Researchers stumped by drug addiction paradox

http://www.physorg.com/news127559887.html

Phys.org

"Throughout history, plants have created their toxins by mimicking their own [errror in article, I think, must mean animals' own] molecules that regulate metabolism, growth and reproduction. When ingested by herbivores, some of these molecules can interfere with nearly every step in the animal’s neural signaling process...

"However, the researchers point to several other studies which show that the detoxification enzymes developed by animals (and which originally evolved in bacteria about 3.5 billion years ago) expanded in animals about 400 million years ago – about the same time that plants were evolving their own toxins. In other words, animals and plants seemed to have coevolved competitive genes in response to each other, which contradicts the evolutionary interpretation.

"As the researchers investigated further, they compiled other studies showing evidence that humans inherited these detox genes from their mammalian ancestors. Interestingly, although many modern animal species can tolerate plant toxins, different species possess different detox function levels. Even among humans from different geographic locations, these functions differ. Often, human populations with greater numbers of toxin-metabolizing genes originate from parts of the world that contain an abundance of those plants. For example, human populations in and near Turkey have a very high frequency of enzymes that can metabolize opiates, and the opiate poppy is native to the Turkish region...

"Based on evidence from previous studies, Sullivan, Hagen, and Hammerstein note that plant toxins may actually have some kind of benefit for animals. For instance, because plant toxins are more harmful to some species than to others, the less affected species might actually consume levels of toxin that are tolerable to themselves but much worse for the parasites or pathogens that feed on them in order to protect themselves. For example, earlier humans that consumed nicotine (in much smaller amounts than today) could have received the benefit of fewer parasitic infections. Of course, the benefits also come with trade-offs."