Comment by Retric

> So yes, it's absolutely true that the body filters out chromosomally abnormal germ cells and zygotes.

> A very large number of zygotes/blastocysts survive until implantation, upwards of 50%. And of those that do, maybe 20-40% are miscarried before 12 weeks.

That’s with sperm going to a filter process for genetic abnormalities before fertilization. If hypothetically 5% fewer zygotes survived that would have real consequences not just for humans but in terms of increasing variability in litter sizes for mammals with multiple births etc.