 develop social attach infanc report devot format develop social attach infanc suggest core attach function repres tendenc young seek proxim member speci suitabl oper definit behavior individu depriv proxim studi take form longitudin follow-up 60 infant investig four-weekli interv earli week year 18 month ag attach scale base everydai separ situat three main paramet explor ag onset specif attach intens attach number object attach form measur fear-of-stranger includ indic ag onset specif attach gener third quarter year preced phase indiscrimin attach behavior intens specif attach increas month onset fluctuat occur individu case long-term predict difficult multipl object instanc specif attach phase rule remain case correl attach variabl well fear-of-stranger measur present examin condit elicit protest proxim loss manner protest express condit termin protest individu differ regard three main paramet explor subgroup 36 infant number variabl examin relat individu differ suggest condit affect manifest attach function data discuss relat theme emerg find natur attach function development origin development trend influenc social set 