A new study suggests that whether animals give birth to more offspring or larger offspring depends on whether males are helping to raise the young.

Biological sciences researcher Holly Kindsvater of Simon Fraser University says that in general, females tend to produce bigger offspring if they mate with a male that helps to look after them.

Kindsvater says that's because bigger offspring have a greater chance of surviving and passing on good genes.

But there are some puzzling instances where females will give birth to bigger babies after mating with a male that slacks on parental duties, and others where they produce a bunch of smaller babies after mating with a supposedly good male.

Kindsvater's study suggests that sometimes, when paired with a lousy mate, the female is better off having just a few large babies because they're more likely to survive without the care of a father.

She says that if males are helping to raise the offspring, then it's better to have many babies of a smaller size because the father will help look after them.