Biologically speaking, if the spouse share a lot of genetic, the probability of genetic deficits/disorder happening increase...that's why

Ye Christian(orthodox) hig nw befit zerachw endayzamed eske 7 eyetekotre nbr emigabut.

Awo tenegna ayhonm. Similar DNA strands don't go along. They wont mutate.

Its a christian law According to science it is considered good beteraraqe qutir gn 7 gid aydelem

It's about culture emnet mnamn I don't think so it have a thing to do with the baby's health

Yes actually. The hybrid baby might come unhealthy or have less immunity if relative marriage happened. Thus, judeo-christianity doesn't allow -7 ancestor while Cushitic Ethiopian usually doesn't allow same clan(temesasay Gosa)marriage.

In some cultures it's enough till 3rd tho