This demonstration from Alice Roberts of the BBC is rather shocking but fascinating!
However, it does make me think. Are all our faults really that bad?
It is helpful to use constructive criticism to double check our thinking. Even though we may not agree with every point, I thought I’d post the Evolution News counter argument, as well. (FYI I do see the errors in the ID note; but sometimes having another point of view illustrates the message better. For example, human feet are better for walking on trees than earth alone, from my understanding)
I was trying to find the numbers but it seems that without medical intervention, ‘natural’ births end in the death of the mother about 1.5% of the time even today, equating to about a 1 in 16 chance of a such an occurrence over the lifetime of a woman in areas of the world that lack medical knowledge or technology (see How many mothers died in childbirth? | Motherhood in prehistory).
Historically this implies that it has been like this for much of recent history and it would have been very common to know at least one woman who died during childbirth. All of this says nothing of the infant itself whose head is 102% of the size of the opening on average. Apparently bipedalism comes with additional challenges (this is a slightly older article so we might know a bit more since then):
The placenta is an example of convergent evolution so I suspect that it would actually be a step backwards, not forwards. I agree with the Evolution News post. Cats ears are cool though!
I’m not quite sure what you are thinking about here. Since marsupials have a placenta (albeit minimal compared to humans) in what sense could this be a ‘step backwards?’ There isn’t any direction to the evolutionary process as lineages can lose and gain genes with no particular pattern. An example of a step backwards in our lineage could be that we used to have 5 genes to digest chitinase (i.e. to aid in digestion of insects) but now only have two. That could be seen as a ‘step backwards’ in that we can’t digest insect skeletons as well as we used to but since we began eating other things more often, we didn’t need them anymore. I.e. see:
The placenta is very interesting because it has arisen independently across many different animal groups including reptiles and many non-mammals:
However one thing that is interesting is that there can often be deep homology underlying convergent evolution (i.e. see Homoplasy and Convergent Evolution - BioLogos). This seems to be the case with the placenta as well with a number of shared ERV insertions that were repurposed by various lineages. A nested hierarchy example of this is how we share several very specific ERVs in homologous locations but they can do something slightly different in different lineages:
That was my least favorite part, as much as I hated being pregnant for the last two trimesters. Can you imagine all the products that would be developed and marketed to women if we had babies pooping and peeing in pouches? That would get stinky and gross. Plus, you know there would be a whole new plastic surgery option for pouch removal, pouch tightening, pouch enhancement.
Ugh, I hadn’t thought about the pooping and peeing part. That would complicate things. But, since I can’t afford plastic surgery I figure it would at least be nice to be able to put that area to use in future years. I mean, since most clothing manufacturers seem to have decided that women don’t need pockets on any of our apparel except jeans. I could even go swimming without having to worry about losing my keys!
“However one thing that is interesting is that there can often be deep homology underlying convergent evolution”
When a trait is convergent (many animals evolve to have it) there must be a good reason for it. Like the fish shape that marine mammals all tend to have. When I say a “step backwards”; I mean that the benefit that was gained by the placenta by the Natural Selection process would be lost. The placenta may be the underlying reason for increased childbirth deaths for mothers but if the child survives; the genes are passed on. Isn’t that the “end game”? To pass on the genes?
Probably just that it helps their overall reproductive success/survival/fitness.
Maybe its just me as a physicist, but minimizing drag force that is proportional to the cross sectional area helps lead to a streamline body-shape. Interestingly enough mammal tails go up and down and fish go side to side so while they both move forward, the mammal tail is necessarily constrained by their land based ancestors’ vertebrae.
Gotcha, thanks for clarifying! Some placenta would still exist as even with marsupials they have a stage where they nourish their little one via similar mechanisms to the placenta-that phase just doesn’t last for as long. So less time being pregnant before a much safer birthing process.
I’m not so sure the placenta plays too much of a role in childbirth deaths (edit: I’m quite wrong on that one, thanks to @Christy for pointing that out below) but more so bipedalism and increased brain size seems to provide some trade offs.
I wouldn’t say there’s a teleology or purpose necessarily built in to the theory of evolution as its neutral to such questions. Questions of meaning and purpose are great questions, but the idea that the evolutionary process just wants to “pass on genes” is to use a language that is foreign to what one could conclude using scientific methods alone. Naturally though, offspring that live to reproduce do help pass on genes + possible variants that are slightly different from their parents.
Placenta previa is the cause of 1/5 of post-birth maternal hemorrhaging. Pre-natal mortality is 18 deaths for every 1000 live births, and 6.6 of the mortalities are placenta previa. Those placentas do get in the way sometimes.
Or perhaps it’s me—I just got done grading for the semester and with the final papers in this Origins class I taught I was closely reading scientific accuracy in every jot and tittle. It’s nice when grading a final paper for science majors but not so nice for… well anything else! I hope you can forgive my pickiness as you helped me see something about myself too.
that’s an interesting concept, though–through evolution we conceivably achieved a desire for life/self preservation (very much an adaptive advantage) and in a way, evolution could be said to inadvertently set up a teleology? Sort of like the Star Trek “Vger” story.
I am a student at James Madison University. I am doing a double major in Biology and Religion. I appreciate when my poor wording is pointed out! I did not end my semester as well as I would have liked. I need to improve both my study and my writing skills. If by participating in this forum, I can better my communication abilities; all the better!
