How Eggs Got Their Shapes

June 23, 2017
bird eggs of various shapes

Image credit: Harvard Museum of Comparative Zoology

The evolution of the amniotic egg — complete with membrane and shell — was key to vertebrates leaving the oceans and colonizing the land and air. Now, 360 million years later, bird eggs come in all shapes and sizes, from the almost perfectly spherical eggs of brown hawk- owls to the tear-drop shape of sandpipers’ eggs. The question is, how and why did this diversity in shape evolve?

The answer to that question may help explain how birds evolved and solve an old mystery in natural history. An international team of scientists led by researchers at Harvard (Prof. L. Mahadevan) and Princeton universities, with colleagues in the UK, Israel and Singapore, took a quantitative approach to this question. Using methods and ideas from mathematics, physics and biology, they characterized the shape of eggs from about 1,400 species of birds and developed a model that explains how an egg’s membrane determines its shape. Using an evolutionary framework, the researchers found that the shape of an egg correlates with flight ability, suggesting that adaptations for flight may have been critical drivers of egg-shape variation in birds.

Continue reading "How eggs got their shapes" by Leah Burrows, June 22, 2017.

Also see Sarah Crespi & Jia You Jun, "Cracking the mystery of egg shape" in Science Magazine, 22 June 2017,, as well as the original research article, also in Science:
Mary Caswell Stoddard, Ee Hou Yong, Derya Akkaynak, Catherine Sheard, Joseph A. Tobias, L. Mahadevan, "Avian egg shape: Form, function, and evolution," Science 356 (23 Jun 2017) DOI: 10.1126/science.aaj1945.