Book Summary: “Lifeways of Hunter-Gatherers” by Robert Kelly

Title: Lifeways of Hunter-Gatherers: The Foraging Spectrum
Author: Robert Kelly
Scope: 4 stars
Readability: 3.5 stars
My personal rating: 5 stars
See more on my book rating system.

Topic of Book

Kelly explains how Hunter Gatherers live, with particularly emphasis on how they acquire their food and the impact this has on other parts of their lifestyle.

If you would like to learn more about long-term human history, read my book From Poverty to Progress: How Humans Invented Progress, and How We Can Keep It Going.

My Comments

This is the best book that I have read about how Hunter Gatherers, and how they acquire enough food to survive and reproduce.

Key Take-aways

  • The previous belief that Hunter Gatherers can acquire abundant food with little effort is wrong. They have to work hard to get enough food to survive, and they often experience long periods of hunger.
  • Most Hunter Gatherer behavior can be explain by the quest for the most energy-efficient food source within their local environment.
  • Hunter Gatherers are extremely good at extracting the maximum amount of food with the minimal level of effort from the local environment. Their foraging behavior is so rational that it can be modeled mathematically, much like economists model prices.
  • Their knowledge passed down from previous generations enables them to focus their efforts on the most energy-efficient food sources, ignoring less efficient foods.
  • With every encounter of a possible food source, they calculate whether it should be exploited or whether to wait for a more energy-efficient food source later
  • Fish and large game have high energy pay-offs, but more likely to lead to failure. Plants have less energy pay-off, but it is more reliable.
  • Hunter Gatherers in Tropical latitudes tend to have a plant-based diet, while those in Temperate and Arctic latitudes focus on hunting and fishing.
  • Hunter Gatherers bands tend to have a size of about 25 people.
  • Virtually all have a strict gender divide with men hunting and women gathering wild plants.
  • They are very focused on meat, likely because they cannot get fatty acids any other way.
  • They have two types of mobility:
    • Movement between camps, often done seasonally
    • Daily movement out to acquire food, and then back to camp before dark.
  • After each camp movement, they start eating the nearest and most energy-efficient food sources. With each day, they walk further from the camp until they reach the maximum distance that can be walked out-and-back in one day.
  • They typically time their movement between camps for just before their present camp runs out of energy-efficient food.
  • Their knowledge passed down from previous generations tells them where the most energy-efficient food is likely to be at that time of year. If it is within one day’s travel they go there.

Important Quotes from Book

“Evolution sees the individual, rather than the group, as the primary locus of selection. Stated most generally, selection operates on variability with a population and favors individuals whose behavior enhances the opportunity to increase fitness”

Thus, behavioral ecologists are interested in the mean fitness of different behavioral choices rather than the fitness of particular individuals. To accomplish its goals, behavioral ecology employs two assumptions: methodological individualism and optimization.

“The optimization assumption focuses on (1) the behavior of individuals making decisions about (2) the available set of behavioral options using (3) some currency (energy, measured as calories, dominates studies that permits and benefits of each option is evaluated, within (4) a set of constraints that determines the options and their benefits. In hunter-gather studies, optimization approaches focus on several questions relevant to foraging, such as: When, where, and how long to forage? How many should forage together? How many should live together? Which food items should be selected? Who should be shared?”

“Evolutionary theory suggests that the goal of a forager should be to forage optimally, that is, to maximize the net rate of food harvest”

Primary plant production and intensity of solar radiation of a location predict the dependence on plant food versus hunting for animals. Hunter-gathers in the tropics depend more on gathering plants, while in the temperate and arctic, they rely more on hunting animals. “It seems that aquatic resources are used when there is insufficient edible plant food.” Food storage also dramatically increases in cold climates

The Diet Breadth Model reaches several nonintuitive conclusions, the most important of which is that aresource’s abundance alone cannot predict whether it will be used. No matter how frequently the Ache encounter a resource with a return rate below 870 kcal/hr, they are not expected to harvest it. More specifically, the model points out that the decision to include a resource depends on the abundance of higher ranked resources.

Seeds and roots, normally have lower return rates than game. In general, the larger the animal, the higher the return rate on energy invested. Fishing has the greatest return, except for the largest animals

Foragers have a fairly strong division of labor in which women gather more reliable foods, such as seeds and tubers (along with some small game and shellfish), while men hunt less reliable large game.

