51 pages • 1 hour read
Brian Hare, Vanessa WoodsSurvival of the Friendliest: Understanding Our Origins and Rediscovering Our Common Humanity
Nonfiction | Book | Adult | Published in 2020A modern alternative to SparkNotes and CliffsNotes, SuperSummary offers high-quality Study Guides with detailed chapter summaries and analysis of major themes, characters, and more.
Chapters 4-5Chapter Summaries & Analyses
Chapter 4 Summary: “Domesticated Minds”
The authors ask: Could humans be self-domesticated? The idea seems counter-intuitive initially, but as researchers learn more about how self-domestication affects animal cognition, it becomes plausible. The evolution of cooperative communication skills in dogs and bonobos aligns with human cognitive evolution. This hypothesis can be tested with our advanced knowledge of human development and neuroscience.
Belyaev’s experiment with foxes shows that selecting for emotional responses, whether friendly or fearful, shapes animals’ communication skills. Jerome Kagan’s subsequent research on human emotional reactivity has revealed that babies’ responses to new situations can predict their future emotional responses. Highly reactive babies tend to remain reactive into adulthood, while low-reactive babies become calmer adults. This emotional reactivity is linked to the amygdala, a brain region activated by threats. In turn, the psychologist Henry Wellman has explored whether this variation in emotional reactivity affects “theory of mind” development in children. Theory of mind, the ability to understand others’ beliefs and intentions, is crucial for cooperative communication. Wellman found that less emotionally reactive children developed an understanding of false belief earlier than their more reactive peers. The early-stage development of theory of mind is linked to language development, giving low-reactive children an advantage in communication and cooperation.
The authors show how further research has supported this connection between emotional reactivity and theory of mind. Brain regions involved in theory of mind, such as the medial prefrontal cortex (mPFC), temporal parietal junction (TPJ), and superior temporal sulcus (STS), are influenced by emotional reactivity. Studies show that highly reactive individuals have less activity in these areas when feeling threatened, reducing their empathy and cooperative behavior. Conversely, less reactive individuals maintain richer theory of mind and higher tolerance even when provoked. This link between temperament and theory of mind suggests that natural selection could have favored emotional reactivity, shaping our cultural cognition and pointing to human self-domestication. However, this hypothesis faces a challenge: Our cognitive abilities far surpass those of other self-domesticated species like bonobos. The answer lies in self-control, regulated by the prefrontal cortex (PFC), which allows us to override impulsive behaviors and make reasoned decisions.
The authors highlight the longitudinal “marshmallow test,” where children choose between a small immediate treat or a larger reward in the future, and this choice is mapped against later outcomes. The test finds that children who wait tend to perform better academically and socially and have more successful adult lives, linking early self-control and strategic decision-making. Researchers Evan MacLean and Brian Hare adapted this test for animals, finding that species with larger brains and more neurons, like great apes, display better self-control than smaller-brained animals. The book shows how Suzana Herculano-Houzel’s research on neuron density contributes to our understanding of this. As primate brains grow, they pack more neurons without increasing their size, unlike other mammals. This higher neuron density likely explains better self-control. Human brains, which have tripled in size over two million years, have the highest neuron density, contributing to our unparalleled self-control and cognitive abilities. Because humans had modern-sized brains 200,000 years ago but evidence of advanced human behavior doesn’t appear until around 50,000 years ago, another factor must also be at play here. This may be the expansion of social networks, allowing for better technology and larger, denser populations. This might also explain why other hominins with large brains, like Neanderthals, eventually went extinct.
Population density can lead to both innovation and violence. The human self-domestication hypothesis suggests that friendliness in the Pleistocene sparked our technological revolution. Natural selection favored individuals with reduced emotional reactivity and increased tolerance, enhancing cooperative communication and leading to the complex cultural and technological advancements that define modern humans.
Chapter 5 Summary: “Forever Young”
This chapter explores how an increase in friendliness among humans has led to developmental changes that manifest as physical and cognitive traits. Development, the process by which organisms grow and mature, plays a crucial role in these changes. Slight adjustments in the rate or timing of development can result in significant differences in body type and behavior. For example, salamanders can retain juvenile features into adulthood, while young cockroaches are highly social, a trait they lose as they mature. The axolotl salamander, which retains its juvenile gills and does not develop hind legs, exemplifies how development can create different adult forms.
This developmental process can also influence social behavior. For instance, Jean-Louis Gariépy’s experiments with mice bred for friendliness showed that these mice retained juvenile behaviors into adulthood, reducing aggression. Similarly, cleaner wrasse fish that maintain their juvenile mouth shape into adulthood exhibit cooperative behaviors, cleaning parasites off larger fish, a relationship beneficial to both parties.
