Researchers have argued that pointy eggs are common to cliff-nesting
birds because they roll in a circle and are less likely to tumble off an
edge. Or that asymmetric eggs pack together more easily and would allow
females with large clutches to incubate their broods efficiently. Or
that spherical eggs are stronger and less prone to breaking, or use the
least amount of shell for a given volume, which would be useful for
birds that can’t get enough calcium in their diet.
“There are a
lot of hypotheses, but no conclusive explanation or theory,” says
Stoddard, who’s an evolutionary biologist based at Princeton University.
“It was a good puzzle.”
To solve it, Stoddard teamed up with L. Mahadevan,
a biophysicist at Harvard University who has studied “how leaves
ripple, how tendrils coil, and how the brain folds, among other things.”
He realized that all eggs could be described according to two simple
characteristics—how asymmetric they are, and how elliptical they are.
Measure these traits, and you can plot every bird egg on a simple graph.
They did that for the eggs of 1,400 bird species, whose measurements
Stoddard extracted from almost 50,000 photos. It was the resulting graph
that revealed the left-field nature of chicken eggs.