Charnov found that to maximize the overall foraging return rate, foragers will move out of a resource patch when the rate of harvest in that patch reaches the average rate for all potential resource patches, with travel time included, and not when the return rate in the current patch has fallen to zero. This is the Marginal Value Theorem.

“All foragers value meat highly… Animals that generally have little body fat are often considered secondary resources or even starvation food.”

“For the most part, humans eat the reproductive parts of plants (nuts and seeds) or their stored carbohydrates (tubers, rhizomes, bulbs, and corns). In areas of high primary biomass (such as tropical forests), plants invest more energy in structural maintenance and the capture of sunlight, relative to reproductive parts or storage, resulting in primary production (PP) that is large inedible or difficult to reach… In areas of low primary biomass, plants invest less energy in structural maintenance and growth and relatively more in reproductive tissue (seeds). Therefore, primary biomass is, in general and within limits, inversely correlated with the effective abundance of edible plant-food. It is also inversely related to faunal abundance and distribution since animals in high primary biomass settings tend to be small (so they can feed in tree tops) or, if large, few in number and widely spaced. Coupled with ET, primary biomass provides a rough relative measure of the potential return for foraging in a given environment.”

Although hunter-gatherers frequently do move campsites on the basis of foraging conditions, they also take into account such things as firewood, tree boughs for bedding, shelter, water, mosquitoes, and how dirty a camp has become). The location of other groups of people can also condition movements, either by attraction or repulsion, depending on the nature of the relationship.

Deserts present a special problem in this regard. Humans need water daily, and it is heavy – and difficult to transport. It’s not surprising, then, that water, more often than food, determines a camp’s location in desert.

As overall habitat quality declines, foragers, whether dependent on hunted or gathered foods, move shorter distances more frequently.

Centralplace foraging models suggest that the farther a forager travels from camp, the more restricted his or her choice of resources becomes. Foragers can only take high return rate resources at long distances from camp; hence, they can harvest a greater diversity of food close to camp.

The effective foraging distance for plants is shorter, in general, than it is for large game since many plant foods provide lower return rates than those of large game. Since large game is usually procured by men, women’s foraging should normally determine when and where camp is moved.


“Sedentism is a product of local abundance in a context of regional scarcity… sedentary villages will be associated with control of a resource-extraction point”


Oswalt also divided tools into simple and complex. Simple tools have parts that “do not change their position relative to each other during use” (e.g., a weighted digging stick5), whereas complex tools do (e.g., the toggling harpoon we just mentioned, since the head detaches from the shaft during use). By dividing a food-getting inventory’s total number of technounits by the total number of subsistants, Oswalt obtained a rough measure of the overall elaborateness of a particular group’s technology. Theoretically, a technology’s number of subsistants and their elaborateness are independent of one another  but, in reality, fragers with complex tools tend to have many such kinds of tools.

“In general, technological innovation is most likely under conditions where risk is high because that is where people have the most to gain from effort invested in new technologies. As an element of risk increases, but perhaps especially the second (the severity of coming home empty-handed), technology must become more reliable.”

Food-getting technology aims to reduce the search or harvesting cost of resources.

Search costs are generally reduced through soft technology, by knowing where plants or game are likely to be found at certain times of the year under different weather conditions. This requires an encyclopedic knowledge of animal behavior and plant responses to climate.

Conversely, food harvesting and processing costs are generally reduced through hard technology.

Tools associated with the acquisition of “risky” resources must be reliable by being overdesigned and/or maintainable by being quickly repairable through interchangeable parts. Both efforts result in complex and elaborate tools. Technology enters the food-getting equation as an up-front cost in terms of raw material procurement and construction and a continuing cost of maintenance.

This technological model leads to three insights: when technology changes, it is expected to change (a) quickly, because the decision to invest in a new technology is normally of the either/or type; (b) pervasively across a population as the benefits of a new technology become obvious and its manufacturing specification known; and (c) usually irreversibly, because it alters knowledge of the net return that is possible with a new technology, and maintenance/construction becomes embedded in other activities and downtime.

But to invent something, one must have ideas, and since ideas are generated by people, the more people who interact with one another, the more ideas are generated. Large populations increase the rate of new ideas… new technologies increase the net return, and if that translates into increased population growth, then it follows that new technologies set off a positive feedback loop and, hence,

increasingly rapid technological change.

If you would like to learn more about long-term human history, read my book From Poverty to Progress: How Humans Invented Progress, and How We Can Keep It Going.

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