Dogs and bonobos, like these fish, maintain juvenile behaviors throughout their lives. Dogs, for example, have an extended period of socialization that lasts much longer than in wolves, allowing them to better adapt to new environments and interactions. This extended socialization period enables dogs to develop behaviors related to cooperative communication early on. Similarly, bonobos show juvenile social behaviors, like playful sexual interactions, from a very young age, unlike their chimpanzee relatives.
The retention of juvenile traits and behaviors into adulthood is often referred to as neoteny. This concept is crucial in understanding how selection for friendliness has shaped various species, including humans. In domesticated animals, neoteny is linked to developmental changes in genes that control growth. These changes can have widespread effects, influencing multiple traits simultaneously. For example, a gene involved in bone growth and pigmentation might also affect social behavior. Neural crest cells, a type of stem cell in vertebrate embryos, play a significant role in development. These cells migrate throughout the body, influencing the development of various tissues, including those related to the domestication syndrome. This syndrome includes traits like reduced aggression, changes in physical appearance, and enhanced social behaviors. The influence of neural crest cells extends to the brain, affecting areas involved in social behavior and cognition.
The chapter also examines the relationship between development and hormone levels. For instance, serotonin and oxytocin, hormones associated with social behavior, are influenced by developmental processes. Changes in these hormones can lead to differences in aggression and social interaction. For example, bonobos have lower testosterone levels than chimpanzees, which may contribute to their more cooperative and less aggressive behavior.
The authors conclude the chapter by highlighting how these developmental changes have made humans unique. Our ability to maintain juvenile traits and behaviors into adulthood, combined with the influence of hormones like serotonin and oxytocin, has allowed us to develop advanced social and cognitive skills. These skills have enabled us to create complex social structures and cooperate in ways that other species cannot. This extended development and the associated changes in behavior and cognition are key factors in our success as a species.
Chapters 4-5 Analysis
In these chapters, Hare and Woods explore the concept of human self-domestication and its implications for understanding human cognitive and social development. This approach is significant as it shifts the focus from pervasive views of human evolution as driven by intelligence and strength to one that highlights The Evolutionary Advantages of Friendliness and Cooperation. By examining the parallels between domesticated animals and humans, the authors propose that our success as a species is largely due to increased sociability and cooperation. The self-domestication hypothesis proposed in these chapters posits that the same processes that led to the domestication of animals like dogs and bonobos also shaped human evolution. As such, this section of the book builds on the previous chapters’ discussions of animal-based knowledge and shows how this can be applied to an understanding of human development and behavior. This moves the narrative toward the third theme of Empathy as a Driving Force in Human Interaction. The authors argue that “the human self-domestication hypothesis proposes that friendliness in the Pleistocene is the spark that ignited Homo sapiens’ technological revolution” (87), encapsulating this idea. This suggests that the development of cooperative behaviors was crucial for the technological advancements that set Homo sapiens apart from other hominins. This perspective challenges the conventional emphasis on intelligence alone as the driving force behind human evolution, highlighting the role of social cooperation and communication.
The textual structure of these chapters is notable for its use of comparative studies to build a compelling case for the self-domestication hypothesis. For instance, the marshmallow test adapted for animals, and research on neuron density, provide empirical evidence linking self-control and cognitive abilities to evolutionary success. The discussion of neuron density explains why humans exhibit unparalleled self-control and cognitive skills. This comparative approach effectively demonstrates how evolutionary pressures favoring sociability and reduced aggression led to the development of advanced social and cognitive traits in humans.
Hare and Woods employ various rhetorical and literary devices to convey complex ideas about human evolution and behavior. The use of analogies, such as comparing human cognitive development to that of domesticated animals, helps make abstract concepts more relatable. The authors also use persuasive imagery such as metaphors to draw in the reader: “Domesticating a wolf brain or an ape brain is impressive. But when you domesticate a human brain—this is when the real magic begins” (88). The word choice “magic” imparts a sense of excitement and awe around the extraordinary outcomes of human self-domestication. In this way, the authors draw in their reader and heighten the narrative’s emotional connection.
These chapters introduce a number of sophisticated scientific theories and concepts, building on the scientific foundations of the previous chapters. The authors’ accessible presentation of high-level academic research continues to facilitate their book’s combination of argument and evidence, characteristic of its genre. In particular, the book uses this evidence to underpin its forthcoming consideration of The Impact of Social Behavior on Human History and Progress. The notions of self-domestication, cognitive development, social communication, and evolutionary adaptations are central here. The authors argue that the selection for friendliness extended the developmental period during which social behaviors are learned and refined, as highlighted by the quote, “Selection for friendliness is really selection for an expanded window of social development” (104). This prolonged period of social learning allowed humans to develop sophisticated cooperative behaviors and social skills, crucial for building complex societies. The concept of neoteny, or the retention of juvenile traits into adulthood, is also explored as a key factor in human evolution. This idea is illustrated through the comparison of different species, such as dogs and bonobos, which maintain juvenile behaviors and exhibit advanced social communication.
