butterflies than un-spotted butterflies were killed by the illness, although the fact that they had spots had no bearing on their risk for illness. Which evolutionary mechanism is this an example of? A)Genetic drift
B)Geographic isolation
C)DNA mutations
D)Reproductive isolation

Refer to this portion of a dichotomous key for fish identification to answer the question. 1. (a) has a single dorsal fin ® 5 (b) has a double dorsal fin ® 2 2. (a) one fin is spiny, the other is smooth ® 3 (b) one fin is not spiny or smooth ® 4 5. (a) has small fin on back near tail ® 6 (b) has no fin on back near tail ® 7 6. (a) has barbs near the mouth ® catfish (b) does not have barbs near the mouth ® 10 7. (a) tail is asymmetrical ® 8 (b) tail is symmetrical ® 9 10. (a) scales are small ® trout (b) scales are large ® whitefish what is the next step to complete to identify a fish that has a single dorsal fin, no fin on the back near the tail, and no barbs near the mouth? step 2 step 5 step 7 step 10