Because you + you = (if you're lucky, mildly scrambled) you. <_< Genetically, that is. And, if you don't go the substitute mother route... that includes the mitochondrial DNA.
And, that's a potential disaster zone. We're not built to be amoebas. The probability is always going to be "horribly scrambled you" as a result, because we don't have error-checking in place to stop terrible things going wrong for that particular scenario.
The good news is: the mistakes are likely to be that bad, the foetus would never get off the ground thanks to most of what we have in place. <_< The problems would start if the errors don't
get picked up as problems thanks to "the cancer thing". You know... because many cancers can avoid the immune system killing them off because they are us?
A foetus can be thought of as a barely tolerated alien that has to jump through hoops as it is. If it happens to be us, but has problems that don't get noted thanks to not being "alien"... <shudders> That's sodding dangerous for all concerned. <_< Because, birth is not just triggered by the mother... The worst-case scenario is... continually growing cancer that started as a form of foetus and, because "us", doesn't trigger birth as it identifies (both to it and our immune system) as an organ, not a foetus-going-haywire.
edited 15th Mar '14 8:14:54 PM by Euodiachloris