If I remember my genetics correctly
You only need a differentiation of 2 to be mostly devoid (80%) of intermarriage genetic defects.
This is first cousins, and you will avoid MOST problems. But, if first cousins keep interbreeding, it gets bad, because genetic differentiation gets to the point of brother - sister.
However, at 2nd cousins, you can interbreed almost indefinately, and still avoid genetic defect. But, you will lose postive recessive traits.
That is why humans traditionaly married at the level of 4th or 5th cousins. This was due to historical geographic isolation. Now, we are much more dispersed, my wife and I have to go all the way back to Ireland in the 1830's to find and intermarriage between our ancestors. |
