“Hypotheses proposed for the adaptive function of egg shape typically invoke a decrease in egg loss for cliff-nesting birds laying conical eggs that roll in a tight circle; an increase in incubation efficiency when egg shape is associated with the number of eggs in a clutch; or other advantages related to strength, diet, and development. For example, spherical eggs might be advantageous because the sphere is uniformly strong and would be robust to incidental damage in the nest.
Spherical eggs, with their minimal surface-area-to-volume ratio, also require the least amount of shell material for a given volume and possibly optimize gas exchange by providing a large surface area for pores. In contrast, conical eggs may be beneficial because they can accommodate an increased concentration of pores at the blunt end, creating a specialized respiratory site for accelerated neural development in precocial birds. Moreover, conical eggs may protect the blunt end (from which chicks usually hatch) from debris contamination or, in colonial breeders, increase resistance to impacts because a larger proportion of the eggshell is in contact with the substrate. Finally, it has also been proposed that adaptations for flight influence egg shape indirectly through the morphology of the pelvis, abdomen, or oviduct.”
and concludes
“Our macroevolutionary analyses suggest that birds adapted for high-powered flight may maximize egg size by increasing egg asymmetry and/or ellipticity, while maintaining a streamlined body plan”
It doesn’t even mention “better protection against drops”.
plus, there's a cost to the parent in making the egg shell arbitrarily drop-proof, so there's a balance of resources required to survive drop versus genetic benefit of surviving the drop
That’s exactly what I said. “Selects out” is the terminology used when discussing evolution. It’s not an active “decision,” it’s a thing that happens. “Natural selection.”
Ok. But what does that mean in the context of the comment that you replied to? (Which doesn’t talk about decisions or nature chasing things, at least as it stands now.)
Is a harder shell which has higher costs than benefits selected out? Maybe we’re all repeating the same thing.
Ah I get what you’re saying. My point is that yes, some other type of shell probably selected out and this one wasn’t. Maybe it was dumb luck, maybe it was a slight advantage in a very specific condition that allowed it to persist, but ultimately we can only theorize.
I would understand the selective advantage if it made the egg shell more resistant to accidental breaking within the nest. But for birds that nest in tree branches or perches, what advantage is there for an egg resisting a fall without breaking? That egg is lost anyway; for most bird and egg shapes, there's no way to bring it back to the nest.
So this is a pretty common mistake people make when discussing evolution. It’s not about what is advantageous, it’s about what survives the selection process. A combination of odds that play out.
Our eyes are not advantageous or chosen by evolution, our eyes were just acceptable enough for us to survive while other variations were not. There was no decision or work/progress towards an end goal. A creature developed along a certain line by chance, the situation in nature was such that they survived and passed on that trait, while others did not. Natural selection in action.
No, I understand how natural selection works. I'm a fan of Stephen Jay Gould.
Please keep in mind the original comment I was responding to:
> Eggs are evolutionarily designed to survive falling out of nests and perches.
My response is "no, they are not". First, like you said, they are not "designed" in any way. But that's the pedantic response. Second, there's no selective pressure for eggs resistant to dropping from a nest, since they are lost anyway and won't pass any genes. It's likely that something else is being selected for -- or at least, that the more resistant shell is not harmful to reproduction of the species -- but there's no selection for nest-drop-resistant eggs because that confers no advantage. Maybe it's just harmless, which can make the trait survive. See the difference?
> There was no decision or work/progress towards an end goal.
It helps to assume everyone understands this, otherwise we cannot get to the meat of the discussion without nitpicking every single sentence.
“Hypotheses proposed for the adaptive function of egg shape typically invoke a decrease in egg loss for cliff-nesting birds laying conical eggs that roll in a tight circle; an increase in incubation efficiency when egg shape is associated with the number of eggs in a clutch; or other advantages related to strength, diet, and development. For example, spherical eggs might be advantageous because the sphere is uniformly strong and would be robust to incidental damage in the nest.
Spherical eggs, with their minimal surface-area-to-volume ratio, also require the least amount of shell material for a given volume and possibly optimize gas exchange by providing a large surface area for pores. In contrast, conical eggs may be beneficial because they can accommodate an increased concentration of pores at the blunt end, creating a specialized respiratory site for accelerated neural development in precocial birds. Moreover, conical eggs may protect the blunt end (from which chicks usually hatch) from debris contamination or, in colonial breeders, increase resistance to impacts because a larger proportion of the eggshell is in contact with the substrate. Finally, it has also been proposed that adaptations for flight influence egg shape indirectly through the morphology of the pelvis, abdomen, or oviduct.”
and concludes
“Our macroevolutionary analyses suggest that birds adapted for high-powered flight may maximize egg size by increasing egg asymmetry and/or ellipticity, while maintaining a streamlined body plan”
It doesn’t even mention “better protection against drops”.