Primate Development & Lifespan

• This presentation discusses the development and life span of primates.

Outline

• Discussed are lifespan, life expectancy, socialization and infant care, puberty and the transition to adulthood, adulthood and aging, and menopause.

Life Expectancy vs Lifespan

• Life expectancy is an average computed over all people, including those who die shortly after birth, in childbirth, early adulthood, or wars, and those who live unimpeded until old age.
• Lifespan refers to an individual and is considered the maximum lifespan, which is an upper bound rather than an average.

Primate Lifespans

• Primates compared to other mammals have long average adult lifespans, and few babies per year for their adult body size.
• Lifespan and body size correlated with larger-bodied animals, including primates living longer.
• Monkeys live 15-30 years.
• Great apes live up to 50 years.
• Humans can live up to 120 years.

Male vs Female Lifespans

• Female primates live longer than males.
• Males tend to have riskier lives due to dispersal, higher intra-sexual competition, and more physical fighting.
• E.g., chimpanzees: 41% of females survive to 15 years of age, while 27% of males survive to 15 years of age.

Non-Human Primate Babies

• Single, generally unassisted births are common in non-human primate babies, and some species demonstrate grasping hands.
• When infants are not parked, they are carried 24/7, which results in continuous opportunities to learn through observation and experience.
• Primate infant brains are underdeveloped at birth.
• Strepsirhines and lemurs/lorises are more altricial, whereas Haplorhines, Tarsiers, monkeys, and apes are less altricial
• Some lemurs and lorises are mothers that are parkers, whereas most haplorhines are mothers are carriers.
• Parkers lactate for shorter periods of time.
• Post-partum mating occurs in mothers that are parkers.
• Natal or Infant coats of primates are different colors than adults.
• These coats signal the need for care, encourage allomaternal investment, identify infants easily for group recognition and protection, and reduce aggression to adults being less likely to harm or reject distinctively colored infants.
• New infants often draw attention from other group members.

Socialization

• Socialization is the modification of behavior through observation of and interaction with others in the social group
• Socialization begins early in life and occurs when infants play, explore, or generally interact.
• Socialization is important in primates with large brains, slow maturation, lengthy periods of dependence, and heavy reliance upon learning for survival.
• Infant socializing agents include mothers, adult males, allomothers, and peers.
• The mother-offspring bond is strong and may persist throughout life.

Maternal Care

• Primates nurse their own offspring.
• There is recognition of visual, olfactory, and auditory clues.
• Rare mix-ups in primate offspring can involve kidnapping or death.
• Adoptions do occur.
• Variability in maternal care depends on the age of the mother, parity of the mother, rank of the mother, temperament of the mother, temperament of the infant, a species differences, and sex of infants.

Adult Male - Infant Interactions

• Adult male - infant interactions are not well studied, although it has been questioned why males interact with infants and what their motivations are.
• Motivations include sexual selection and female choice, parental investment and paternity certainty, and kin selection.
• Direct paternal care is favored when infants require a high level of investment, such as callitrichids.
• Male care is predicted to be higher when paternity certainty is higher for example, in monogamy.
• Paternal care is divided into types: Indirect and Direct.

Categories of Adult Male and Infant Interactions

• There are five categories of adult male and infant interactions/relationships.
• Use and abuse and tolerance, occasional affiliation, affiliation, and intensive caretaking

Intensive Caretaking

• Males spend a large portion of the day in infant caretaking, and parental duties are split.
• Male care ends when the infant is capable of independent movement, which is most common in the monogamous New World Monkeys.

Callitrichids

• Infants spend 50-90% of their time away from their mother being carried by the fathers.
• Non-maternal caregivers provide solid food.
• Help is critical to the infant's survival.
• In females, prolactin stimulates the mammary glands of mothers to make and secrete milk, and elevated levels have also been found in males that participate in parental care, such as cotton-topped tamarins.
• Males carrying infants had high levels of prolactin, and the prolactin levels when carrying infants are similar to the levels of nursing females.
• Prolactin inhibits testosterone.
• Paternal prolactin levels are a response to hormonal or behavioral cues from pregnant females.

