Anthropology 160 Lectures 6 and 7
Homo is an outlier among Primates
(Primates are high in intelligence and lifespan cf mammals)
1.
Longevity
2.
Brain Size
3.
Period of
dependency and multiple dependency
4.
Three-generational
system of wealth flows
5.
Contribution of
men to the energetics of reproduction
6.
Complexity of
cooperative arrangements
Compared to other primates and mammals, there are at least four distinctive characteristics of human life histories: 1) an exceptionally long lifespan, 2) an extended period of juvenile dependence, 3) support of reproduction by older post-reproductive individuals, and 4) male support of reproduction through the provisioning of females and their offspring. Another distinctive feature of our species is large brain size and its associated psychological attributes: increased capacities for learning, cognition and insight.
Brain weight and Lifespan among Primates T3
Survival of H/gs and Chimpanzees T4
Age-specific Mortality rates Ache and Chimps T5
5. Survival to 15 and expected age at death T6
50% chance of reaching age 60 if make it to reproductive age, and in fact, the expected lifespan at first reproduction among the Ache, for example, is about age 62. This means that most women who make it to repro age will experience about 20 years of post-reproductive life
6. comparative brain size T7
Brain: opposite to overall growth delay, develops in advance of the body and matures rapidly so that 90% of ggrowth occurs by age 6. Energetically expensive organ, accounts for over 50% of BMR during first year, and 1/3 or more during childhood.
this is also associated with very slow early growth. Human growth spurt very late cf. to other primates, even after controlling for adult body size
7. Feeding ecology of apes and humans T8
Most rely on plant foods that must be extracted from protective substrate, but which produce large packages
large costs to this strategy, especially in terms of early life
8. Principle differences between Human and
Nonhuman primate diets T9
Now to Slides
Tour of worlds extant hunter-gatherers who are subsisting mainly on hunted and gathered foods
Most rely on plant foods that must be extracted from protective substrate, but which produce large packages
4,5. Hadza root extraction ha1,2
6. Hiwi
root h129
7. Alyara root 8
8,9. kung mongongo nuts k8, k10 (requires
extraction from two shells)
10,11. Ache palm fiber and larvae ac245,
ac247
12,13 Alywara seeds a1, aly17
14. hadza fruit hdz20
15,16. Ache honey (100,000 cals) ac 227,33
Hunting
17-25. Ache tress, land, underground,
logs w/dogs, underwater, with poison ac87,5,81,93 ma283, h136,ma 282, ma259,
ma229
26,27 medium and large as well, Kung ?, hdz
?
28,29 children do little work hdz?, ma 164
large costs to this strategy, especially in terms of early life
10. forager age profile of production fi29
T10
11. forager vs chi mp age profile of prod
and consumption T11
Extracted resoursces take a long time to get good at
12. Ache hourly return rates for meat and
palm T13
A. difficulty of finding prey - requires knowledge of feeding ecology, grouping patterns, repro ecology, predator avoidance techniques in different micro-ecologies, use of water, for each prey species.
B. Hunting with dogs shows that while dogs can follow a scent well and run fast, they often lose it and the hunters study the tracks and other signs and then send the dogs off.
C. Great line in N!ai where they have shot a giraffe with poison arrow and must track it for five days in dry season hard pan, and the narrator remarks that they tracking was so difficult that the lead hunter almost had to think his way to the Giraffe
d. Social intelligence and hunting
Hunting shows big age-effects for Chimpanzees as well (as do other extractive tasks like termite fishing, Graph shows that there are no ambushes until about age 10 and increase with age
Fruits are much easier By age 5, children are alreadyh getting about 30% as much as adults per hour of work
Huge effects for young kids, but smaller effects for older kids who can do other things
Summary Table
The theory is that human life history characteristics and extreme intelligence are co-evolved responses to a dietary shift towards high-quality, nutrient-dense, and difficult-to-acquire food resources. The following logic underlies our proposal. First, high levels of knowledge, skill, coordination, and strength are required to exploit the suite of high-quality, difficult-to-acquire resources humans consume. The attainment of those abilities requires time and a significant commitment to development. This extended learning phase during which productivity is low is compensated for by higher productivity during the adult period, with an intergenerational flow of food from old to young. Since productivity increases with age, the time investment in skill acquisition and knowledge leads to selection for lowered mortality rates and greater longevity, because the returns on the investments in development occur at older ages. This in turn will favor a longer juvenile period if there are important gains in productive ability with body size, and growth ceases at sexual maturity.
