The following was a presentation I gave on 20 Feb 2016. I claim to be no expert in these matters, so if you can find any factual or historical errors I'd be greatly obliged if you'd bring them to my attention in the comments below. Likewise, if you disagree with my scriptural exegesis then I'd appreciate hearing your input.
I've often thought that inbreeding depression might be part of the reason why the Patriarchs' wives had difficulty producing children. Abram married his half-sister. Isaac married his double-first-cousin-once-removed. Jacob married two of his first-cousins who were also simultaneously his double-second-cousins-once-removed. And those are just the genealogical details that we *know* about; if we knew more details about the wives beyond Terah's generation I'm sure it'd be even worse. These are not healthy practices. It's reminiscent of European royalty! Thankfully this pattern seems to have dissipated as the Israelites became larger and vastly increased their gene pool (presumably by marrying slaves/converts/Egyptians/Canaanites/whomever).
