The Real Reason Why Eggs Come in So Many Shapes and Sizes May Be Childishly Simple

Photo: woodleywonderworks [CC BY 2.0]/Flickr

I spent an unhealthy part of my childhood obsessing over the pointiness of eggs. Not round ones that cracked too easily, but eggs with at least one side that had a tip like a talon.

That’s because, in my family, you could go far with a sharp egg.

You see, every Easter Sunday, cousins and aunts and uncles would descend on my grandparents' house for the Great Egg Crack-up.

The contest was simple: Pick a painted, hard-boiled egg from a basket and then smash the tip of that egg into an opponent's egg. Whoever emerged from that collision with an uncracked egg moved on to the next round.

Collide. Crack. Repeat. Until ... Grandfather.

He was always the last scary stop, his massive hand wrapped around the egg so just the pointiest tip was exposed.

A serious competitor, grandfather always laid claim to the sharpest egg in the basket — and inevitably crushed us with it.

For the rest of us, there were never enough pointy ones to go around. Eggs can teach us a lot, it seems, about equality.

easter eggs large
In this Easter game, whoever held the last uncracked egg was the winner. Sarah Laval [CC BY 2.0]/Flickr

But maybe we could have all had a fighting chance against our impenetrable patriarch if we knew where sharp-tipped eggs came from. Apparently, it’s a question that’s been bedeviling people long before our young hearts were bashed along with our eggs.

Why do they come in so many shapes and sizes?

Well, science has finally waded into the debate, offering a surprisingly simple answer.

The shape of an egg, according to a 2017 report in the journal Science, depends on how much time a bird spends in flight.

For the study, Mary Caswell Stoddard, an evolutionary biologist at Princeton University, looked at hundreds of eggs from countless kinds of birds.

"We mapped egg shapes like astronomers map stars," Stoddard told The Atlantic. "And our concept of an egg is on the periphery of egg shapes."

eggs from birds, reptiles and insects
An early 19th-century illustration of various types of eggs, including those from reptiles and insects. Adolphe Millot [public domain]/Wikimedia Commons

In fact, when most people think of eggs, they think of chicken eggs. Sometimes, they have a sharp tip; sometimes they’re rounded at both ends. But they’re almost always roughly oval in shape.

But hummingbird eggs? They’re wildly asymmetrical, befitting of a bird that spends most of its time in the air.

In all, the computer program developed by Stoddard's team analyzed 13,049 pictures containing 49,175 individual bird eggs.

Keep in mind, it’s not the shell that determines the egg, but rather the membrane beneath it. And that membrane is shaped by the oviduct — the organ that the egg passes through before it’s laid.

Birds that spent a lot of their lives in the air had developed naturally streamlined bodies for maximum airborne efficiency. The oviduct, too, had become streamlined. And a long, tight oviduct spelled long, pointy-tipped eggs.

Chickens, on the other hand, spend next to little time in the air. So their eggs would be largely oval, with the occasional tip as an outlier. For an even more uniform example of roundness, take a gander at an ostrich egg.

ostrich egg at museum
Ostrich eggs may not be so pointy because the birds never developed streamlined organs for flight. Klaus Rassinger und Gerhard Cammerer, Museum Wiesbaden [CC BY-SA 3.0]/Wikimedia Commons

Of course, there are exceptions to the rule that the more a bird flies, the pointier the eggs. And Stoddard is quick to point out, the findings may show correlation rather than cause.

However, some scientists were a bit skeptical of Stoddard's idea that flight is a primary influence in an egg's shape. Tim Birkhead, an evolutionary biologist at The University of Sheffield in the United Kingdom, noted that Stoddard's study stated that flight only accounted for 4 percent of an egg shape's variability, reported Science Magazine.

Birkhead, along with other scientists, said incubation plays a larger role in an egg's shape: where a nest was located and how birds laid on eggs to prevent them from rolling away. The more pointed an egg was the more likely it was to not roll away — especially in a nest located on a narrow ledge. In the study, they noted that a nest's location explained two-thirds of the variations in egg shape.

Whether it's flight or where a nest is located, these studies do go a long way toward helping me develop my own theory on why I lost so many egg battles as a child.

Instead of wobbly, unpredictable chicken eggs, we should have all been using reliably sharp hawk eggs.

Eggualiuty for all.

Not that it would have helped us for the Great Egg Crack-up.

You see, I managed to make it to the final round of the competition once. My grandfather was waiting, his unbreachable egg poised to demolish mine.

And it did. But here’s the thing. Just before our eggs met, I’m sure I saw him twitch his thumb slightly, so it covered the tip of his egg,

He was using his thumb to crush competitors.

Of course, I would say nothing. Because for all his dinner-table joviality, my grandfather had a bit of a reputation for having a very thin shell.

Besides, maybe that crafty old Calabrian was trying to teach us another life lesson — like how to get ahead in life, no matter what.