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TechnicalSymbiote t1_jdlxdnp wrote

Reply to comment by _Dnikeb in TIL, the placenta that forms with a fetus isn't created by the mother. It grows from the fertilized egg and some fetuses actually develop outside the uterus attached to the intestines in the body cavity. by darw1nf1sh

What about other animals placenta? How far back of an ancestral origin are we talking about, the first mammal?

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_Dnikeb t1_jdlxs4v wrote

Said viral infection took place in the common ancestor of all placental mammals (who lived much later than the common ancestor of all mammals, that's why not all mammals are placentals), so humans specifically inherited it through evolution

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TechnicalSymbiote t1_jdly9vi wrote

That's some pretty cool information. Thanks, u/_Dnikeb

spelling your username backwards made me smile, too, so thank you for that as well :)

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_Dnikeb t1_jdlystv wrote

You're the first to notice that!

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CulturedClub t1_jdmmwyg wrote

Beckoned? Baconed? I don't get it....ahh, wait.

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whhe11 t1_jdmqq7f wrote

A large portion of our DNA is endogenous retroviruses, and it increase from say fish-amphibiam-lizard/snake-bird/dinasour(probably)-mammal-placental mammal-primate-human. It helps reshuffle DNA and insceases errors and mutations, which requires the development of better DNA repair functions to survive and increases the speed with which new adaptations emerge. Which is why say an alligator or a bird is pretty close to it's relatively distant ancestry and we're pretty different then our relatively close ancestry, with adaptations such as increase salt intake and decreased water requirements compared to chimps and banobos, nerve activated water grip mode for our digits, more efficient sweating for heat reduction and our very high endurance and more efficient bipedal walking, jogging and running.

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Mosenji t1_jdn19jg wrote

Nerve-activated water grip mode. I had no idea, how does this work?

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Black_Moons t1_jdnke3i wrote

Dunno exactly, but for whatever reason your hands/feet getting pruney in water is not a physical reaction from water entering your skin, its something your nerves cause in response to detecting water.

People with nerve damage to hands/feet don't get pruney hands/feet.

Also why it doesn't happen to the skin anywhere else on your body.

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Krilesh t1_jdmyu75 wrote

love the my mammal Human’s robust feature set

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NotAnotherScientist t1_jdmyu32 wrote

Really cool information. Thanks for sharing!

For those curious, I looked up non-placental mammals and as I was expecting, it's marsupials and the duck-billed platypus among others. What surprised me to learn is that the anteater is also a non-placental, non-marsupial mammal. Now I want to read more on the anteater.

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camwhat t1_jdmspuj wrote

I just want to do my own further research. Do you have a source? Thank you 😊

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_Dnikeb t1_jdn2keh wrote

This article explains it very well.

Here's a shorter version of the story: some viruses exist as virions, ie. the virus itself is hidden within a little envelope of phospholipids. On the surface of this envelope, there is a protein called syncytin that can merge cell membranes (also made of phospholipids). Its role is to fuse the virion with the cell membrane so that the actual virus inside the virion can trojan horse itself into the cell and infect it. Infection consists of the virus releasing its DNA in the cell's cytoplasm, turning the whole thing into a virus factory. Sometimes, the virus' DNA gets fused together with the host cell's DNA. When that happens, that's what you'd call a retrovirus.

Now, At some point some 200 million years ago, for some freaky joke of nature, a virus entered a mammalian egg cell, transitioned into a retrovirus, that egg cell got fertilized, and the result was a mammal that could produce its own syncytin and thus have the ability to merge cell walls. That allowed for the evolution of a structure known as syncytiotrophoblast, which develops on the point of contact between the embryo and the womb and is basically created by many embryonic cells merging together into a single cavity. The whole point of this structure is to act as a buffer zone, allowing nutrient exchange between the mother and the embryo while at the same time preventing the mother's immune system from reaching the embryo and killing it. Thus the placenta was born.

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