Although the effect of Neanderthal DNA on our skin had been hypothesized, the connection with depression and mental disorders was less expected.

Especially a link between Neanderthal DNA and nicotine addiction — after all, nicotine comes primarily from tobacco, a plant that didn't exist in Eurasia at this point in time..

Anyone else perplexed by this statement?

The propensity of neanderthals toward addiction of a certain substance wouldn't be dependent on the substance being present. The opposite would probably be true, since tobacco is poisonous.

a propensity for cocaine addiction, or heroin addiction is present in humans due to the presence of underlying physiology, not because our ancestors were doing lines in the outhouse.