tobacco may have some chemical to cure?
why did evolution gave us tobacco ?
Tobacco plants evolved nicotine as a response to selection pressure from pests - those plants with nicotine in their leaves were less likely to be attacked by pests, and therefore more likely to reproduce.
The hypothesized reason that humans are able to get a 'buzz' from nicotine is that we are closely related to those pests - all life shares many similarities of biochemistry - and pests who were tolerant to nicotine and similar toxins were less likely to be poisoned, and more likely to find food that they could tolerate in times of famine, and so mammals with nicotine tolerance (including our ancestors) were more likely to reproduce than those with less or no tolerance.
Essentially it was an arms-race - the plants evolved alongside animals that provided a selection pressure favoring those that were more toxic, and the animals that evolved alongside those plants were provided with a selection pressure towards greater tolerance for (or even enjoyment of) those toxins.
So now nicotine causes changes in our brain chemistry that are non-fatal at small doses. And human brains seem to respond in pleasurable ways to small doses of many toxins - an evolved stimulus towards consumption of foods for which there was less competition, or that were less likely to be infested by insects, perhaps.
Evolution doesn't work on population effects that mostly kick-in after reproductive age, so there's not much selection pressure against a behaviour that causes deaths in fifty+ year old humans. They've mostly passed on any genes they are going to pass on by that stage anyway.