Affiliation

• Males spend part of their day in friendly interactions with one or more specific infants.
• Males are often "friends" with a mother.
• Infants attracted to males form bonds and turn to them in times of distress.
• Males babysit while mothers are away
• Males protect infants from other group members.

Occasional Affiliation and Tolerance

• Males typically tolerate infants and permit them to be near but rarely direct affiliative behaviors toward them.
• Males may show occasional affiliative behaviors, such as brief social interactions or play.
• There is no consistent investment in infant care, as interactions are often opportunistic rather than a regular pattern of paternal care, such as in Japanese and rhesus macaques.

Common use and abuse

• Males interact in ways that may be beneficial to the male but potentially harmful to the infant.
• Mothers may resist the males behavior, and they are often drawn in to support the male.
• Agonistic buffering describes a triadic male-infant interaction where males grab or hold infants during conflicts with other males.
• This reduces the likelihood of aggression from opponents, since attacking a male holding an infant could harm the infant and provoke the mother.
• However, this strategy is advantageous to the male, but dangerous for the infant.
• Infant mortality covers topics involving disease, stochastic events, and infanticide.
• Allomothering means "allo" = other.

Allomothering

• Allomothering covers topics exploring who cares for or interacts with infants besides the mother and potential sire.
• This includes female kin and juvenile females.
• Learning to mother and mother relief make up the main hypotheses for why primates take care of someone else's infant.
• Both benefit from the allomother being kin.
• The allomother gains experience, and the mother gets relief, while the behavior increases the survival chances of shared genes.
• Very young infants are handled most by subadult/nulliparous females, and there are cases of affiliative infant handling and neglect/abuse. Alloparenting is more common in cercopithecides.

Colobines vs Cercopithecines in regards to Alloparenting

• Colobines are egalitarian, and have high levels of allomothering.
• Females readily share infant care with infants being frequently handled even by non-mothers.
• They demonstrate permissiveness in allowing others to interact with infants.
• Cercopithecines are despotic or hierarchical, with overall lower levels of allomothering.
• Mothers are more protective, and infant handling is rank-dependent.
• High-ranking (HR) females have more access, and mothers may limit interactions due to risks.
• Infant socializing agents include mothers, adult males, allomothers, and peers.

Peers and Play

• Young primates interact with age mates, demonstrate their first experience with non-relatives, and are presented with their first opportunity to learn social skills outside of kinship contexts.
• Play is easy to recognize, but hard to define.
• Characteristics of play include it being exaggerated, repeated, and restrained, and often accompanied by a "play face".
• Play can be solitary, solitary with objects in the environment, and social with others.

Function of Play

• Practice for adult skills, physical & social.
• Teaching
• Bonding
• Skill acquisition/demonstration
• Stress relief
• Learning
• Who they have to play with depends on group composition and dispersal
• MM-MF female-bonded: play with kin & friends
• Monogamous: play with neighbors, siblings, and parents
• Solitary play is common.

Infant Mortality

• Occurs because of disease, stochastic events, and infanticide.
• Lactation Time / Gestation Time
• Females with long lactation periods tend to undergo postpartum amenorrhea and no post-partum mating occurs.
• A loss of the infant means the female resumes estrus sooner.

Parks vs Carriers

• Some lemurs and lorises are classified mothers as parkers, whereas most haplorhines are mothers and carries.
• Short lactation is most common among parkers
• Postpartum mating is also more common among parkers.
• No Infanticide occurs among parkers due to the nature of communal care.
• Infanticide does occur among carriers.
• The correlates of infant care and infanticide are classified by lactation, postpartum mating, and males engaging in infanticide.
• More gestation is observed among carriers. and postpartum mating is higher among parkers.
• Male infanticide is only observed among carriers.

