For Intro to Anthropology, after finishing chapter 3, we read Chapter 4, “Primates: Our Closest Relatives.” Next: Chapter 5 on Bipedalism.
Key Concepts: Primate Diversity and Human Evolution
- We ARE primates, not evolved “from” them. Carl Linnaeus classified humans in the primate order based on shared anatomy, and he did it as a creationist three decades before Darwin was born (108)—grouping us with apes and monkeys was never an evolutionary trick.
- Primates trade smell for sight. Most large primates are diurnal (96), with reduced snouts and forward-facing eyes giving stereoscopic 3D vision (90)—evolution works through tradeoffs, not free upgrades.
- Grasping hands and opposable thumbs let primates manipulate objects, pick out insects, and—in humans—write, hold tools, and text.
- Extended childhood and alloparenting. Primates depend on caregivers for years (93), often including alloparents beyond the biological mother and father (91-92); this long dependency is what makes learned behavior so central to primate—and especially human—life.
- No single primate body plan. Body size runs from 1-ounce lemurs to 350-pound gorillas (88); locomotion ranges from human bipedalism to quadrupedalism to brachiation (89).
- Enormous social diversity. Female-dominated lemurs, male-dominated chimpanzees (85), egalitarian groups, and solitary orangutans (100-101)—there is no one “natural” primate social pattern.
- Avoid the “species-level trap.” Barbara J. King warns against summing up a whole species in a single behavioral label; gentle chimpanzees and aggressive bonobos both exist.
- We are equally related to chimpanzees AND bonobos. Our most recent common ancestor with both dates to roughly 6 million years ago; the chimp-bonobo split came afterward, so you cannot cherry-pick one as the human model.
- Contemporary primates are not frozen ancestors. Chimpanzees today are not the chimpanzees of 5 million years ago—every lineage has kept evolving, including ours.
- Human sexual dimorphism is shrinking. The male-female size gap has narrowed from roughly 10-15% to about 8-12% in a century, tracking changes in nutrition and activity—evidence that social factors shape biological traits even within one species.
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We Didn’t Evolve From Primates—We ARE Primates
When your friends ask “How did we evolve from primates?” the correct response is: we didn’t evolve from primates—we are primates. Right now. This seems like something a cruel person would have done to us, lumping humans together with lemurs and chimpanzees. But the person responsible was Carl Linnaeus, a Swedish naturalist who lived most of the 18th century (1707-1778) and gave us that Kingdom-Phylum-Genus classification system we all had to memorize.
Here’s what’s interesting about Linnaeus: he was a firm creationist (108). Darwin wasn’t even born until 1809—Linnaeus had been dead for 30 years. So Linnaeus believed he was classifying God’s creation according to divine design. It turns out his classification system worked beautifully for evolution anyway. But grouping humans with primates wasn’t an evolutionary trick. Linnaeus did it based on shared anatomical features he could observe.
Why Do Anthropologists Study Primates?
There are two main reasons. First, we’re looking for clues about evolution—not searching for a “missing link,” but trying to understand what our most recent common ancestors might have been like. Second, we’re looking for parallels with contemporary human behavior: mating patterns, social organization, tool use.
But there are two dangers when observing non-human primates. The first is anthropomorphism (87)—assuming “they’re just like us!” We dress chimpanzees in clothes and have them do tea parties, projecting ourselves onto them rather than seeing them for what they are. The second danger is the opposite: “They have nothing to do with us.” That’s also wrong. There are real similarities, which is why Linnaeus grouped us together. The challenge is navigating between these extremes.
What Makes Primates Different?
Linnaeus classified humans as primates because of derived traits—characteristics that emerged in the common ancestor of primates but weren’t present in earlier mammals. For the large primates especially—monkeys, apes, and humans—several traits stand out.
Most large primates are diurnal, active during the day (96). We traded smell for sight—a dog has a much greater range of smell than humans, but primates developed forward-facing eyes with stereoscopic 3D vision (90). We have grasping hands with opposable thumbs, which is what lets you write, hold tools, or text. And we have extended childhoods with long periods of dependency (93), relying on alloparents—caregivers other than biological parents—to help raise young (91-92).
