A Practical Approach, Second Edition=Ronald D. Ho.pdf

POSTNATAL DEVELOPMENTAL MILESTONES 1121Around 15 to 20 years of age, the adolescent begins to solidify her own ideals and values. She alsobegins to function as an independent thinking individual with a reasonable state of equilibriumamong instinctual drives, self-needs and the outside world.RatsIn rats, the earliest forms of social interactions are at birth with the competition to nurse and clustertogether to sleep (Bolles and Woods, 1964). After PND 14, a new interaction begins to emergewhere one pup may appear to spontaneously jump, and a chain reaction occurs involving all thelittermates. Panksepp (Panksepp, 1981) evaluated the development of play behavior in young ratsby observing the frequency and duration of pinning behavior. Play increased from 18-28 days,peaked during 32-40 days of age, and then gradually declined. He also found that social isolationof rats resulted in a marked increase in play behavior. One function of play may be to establishstable social relationships and help rats find their place in the existing social structure of a group.Grooming in rats may be thought of as a social behavior because it results in the intimateinteraction of siblings. Grooming consists primarily of three different kinds of behavior (Bollesand Woods, 1964). Face-washing and scratching in rudimentary forms can be observed as early asPND 2. By PND 10-12 both face-washing and scratching resemble the adult pattern and includethe characteristic licking of the paw. Around PND 13, the third component, fur-licking, begins. Inaddition, grooming of its littermates also begins around PND 13 and is quite common in PND 40rats. However, sibling grooming declines somewhat in adulthood. The younger animals spend aconsiderable amount of time washing their front paws and face and scratching with the hindpaws.However, licking the fur is the prevalent component of grooming in the adult. Grooming is theonly activity other than eating and sleeping in which young animals will persist at for 5 or moreminutes.DogsAround 3 to 3.5 weeks of age, pups begin the earliest forms of playful social interactions (Fox,1971). They will chew on each other’s ears and lick faces of one another, but will either avoid orelicit a distress vocalization if the stimulation becomes too intense. Between 4 to 5 weeks of age,play-fighting, scruff-holding and “prey-killing” (i.e., head shaking movements) appear, along withpouncing, snapping and aggressive vocalizations (e.g., growling and snarling with teeth bared)(James, 1955; James, 1961). Submissive postures and play-soliciting gestures (e.g., ears pricked,tail wagging, vocalization) also appear around this time. By 4-months of age, dominant-subordinaterelations are established between littermates (Fox, 1971; Pawlowski and Scott, 1956; Scott andMarston, 1948). In general, male pups also indulge in more rough-and-tumble play and biting thanfemales, but there are differences in aggressiveness depending on the breed of dog (Fuller andDuBuis, 1962).Non-Human PrimatesPlay behavior in the macaque has two forms: movement play and social play (Hines, 1942). Assoon as the infant monkey is able to move easily (i.e., about 3 weeks of age), she will repeatmovements such as jumping, running and climbing. Around 4 weeks of age, bouncing on a wiremesh is possible. Social play begins around 5 weeks of age and is described as dodging and chasinggames with older monkeys that were allowed to run loose in the room. Around 6 weeks of age,the infant monkey begins stealing food from another monkey’s cage in spite of the presence of anabundance of food in her own cage. Stealing food from another monkey’s cage is a well-establishedbehavior in the adult monkey. Around 7 to 9 weeks, infants will approach each other with armsextended and then lightly slap each other. This appeared to be a signal to initiate rough-and-tumble© 2006 by Taylor & Francis Group, LLC