Imag­ine this: an or­gan­ic di­et pill that kills the ap­petite and at­tacks obe­si­ty. It has no known side-​ef­fects, and con­tains a molecule that fools your brain in­to be­liev­ing you are full. Deep in­side the African Kala­hari desert, grows an ug­ly cac­tus called the Hood­ia. It thrives in ex­treme­ly high tem­per­a­tures, and takes years to ma­ture. The San Bush­men of the Kala­hari, one of the world's old­est and most prim­i­tive tribes, have been eat­ing the Hood­ia a plant for thou­sands of years, to stave off hunger dur­ing long hunt­ing trips. When South African sci­en­tists were rou­tine­ly test­ing it, they dis­cov­ered the plant con­tained a pre­vi­ous­ly un­known molecule, which has since been chris­tened P 57