Second, the feeding niche specializing on large, valuable food packages promotes food sharing, provisioning of juveniles, and increased grouping, all of which act to lower mortality during the juvenile and early adult periods. Food sharing and provisioning assist recovery in times of illness and reduce risk by limiting juvenile time allocation to foraging. Grouping also lowers predation risks. These buffers against mortality also favor a longer juvenile period and higher investment in other mechanisms to increase lifespan.
Thus, the long human lifespan co-evolved with the lengthening of the juvenile period, increased brain capacities for information processing and storage, and intergenerational resource flows, - all as a result of an important dietary shift.
If humans lived only as long as chimps, very few would reach the age of peak productivity
Males also make a big difference in the human case, because of high returns from hunting. Nonhuman primate females must increase work after a baby is born, whereas human females reduce work to concentrate on high quality childcare
Ape and Human Reproductive Ecology T19
Human Life history stages
Evolutionary Scenario for the co-evolution
of Brains and mortality due to feeding niche T21
Life history model of lifetime Time and Resource allocation T22
Embodied Capital Theory of Life history
Evolution T23
1. The embodied capital approach to life history theory
Soma as a vehicle for gene replication
Soma can be thought of as investment in future reproduction
Development can be seen as a process in which individuals and their parents invest in a stock of embodied capital. In a physical sense, embodied capital is organized somatic tissue. In a functional sense, embodied capital includes strength, immune function, coordination, skill, knowledge, all of which affect the profitability of allocating time and other resources to alternative activities such as resource acquisition, defense from predators and parasites, mating competition, parenting and social dominance. Since such stocks tend to depreciate with time due to physical entropic forces and to direct assaults by parasites, predators and conspecifics, allocations to maintenance such as feeding, cell repair, and vigilance, can also be seen as investments in embodied capital.
One set of investments buys time in the future by lowering mortality
Another set of investments affects future income
Orgs go through nonreproductive phase in which all energy is directed towards embodied capital, followed by a reproductive phase in which energy is divided between repro and embodied capital
Embodied capital and two fundamental life history tradeoffs
Figure 6 illustrates the basic model underlying the analysis. The figure depicts two fundamental life history tradeoffs. The first is the tradeoff between current and future reproduction; the second is the tradeoff between quantity and quality of offspring.
In the first part of the Figure , we begin with lifetime income. By income, I mean the total value of time allocated to alternative activities, such as resource acquisition, child care, rest, etc. At each age, an individuals income will be a function of her embodied capital. Income can be invested directly in reproductive effort, or in embodied capital. Embodied capital, in turn, can be divided into stocks affecting the ability to acquire the resources for reproduction and stocks affecting the probability of survival.
The solid arrows depict investment options. The dotted arrows depict the impacts of investments. Investments in income-related capital, such as in growth, physical coordination, skills and knowledge, affect lifetime income through the value or productivity of time in the future. Investments in survival-related capital, such as immune-function, predator defense, and tissue repair, affect lifetime income through increasing the expected lifespan of earnings. However, an organisms which does not reproduce leaves no descendants. Thus, the optimization problem acted upon by natural selection is to allocate lifetime income among investments in future income, survival and reproduction at each age so as to maximize total allocations to reproduction.
This reproductive effort can be in the form of producing babies but also in the form of investing in their embodied capital. The optimal strategy will be the one that maximizes resources for reproduction over the life course.
The
second part of the figure shows the relationships between investments and
outcomes for two generations. Here,
both the parent and the offspring can invest in the offsprings survival- and
income- related capital. The
optimization problem for the parent is then to allocate investments in
fertility and in embodied capital of offspring so as to maximize the total
lifetime allocations by offspring to their own reproduction (summed over all
offspring). If individuals in each generation allocate investments in own and
offspring embodied capital optimally, then the dynastic fitness of the
lineage is maximized. The
multi-generational decision path is illustrated in Figure 7.
Human Life history phases T24
Menopause
Two alternative theories of menopause
1) Grandmothering
2) Selection favors extension of life past menopause due to the effects of grandparenting and long juvenile dependence, but menopause results from selection on follicle depletion and genetic quality of gametes
Possible effects of investment in embodied
capital and adult survival
Summary of the argument T26
Investments in embodied capital have same age effects in modern times
