Humble Origins
For over 150 M years dinosaurs were firmly established at the top of the food chain, with mammals and other animals surviving in tiny but livable niches. (1) Everything changed some 65M years ago, when an asteroid a few miles wide slammed into the earth, causing wanton destruction. The skies filled with debris and dark soot, a darkness that would block out the sun for over a hundred years and kill over 70% of land-living vertebrates. School kids are familiar with this story, as this event caused the extinction of T Rex along with other dinosaur species. As noted by Max Bennett (2), Our little mammalian ancestors did not know it at the time, but this was to mark the beginning of the era of mammals. With the disappearance of the dinosaur predators, mammals explored new niches, evolved into new shapes and sizes, and claimed spots much higher up in the food chain.
Our direct ancestors were the ones who found refuge in tree forests in Africa some 10M to 30M years ago - the very first primates. Along the way they shifted from being nocturnal to day living, and from a diet of insects to one based primarily on fruit. They lived in groups, were relatively free from predation, and had food in abundance. Most important, primate groups evolved to be unlike those of other mammals.
Group Living, with a Twist
Modern primates exhibit varied and complex social behaviors, which are foundational to how humans interact with one another. How did such behaviors evolve starting with early primates?
Early primates had a diet primarily based on foraging fruit in treetops. This enabled them to have easy access to food, and limited competition from other species. Easy access to abundant food gave primates an abundance of calories, energy which could be used on bigger brains and bodies. It also gave early primates free time - a rarity as most animals have no choice but to spend the bulk of their active time foraging and eating. The combination of abundant energy and free time opened the door to a new evolutionary option in climbing up the social hierarchy of the group and tipping the scales to their advantage (as individuals higher up in the hierarchy are better fed and mate more often, leading to more numerous and healthier offspring). Instead of using energy to develop bigger bodies and muscles to fight their way up, they could instead evolve bigger brains and get ahead by playing politics. An astute primate could use its free time to socialize, build alliances, and get the lay of the land.
This might have created a new evolutionary arms race for political savvy. Primates who were adept at currying favor and gaining allies would have better survival odds and more offspring - this put pressure on other primates to up their political game to keep up and gain an edge. Robin Dunbar, Frans de Waal, and other scientists theorize that the growth of the primate brain was primarily driven by social demands, with Dunbar noticing a correlation between primate group size and the size of their neocortex. (3)
Primate Social Improv
Belonging to a group brings enhanced security and protection from predators. It also requires navigating the social complexities associated with living in a group and dealing with competition and occasional conflicts. Primate groups are typically governed by a hierarchy of power led by an alpha individual, usually male. Dominance relationships are not static - they provide stability for a time, but are subject to change through fights, gaining new allies, or manipulating opponents. This flexibility helps the group adapt to changing circumstances and reflects primates' creativity in devising social arrangements and avoiding unnecessary violence. Alpha males can lose their spot due to accidental injuries, direct fights, or switching alliances. When this happens, a dominant male is often ostracized and left to fend for themselves. After a time, they may curry favor again with the group by changing their ways - grooming and playing with the young, having a calm demeanor and being submissive to other males. A formerly fierce alpha male can turn into a cuddly, humble, and wise member of the group. This example and others clearly show that primates are highly skilled at adapting to changes in social dynamics, and devising creative solutions when circumstances demand it.
Primates keep track of evolving relationships within their group and are eminently aware of the hierarchy of individuals and families around them at any given time. As stated by Agustin Fuentes (4), if you throw a banana on the ground between two monkeys, nine times out of ten they won't both go for it - after a quick look at each other to determine who is in the more powerful position, one will back away, ceding the banana. Primates have made social lives and social flexibility and innovation central to how they deal with challenges and pressures from the environment. This level of political savviness required primates to infer what others want, so as to figure out whom to cozy up to and how. As noted by Max Bennett, only by understanding intent can individual primates figure out who is likely to become more powerful in the future, whom to make friends with, and whom to deceive (it is no accident that this feels like the soap opera plot of the once popular "Survivor" show!). This ability to infer intentions, feelings, personality, and knowledge of others represented an intellectual feat - what scientists refer to as "theory of mind". (5)
Learning By Imitation
Studies have shown that similar to humans, primates are able to learn new skills through observation. The ability to learn through observation is common amongst animal species; but is typically limited to selecting an already known behavior or skill to match a specific situation. In contrast primates are able to learn entirely novel skills by observation - by learning the intent of a complex skill and enabling them to filter out any extraneous or unintentional movements and focusing only on the relevant ones. This also enabled individuals to stay focused and committed to learning for long periods of time. These combined factors helped propagate newly discovered skills through a group and on to the next generations. This is why for instance primates are uniquely good tool users compared to other animals, with a wide variety of unique tool-using behaviors across different groups and environments. This helped primates adapt and survive in new or changed environments.
What's For Dinner?
