Chapter 15: The Arms Race for Political Savvy

Core Idea

After the asteroid impact about sixty-six million years ago, which killed over 70 percent of land-living vertebrates, small mammals spread into the empty niches. (The book calls it the Permian-Triassic extinction. The extinction at that date is usually called the Cretaceous-Paleogene extinction.) Our ancestors moved into the trees of Africa, became day-living fruit eaters, lived in groups, and grew brains well over a hundred times their original size. Bennett backs the social-brain hypothesis: primate brains grew because of the demands of primate social life. Primate groups are special because rank depends on political power as well as physical power. A fruit diet gave early primates spare calories and spare time. They spent both on politics, which started an evolutionary arms race for political savvy. The mental skill underneath that politics is theory of mind.

The part opener (“Your brain 15 million years ago”) shows a monkey on a rock touching its own reflection in water. This points to the theme of the part, which is modeling one’s own mind.

Frameworks Introduced

• The social-brain hypothesis (Nicholas Humphrey, Frans de Waal, Robin Dunbar; 1980s–1990s):
  • Claim: primate brains grew because of the social demands of stable mini-societies, not the ecological demands of jungle life.
  • Test: Dunbar compared neocortex size (relative to the rest of the brain) with social-group size across primates. The bigger the neocortex, the bigger the group.
  • Figure 15.2 plots mean group size against neocortex ratio on log scales, with a dotted trend line. Lemurs sit low (ratio about 1.5, groups under 10). Macaques sit near ratio 2.6 with groups of about 40. Chimpanzees sit near 3.2 with groups of about 50–60. Humans sit at about 4 with groups of about 150. Gorillas fall well below the line (ratio about 2.6, groups under 10).
  • Failure mode: the correlation does not hold for most other animals. A buffalo in a thousand-member herd does not have a much bigger brain than a solitary moose. So group size alone is not the driver; the type of group is.
• The evolutionary tension between the collective and the individual:
  • Group living helps animals avoid predators. One antelope that spots a lion cues the whole herd.
  • Group living also creates competition for food and mates, and fights waste energy.
  • Group-living animals reduced this cost in two ways. First, they evolved signals of strength and submission instead of real fights (locking horns, baring teeth; dogs rolling over, deer lowering heads). Second, they kept rigid hierarchies.
• The four common social structures found in mammals (book’s table):

	Solitary	Pair-bonding	Harems	Multi-male groups
Members	Independent	One male, one female	One male, many females	Many males, many females
How they live	Live mostly independently in adulthood	One male and one female live and raise children together	A single dominant male lives with a group of females who have their own hierarchy	Separate male and female hierarchies
Examples	Tigers, jaguars, moose	Red foxes, prairie voles, giant otters, pygmy marmosets	Mongolian camels, fur seals, gorillas	Lions, hippopotamuses, lemurs, chimpanzees, baboons, macaque monkeys

• The arms race for political savvy:
  • When to use: to explain why primate brains, and especially the neocortex, grew so fast.
  • How: fruit picked in treetops gave easy calories (energy for bigger brains) and free time. Instead of growing bigger muscles to fight to the top, primates could grow bigger brains to politick to the top. Any primate with better tricks for gaining allies had more babies, which pushed others to get smarter too.
  • Why it works: rank pays. Higher-ranking monkeys get first pick of food, grooming partners, mates and resting sites, have more children, and die less often from disease.

Key Concepts

• Theory of mind: inferring the intent and knowledge of others. Bennett argues it was absent in early mammals and emerged in the human lineage with early primates (or at least by early apes).
• Machiavellian apes: Menzel’s chimpanzees, who deceived each other and countered the deceptions.
• Grooming as politics: grooming time correlates with group size, not body size. Monkeys keep specific grooming partners for long periods, even lifetimes.
• Explicit social hierarchy: vervet dominance is consistent across contexts and transitive (if A submits to B and B to C, A submits to C), and it can last for generations.
• Hierarchy of families: a female ranks by her family; a daughter inherits her mother’s rank. A frail juvenile from a powerful family can scare off a bigger adult from a lower family.
• Allyships: in about 20 percent of aggressive displays, nearby monkeys join in. About a third of the helpers are not family. Recruiting unrelated allies predicts rank, and hierarchy reversals happen most often when a monkey fails to recruit allies.
• Reciprocity and trust: if A grooms B, B is more likely to defend A later. Chimps let an experimenter give a better snack to another chimp (who might share) only if that chimp is a grooming partner.
• Reconciliation: after fights, monkeys hug and groom former opponents and spend double the usual time with the opponent’s family.

