<unk>  has been the subject of considerable study with focus both on human females and males and on females and males of other mammalian species.<unk>  as an adaptive problem in mammals involves specific endocrine signals that were naturally selected to respond to infant cues and environmental inputs. Infants across species produce a number of cues to inform caregivers of their needs. These include visual cues, like facial characteristics, or in some species smiling, auditory cues, such as vocalizations, olfactory cues, and tactile stimulation. A commonly mentioned hormone in<unk>  is oxytocin, however many other hormones relay key information that results in variations in behavior. These include estrogen, progesterone, prolactin, cortisol, and testosterone. While hormones are not necessary for the expression of maternal behavior, they may influence it. Based on cross species evidence, some aspects of these mechanisms have been phylogenetically conserved from rodents to humans, meaning that these mechanisms are adaptive for mammalian<unk>  and that the environment of evolutionary adaptedness of some<unk>  mechanisms may have evolved when mammals first evolved. The importance of these mechanisms are to regulate parental investment and to inform offspring about their environment, primarily those involving responsiveness and sensitivity. These are commonly mentioned in humans as important<unk>  characteristics that inform their infants about their environments.
Endocrinology of parenting
Prenatal and perinatal psychology
Nutrition psychology
Reproductive technology
Cardiac psychology
Sexual motivation and hormones
Psychiatric genetics
Genetics of obesity