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.
1 Mitochondrial DNA is only herited from the Mother, so it is the ideal test to see if siblings have the same biological mother. 2  The accuracy of the test depends very much on the type of mitochondrial DNA you have.