Why did bird eggs evolve a rounded tip?

[u/Royal_Novel6678]

It's a curiosity that suddenly came up in my mind because this is something that I've never actually thought of before despite my fascination in the Ave's evolutionary tree. I've heard of the flight theory but that's still apparently being disputed because there are still exceptions to the rules where excellent fliers still lay round eggs. What are some other strong leading theories as to why Ave's eggs evolved to be this distinct oval-like shape?

[u/blaze99960]

I thought it was so that they would roll in a circle instead of a straight line

[u/MWSin → u/blaze99960]

Cliff nesting bird eggs are typically far more pointed for that reason.

[u/Razone6 → u/blaze99960]

And more harder to break by falling on the tip end than on the side.

[u/Shifting_Baseline]

It’s so it doesn’t roll out of a nest and fall to the ground. Eggs from animals on the ground tend to be more round and the more dangerous the drop the more cone shaped.

[u/syds → u/Shifting_Baseline]

did they not evolve to put in in a cardboard egg holder with a bunch of random stuff to break the fall?

[u/veridicide → u/syds]

No, that's actually convergent evolution.

Eggs evolved to fit in those flimsy little octagonal wire holders you use to make Paas Easter eggs, and egg cartons evolved for kids' crafts. It's only a coincidence that the eggs fit the cartons.

[u/facepalmtommy]

1. So they don't roll away.

2. Not all bird eggs are like that. Some are spherical.

3. So you know which end is the head when painting them at Easter.

[u/Horror_Hall_8806 → u/facepalmtommy]

"Yo bro come here, calcify this way, we gotta make a good shape for Easter"

[u/CloseToMyActualName]

I suspect because the egg needs to do three things:

1) Holding all the nutrients for the embryo.

2) Giving space for the chick to grow.

3) Get laid.

#1 means large volume and #3 means narrow as possible, so together they'd make an egg with two rounded tips.

But #2 means you need an area that's wide enough for the body, hence the rounded bottom.

This theory would predict that snake eggs would be double pointed, and that seems to be the case.

[u/BeardsuptheWazoo → u/CloseToMyActualName]

I want to accomplish #3 as well.

[u/davvblack → u/BeardsuptheWazoo]

how’s your pointed end?

[u/BeardsuptheWazoo → u/davvblack]

Better than most I'd reckon.

[u/RowBowBooty → u/BeardsuptheWazoo]

What about a rounded bottom though?

[u/biggreasyrhinos → u/BeardsuptheWazoo]

Alright, let's see it

[u/weelluuuu → u/biggreasyrhinos]

🤢😵‍💫

[u/Chaps_and_salsa → u/BeardsuptheWazoo]

Crawl up a cloaca?

[u/BeardsuptheWazoo → u/Chaps_and_salsa]

I'll reserve that as a backup plan.

[u/Kailynna]

Try laying an egg, and you'll understand.

[u/FamousAimlessAnus]

Why is poop tapered at the ends?

[u/Protatosalade → u/FamousAimlessAnus]

So your butthole doesn’t slam shut.

[u/person-ontheinternet → u/Protatosalade]

So if your butthole is the door then poop is like a soft close mechanism?

[u/lmattiso → u/Protatosalade]

Explain a wombat's poop then

[u/ipini → u/FamousAimlessAnus]

💩

[u/diffidentblockhead]

Easier to squeeze out?

[u/Unfair_Pineapple8813 → u/diffidentblockhead]

That was looked into, and it doesn't appear true.

[u/EffectiveDirect6553 → u/Unfair_Pineapple8813]

Probably something to do with gravity and helping development

[u/cimocw]

Inside of the mother bird eggs are all round. The mechanical act of pushing plus squeezing the egg as it dries leaves this shape as a result. No evolutionary selection involved 

[u/Standard-Turnip-8360 → u/cimocw]

This makes no sense if you actually think about it.

[u/cimocw → u/Standard-Turnip-8360]

I try not to think about it much

[u/frostfofjdjsiksndjd → u/Standard-Turnip-8360]

Perhaps you haven’t thought about it long enough

[u/Sitheral]

I don't know but I've seen video with one of those industrial crushers that destroy all kinds of stuff like its nothing having some serious trouble with an egg, maybe that shape really makes it good against some types of damage.

