ANTH Final: Part 7 - Cooperative Breeding

Have some general understanding of variation in life history rates in primates and other mammals. What sorts of parameters (birth rates, developmental times, lifespans, etc.) lead to the “slow/fast” continuum, and what do “slow” and “fast” mean?

Life history variation includes birth rates, growth and developmental timing, age at reproduction, and lifespan.

• “Fast” life histories = early reproduction, frequent births, short lifespan (e.g., mice).

• “Slow” life histories = delayed reproduction, fewer offspring, longer development, long lifespan (e.g., elephants, primates).
  These patterns are linked to ecological pressures like predation, food availability, and body size.

Human life histories are slow in most respects, as expected from comparative data on the relationship between brain size and life histories in primates. However, we are unexpectedly fast in one respect. What is this? How do we compare to chimpanzees in this respect? How do chimpanzee life histories and those of humans compare and contrast in general?

Humans are unusually fast in reproductive pace once reproduction begins—shorter birth intervals than expected given our brain size and lifespan.

• Compared to chimpanzees, human females can have more surviving offspring over a lifetime, due in part to shorter interbirth intervals and longer lifespan.

• Chimpanzees mature faster and reproduce earlier but have longer spacing between births and shorter lifespans.
  So overall, humans are slow developers but efficient reproducers.

Some nonhuman mammals (and some birds) are “cooperative breeders”. What does this involve? What is allocaretaking? What are some of the forms it takes, and the associated potential costs and benefits?

Cooperative breeding involves individuals other than the biological parents helping to care for offspring.

• Allocaretaking (or alloparenting) includes babysitting, feeding, grooming, carrying, or protecting young.

• Benefits: increases offspring survival, allows mothers to reproduce sooner, spreads parenting burden.

• Costs: helpers expend energy and risk without direct reproductive benefit.
  Species like meerkats, wolves, and some monkeys show this behavior—and humans do too.

What does it mean to say that allocaretaking is “obligatory” in animals like tamarins, marmosets, and meerkats? What is important about infant growth rates in these species, and how is this different from infant growth rates in humans?

• Obligatory allocaretaking means that infant survival depends on help from others, not just the mother.

• In tamarins, marmosets, and meerkats, infants grow very rapidly and are often twins, creating a burden that a mother cannot manage alone.

• In contrast, human infants grow more slowly and require long-term, low-intensity care, with multiple caregivers but not in an obligatory way for survival.

Humans have a life history stage that is unique among primates: “childhood”. What is this?

Childhood is a distinct stage after weaning but before full self-sufficiency, marked by slow growth, dependency on caregivers, and intense learning and brain development.
No other primates have this prolonged, post-weaning phase where individuals are dependent but not nursing.

The “embodied capital” model of human life history evolution proposes that our ancestors entered in a feedback cycle in which reliance on large, high-quality food “packages” combined with widespread food sharing helped allow for faster female reproductive rates without penalties imposed by increased maternal or infant mortality rates. In turn, lower mortality risk for infants and “juveniles” led to selection in favor of genetics variants that slowed maturation rates and allowed more time for learning how to be skilled foragers. Have some general idea about what foraging challenges/opportunities could have been and some of the ways in which our ancestors could have met these.

Foraging challenges included:

• Locating patchy or seasonal high-quality food (e.g., nuts, roots, meat)

• Using tools or strategies to access food

• Learning complex ecological knowledge, like which plants are edible
  Opportunities were met through:

• Skill-intensive foraging, teaching and imitation

• Food sharing among group members

• Long juvenile periods that allowed skill acquisition
  This feedback loop led to larger brains, slower maturation, and greater cooperation.

Finally: what is the difference between female baboons and women in hunter gatherer societies in the amount of available time devoted to foraging per day? Why did/does this difference exist?

• Female baboons forage for about 75% of their waking hours, while hunter-gatherer women typically forage only 25–35% of the time.

• This difference exists because humans share food, especially from skilled foragers (like men bringing meat), and cooperative childcare reduces women's direct burdens, allowing shorter, more efficient foraging time.