Shyness in Early Infancy: Approach-Avoidance Conflicts in Temperament and Hypersensitivity to Eyes during Initial Gazes to Faces

‘Infant shyness’, in which infants react shyly to adult strangers, presents during the third quarter of the first year. Researchers claim that shy children over the age of three years are experiencing approach-avoidance conflicts. Counter-intuitively, shy children do not avoid the eyes when scanning faces; rather, they spend more time looking at the eye region than non-shy children do. It is currently unknown whether young infants show this conflicted shyness and its corresponding characteristic pattern of face scanning. Here, using infant behavioral questionnaires and an eye-tracking system, we found that highly shy infants had high scores for both approach and fear temperaments (i.e., approach-avoidance conflict) and that they showed longer dwell times in the eye regions than less shy infants during their initial fixations to facial stimuli. This initial hypersensitivity to the eyes was independent of whether the viewed faces were of their mothers or strangers. Moreover, highly shy infants preferred strangers with an averted gaze and face to strangers with a directed gaze and face. This initial scanning of the eye region and the overall preference for averted gaze faces were not explained solely by the infants’ age or temperament (i.e., approach or fear). We suggest that infant shyness involves a conflict in temperament between the desire to approach and the fear of strangers, and this conflict is the psychological mechanism underlying infants’ characteristic behavior in face scanning.     

Parity of female goats does not influence their estrous and ovulatory responses to the male effect

The objective of the present study was to determine whether parity is a factor that influences the estrous and ovulatory responses of female goats when they are stimulated by males that show increased sexual activity. To stimulate sexual activity, four adult male goats were subjected to photoperiodic treatment for 2.5 months comprising long days, with the treatment commencing on 1 November. On 14 April at 1900 h, a group of multiparous females (n = 21) and a group of 16 months-old nulliparous females (n = 19) were exposed to four bucks (two per group) for 15 days. Throughout the study period, the estrous behavior of these female goats was detected twice on a daily basis. Ovulations of the female goats were determined by ecography on days 7 and 18 after exposure to males. The sexual behavior of males was recorded twice every day from 0800 to 0900 h and from 1730 to 1830 h during the first 4 days after introduction in the pen of females. The total cumulative proportion of multiparous females that had ovulations (100%) and displayed estrous behavior (100%) during the 15 days of exposure to males did not differ (P > 0.05) from that of nulliparous females (100% and 95%, respectively). The interval between introduction of males and onset of estrous behavior did not differ (P > 0.05) between multiparous (1.9 ± 0.1 days) and nulliparous (1.7 ± 0.2 days) females. The proportion of females displaying a short estrous cycle was greater (P < 0.05) in multiparous (13/21, 62%) than in nulliparous (5/19, 26%) females. Duration of these shorter than typical estrous cycles did not differ (P > 0.05) between groups (multiparous: 5.2 ± 0.3 days, nulliparous: 4.5 ± 0.1 days). The number of anogenital sniffings was greater (P < 0.001) in males exposed to nulliparous than in those exposed to multiparous females. In contrast, the number of mounting attempts was greater (P < 0.01) in males that were introduced to multiparous than in those that were introduced to nulliparous does. The number of flehmen, nudging, self-marking with urine, and mounts was not different (P > 0.05) between males that were in contact with multiparous and nulliparous females. These results indicate that regardless of parity, female goats respond to male introduction if they are stimulated by males that were previously exposed to artificial long days to increase their sexual behavior.     

Resource base,parity, and reproductive condition affect females' feeding time and nutrient intake within and between groups of a baboon population

Summary We examined within- and between-group differences in aspects of feeding and nutrient intake among adult females of a single population of baboons (Papio cynocephalus) in Amboseli National Park, Kenya. Differences in time spent feeding, daily energy and protein intake and feeding efficiency (nutrient intake per minute spent feeding) reflected differences in resource base, reproductive condition and parity. Baboons that partially fed from a lodge garbage dump spent less than half the time feeding than those that were feeding totally in the wild. During this greatly reduced feeding time, the garbage-feeding group had a similar daily energy intake and only a slightly lower daily protein intake relative to wild-feeding baboons. Consequently, the feeding efficiency of the semi-provisioned baboons was appreciably higher than that of the non-provisioned baboons. For the totally wild-feeding baboons, samples were large enough to permit analyses of feeding time and nutrient intake during different reproductive states and parity. Females spent more time feeding and had higher daily energy and protein intake when they were pregnant or lactating than when they were sexually cycling. Nulliparous females spent more time feeding than their multiparous counterparts. The daily energy intake of nulliparous females was higher than that of their multiparous counterparts, but their daily protein intakes did not differ significantly. Pregnant or lactating and nulliparous females had higher feeding efficiency than their sexually cycling and multiparous counterparts. The two nulliparous females in the garbage-feeding group spent more time feeding but did not take in more energy or protein per day than their multiparous counterparts.     

