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.
3 Fraternal twins are as genetically similar as any other siblings. Just as any brothers and sisters, fraternal twins will have about half of their genetic makeup in common. They will share about 50% of their DNA, the same as any siblings. Each individual receives half of their DNA from Mom's egg and half from Dad's sperm, and so any two offspring will have some overlapping qualities.