Mental Models

• Think of a primate troop as a political system, not a pecking order of strength. Rank depends on family, friends and alliances.
• Use spare free time plus spare calories to explain where costly brain growth comes from. Primates today spend up to 20 percent of the day socializing, and giving them easier food makes them socialize more.
• Think of political skill as impossible without theory of mind. You can’t know whom to befriend, whom to fear, or whom to deceive without inferring what others want and know.
• Test theory of mind by asking whether an animal tracks what others know, not only what they want. Belle sitting on the food was an attempt to manage Rock’s knowledge.

Anti-patterns

• Assuming grooming is about hygiene: that was the view in the first half of the twentieth century. Grooming tracks group size, not body size, and poorly groomed monkeys don’t groom themselves more.
• Assuming primate hierarchies work like other mammals’: in most mammals the strongest, biggest and toughest win. In primates, a weak member of a strong family or a well-connected low-ranker can outrank a stronger animal.
• Assuming any group-living animal needs a big brain: the buffalo-versus-moose comparison shows it doesn’t.
• Assuming dogs read human knowledge: a dog that saw two treats hidden, one without the trainer present, runs to either spot equally when told “Get the treat”.

Rules of Thumb (author’s wording)

• “the bigger the neocortex of a primate, the bigger its social group.”
• For primates, “it is not only physical power that determines one’s social ranking but also political power.”
• Primates found that “instead of spending energy evolving bigger muscles to fight their way to the top, they could spend energy evolving bigger brains to politick their way to the top.”
• Free time is extremely rare in the animal kingdom.

Worked Example

Emil Menzel’s chimpanzees, Belle and Rock (1970s). Menzel was testing chimpanzee spatial memory in a one-acre forest, inspired by Tolman’s work on mental maps in rats.

1. Menzel hid food and showed the spot to Belle, a subordinate female. At first she alerted the group and shared.
2. Rock, the dominant male, took all the food for himself. After a few times, Belle stopped sharing.
3. Belle sat on the food and uncovered it only when Rock was far away. Rock learned this and pushed her off.
4. Belle waited until Rock looked away before going to the food. Rock then pretended to look away, and ran to the food when she moved.
5. Belle led Rock in the wrong direction. Rock caught on and searched in the opposite direction from where she led him.
6. Each move shows that both chimps understood the other’s intent and knew they could change the other’s beliefs.

Related tests point the same way. Apes pick the box an experimenter marked on purpose and ignore one marked by a dropped pen. Chimps return to a person who was unable to give food rather than one who was unwilling. Chimps who tried opaque and see-through goggles ask for food from the human wearing the see-through pair. In a 2003 playback study, baboons ignored a high-ranker’s dominance call followed by a low-ranker’s submission call, but stared at the speakers when the order of rank was reversed.

Key Takeaways

1. Primate brain size tracks social-group size, and within primates the type of group matters more than group size alone.
2. Primate rank depends on political power: family, allies, grooming partners and reconciliation.
3. A fruit diet gave early primates spare calories and spare time, which they spent on politics.
4. This started an arms race in which better politicians had more offspring.
5. The skill under all this politics is theory of mind, the inference of others’ intent and knowledge.

Connects To

• Figure 15.1 (tree of mammals): from the first placental mammal, branches lead to Xenarthra, Afrotheria, Ferae (lions, tigers, dogs, raccoons), Ungulata (horses, sheep, pigs, deer, whales, dolphins), bats, rodents, and the first primates. The primate node splits into lemurs, monkeys and apes (chimpanzees, gorillas, humans). Rodents are the closest group to primates in the figure.
• Ch 10–14 (Breakthrough #3, Simulating): early mammals could already simulate and build mental maps; Menzel built on Tolman’s rat mental-map experiments.
• Ch 16: explains how primate brains do theory of mind.
• Ch 17: theory of mind repurposed for imitation learning and tool use.
• Ch 18: the ecological-brain hypothesis is the rival explanation, and Dunbar says the two fit together.