Social and seasonal influences on the reproductive cycle in female mandrills (Mandrillus sphinx)

We present 12 years of perineal swelling data for a semifree-ranging colony of mandrills (Mandrillus sphinx), and evaluate the influence of rank, parity, and seasonality on reproductive parameters. Female sexual swellings showed a seasonal pattern, with August the median month of ovulation. Overlapping periovulatory periods did not decrease the likelihood of conception. Females showed their first genital swelling at age 3.6 years (n = 28; range, 3.2-4.6 years), and higher-ranking females experienced their first swelling earlier than low-ranking females. Median postpartum amenorrhea (PPA) duration was 208 days (n = 92; range, 74-538 days). PPA was longer in primiparous females than in multiparous females, but PPA duration was unrelated to female rank. Median follicular phase duration was 24 days for the first cycle after parturition (n = 84; range, 12-40 days), shortening to 17 days in subsequent cycles (n = 55; range, 6-39 days). The follicular phase was longer in nulliparous females than in parous females, but was unrelated to female rank. Median cycle length (from one sexual swelling breakdown to the next) was 38 days (n = 57; range, 18-108 days). Eighty-seven percent of conceptions occurred within two cycles, and half of the nulliparous females conceived during their first swelling cycle. Lower-ranking females were more likely to require more cycles to conceive than higher-ranking females. The cycling phase was significantly longer in nulliparous females than in parous females, and was also significantly longer in lower-ranking females than in higher-ranking females. We discuss the influence of provisioning on female reproductive parameters, the influence of parity and rank on the different phases of the interbirth interval, and the evolution of long and variable follicular phases in mandrills.     

Early agonistic experience and rank acquisition among free-ranging infant rhesus monkeys

Several aspects of agonistic experience are described for freeranging infant rhesus monkeys (Macaca mulatta)on Cayo Santiago. Even before infants are fully integrated with peers in rank dominance based on maternal ranks,infants of highranking mothers tend to be threatened less frequently by other members of the group and are less likely to be threatened by unfamiliar individuals than are infants of lowranking mothers. There is no evidence that fearful interactions between pairs of infants are related to their mother’s ranks before 22 weeks of age. However, an imperfect hierarchy can be constructed for infants between 27 and 30 weeks of age. At this age,infants of higherranking mothers are also more likely to receive protection when threatened than are infants of lowerranking mothers. When protected, their protectors are less likely to emit fearful gestures to the infants’ threatener. Close female relatives appear to play a large role in the protection of infants and may be more directly responsible for the differences described above than the mother, other relatives, or other highranking members of the group. It is suggested that more than one mechanism, including intervention by the mother and by close female relatives,may be important in rank acquisition among peers.     

How rhesus monkey mothers and infants keep in touch when infants are at risk from social companions

Ten-to 17-week-old rhesus monkey infants that received hits from companions other than their mother at high rates (relative to their rates of involvement in playful social encounters with those companions) tended to be members of mother-infant dyads that were vigilant. Criteria of vigilance were frequent contacts between mother and infant during the first 5 sec of the infants’ social encounters and/or a bias of mother-infant contacts toward that time. Infants that received few hits per encounter came from both vigilant and nonvigilant dyads. When analyzed alone, mothers’ rates showed the same trends. High levels of vigilance tended to reduce infants’rates of making social contacts. Maternal social rank and other measures of the infants’ social involvement were not correlated with vigilance. There is no evidence that mothers and infants were in conflict with each other about interrupting the infants’ encounters. Understanding vigilance becomes important whenever vigilant activity conflicts with other activities. Special problems arise because decisions about vigilance levels require judgments of risk based on the kinds of events that occur only rarely if vigilance is effective. A model providing a framework for studies of vigilance against the risks of infants’ social activities was developed. It recognizes that (1) risk-reducing vigilant behavior can conflict with acquiring information about risk; (2) in social situations where reliable estimates of risk are impossible, individuals might follow rules of thumb (e.g., be restrictive) rather than modify behavior moment by moment according to the current situation;and (3) at the dyad’s optimum balance between vigilance for the current infant and investment in subsequent off-spring, the infant will not be totally protected, so that while dyads at higher risks are more vigilant, the risks are also realized to a greater extent (e.g., itin terms of the number of hits received per encounter).     