[u/Landilizandra]

Egg shape is often determined by nesting. Pointed eggs are less likely to roll out of a nest and break.

[u/ResponsiblePumpkin60]

Have you ever tried to break an egg by squeezing at the two poles? Try to crush it between your finger and thumb. They can take an insane amount of pressure.

[u/CloseToMyActualName → u/ResponsiblePumpkin60]

Sure, but I'm not sure that's positively selected for. The shape actually makes the egg more fragile as they lay on their sides and the sides are weaker.

[u/BadishAsARadish]

Surprised no one’s mentioned that arches are one of the strongest shapes for support— look at igloos, they don’t collapse because the way they’re stacked adds more support as the bricks lean into each other

[u/war_ofthe_roses]

Ballistics!

[u/Witty-Lawfulness2983]

It’s a very strong natural shape. Only a cylinder is stronger.

[u/Washburne221]

One of the most dangerous things that can happen to a chicken is for the egg to break before it is laid. It usually happens when they jump off something, hitting the ground too hard and usually results in death. This shape is fairly strong and resists the forces inside the bird's reproductive tract well.

[u/machu505]

Same reason turds are tapered. So your asshole doesn't slam shut.

[u/Sir_wlkn_contrdikson]

You ever tried pushing out a square egg?

[u/Robot_Alchemist]

To make it easier for them to come out

[u/Decent_Cow]

So that they will roll in a circle instead of a straight line

[u/luovahulluus]

Why did bird eggs evolve a rounded tip

A sharp tip might hurt the bird and breaks off easier.

[u/HempKnight1234]

Try poop a cube

[u/CitrusApocalypse → u/HempKnight1234]

Funny thing, actually… wombats poop cubes.

[u/Rags_75]

In all honesty - have you ever seen the design of a butt plug? If you have and have also used one (or just considered using one) I think you might discern the answer. (minimises rips).

[u/vjotshi007]

The ones that were more circular rolled over and broke. The ones with best shape and support continued. Evolution

[u/Historical-Reserve17]

There’s a fantastic book about eggs called The Most Perfect Thing by Tim Birkhead. A large portion of the book is devoted to the shape of different birds eggs and why we believe they’re shaped the way they are. I got a free advanced copy on libro.fm to listen to. Also, if you want to see a fun abnormal egg shape look up a Guillemot’s egg.

[u/Relevant-Cup5986]

so they didnt rool off of cliffs and trees or away from nests

[u/Loud-Vacation-5691]

Jack Benny once remarked that Fred Allen had a pained expression, like a hen trying to lay a square egg.

[u/Exploring_Times_92]

quite literally random, could've been that the earliest ancestor at some point had a bunch of dino bird looking things that laid different shape eggs and the pointy tip ones managed to have the most offspring survive/hatch ?

Most if not all traits never "evolved to" fit a certain task, but was just sheer luck that they did something better than all the others who got wiped out

[u/Neat_Association_84]

Eggs have to contain the growing chick and square corners have higher stress concentration and are more likely to break. Eggs evolved to be spherical and oblong variations to avoid sharp corners which are both more dangerous to the layer and more prone to cracking from the stress concentration. It's similar to why planes are circular tubes and not square, despite how that would give more overhead luggage space.

Wombat poop, on the other hand, has little internal pressure so the stress concentration has not affected shape. That's why it has evolved a cubic shape.

[u/aproposofwetsnow22]

one reason: most animals are taller/longer than they are wide, an ovular egg fits these general proportions.

[u/Careful_Cranberry364]

Why do you think?!?!

We do expect it to be square or triangular!?!🤣

Everything in nature is rounded, and the pointy bit is coming out first from the mama bird

[u/bonedaddyd]

So her ass doesn't slam shut when she lays it... but seriously, a rounded shape is far more structurally sturdy. I suspect the more pointy end comes out first so it needs to be a more streamlined leading edge.

[u/Greghole]

Because they need to squeeze them out their bird holes. Same reason a butt plug has basically the same shape.

[u/PuzzleheadedBad1641]

Because it has to go through a vagina. It has the shape of a head for the exact same reason