In mammals, a robust physiologic system acts to maintain relative constancy of weight. A key element of this system is leptin. The nature of this "brain-somatic" cross talk is as yet poorly understood, but it is likely to have important implications for the pathophysiology and treatment of obesity, diabetes and other metabolic disorders.

SocialBonding,aProductofEvolution: anIntroductiontotheVolume Mechanisms underlying reproductive and maternal functions or coping represent the initialstructuringforcebehindmanysocialbehaviors.Theyareaccompaniedbysel- tivehormonalenvironmentsaimedatfacilitatingor stabilizingthem.Sexandadrenal steroids are major players in the regulation of reproductive functions and coping challenges, but other hormones also participate in a variety of social behaviors (in particular,oxytocinandvasopressin,twophylogeneticallyveryoldmoietiesoriginally associated with maternal care and water balance) and are receiving increasing att- tion. Their role is highlighted in the present volume, which gathers contributions to theColloqueMedicineetRecherche"HormonesandSocialBehavior"organizedbythe FondationIPSENinDecember 2007. Whatisthekeytounderstandingtherationaleofhormonalsubstratesofbehavior? Evolution, of course. Higher manifestations of social behavior have evolved from - productivebehavior,characterizedbyErnstMayras"theleadingedgeofevolutionary change." As formulated by one contributor to thisvolume, however, "the evolutionary increase in neocortex seen in primates has induced a signi?cant emancipation of - havior from hormonal determinants, and in parallel, an increasing role for intelligent socialstrategies"(Keverne 2008). In so-called "lower" mammalian animals, many social behaviors are closely - pendent upon the olfactory system, a component of autonomous regulation of such importancethatitexpressesalargeproportionofallreceptorgenespresentinthebrain. Whenonelooksat"higher"mammalssuchasprimates,olfactorycontrolbecomesless stringent. Olfactory structures exhibit the same number of receptor genes, but a large number are transformed into non-coding "pseudogenes." In parallel, hormones i- tially targeted on physiological functions become increasingly associated with more diversi?edcognitivefunctions.

We are now on the verge of viewing effector molecules and other regulatory sites as therapeutic targets for the amelioration of human and animal disease. The recognition, for example, that mutant proteins are frequently misrouted molecules, rather than functionally defective ones, changes our approach to "inborn errors of metabolism" and offers new approaches for pharmacological discovery, based on rescue of receptors, ion channels and enzymes with pharmacoperones. Ion channels, regulators of G-protein signaling and enzymes engaged in regulation, now present opportunities for drug development.

The state of our art also benefits by the availability of superior tools that allow measurement of interactions and afford unprecedented insight into the biomolecular interactions that present novel approaches to drug design.

In mammals, a robust physiologic system acts to maintain relative constancy of weight. A key element of this system is leptin. The nature of this "brain-somatic" cross talk is as yet poorly understood, but it is likely to have important implications for the pathophysiology and treatment of obesity, diabetes and other metabolic disorders.