Maternal Infant Monitoring in a Free-ranging Group of Japanese Macaques (<Emphasis Type="Italic">Macaca fuscata</Emphasis>)

In nonhuman primates, females with infants visually monitor their infants from a distance to detect and consequently avoid potential threats to their infants. We recorded maternal visual monitoring of infants (infant monitoring) ages 7–18 wk in a free-ranging, provisioned group of Japanese macaques (Macaca fuscata). The infant monitoring rate declined as a function of infants’ ages in weeks and increased when the infants were beyond their mother’s reach, indicating that infant monitoring reflects the vulnerability of infants. Females with infants increased infant monitoring when their infants were handled by other group members but not when their infants moved alone. This suggests that intragroup threats (harassment/mishandling or kidnapping) have a relatively stronger influence on infant monitoring than external threats (predation or infanticide) under the condition of this study. Infant monitoring of middle-/low-ranking females was more frequent than that of high-ranking females when their infants were handled by other individuals. This may reflect greater intragroup threats to infants of middle-/low-ranking females; however, further study is needed to confirm this. During important activities (feeding or grooming), the infant monitoring rate was lower than that during other activities (resting or self-directed behavior). However, even during important activities, females with infants increased infant monitoring when infants were handled. This indicates that females with infants face a trade-off between infant monitoring and other important activities, and even if females have to reduce the time spent on important activities, they increase infant monitoring when their infants face greater potential intragroup threats.     

Evidence for Sex-Biased Behavioral Maternal Investment in the Gray Mouse Lemur (Microcebus murinus)

To study sex-differential allocation of maternal behavior in Microcebus murinus, I recorded behavioral patterns on 21 litters from parturition to the weaning period. After a pregnancy of 61.5 ± 0.9 days, females may produce from one to four young per litter. Litters were weaned in 40 days by mothers. Behavioral observations at the beginning of the nocturnal activity period demonstrated that close contacts between mothers and infants were more frequent in multiparous mothers than in primiparous ones (p < .01). Time in close contact with offspring aged >15 days old compared to contacts with neonates is significantly lower only in single-sex litters and is more marked for all-female litters (p < .01). Mother's approaches toward mixed litters or all-male litters were always significantly greater than approaches toward all-female litters (p = .04). However, mother's approaches within mixed sex litters were not biased toward either sex (p = .7). Males in a litter may be interpreted as a stimulator of maternal behavior. Similarly, using retrieving tests of 15-min duration, a significant maternal preference for male neonates is evident. Latency to first retrieval is significantly shorter in multiparous females than in primiparous ones (p < .05) independent of size and sex ratio of the litter. For multiparous females only, male neonates were chosen first for retrieval more often than females (p < .05). Finally, the calls of young played a stimulator effect on maternal retrieving (p < .001). Accordingly multiparous mothers exhibit more interest in their young, which appears to be biased toward male neonates.     

Effects of age,lactation, and repeated cycles on rhesus monkey copulatory intervals

Young, sexually mature female rhesus monkeys copulate on more days prior to conception than do older females, and this prolonged discrete mating period is associated with an earlier rise in serum estradiol prior to the first ovulation of the breeding season. The influence of repeated ovulatory cycles and the presence of a suckling infant on the copulatory patterns were examined in two separate analyses. Extending previous work, young, nulliparous females copulated on more days at the first ovulation of the breeding season than did older, multiparous females. However, the duration of the copulatory period at the second ovulation of the breeding season was similar and significantly shorter for both age groups. Furthermore, the presence of a suckling infant did not influence the duration of the mating periods in adult, multiparous females. The onset of copulatory behavior for all females was associated with serum estradiol concentrations of approximately 90 pg/ml, indicating that the age and cycle differences in the duration of the copulatory periods are due to the time course of serum estradiol prior to ovulation. A separate, longitudinal analysis of the duration of the mating period associated with the first ovulation of three successive breeding seasons indicated that females copulated on more days during their first ovulatory cycle of their first breeding season. These data indicate that the copulatory interval is longer for females during the first ovulation of the breeding season, and this pattern is accentuated in young, sexually mature animals.     

