Thomas Malthus?  I figured you would know about him...

He is the father of nineteenth century biologism.  He has influenced both Right and Left.  The idea is that there are limits to population (true) and that such limits require that the poor be thought of as a great big herd to be culled whenever the ruling classes want (false).  

Donald Rumsfeld is probably a Malthusian, but so might Paul Ehrlich.  Darwin read Malthus, although Malthus himself was a clergyman.