So, as one of the many, many consequences of modern day humanity being given access to a runic magic system by an unknown party, nearly the entire human race discovers one morning that they've been given an entirely separate body they can shapeshift into and out of at will. This species is largely humanoid in structure, and all of the major organs are pretty much identical, but a few parts of their body are clearly operating under magical rules rather than physical ones.

Due to previous knowledge of the world's magic, humanity knows that they'll have access to this second body for a week, and that whatever body they're in when that week is up becomes their new body forever. Some people are considering keeping this new body for various reasons, but one question that will probably be a big deal to a lot of people is whether or not this body is capable of having children, either with humans or with its own kind (they can with each other, as it turns out, but not with humans). The nearly identical organs suggest they would indeed be fertile, but due to the magic involved with how their bodies function in other ways, people want to make sure that they actually can and that those organs aren't just for show.

Assuming their reproductive organs work just like humans, how long would it take to confirm that a successful pregnancy in one of these bodies has occurred? And how soon would it become apparent that inter-species conceptions are impossible?

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    $\begingroup$ I changed "themselves" to "each other" because the former implies they're self-fertile, which doesn't seem to be what you're implying. Please change it back if I'm wrong. $\endgroup$
    – Cyn
    Commented Sep 1, 2019 at 0:53
  • $\begingroup$ @Cyn No you are correct. I was thinking of changing that, but I wasn't sure if it was worth an edit to change a single word when the original wasn't entirely wrong. $\endgroup$ Commented Sep 1, 2019 at 1:02
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    $\begingroup$ Thanks for saving it for me. It adds to my count towards my Illuminator badge. :-) $\endgroup$
    – Cyn
    Commented Sep 1, 2019 at 1:09

1 Answer 1


Run tests via in vitro fertilization

Use multiple women at multiple fertility clinics to make sure the process works in at least a few of them. You can use any woman who is just about to ovulate but it would be best to use women who were already in the process of doing IVF and were scheduled to have their eggs harvested anyway.

It takes 5-6 days after fertilization in a petri dish for an embryo to "hatch." This does not tell you if the embryo can be successfully implanted in a "new" uterus and if it will gestate. But it will at least tell you that conception is possible (or not).

Coordinate these tests worldwide, on hundreds, or thousands of eggs. Use eggs and sperm from women and men who are both transformed. Also run tests on transformed women with human men and human women with transformed men.

Do sperm analysis

In transformed men you would also do sperm analyses. Hundreds/thousands of them. Put the results online. If the transformed men are not producing viable appearing sperm, you've more or less answered your question, though you still want to test it with live eggs either way.

Try frozen embryo transfer

When people create embryos via IVF, it's common to freeze "extra" ones you are not implanting that cycle. Some people later donate these embryos when they no longer need them, which means they're available to women who wish to get pregnant using them.

When you implant an embryo, it's done a few days after ovulation, which means that pregnancy detection can be done sooner than if you're timing it from a natural conception, which must happen the day of or a few days before ovulation. Chances are good that you could know that implantation was successful within a week of doing the procedure.

These embryos of course will be fully human and successful implantation will not tell you anything about conception in transformed humans. But they will give you information about a transformed uterus, if it is capable of accepting an embryo and starting the gestation process.

Like with the IVF tests, use women who were already about to be implanted but who are now transformed. It doesn't matter if they're using their own stored embryos or donated ones.

Finding fertility clinics

In the US alone, "there are about 480 U.S. fertility clinics, 100+ sperm banks, an unknown number of egg donors, and 1,700 reproductive endocrinologists." A large number of them will have some women who are just about to undergo egg harvesting or embryo implantation. You may be able to include more women in the trials if necessary, especially if they're women who were not doing IFV or embryo transfers but were trying to get pregnant and carefully monitoring their cycles (with ovulation prediction) and taking hormones (progesterone after ovulation being very important here).

Use every country with fertility clinics/doctors and put all the information on a single site on the internet (like StackExchange). Allow people access to the data so it gets analyzed in hours, not days. Crowdsourcing, reports on Twitter, whatever it takes.

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    $\begingroup$ One big thing I'm getting from this is that ideally all of the female new bodies would be ovulating. See, the bodies don't sync one to one with the humans who have them. If you cut off the arm of one, the other one will still have both arms. Just because a human woman is ovulating when she gets the second body doesn't mean the second body will be ovulating. So either I should make them all ovulating when the week begins or I should at least make it random so at least some of them are? $\endgroup$ Commented Sep 1, 2019 at 4:04
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    $\begingroup$ @JasonClyde Ahhh. I was assuming (hoping) there'd be some crossover. Even if only 1% of the women are in the right pre or post ovulation state, that's a lot of women worldwide and plenty to run these experiments. But yeah, you have to have some women in the right place in their cycles or none of this works. In a city of a million people though you could still get a couple dozen women willing to participate whose timing is right. It's a little harder if you have no one whose hormone treatments carried over, but still doable. $\endgroup$
    – Cyn
    Commented Sep 1, 2019 at 4:39
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    $\begingroup$ Alright, good to know. Thanks for the answer, very helpful! $\endgroup$ Commented Sep 1, 2019 at 4:43

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