Effect of service on estrus duration in dairy goats

The objective of this research was to determine the effect of sterile service on estrus duration in multiparous and nulliparous dairy goats. Twenty Nubian goats (10 multiparous and 10 nulliparous) were randomly assigned to of 4 treatment groups (n = 5 animals per group). Group MNS, multiparous without service; Group MS, multiparous with service; Group NNS, nulliparous without service and Group NS, nulliparous with service. Estrus was synchronized by utilization of fluorogestone acetate intravaginal pessaries (40 mg.) over a 12-day period plus 250 IU, i.m. of pregnant mare serum gonadotropin (PMSG) at pessary removal. Estrus was detected with the aid of a vasectomized buck for 5 days after pessary removal for 6-hour intervals (0600, 1200, 1800 and 2400 hours). In the groups that were not serviced the teaser was equipped with an apron and was only allowed to mount. In the serviced groups, the teaser was permitted to mount and service each female on 2 occasions during the first 12 hours of estrus. Estrus initiation for Groups NNS, NS, MNS and MS were (mean +/- SD) 61.5 +/- 29.5, 61.2 +/- 35.4, 63.0 +/- 22.2 and 69.6 +/- 32.5 hours, respectively (P>0.05). Estrus duration for the same groups were (mean +/- SD) 42.0 +/- 12.0, 30.0 +/- 6.0, 42.0 +/- 7.3 and 28.8 +/- 10.7 hours, respectively. These results show that estrus duration was shortened by serving (P<0.01), and that there were no differences between multiparous and nulliparous goats with or without serving (P>0.05). It is concluded that estrus duration in goats is shortened by serving and that no differences in duration exist between multiparous and nulliparous.     

Changes in relationships of nulliparous and parous females of Japanese monkeys at arashiyama with some aspects of troop organization

Social interactions of the adult females (nulliparous, primiparous, multiparous young, and multiparous old) of the Arashiyama-B troop of Japanese monkeys were studied. Using focal-animal and instantaneous sampling techniques, specifically identified social interactions involving allogrooming, social play, and agonism, nonspecific body-contact with and proximity to other animals were recorded from 1975 to 1978. By identifying the animals who had the above mentioned social interactions with the focal females, an attempt has been made to analyze the changes in relationships between the females of different classes and their closest kins, distant kins, and non-kins. Multiparous young females spend more time in social interactions involving allogrooming, nonspecific body-contact, and proximity than do females of the other classes and most of their social interactions are centered around their own offspring. Social interactions of the nulliparous females are fewer than those of the young mothers. But, the social interactions of the nulliparous females with their kins are much more frequent than those of the other females, i.e., once a female bears offspring, she concentrates her efforts in raising it and her social life becomes closed than before. Social interactions of the old mothers decrease and their social life is also centered more around their own young offspring. However, the social interactions of the females with non-kins, the interactions which strengthen troop integration, are independent of the class of the females. This report constitutes one part of the thesis submitted by the author to the Faculty of Science of Kyoto University in 1979 for the award of degree of Doctor of Science.     

Social behavior of infant and mother Japanese Macaques (Macaca fuscata): Effects of kinship,partner sex,and infant sex

The behavioral interactions of 22 infant and mother Japanese macaques with other group members were studied. Focal-animal observations were made from the time of each infant’s birth until 1 year of age. Infants and mothers both displayed exceedingly strong preferences for associating with matrilineal kin and, specifically, for female kin. The degree of genetic relatedness was positively correlated with levels of spatial proximity, contact, grooming, aggression, and play. Overall frequencies of interactions with nonkin were very low, and partner sex was not an important factor in interactions with nonkin. There were no significant differences between male and female infants in interactions with kin versus nonkin. There was only one significant difference between male and female infants in interactions with males versus females: female infants showed stronger preferences for initiating proximity with females over males than did male infants. Because mothers provide the focal point for infant interactions during the first year of life, we compared the behavior of infants and mothers. Mothers were the recipients of more social interactions than were infants, mothers engaged in more grooming than did infants, and infants engaged in more social play than did mothers. These findings are only partially consistent with kin-selection theory, and the inadequacies of studying matrilineal kin discrimination to test kin selection are reviewed. The near-absence of infant sex differences in associations with social partners suggests that although maternal kin other than the mother are important to infant socialization, they probably do not contribute to the development of behavioral sex differences until after the first year of life.     

