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Eclectic eggs and suggestive circles

by Alexandra Taylor
July 31, 2017 | A version of this story appeared in Volume 95, Issue 31


Cracking the egg-shape code

A collection of eggs of varying shapes, sizes, and colors.
Credit: Shutterstock
Eggsplained in the membrane: Stoddard’s team searched for the origin of egg-shape diversity.

Eggheads everywhere might need to reconsider the shape of their skulls’ silhouettes. It turns out what we think of as egg-shaped may be a little off.

Princeton evolutionary biologist Mary C. Stoddard and her interdisciplinary team of researchers set out to determine why eggs are shaped the way they are and why different species lay differently shaped eggs—for example, why owls lay spherical eggs but hummingbirds lay ellipsoidal eggs (Science 2017, DOI: 10.1126/science.aaj1945).

To understand this diversity, Stoddard and her team mapped the shape of nearly 50,000 digitized photos from the egg collection at the Museum of Vertebrate Zoology in Berkeley, Calif. They built a custom computer code called the Eggxtractor to zero in on the egg in each photo and determine its ellipticity (how elongated it is) and asymmetry (how pointy it is). By mapping these data, the team was able to visualize variations in egg shape. “Sort of like an astronomer might map the stars, we were mapping the world of egg shape,” Stoddard tells Newscripts.

The researchers then modeled a bird’s oviduct—the stretchy tube where eggs are formed—to figure out how these shapes arise. They believe the egg’s membrane, not its shell, is where the variation originates. When the egg forms, the membrane may be thicker in some areas than in others. Much like a balloon, when pressure is applied, the membrane can generate different shapes.

The team examined details of the birds’ lifestyles, such as nest location, nest size, and flight ability, to search for correlations. It found that stronger fliers tend to lay eggs that are pointier and more elongated. “Flight and eggs are two features we associate with birds, but we don’t often think about the two being linked in a concrete way,” Stoddard says.

As the birds’ bodies adapted to power flight, the team believes the abdominal cavity and some of the internal organs were squished in a way that influenced the egg-shaping process. A bird can pack more volume into an egg that is elongated or pointy while maintaining its sleek, soaring physique.

This conclusion contradicts some existing hypotheses for egg shape, such as that it is related to nest size, diet, or habitat. Stoddard’s research has inspired her to pronounce a new canonical egg shape, that of Prinia gracilis. Also known as the graceful prinia, this small warbler’s eggs tend to be pointier than a chicken egg. “That should be the new shape we think of when we think of the classic egg shape,” Stoddard says.

Drawing circles around the world

Credit: C&EN/Shutterstock
Regular ring: Ha and Sonnad found that most of the world draws their circles counterclockwise.
A hand holding a red marker draws a circle counterclockwise.
Credit: C&EN/Shutterstock
Regular ring: Ha and Sonnad found that most of the world draws their circles counterclockwise.

While Stoddard was running eggs through the Eggxtractor, journalists Nikhil Sonnad and Thu-Huong Ha at Quartz were using data from a Google game to understand how people from different countries draw circles.

The game, called “Quick, Draw!” collects data on how participants draw to train Google’s machine-learning algorithms to recognize human sketches in all their often-messy imperfection; Google makes all the drawings available online. Ha and Sonnad looked at a few simple shapes but focused their analysis primarily on the circle because “there are really only two ways to draw one: You can either go clockwise or counterclockwise,” Sonnad tells Newscripts.

When the team tagged more than 100,000 circles in the data set based on how they were drawn and sorted them by country, they began to notice some interesting patterns. Eighty percent of the circles from Japan and 56% of the circles from Taiwan were drawn clockwise, while the rest of the countries they looked at drew them mostly counterclockwise. The team believes this may have to do with how languages from each country are written. The circle “seems like a very universal and basic shape, but even though that’s true, every culture may have a different association with the circle and what direction it should be drawn in,” Sonnad says.

He notes that their results have gotten him and Ha thinking about how they can approach cultural questions and norms, “usually the domain of think pieces and sentiment,” using these big data sets.

Alexandra Taylor wrote this week’s column. Please send comments and suggestions to



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