Talk:Mountain Men/Harvest Project/@comment-25176701-20150208040029/@comment-26247132-20150408195234

The biggest problem with all of the Sky People having O blood type is that O is a universal *donor,* not a universal *receiver* (that's AB type). That means they can donate to anyone of any blood type but they can only receive either their own type (O) or AB.

Either :

1. *Most unlikely* The Grounders would also have to all be genetic type O for it to not matter for the MM.

2. The MM had to all be genetic type AB to indiscriminately use Grounder blood. This would also allow the Sky People (type O) to be able to filter their blood. Maybe they had some sort near-extinction event when they first started using Grounder blood 50 years ago so only the AB types survived. This might also explain how there were only 300-400 people in Mount Weather after 97 years vs. the 3000-4000 on the Ark.

3. *Most likely* Blood types no longer matter in the future because they've found a way around it

Then there's the +/- (like O+) that also restricts donations/receptions, so it's safe to assume they've done away with the necessity of blood type matching in the future (Option 3).