Differences in fertility and suckling patterns between primiparous and multiparous rhesus mothers (Macaca mulatta)

Primiparous females gave birth around the same time as multiparous nonlactating females, and earlier than did multiparous lactating females. No differences in birth sex ratio were found between primiparous and multiparous females. During the breeding season following birth, primiparous mothers returned to oestrus later than did multiparous mothers, and while few primiparous mothers conceived successfully during that season, most multiparous mothers did. Primiparous females suckled their infants more frequently than did multiparous females at all ages; infants of primiparous females also made more nipple contacts per bout, and had shorter sucking bouts. When mothers came into oestrus, suckling frequency drastically increased for primiparous females, but not for multiparous females, magnifying the differences between the two groups. After the first oestrus, suckling frequency declined for all mothers, but multiparous mothers had consistently lower suckling frequencies than did primiparous mothers. The high suckling frequency, and numerous nipple contacts per bout, found among primiparous mothers are likely to be related to the low reproductive chances that these females faced during the breeding season. Multiparous mothers seemed to compensate for their low suckling frequency by lengthening the suckling bouts, and this suckling pattern did not hinder their reproduction. It is argued that primiparous mothers might have to suckle their infants more frequently because they can only produce milk at slow rates, being in this way forced into a reproductively inhibiting suckling pattern. However, the delay in subsequent reproduction could be ultimately advantageous for primiparous mothers if it enhanced infant survival, and allowed the mothers to regain physical condition before reproducing again.     

Reproductive patterns and birth seasonality in a South-American breeding colony of common marmosets,Callithrix jacchus

We analyzed data on captive-born and wild-caught females housed under natural conditions in a colony located in northeastern Brazil. No differences in reproductive performance were found between captive-born and wild-caught females. Twins were the most frequent litter size, followed by triplets and singletons. No parity effect was observed, with similar infant survival for nulliparous and multiparous females. No significant departures in sex ratio were detected for births and mortality of the male and female infants. The age of the females at the time of pairing showed a negative correlation with pairing-parturition length, but did not affect infant survival. The prolongation in pairing-parturition interval (PPI) and interbirth interval (IBI) was related to birth seasonality. The births were clustered in the second half of the dry season and the beginning of the wet season (November–March), and the time of pairing and the time of infant birth influenced the PPI and IBI, respectively. The use of outdoor cages, which allowed the animals to be aware of the seasonal variations in photo-period and rainfall seems to be sufficient to time the reproductive activity, even when the animals are maintained on a constant food supply.     

Demography and reproductive parameters of a free-ranging group of Japanese macaques (Macaca fuscata) at Katsuyama

Demographic and reproductive data were analyzed for a period of 28 years in the females of a free-ranging group of Japanese macaques at Katsuyama, Okayama Prefecture, Japan. The overall mean, age-specific fecundity rates were 5.43% for 4-year-olds and 41.86% for 5-year-olds, increasing to a peak of 66.67% for 13-year-olds. Fecundity remained relatively high (52.31–54.24%) in 16–19-year-olds, but decreased sharply (45.45–17.86%) in 20–23-year-olds, and became very low in 24–26-year-olds. Females aged 27 years or more did not produce infants. The average age at first birth was 5.41 years. Births peaked in mid-May. The timing of the first births each year remained essentially unchanged during the study period, whereas the timing of the median and last births shifted towards the later part of the season. The mean interbirth interval for all females was 1.56 years. The value was 1.54 years for multiparous females and 1.29 years for females following infant loss. These intervals were significantly shorter than those for primiparous females, and females with surviving infants. The overall mean infant mortality within the first year of life was 10.2%. The value was 8.6% for 10–14-year-olds, and 7.5% for 15–19-year-olds. The timing of birth differed among the four female matrilineal dominance rank-classes. The female fecundity rates increased as a function of matrilineal dominance rank. It is suggested that all demographic and reproductive data should be analyzed in detail with respect to the group's history.     

