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.

I wouldn't be a very good hunter without these glasses. I'm not a very good hunter with these glasses, but I'd be even worse without them, so that would put a crimp in how many kids I could have, so all of these medical advances have at least in some parts of the world blunted natural selection.

We have Borna virus genes. We're part Borna virus, which is weird, but apparently our cells and our genomes in a weird way might actually be grabbing these viruses, grabbing genetic material from the viruses that are infecting it and pulling them into their own genome.

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.

Medicine allows people to live who would otherwise die, so antibiotics will let people survive infections that they might be otherwise very vulnerable to and even little things might make a big difference, so I wear eyeglasses because my eyes aren't particularly strong, before there were eyeglasses someone at my age would probably not be good for much.

Everybody can digest milk when they're little.