I would also venture that much of the transitions are feedback loops. So person A makes a new shiny in python for no reasons relating to superiority of language

I would also venture that much of the transitions are feedback loops. So person A makes a new shiny in python for no reasons relating to superiority of language for job x, but because person A is good with it. Well, if what he makes is good, people start using it. Then it breaks, and they have to fix it, or maybe get an idea to fork it. Suddenly, person A's software just encouraged 20 people to hop into python for no real concrete reason. On the bio side, bio-python is just much more intuitive imho, vs bio-perl.