The Fourth Drive

In the past week, I decided to join a number of online Facebook communities having to do with entheogens.  It was kind of illuminating, just seeing the names and number of members for each one:
***********************
Ayahuasca: 41,599Ayahuasca Social Club: 5,418
Entheogens for a More Enlightened World: 393
Entheogenic Anthropology: 2,126
The Terence McKenna Experience: 15,877
Terence McKenna Community: 6,900
Acid Math: 41,599 (I am suspicious because this is the exact number on the Ayahuasca site, but...?)
Acid Math Arts: 5,694  
************************
Anyway, you get the idea - entheogens are quite popular subjects these days!

I specifically wanted to pose this question on these forums, for my book research: does the human species have an innate, biological drive towards altering consciousness?  Is there proof, and if so, what is it?

I received a wonderful variety of responses, which were informative, humorous, and helpful.

How We Got Here
Here is the first (and I apologize, but I do not have a source listed for this, except for Facebook!):