Most of us know that incest is wrong, either through cultural conditioning or what appear to be innate evolutionary cues, yet some humans can’t seem to resist the urge to have sex with their relatives. In fact, since the DNA of every living human is 99.9 percent the same, it may be much more common than we think. Still, that doesn’t mean incest can be acceptable in any case. As we will see, breeding with a close relative can result in some dire consequences.
In 1987, geneticists studied the mitochondrial DNA of 147 people of different races and found that the DNA of all living people fall within one of two human lineages. One of these lineages descended solely from Africa, while the other contains traces of all other races. According to one geneticist, humans actually share more mitochondrial DNA than most primates. The mitochondrial DNA of two humans has only about half as many differences as the DNA of two other primates of the same species, suggesting that humans have a much more recent common ancestor than other primates. In fact, geneticists have traced everyone’s DNA to a single woman, nicknamed Mitochondrial Eve, who probably lived around 200,000 years ago in Africa.
If you happen to have blue eyes, you and every other blue-eyed person on Earth share a single common ancestor who lived between 6,000 and 10,000 years ago. Before this common ancestor, every human being had brown eyes. Scientists aren’t sure why blue eyes spread so quickly around Europe, but theories have sprung up that blue eyes may be more useful in certain levels of daylight or were just seen as sexually attractive to potential mates.
If you’re of European heritage, your lineage and the lineage of every European alive today can be traced to a set of ancestors that lived only 1,000 years ago, as researchers discovered after testing the DNA of over 2,000 people all across Europe. Researchers also found that, naturally, populations that lived closer together tended to be more related. Italians are slightly less related than other European populations, perhaps because they had a stable, independent population for many years, while people from the United Kingdom are more related to people from Ireland than people from other parts of the UK. Meanwhile, Eastern Europeans tend to be more related than the rest of Europe, which may be the result of the Slavic population boom that occurred about 1,000 years ago.