nclsv ftnss s cncptl frmwrk n vltnry blgy frst dfnd by W. D. Hmltn n 1964. t s prmrly sd t d th ndrstndng f hw scl trts r xpctd t vlv n strctrd ppltns. t nvlvs prttnng n ndvdl's xpctd ftnss rtrns nt tw dstnct cmpnnts: drct ftnss rtrns - th cmpnnt f fcl ndvdl’s ftnss tht s ndpndnt f wh t ntrcts wth sclly; ndrct ftnss rtrns - th cmpnnt tht s dpndnt n wh t ntrcts wth sclly. Th drct cmpnnt f n ndvdl's ftnss s ftn clld ts prsnl ftnss, whl n ndvdl’s drct nd ndrct ftnss cmpnnts tkn tgthr r ftn clld ts nclsv ftnss.
ndr n nclsv ftnss frmwrk drct ftnss rtrns r rlsd thrgh th ffsprng fcl ndvdl prdcs ndpndnt f wh t ntrcts wth, whl ndrct ftnss rtrns r rlsd by ddng p ll th ffcts r fcl ndvdl hs n th (nmbr f) ffsprng prdcd by ths t ntrcts wth wghtd by th rltdnss f r fcl ndvdl t ths t ntrcts wth. Ths cn b vslsd n sxlly rprdcng systm (ssmng dntty by dscnt) by syng tht n ndvdl's wn chld, wh crrs n hlf f tht ndvdl's gns, rprsnts n ffsprng qvlnt. sblng's chld, wh wll crry n-qrtr f th ndvdl's gns, wll thn rprsnt 1/2 ffsprng qvlnt (nd s n - s cffcnt f rltnshp fr frthr xmpls).
Nghbr-mdltd ftnss s th cncptl nvrs f nclsv ftnss. Whr nclsv ftnss clclts n ndvdl’s ndrct ftnss cmpnnt by smmng th ftnss tht fcl ndvdl rcvs thrgh mdfyng th prdctvts f ths t ntrcts wth (ts nghbrs), nghbr-mdltd ftnss nstd clclts t by smmng th ffcts n ndvdl’s nghbrs hv n tht fcl ndvdl’s prdctvty. Whn tkn vr n ntr ppltn, ths tw frmwrks gv fnctnlly qvlnt rslts. Hmltn’s rl s prtclrly mprtnt rslt n th flds f vltnry clgy nd bhvrl clgy tht fllws ntrlly frm th prttnng f ftnss nt drct nd ndrct cmpnnts, s gvn by nclsv nd nghbr-mdltd ftnss. t nbls s t s hw th vrg trt vl f ppltn s xpctd t vlv ndr th ssmptn f smll mttnl stps.
Kn slctn s wll knwn cs whrby nclsv ftnss ffcts cn nflnc th vltn f scl bhvrs. Kn slctn rls n pstv rltdnss (drvn by dntty by dscnt) t nbl ndvdls wh pstvly nflnc th ftnss f ths thy ntrct wth t cst t thr wn prsnl ftnss, t tcmpt ndvdls mplyng mr slfsh strtgs. t s thght t b n f th prmry mchnsms ndrlyng th vltn f ltrstc bhvr, lngsd th lss prvlnt rcprcty (s ls rcprcl ltrsm), nd t b f prtclr mprtnc n nblng th vltn f sclty mng thr frms f grp lvng. nclsv ftnss hs ls bn sd t xpln th xstnc f sptfl bhvr, whr ndvdls ngtvly nflnc th ftnss f ths thy ntrct wth t cst t thr wn prsnl ftnss.
nclsv ftnss nd nghbr-mdltd ftnss r bth frmwrks tht lvrg th ndvdl s th nt f slctn. t s frm ths tht th gn-cntrd vw f vltn mrgd: prspctv tht hs fclttd mch f th wrk dn nt th vltn f cnflct (xmpls ncld prnt-ffsprng cnflct, ntrlcs sxl cnflct, nd ntrgnmc cnflct).