This extended learning period correlates with large, complex brains relative to body size. We don’t come out ready to survive. We have to be taught how to walk, how to eat, how to do everything. The importance of learned behavior in primates is enormous—which is why you’re still in school after all these years.
So Many Primates: No Single Pattern
I once asked students to write about their most recent anthropology course, explaining what they liked best and what they liked least. One student chose “Primates and Primatology” and wrote the same thing for both: “So many primates.” It certainly does seem like primate species are an ever-proliferating category. As Jonathan Marks has documented, in the 1980s there were fewer than 200 primate species; primatology now acknowledges over 400. Somewhat ironically—and sadly—this proliferation is concurrent with habitat loss and endangerment for many primates. As Marks notes, species designations are bio-political units.
One thing you notice about primates is how difficult they are to categorize. Body size ranges from 1-ounce lemurs to 350-pound gorillas (88). Locomotion varies from habitual bipedalism (humans) to quadrupedalism to brachiation—swinging by arms (89). Diet is flexible; larger primates tend to be omnivorous, and their diets shift by location and season (90). We once thought we could sort primates by whether they ate mostly vegetation, fruit, or insects—but it turns out many shift between these month to month across the year, so they are even more flexible than we assumed.
Most importantly, there’s tremendous social variability. Some groups are female-dominated—among lemurs, aggressive females run things. Others are male-dominated; chimpanzees are famously so (85). Some are relatively egalitarian with no clear dominance hierarchy. And some primates are loners—orangutans are famously solitary, with males and females staying far apart (100-101).
Mating patterns vary just as much: one male with multiple females, multiple males with multiple females, monogamous pairs, solitary individuals. There’s no single “primate mating pattern.”
Barbara J. King and the “Species-Level Trap”
Anthropologist Barbara J. King urges us to avoid what she calls the “species-level trap”—the tendency to characterize an entire species by a single behavioral pattern. As she writes in “Humans And Other Animals: A Voice From Anthropology”: “You’ve heard the claims about chimpanzees and bonobos? Chimpanzees are the male-violent, make-war apes, whereas their close cousins the bonobos are female-empowered and sexy-pacific. Don’t believe it, at least not in this overly-simple form. Gentle chimpanzees and feisty bonobos exist, as do apes who one day are kind and the next cruel, shaped (as are we humans) by some combination of how they were raised, their day-to-day social encounters and their genetics.”
This matters. If somebody tells you “we live in a male-dominated society because of our primate heritage,” the correct response is: primates show all different models. As MacKinnon and Fuentes put it, there is no one generalized primate pattern in nature but a variety of patterns sharing some common themes. You can’t cherry-pick one species and claim it represents primate nature.
From Lemurs to Great Apes
The wet-nosed primates (strepsirrhines) include lemurs—cute, but evolutionarily distant from humans. Among the dry-nosed primates (haplorhines), the platyrrhines or “New World” monkeys live in Central and South America. (Anthropologists increasingly avoid “New World” and “Old World,” which name the Americas from a European vantage point.) They’re all arboreal tree-dwellers, generally smaller, with prehensile tails that can grab branches and little sexual dimorphism. How did they get to the Americas? Almost certainly by drifting from Africa on eroded patches of forest—floating rafts of vegetation that broke off at river mouths. The continents were closer together then, and these monkeys evolved separately in the Americas for 30-40 million years.
The catarrhines or “Old World” primates in Africa and Asia are much closer to humans evolutionarily, branching from the platyrrhine line around 25 million years ago. They include baboons and mandrills—larger, often ground-dwelling, no prehensile tails. More serious primates.
The hominoids include apes and humans (99). The easiest way to tell an ape from a monkey? Apes don’t have tails. When people at zoos point at chimpanzees and say “look at that funny monkey”—they’re wrong. They’re apes. Apes and humans also share the Y-5 molar cusp pattern—the same basic dental architecture.
Our Closest Relatives: Equally Related to Both
Genetic evidence shows orangutans diverged 9-13 million years ago, gorillas 8-12 million years ago, and our most recent common ancestor with chimpanzees and bonobos was around 6 million years ago. After that, chimps and bonobos split from each other. This means humans are evolutionarily equidistant from both species—don’t believe anyone who claims we’re closer to one than the other. These divergences weren’t instant: lineages separate, sometimes rejoin and hybridize, and split again over long stretches of time.
