Alkaloids constitute a very large group of natural nitrogen-containing compounds with diverse effects on the human organism. A large variety of plant-produced alkaloids have strong pharmacological effects, and are used as toxins, stimulants, pharmaceuticals or recreational drugs, including caffeine, nicotine, morphine, quinine, strychnine, atropine and cocaine. Atropine, used to dilate the pupils of the eye, and the addictive drug cocaine are both tropane alkaloids which possess two distinctive, inter-connecting five- and seven-membered rings.

Microorganisms in the human gastrointestinal tract form an intricate, living fabric made up of some 500 to 1000 distinct bacterial species, (in addition to other microbes). Recently, researchers have begun to untangle the subtle role these diverse life forms play in maintaining health and regulating weight.

In a finding that could fundamentally re-write science's understanding of how some parasite-host relationships work, Harvard researchers have found that, despite being separated by more than 100 million years of evolution, the parasitic "corpse flower" found in southeast Asian rainforests appears to share large parts of its genome with its host vines, members of the grapevine family.

A genetically-modified version of the rabies virus is helping scientists at Harvard to trace neural pathways in the brain, a research effort that could one day lead to treatments for Parkinson's disease and addiction.