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How the placenta evolved from an ancient virus

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Re: How the placenta evolved from an ancient virus

#33

I'm just realizing that several shark and snake species also give birth to live young, but I don't know whether they have placentas or similar structures. I'm sure they couldn't be homologous to mammal placentas, right? (Certainly not if this article is right about the timeline.) To what extent do viviparous animals converge when it comes to the mother/child interface? So some sharks have placentas, as mentioned in t…

Seahorses are also interesting in this regard, not only do they also have internal pregnancy and a placenta-like structure, it's also the males that get pregnant.

Sorry for asking a simple question, but how do we distinguish sexes? If male seahorses can be pregnant, it's obviously not by which sex gives birth.

Re: How the placenta evolved from an ancient virus

#35
post #27

Earlier quoted context omitted.

The best time to plant a tree is 20 years ago.

The best time to get retroviral gene integration is hundreds of millions of years ago.

Best time to get in trouble is when you're already out of it.

Re: How the placenta evolved from an ancient virus

#36
For anyone fascinated by this topic, the book I, Mammal[1] by Liam Drew is highly recommended. A whole chapter is dedicated to the importance of placenta in evolution of mammals, along with other chapters on other mammalian features like lactation, hair, locomotion, homeothermy etc.,

[1] https://www.goodreads.com/book/show/30038815-i-mammal

Re: How the placenta evolved from an ancient virus

#37
post #33

Earlier quoted context omitted.

Seahorses are also interesting in this regard, not only do they also have internal pregnancy and a placenta-like structure, it's also the males that get pregnant.

Sorry for asking a simple question, but how do we distinguish sexes? If male seahorses can be pregnant, it's obviously not by which sex gives birth.

I am not a biologist but what I remember from biology is that female seahorses have the eggs. Sexual reproduction happens when two haploid cells combine and the sex is determined based on this system.

Re: How the placenta evolved from an ancient virus

#39
post #28

Earlier quoted context omitted.

Viruses are ultimately bits of genetic code wrapped in a shell and injection mechanism. IANAB, so this is pure conjecture, but: it wouldn't surprise me if it turned out that viruses are a kind of degenerative state - something evolution may just spit out as it makes mistakes trying to improve on cells. If that's the case, then viruses may exist simply because they are a waste product of natural selection of more comp…

This implies that evolution has a goal and that we are that goal. This shows a fundamental misunderstanding of evolution of natural selection that is common. Who is to say that viruses won't be the end result of life on the planet earth? Complex life more evolved life. It's just differently evolved.

I know that evolution doesn't have a goal. I may have antropomorphosized it too much, but my goal was to follow a sort of temporal/casual trail that we find interesting.

The way I imagine my idea is that, if you pick a species and its interesting descendants, and order on a timeline like such:

  A --> B --> C --> D
What really happens is more like:

  [bunch of other spinoffs]
    ^
    |
  A --> B --> ...
And that some of those spinoff could be viruses. Imagine a mutation to A causes a bunch of functionality in the organism to shut down (and in subsequent generations disappear), while leaving a viable organism. For a sufficiently uncomplicated A, the result of such mutation could be a bundle of genes wrapped in a shell with an injection mechanism. That's a virus.

Re: How the placenta evolved from an ancient virus

#40
post #33

Earlier quoted context omitted.

Seahorses are also interesting in this regard, not only do they also have internal pregnancy and a placenta-like structure, it's also the males that get pregnant.

Sorry for asking a simple question, but how do we distinguish sexes? If male seahorses can be pregnant, it's obviously not by which sex gives birth.

It’s entirely determined by the gametes. Males produce sperm, females produce eggs.
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