You are the result of an incestuous relationship, and I can prove it with simple math. Two people were needed to create you. Four people to create those two. Eight to create those four, and so on. We put two to the power of the generation that we wish to look back on to determine the number of people required for your creation. If we look back fifteen generations, all we need to do is solve for 2^15, and we find out that 32,768 people were needed for your creation. Quite the army, wouldn’t you say?

Assuming life expectancy was on average fifty years, looking back 15 generations would lead us to the 12th century. We’re in the middle of the High Middle Ages, and population in Europe is increasing rapidly because of favorable economic conditions. Now let’s look back forty generations, to the 4th century BC. Solving for 2^40 gives us a number over a trillion (1,099,511,627,776 to be precise), which is much higher than the number of people that have ever lived. How is this possible? Incest, and quite a lot of it.

You might now nod and think this explains much of your behavior, but this isn’t necessarily the case. Much of the incest in your family tree has been of the harmless kind, e.g. with a very distant cousin from your mother’s side who worked as a clerk in a dingy office and could only afford meat once a week. In fact, if you are currently together with someone from your own race and country, the chances are high that you are in some way related. Next time you’re on the London Tube during rush hour, have a look around and realize that most of the people you see squeezed together are family.

It doesn’t end there. You’re not just very likely to be related to the person you have a crush on, but you’re also 99.9% genetically similar to him or her. Let me explain: each cell has a nucleus, inside of which float a number of chromosomes. A few exceptions aside, all your cells have 46 chromosomes in each nucleus, 23 from your father and 23 from your mother. Each chromosome is made up of deoxyribonucleic acid, or DNA, which is responsible for the creation of protein, the key ingredient to life.

As you can see in above picture, DNA consists of only four basic components, called nucleotides: adenine (A), thymine (T), guanine (G) and cytosine (C). The order in which these nucleotides occur constitutes the human genome. As far as we know today, only 3% of all combinations of DNA (genes) constitute a useful function in our body. The other 97% seems to have no particular function and is called non-coding DNA.

DNA replicates by splitting in half along the length of the spiral helix and connecting with a different half. Adenine can only connect with thymine and guanine can only connect with cytosine. This makes DNA replication a fairly simple and perhaps even boring process, but one that is incredibly accurate. However, the interesting part is when the process is not accurate, i.e. when a nucleotide arrives in the wrong place.

Biochemists call this wrongly placed nucleotide connection a single nucleotide polymorphism, or snip. Most of the time, snips happen in non-coding DNA and will not make a difference. But every once in a while, a snip occurs in an important gene, which would leave the person in question with either a peculiar advantage, such as protective pigmentation, or a disadvantage, such as a predisposition to a particular disease. It’s exactly these snips that account for the 0.1% difference between you and every other person.

Your snips will most likely be in a different place than any other person’s. That means there is no such thing as a single human genome. If we look at a certain strand of DNA in a particular place, it is highly likely at least one person will not have the same DNA there, but will have a snip instead. So although we are 99.9% genetically the same, each individual is also very different from any other person. Together we are unique. Truth again is found in a dichotomy.