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Narrator: Listen to part of a lecture in a biology class. Professor: So today we're going to talk about a fascinating adaptation in some fish species—the ability to change sex. This is called sequential hermaphroditism. Now, in many reef fish, like the clownfish, the social structure is dominated by a breeding pair. The largest individual is the female, and the next largest is the male. If the female dies, the male will actually change into a female to take her place. This ensures that reproduction can continue. On the other hand, in species like the wrasse, the opposite occurs. The largest male dominates a group of females. If that male is removed, the largest female will transform into a male. This sex change is triggered by social cues, not by age or size alone. Interestingly, the transformation involves hormonal changes and can take just a few weeks. This flexibility gives these species an evolutionary advantage in unstable environments. So, as you can see, gender in these fish isn't fixed—it's a dynamic and strategic response to their social surroundings.