Cracking the egg mystery: what makes eggs round or pointy?

Scientists may have just cracked the mystery of why bird eggs come in all shapes and sizes: it has to do with the bird’s ability to soar up in the sky — and the body changes wrought by years of evolution.

Egg shapes are incredibly diverse among bird species: hummingbirds lay eggs in the shape of Tic Tacs; owls make globe-like eggs; and sand pipers lay pointy eggs shaped like raindrops. But how did different egg shapes evolve, and why?

Through the years, scientists have come up with many explanations: birds that make their nests on cliffs tend to lay pointy eggs because if a pointy egg is bumped, it will spin in a circle instead of rolling off the edge of the cliff. Birds with a diet low in calcium make round eggs because they require the...

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