Not much to expand upon, here. It seems to me that morning sickness is a fact of life for most women who get pregnant, during some period of the pregnancy. While there are individual variations in how it gets expressed, and to what degree that happens, it seems to me that the default is for morning sickness.
My understanding of evolutionary theory is that if a trait is nearly universal in a population or species, then at some point there was a selection pressure in favor of that trait.
So what is the benefit of morning sickness?
My best guess at this point is along the lines of a biological means test: Does the family unit have access to a ready supply of excess foods to accommodate the increased demands an infant would bring to it? Which strikes me as a very bad theory, from a biological standpoint, given just how many species, even mammals, breed to beyond the ability of their environment to support them, and count on negative feedback to keep numbers in check.
There is none. It’s caused by the change of hormonal levels due to pregnancy. I never had it myself but I know it’s not unusual for a woman to lose weight during the first trimester due to morning sickness. It’s kind of like trying to figure out the evolutionary benefits of headaches since everyone gets them. There is none. It just is something sucky that happens.
That’s not really the way natural selection works. As long as a trait doesn’t inhibit your ability to survive and reproduce, that trait can be passed on. A trait doesn’t necessarily have to provide a benefit.
The leading theory I’ve heard is that it prevents the mother from ingesting foods or quantities of food that may be toxic to the developing fetus. Here is a blog post that talks about it a bit.
And even if it did work such that a change had to be a benefit, that does not mean that every trait based on that change needs to be explained. If the hormone change by itself is useful, the fact that a hormone change causes sickness does not have be explained in the context of sickness benefit, it is just a nasty side effect - the hormone change on balance is still beneficial.
Not necessarily. Some less-than-perfect traits are simply the best that evolution could do with the kit at hand - the eye’s blind spot comes to mind. There has been no selection pressure towards eyes with blind spots, yet we have them. Evolution made its best possible eye with the genetic material present in the population. A lot of biological structures are seriously MacGyvered like that. “Climbing Mount Improbable” has a great description of this phenomenon.
I sort of disagree. Technically, you’re correct that the trait doesn’t have to provide a benefit. But if lack of that trait is a disadvantage, then eventually, the trait will spread by default.
A lot of questions like this turn into evolutionary “just-so” stories. We know it happens, make an unwarranted assumption that there is a benefit, then come up with a theory as to what the benefit is.
Not to say that that kind of thinking is entirely fruitless (we might learn something useful about biology, history, etc.), but the just-so story is rarely testable or verifiable and not very scientific.
But if morning sickness can only be neutralized by some other process that is either expensive in terms of energy (i.e. extra protein production), or has other side effects (e.g. reduced immune system, increased metabolism, etc.) , then morning sickness would remain. Our bodies are so complex and the interplay with the environment even more so, seems like it would take lots of study to figure it out one way or another.
And in this particular case, morning sickness seems to have a lot to do with the overload of hormones necessary for pregnancy to occur. Decreasing the amount of hormones necessary to significantly reduce the occurence of morning sickness may increase the occurence of far worse issues in pregnancy.