How old are Viruses? – Viruses

00:01 How old are viruses? You know earth was formed four and a half billion years ago, when since then did viruses appear. Well we have good evidence that T Rex was infected by a herpes virus. So that's a herpes virus to the right of the T Rex and by looking at the DNA sequence of different herpes viruses, we think it was around a hundred forty million years ago or so, when dinosaurs were present. But there is other evidence that suggests that viruses are even older. And in fact, now the first life on earth arose about four billion years ago and some scientists feel that that first life form was in fact a virus. Not a virus as we know today, but simply a nucleic acid that was able to reproduce. So viruses are very old and it may be that all cellular life actually originated from viruses, kind of a sobering thought. Not only are you 8% viral but your ancestors may be viruses as well.

01:06 Now viruses were discovered not too long after bacteria were discovered, so I think it's useful for us to look at the history of the concept of microorganisms to understand the discovery of viruses. Now Leeuwenhoek made his own microscopes in the 1700s, he was the first to see microbes and fluids of various sorts. Louis Pasteur showed that bacteria could replicate in a broth and were responsible for good things like bread and cheese and wine, and Robert Koch proved that bacteria could cause human and animal diseases.

01:45 So Koch worked at the end of the 1800s and it was about that time that viruses were discovered.

01:51 So we already had a concept of what bacteria were and now viruses are introduced. The first virus discovered was actually a virus that infects plants, it's called tobacco mosaic virus and it causes this disease of plant leaves that you can see here, which is a mottling of the leaf and as a consequence you can't sell the leaf to make tobacco.