Research conducted by these investigators suggested that extraordinary efforts
might be necessary to overcome the effects of early separation. In many cases,
therefore, mothers denied early contact with their infants might appear deficient
months and even years later ( de Chateau, 1980b; Klaus & Kennell, 1976; Sugar-
man, 1977; Trause, 1981).

Klaus and Kennell's critique of contemporary obstetrical practices occurred at
a time when these practices were being critized by mothers and nurses who
objected to the common view that childbirth was the surgical culmination of a 9-
month illness. Klaus and Kennell's work provided the scientific support needed
to convince the skeptical medical establishment to accept changes that should
have been welcomed on humanitarian grounds alone. Many institutions have
since attempted to make childbirth an event in which new parents can experience
and express the exhilaration and emotional fulfillment that accompanies the
transition to parenthood with as little intrusion by medical personnel as possible.
Few would argue that these reforms have been undesirable, and we owe a great
deal to Klaus and Kennell for facilitating the humanization of birthing practices.
Any reforms that permit parents to enjoy and share the emotions engendered by
this rare and special experience are laudable, regardless of any long-term direct
effects on the infant-mother relationship. Changes in parental attitudes and feel-
ings are sufficient justification for continuation and extension of the reforms
facilitated by Klaus and Kennell. It is important, however, to evaluate the evi-
dence upon which Klaus and Kennell's argument was based, because their con-
clusions have far-reaching implications for understanding the determinants of
human behavior and development.

Klaus and Kennell's speculations concerning the existence of a sensitive
period for mother-infant bonding were based partly on evidence concerning the
determinants of maternal behavior in other species ( Trause, Klaus, & Kennell,
1976). Consequently, we begin our review with an evaluation of the pertinent
animal studies and of their relevance to our understanding of human social
behavior and its determinants. In the second section, we consider the literature
on maternal behavior in humans. Thereafter, we briefly summarize the implica-
tions of these findings for medical and social policy. The issue of maternal-infant
bonding has provided an excellent example of the wide-reaching effects that can
be initiated by the dissemination of research findings. We submit that important
lessons can be learned from this experience.

Those who theorize about the biological bases of maternal behavior frequently
propose the existence of critical or sensitive periods. These terms, which are
aptly applied to aspects of prenatal development in the embryonic phase, have

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