Same-sex unions are recorded in the history of a number of cultures, but marriage or similarly formalized same-sex unions were rare or nonexistent in other cultures.
Using this measure, siblings are actually 99.95% the same. The 50% refers more to the amount of DNA we get from mom and the amount we get from dad. So we are more similar to our relatives than we are to a mouse. Let's explore in a bit more detail what the 99.95% and the 50% numbers mean.
Legally your kids and your sisterâs kids are first cousins but at the DNA level they are half siblings. They share twice as much DNA as run of the mill first cousins! What I thought Iâd do for the rest of the answer is go into a bit more detail about why you and your sisterâs kids share 25% of their DNA.