In my "Tadpole" video I discuss something called Parental Care. Parental care means how much help you need from a parent as a baby. So insects like butterflies or frogs have no parental care. The butterfly lays her eggs on a leaf (or another food source) and then never sees her babies again. When a bear has a baby (for example), the baby stays with their mother for years while they teach them new skills. Bears have more parental care than butterflies. Humans require the most parental care of all!
The more parental care an animal needs as a baby, the fewer babies that animal has at a time. Butterflies lay hundreds of eggs, but humans only usually have 1 baby at a time. This is because when parents take care of their babies, they are more likely to live a long healthy life. Because animals like butterflies or frogs don't take care of their babies, they need to lay LOTS of eggs to make sure that some of them make it to adulthood. Their eggs are often used as a food source for bigger animals too, as they are on the bottom of the food chain. Survival would be nearly impossible if they only laid one egg at a time.