Scientists think they know birds' eggs are different . Some are , some are potato-shaped, and others are . Two thousand years ago, Aristotle said flatter eggs had female chicks inside and eggs contained male chicks. But he was wrong. A study says that the shape of the egg depends on well the female bird flies. A professor said she noticed that birds have evolved to lay eggs that have shapes. They are all in form, "everything from a spherical owl egg to a sandpiper egg".
The professor and her made a for the shape of eggs. They looked at 50,000 eggs from 1,400 different bird . They put the shape, length and of the eggs into a computer. They also looked at how the eggs were. The researchers found that the birds with the most-oval-shaped eggs were the fliers. The professor said: "We were to see that one of the best explanations for egg shape [difference] was flight ." Hummingbirds laid the most-oval-shaped eggs; owls laid the roundest eggs; and birds laid the pointiest eggs.