Parent-Offspring Conflict

• Weaning is a major time for conflict.
• Offspring demand more from their mothers and fathers than they are willing to give.
• Mothers stops investing in offspring sooner than it wants.
• There are sex differences in weaning.
• Mothers might be expected to wean one sex later than others if the extra investment translates into higher maternal inclusive fitness.
• E.g., High-ranking chimpanzees: Females might invest more toward sons rather than daughters, resulting in weaning sons later.

Juvenile Life

• The juvenile period is from weaning to sexual maturity.
• Unlike infants, juveniles are likely to survive the death of their mother.
• Two strategies for surviving as a juvenile include minimizing the time spent as a juvenile or growing slowly.
• Strepsirhines minimize the time spent as a juvenile, whereas Haplorhines grow slowly.
• Growing slowly can have the benefit of niche separation.
• A smaller body allows feeding on terminal branches.

Growing Slowly Cost

• Feeding efficiency and diet are commonly less than adults.
• Female yellow baboons who had poor juvenile diets show shorter reproductive lifespans and produced fewer offspring whom showed lower survival rates.
• During this time they must develop their juvenile social skills
• Relationships are established through play.

Puberty

• The hypothalamus releases hormones that activate the pituitary glands and affects the gonads.
• This results in stimulated Testis to produce testosterone and Ovaries to produce progesterone and estrogen.
• Secondary sex characteristics start to appear.
• Puberty transitions into adulthood more gradually for males than females.
• Dispersal usually takes place before puberty or before dispersing individual becomes sexually active, and high mortality is observed due to increased predation risk, aggression from other groups, challenge finding food/allies and reproduction demands.
• Sex differences in behavior is most obvious at puberty; however they do exist in infants in some species.
• Rhesus macaque male infants express more assertive/aggressive behaviors, more rough and tumble play, more independence from their mothers, less interest in grooming, and less interest in general infants.

Adulthood

• More or less continuous from puberty to death.
• No major stages or categories exist within the life course after transitioning into adulthood.
• Social relationships can be identified by either patrilocal or matrilocal groups.

Aging

• Aging has no distinct social role or behavior for old NHPs as there is for humans, which are different due to differences in division of labor, awareness of mortality, and menopause.
• Non-human primates do not share food; each individual is a complete subsistence unit.
• There is no opportunity to become dependent on others, so a loss of ability to feed oneself results in death.
• Humans on the other hand, do share food, with each individual dependent on a system of production and exchange.
• Humans are highly interdependent, so a change in ability to produce results in a change in social role, but does not usually result in death.
• Non-human primates are unlikely to be aware of their own mortality. They are unlikely to be objects unto themselves or be aware that they are temporary, or that society will move on. There is no anticipation that death is coming with old age.
• Humans however, are aware of our own mortality. They are able to think about themselves are separate and temporary, as well as know that they will die at old age. We as humans attribute give meaning to biological changes, anticipate mortality, and change behaviors.

Menopause in NHPs

• Menopause is defined as a reproductive cessation.
• In humans, other organ systems remain healthy, distinguishing humans from NHPs.
• Humans present a universal (population-wide) midlife occurrence, and are temporally distinct from the overall aging of the organism, occurring in healthy middle age.
• It is associated with increased production or survivorship of grandchildren.
• Only 7% of wild chimps reach age 40, and these chimps tend to remain fertile until death.
• The grandmother hypothesis states that menopause is directly adaptive via increases in the production or survivorship of descendants.
• Women stop reproducing because there are greater fitness benefits helping with offspring by helping daughters and grandkids than by having more babies on you own.
• In general, older females in matrilocal societies are more likely to stay integrated with others, rather than older males that often become isolated in patrical settings.

Ageing

• Experiencing old age depends on the social organization of the group/species, and the reproductive history of the individual.

Primates Summary

• Have slow life histories.
• Infants tend to be altricial and dependent on social learning.
• Mothers are the main caretakers, although other individuals are also important.
• Peers become more important during juvenilehood.
• Puberty leads to higher mortality for the dispersing sex.
• Adulthood is a long, continuous state.
• Aging is less pronounced in NHPs compared to humans.
• Menopause may only occur with regularity in humans.
• The grandmother hypothesis may explain the existence of menopause in humans.