The researchers suggest marrying third and fourth cousins is so optimal for reproduction because they sort of have the best of both worlds. While first-cousin couples could have inbreeding problems, couples who are far-removed from each other could have genetic incompatibilities. (Children of siblings are cousins.

What is the relationship between 3rd cousins?

It means that the closest ancestor that two people have in common is a grandparent. (If they were any more closely related, they would be siblings.) Second cousins means that the closest common ancestor is a great-grandparent. Third cousins, then, have a great-great-grandparent as their most recent common ancestor.

Can third cousins have kids together?

Its legal in all 50 states to marry a cousin whos your second cousin or further. And as a result, marriages between third and fourth cousins produce more children and grandchildren than other couples.