The history of accidental and deliberate acts of poisoning predates the arrival of humans. Toxins of some kind have been used by both animals and plants to avoid being predated upon or to deter other species from competition.
Neurotoxins are a group of chemicals which directly affect the functioning of neural tissues. It is tempting to think of this group in the aftermath of recent events in Salisbury as being man made and of recent origin. For some this is true, but others have a much longer pedigree.