It used to be thought that only a certain kind of virus could get into our genome and it's called a retrovirus and that's a virus that might be HIV for example.

In 1494, King Charles VIII of France invaded Italy. Within months, his army collapsed and fled. It was routed not by the Italian army but by a microbe. A mysterious new disease spread through sex killed many of Charles’s soldiers and left survivors weak and disfigured. French soldiers spread the disease across much of Europe, and then it moved into Africa and Asia. Many called it the French disease. The French called it the Italian disease. Arabs called it the Christian disease. Today, it is called syphilis.

If you're looking for your own idea of your own identity you know the human genome may not be the best place to look for it. You're just looking at a bunch of viruses.

When you get sick with the flu you get infected with flu viruses and they make lots of new flu viruses, but those new viruses are not exact copies of the old ones. They have mutations in them. A lot of those mutations are harmful.

Viruses don't just make us sick. They can actually sometimes end up in our genomes.

Evolution has led to some populations of people being able to digest milk without much trouble when they're adults as well.

The reason that viruses are so hard to fight, the reason for example we need a flu virus every year is that they evolve very fast.