Parasites are not only incredibly diverse; they are also incredibly successful. There are parasitic stretches of DNA in your own genes, some of which are called retrotransposons. Many of the parasitic stretches were originally viruses that entered our DNA. Most of them don't do us any harm. They just copy and insert themselves in other parts of our DNA, basically replicating themselves. Sometimes they hop into other species and replicate themselves in a new host. According to one estimate, roughly one-third to one-half of all human DNA is basically parasitic.

About 1.2% of the human genome is made up of genes, things that encode for proteins, the stuff that we consider us. There is about 8.3% that's a virus. In other words we're probably about seven times more virus than we are human genes, which is kind of a weird way to thinking about yourself.

We may be sucking in all sorts of viruses and we really don't know the full range of them. Maybe we've got flu virus inside of us. That's a possibility. Maybe we're part flu.

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.

Everybody can digest milk when they're little.

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

Over millions of years the viruses in our genome mutate more and more so the look less and less and less recognizable as viruses and so if there was a virus that infected our pre mammal ancestors like 250 million years ago, which it probably did, we can't see it because it just looks totally random.