How the placenta evolved from an ancient virus (2020)

[mlcrypto]

Kinda morbid thinking about all the failed mutations as laying eggs evolved into the placenta

[jmyeet]

Here's another sobering thought: you represent an unbroken chain from the universal common ancestor of successful reproduction going back billions of years and probably trillions of generations (given that many of those were as a single-celled organism). Every one of those generations a success.

So if you fail to reproduce you will break that billion year old chain of evolutionary success.

Here's another: you have 2 biological parents, (up to) 4 biological grandparents (go look at Cleopatra's family tree) and so on to an upper bound of 2^n ancestors for the n'th previous generation. At some point this number exceeds the number of organisms that were alive at that time so there are likely one or more individuals in the past who are direct ancestors to everybody.

A consequence of this is that if you go forwards in time ultimately your genetic line will either die out or you will be the direct ancestor of everybody given sufficient time.

[pfdietz]

There's a reason religious types recoiled from Darwin's idea. It paints God as a vivisectionist on the grandest scale.

Darwin experienced this as a father, watching his oldest child die slowly and horribly (probably from cerebral tuberculosis). It would not be a stretch to imagine this experience soured him on traditional religious dogmas.

[nkrisc]

Even the current version fails on its own quite often.

[dang]

Related:

How the placenta evolved from an ancient virus - https://news.ycombinator.com/item?id=25655346 - Jan 2021 (106 comments)

[chasil]

One way that viral elements are expressed are as transposons.

There is even an infectious variant, a gypsy transposon, that can move to neighboring cells.

https://en.m.wikipedia.org/wiki/Transposable_element

[ta8645]

It's a little odd to consider the idea that fighting off modern viruses today, might actually be impeding human evolution in some way we can't foresee.

[boredgargoyle]

There are probably thousands (and my guess would be much more) viruses that that dance on the information playground that is our genome, metagenome, and the genomes of the organisms we host. Fighting a few of them is probably not going to be a significant issue.

Having more individuals around by itself would also lead to mutations which the environment may select for in the future. By itself there is no such thing as a beneficial mutation (gene import) unless the environment proves it to be.

[AdmiralAsshat]

I suppose the ethical question would be: how many current humans are you willing to let die from exposure to a virus in the hopes that one of them might mutate something useful?

[pazimzadeh]

Yeah, if I remember correctly the RAG recombinases that enable crazy diversity in your B and T cell receptors of your adaptive immune system are also thought to come from a retrovirus that got into our ancestors germ cells.

[badosu]

It is required some process of natural selection for mutations to be selected against, do we know how this occurs with the modern homo sapiens?

[6177c40f]

I think the tradeoff is worth it, viruses are far more likely to do us harm than to help us out. Besides, we're entering the age when we can direct our own evolution.

[juggertao]

Umbrella Corporation is working on the innovative t-Virus for the next step in human evolution. But people FUD it.

[pitdicker]

> The syncytiotrophoblast is the outermost layer of the placenta, the part that is pressed against the uterus. It’s literally a layer of cells that have fused together, forming a wall. ... There’s no other structure like this anywhere else in the body.”

> When evolutionary biologists like Chuong mapped the genomes of these cells, they found that the protein that allowed these cells to fuse into a wall, called syncytin, didn’t look like it came from human DNA. It looked more like HIV.

So the entire premise of the placenta evolving from a virus rests on the fact that the organ has a unique function requiring a unique protein in the body. Saying the source probably is a virus seems quite a leap of thought. And aren't there many highly specialized proteins in the body?

Has anybody has some more information on what protein in a retrovirus looks similar to syncytin?

[pitdicker]

Paper that discusses similarities between the envelope glycoprotein of retroviruses and syncytin: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3758191/

This field is called paleovirology, and the paper also discusses in some more detail how fragments of viral DNA can end up in human DNA.

[zakki]

If every part of a human coming from evolution, how it synchronize between each part? Is there any books explaining evolution in detail? How cell formed? How they found a way to multiply? How they choose DNA to store the information? And so on.

[getoffmycase]

There is literally a world of biology (text)books that describe the process of evolution and how life came to be. I would recommend finding a syllabus at a local college for a biology class, getting the textbook second hand and then reading it

[taneq]

It doesn't. Everything that's poorly 'synchronized' just dies out and the more effective organisms keep reproducing. This explains basically everything past the original question of how the original self-replicating chemical reaction started.

[Log_out_]

Cells left behind can make the mother a chimera with out knowing. https://en.m.wikipedia.org/wiki/Chimera_(genetics)

[Sakos]

This seems to be a common thing. We're an amalgamation of different viruses and bacteria that somehow over billions of years coalesced and evolved together into what we are now. I'm never not astounded when I think about it.

[dirtyhippiefree]

Think about it.

The species that is now Mitochondria was an entirely different species.

We carry Mitochondrial DNA, while the human side is Nuclear DNA…nucleus of every cell.

Birth as we know it wouldn’t have happened without a third species invading our cells. We know it as placenta.

Profound that we fight microbes, but without two (that we know about), our species literally (accurate use) would not exist.

At all.

Just, wow.

[deadbeeves]

I mean, everything would seem to indicate that mitochondria were assimilated while our ancestors were still microbes themselves. But that aside, our species is the result of everything that happened prior to its appearance, including for example the Cretaceous–Paleogene extinction event. Arguing that we should not attempt to prevent such events (if we're able to) because it would evolutionarily benefit the survivors is suicidal.

There's nothing special about our species. If things had happened different would the species that would have been in our place (whatever that means) be better or worse by any metric one chooses? There's no point in wondering about that.

[ddgflorida]

Dream on

[pfdietz]

You're assuming it happened all in one go. Instead, the protein was probably inserted into a germ cell by a retrovirus, and then was available in descendants as grist for further evolution, eventually being incorporated into the placenta.