Early primates had a diet primarily consisting of fruit - with fruit assumed to be abundant at the time. A fruit-based diet does present unique challenges however: there is a small window of time when the fruit is ripe and has not fallen off the tree. (6) Some fruit such as bananas have limited animal competition due to their protective skin, others such as figs are easy pickings for a wide array of other animals and tend to disappear quickly once ripe. All this presented a dilemma for early primates - they had to keep track of a variety of fruit in the forest and know which area would have fruit ripe for the taking on any given day. This required early primates to do some planning - such as picking nesting spots close to fruit such as figs that disappear quickly, rising early in the morning to forage competitive fruit, knowing when to pick less competitive fruit before it over ripened and fell to the forest floor. Scientists have shown that monkeys and other primates are able to make decisions in anticipation of their future needs, whereas most other animals will seek immediate gratification. Several have theorized that this ability is another manifestation of the theory of mind - in this case the primate imagines the wants of its future self, as opposed to the want of others. Be that as it may, our human ability to make decisions for faraway or abstract goals was seemingly inherited from tree faring primates.
Nurturing the Young
The ability to succeed as a group starts at birth. Mammals are born in various states of readiness, but all infants are highly dependent on their mom for milk and protection for weeks, months, and in some cases years. Mothers have an extraordinary strong bond with their infant and will typically go to any length to care for their offspring.
Primates have infants that rely on mom for a long time, typically several years, with some apes staying with their mom for up to eight years. The long period is due to two key factors: Primates have large brains that take a while to develop, and primates have complex social lives - young primates need quite a bit of time to learn the ropes as a result. Mom does the bulk of the work, but other members of the group are also vested in seeing junior make it to adulthood and help raise the young from early on. Years of evolution have resulted in primates having a deep drive to nurture and care for the young.
Getting Ahead and Getting Along
Primates survive far better as a group than as isolated individuals - security is a fundamental reason for individuals to commit to their group. In addition, groups that are cohesive will tend to outperform their peers (7). Group success require individuals to subordinate their own selfish interests to those of the group when needed. All animals exhibit altruism towards kins (with clear evolutionary benefits in helping to propagate their genes), and most animals exhibit a form of reciprocal altruism - helping a peer with the expectation to be helped in return ("I'll scratch your back if you scratch mine").
Primates have been shown to exhibit additional forms of altruism, such as evidence of females adopting and caring for unrelated orphan infants, or males risking life and limb on patrol missions in spite of having no offspring or kins in the group. (8) A reasonable hypothesis is that the flexibility and complexity of primate social groups enables a wider variety of ways for groups to adapt and grow, and for individuals to gain recognition.
In order to thrive, primates have to figure out how to get ahead while getting along. Competition stimulates flexibility and innovation, while the sense of community preserves the wellbeing of the group. Our human competing drives to gain status/recognition, and to belong have very deep evolutionary roots. They are not traits unique to humans, though humans added a level of sophistication and scale as we shall discuss later on. (9) (10)
(1) Much of this article/blog entry is based on A Brief History of Intelligence: Evolution, AI, and the Five Breakthroughs That Made Our Brains, Chapters 15 through 18, by Max Bennet, The Creative Spark: How Imagination Made Humans Exceptional, Chapter1 and 2, by Agustin Fuentes, and Human Evolution. Our Brains and Behaviors, Chapters 1 through 3, by Robin Dunbar.
(2) See note (1) above
(3) Interestingly in most mammals and birds monogamously pair bonded species have significantly larger brains than species that are not monogamous. The assumption is that long lasting monogamous bonds are cognitively much more demanding than casual relationships - as the individuals have to take into account their partner in everything they do and arrive at successful compromises. Successful monogamy takes work!
(4) See note (1) above
(5) See Evolutionary biology: Great apes 'know when wrong decisions are made' | Nature | News | Express.co.uk
(7) Biologists refer to this as "group selection" - the fact that natural selection can operate at the level of groups and favor traits that are beneficial to the group as a whole, even if those traits can be disadvantageous to individual members of the group. The idea was first proposed in 1962 by the English zoologist V.C. Wynne-Edwards in his book Animal Dispersion in Relation to Social Behaviour. He was ahead of his time and his ideas were widely criticized and largely dismissed by evolutionary biologists for several decades. In recent years there has been a resurgence of interest in the concept of group selection to explain cooperation and altruistic behaviors which are difficult to explain through the sole lens of individual-level selection. The biologist Edward O. Wilson was a proponent, his books are listed in the bibliography section of the web site.
(8) True altruism seen in chimpanzees, giving clues to evolution of human cooperation | Science | AAAS
(9) See the section on Values - A Darwinian Social Contract in chapter 3 of Geoffrey Moore's book The Infinite Staircase for an interesting discussion of the fact that some of our values have deep mammalian roots.
(10) The upcoming webinar by Jenny Tung, professor or biology and evolutionary anthropology at Duke University, should shed additional light for those of you interested A Proper Study for Mankind: Understanding the Human Condition through the Lens of other Primates | NIH Office of Intramural Research