Why are female dolphins bigger than males?

That's not quite right! Male dolphins are typically larger than females in most species. This is a common pattern in many mammal species, and it's generally attributed to the effects of sexual selection.

Here's why:

* Competition for mates: Larger males are more successful in competing for mates. This could be due to physical dominance in fights, or simply because females prefer larger males.

* Sperm competition: In some species, larger males may produce more sperm, giving them an advantage in fertilizing eggs.

However, there are some exceptions:

* In some species, like the Amazon River dolphin, females are larger than males. This is likely due to the fact that females carry and nurture the offspring.

* Size differences between males and females can vary greatly within a species. Factors like age, food availability, and genetics all play a role.

It's important to remember that generalizations about animal behavior and biology should always be considered with caution.