Sex differences in infant integration in a semifree-ranging group of Barbary macaques (Macaca sylvanus,L. 1758) at Salem,Germany

Sixteen multiparous Barbary macaque females with newborns were studied over a 16 month period within the context of their naturally formed group. Analysis of their social behavior revealed 1) triadic interactions involving focal females, their newborns, and other group members occurred mainly with other females; and 2) mothers with female newborns interacted mainly with females of their own matriline, while mothers with male newborns interacted mainly with nonmatriline females. Observed in two successive birth seasons, this pattern indicates that partners of maternal interactions chose each other according to the sex of the newborn. Measures of distance from the mother also reflected differences between infants of different sex. At about five months of age, female infants were observed close to their mothers significantly more often than males. This finding follows the pattern of a sex-specific infant socialization process which integrates female infants into the network of their matrilines and male infants into the broader group. This sex-specific integration pattern is interpreted as supporting female philopatry and male dispersal. © 1995 Wiley-Liss, Inc.     

An experimental examination of female responses to infant face coloration in rhesus macaques

In many primates, infants possess distinctive coloration that changes as a function of age. This colour is thought to serve the purpose of eliciting caretaking behaviour from the mother as well as other conspecifics. The present study investigated the responses of adult female rhesus macaques (Macaca mulatta) to pictures of infant faces in relation to infant age and facial coloration. Study animals were shown digitized images of neonates and 5-6-month-old infants displaying either unaltered facial colour, pink neonatal colour, or novel (green) facial colour. While infant and neonate faces of all colours elicited the attention of adult females, pink neonatal facial coloration did not appear to be especially attractive to subjects in contrast with the findings from an earlier study [Higley, J.D., Hopkins, W.D., Hirsch, R.M. Marra, L.M. Suomi S.J., 1987. Preferences of female rhesus monkeys (Macaca mulatta) for infantile coloration. Dev. Psychobiol. 20, 7-18]. The results suggest that infant facial colour is not particularly important in mediating infant attractiveness to rhesus macaque females as previously suggested or that other infantile facial characteristics might be more important than colour in eliciting caretaking behaviours amongst females.     

The relationship between female rank and reproductive parameters of the ringtailed lemur: a preliminary analysis

We used data from a 13-year field study of wild ringtailed lemurs to analyze the relationship between female rank and reproductive parameters. In medium and small groups there were no significant differences in birth rate, infant mortality rate, and the number of surviving infants between the female rank categories. On the other hand, in large sized groups low-ranked females had a smaller number of surviving infants than middle-ranked females. This suggests that in large sized groups, within-group competition lowered the values of reproductive parameters of low-ranked females. On the other hand, high and low-ranked females of small sized groups tended to have a smaller number of surviving infants than high-ranked females of medium sized groups and middle-ranked females of large sized groups. Between-group competition should lower the values of their reproductive parameters. In sum, these results fit the expectation from Wrangham’s (1980) inter group feeding competition model.     

What defines successful integration into a social group for hand-reared chimpanzee infants?

Hand-rearing of captive great ape infants is sometimes necessary but can have negative behavioral consequences. Modern hand-rearing protocols, including early integration into a diverse group of conspecifics, appear to reduce the negative consequences of hand-rearing, but the process of integration is not well studied. We investigated six potential metrics of success during the introduction of two hand-reared chimpanzee infants into a troop of nine other chimpanzees at the Maryland Zoo in Baltimore. Little aggression was observed and the infants continue to be maintained in the troop at publication. As we predicted, during the introduction the hand-reared infants showed consistent levels of stress-related behaviors, participated in affiliative interactions with all available partners, and acted, received, and mutually engaged in these interactions. Solitary behaviors by these infants were similar to a mother-reared infant in the same group. Each infant also formed a relationship with a specific female that involved nest-sharing, carrying, retrieval, and intervening to reduce risk to the infant; these relationships could be classified as allomothering because they involved maternal behavior but occupied significantly less of the infants’ time than a maternal relationship. Contrary to our prediction, the hand-reared infants therefore spent significantly less time in social behavior than a mother-reared infant of the same age. In addition, the hand-reared infants continued to show strong social preferences for each other as introductions progressed and to direct a low but consistent number of nonfeeding social behaviors to humans. The successful introduction of hand-reared infants appeared to involve adding conspecific social relationships to the infants’ social repertoire, but not eliminating social interactions directed at humans.