This sounds like a reference to the theories of eugenics that were (sadly) popular in the early decades of the 1900s. "Elements" here doesn't mean chemical elements like carbon or nitrogen; it refers to portions of the society. A common phrase still in use is "the criminal element," meaning criminals, considered as a social group. "The biologically poorest elements" probably means people who are less intelligent, those with medical problems (e.g. epilepsy), and those thought to be genetically inferior--that is to say, to speak plainly, belonging to supposedly "inferior" races. At one time there was a theory that the intelligence of the human race was steadily decreasing because those of lower intelligence reproduced faster than those of higher intelligence.