Sexual dimorphism varies widely across primates. Gibbons show minimal difference between males and females (100). Orangutan males can be twice as large as females. Gorilla males run about 50% larger—though even this varies by group, between mountain and lowland gorillas. Humans? Males are on average about 8-12% larger than females—similar to chimpanzees and bonobos.
Interestingly, 50 years ago we would have said human males were 10-15% larger than females. The difference has decreased, likely due to better nutrition and more physical activity for girls and women—where some families once fed boys more protein to “prime them for work” and gave girls more carbohydrates. This shows how social factors can influence biological traits even within a single species over just a hundred years. And note that the gap is an average: variation runs across species, across groups, and across individuals, so it is not that every male is larger than every female.
Chimpanzees and Bonobos
Chimpanzees (Pan troglodytes) are known for aggressive behavior and male dominance. They also make and use tools and pass on traditions (102)—Jane Goodall was among the first to observe a chimpanzee stripping a stick to fish termites from a mound. When people want to claim humans are “naturally” aggressive, they often point to chimpanzees. Take that with a grain of salt: some of the earliest chimpanzee studies, Goodall’s included, were conducted as habitats shrank and researchers provisioned the animals with food, which altered their societies. Chimpanzees can be aggressive, and have been observed committing what looks like intergroup and intragroup killing—but the conditions of observation matter.
Bonobos (Pan paniscus) are known for something different: using sexual activity to diffuse tension between individuals and groups (101), especially around food. They have a broad, largely non-reproductive sexual repertoire involving all combinations of sexes. Bonobos show aggression too, but have not been observed committing the lethal violence documented in chimpanzees. When people want to claim humans are “naturally” peaceful and sexy, they point to bonobos.
One curious wrinkle: both signature behaviors intensify in captivity and boredom—bored bonobos tend toward sex, bored chimpanzees toward fighting—which raises the question of how much either tells us about life in the wild. The larger point holds: we’re equally related to both species. You can’t cherry-pick the one that supports your preferred story about human nature. For more on how human-primate connections and the concept of ethnoprimatology complicate simple readings of primate behavior, see the 2021 lecture on that topic.
Frequently Asked Questions
Did humans evolve from monkeys or apes?
Neither, in the way the question implies. Humans did not descend from any living monkey or ape; we share common ancestors with them. We are ourselves apes—members of the hominoid group—and our most recent common ancestor with chimpanzees and bonobos lived around 6 million years ago. Living primates are cousins, not ancestors.
Why did Linnaeus classify humans as primates if he didn’t believe in evolution?
Linnaeus was a creationist who died in 1778, three decades before Darwin was born. He grouped humans with apes and monkeys because of observable shared anatomy, believing he was describing God’s design. His classification later proved useful for evolutionary theory, but that was not his intent (108).
Are humans more closely related to chimpanzees or bonobos?
Equally related to both. Humans share a common ancestor with the chimpanzee-bonobo line; chimpanzees and bonobos only split from each other after that shared ancestor. So neither species is “closer” to us, and neither can be cherry-picked as the model for human nature.
Does our primate heritage mean humans are naturally aggressive or male-dominated?
No. Primates display female-dominated, male-dominated, egalitarian, and solitary social organizations, plus every kind of mating pattern. Barbara J. King calls the move of summing up a species in one behavioral label the “species-level trap.” Primate diversity reveals human possibilities, not a single biological destiny.
Why is human sexual dimorphism decreasing?
The male-female body-size gap has narrowed from roughly 10-15% to about 8-12% over the past century, likely because of more equal nutrition and physical activity. It is a clear case of social factors shaping a biological trait within a single species in a short time.
Continue Your Journey
For how human evolution proceeded from our primate ancestors, see the next chapter on Human Origins. For more on human biological variation and why race is not a valid biological category, return to Biology and Power. For the concept of ethnoprimatology and how human presence shapes what we observe in primates, see Human-Primate Connections. Explore the Human Origins hub for more on evolution and anthropology. Also see Animals Are Us for more on human-animal relations and multispecies anthropology.