This is because the American slave owners wanted to be able to sell their own children.

After raping a slave, if she got pregnant they could free their child or keep them as a slave.

Thomas Jefferson's concubine, Sally Hemmings, was probably 3/4 white, and at least 1/2 white. Her granddaughter created a scandal when she 'passed' for white.

If an american tries to call themselves Native because they are 1/32 Native, people laugh at them. But up until a few years ago, being 1/64 Black made you Black.