If you've ever watched James Burke's "Connections" series (and you should - it's excellent), one of the things he mentions is that the introduction of the steam

If you've ever watched James Burke's "Connections" series (and you should - it's excellent), one of the things he mentions is that the introduction of the steam engine increased the genetic diversity in the UK, because now you weren't limited to dating people from your local town or village. You could be 50 miles away in less than a day and meet all-new people.