Question

Red dotted line shows a normal distribution

Answer 1

the size of the male salmon anatomy used to be around medium sized, however, since the small males have snuck into the territory and interbred with the females, the distribution of salmon sizes has expanded to small, medium, and large sizes. This is different than the initial weight span because before the small salmon snuck in, the span of weight for the male salmon wouldn't really go into the small or large category, they would stay mostly at medium.