evolution

Domestication of Humans: Speciation?

The fossil record continues to grow. And with it, so does the contradiction at the heart of the study of human evolution. Each year brings new hominin fossils—jaws, skulls, infant mandibles—that confuse our picture of early human evolution. Instead of revealing a coherent lineage shaped by adaptive refinement, the evidence points to mounting morphological diversity among hominins that shared time, space, and ecological strategies. This is a problem for the theory of human evolution, as typically framed, because natural selection should reduce such variation—not preserve or multiply it—especially once a powerful adaptation like bipedality or tool use takes hold.

Two recent studies sharpen the problem. In Nature Communications (June 2025), researchers published an analysis of three infant Homo fossils—two from South Africa and one from Ethiopia—dating to around two million years ago. What is striking is that even at this early stage of life, the mandibles already show distinct morphologies. These are not subtle variations of a common type; they reflect different developmental trajectories, pointing to divergence from birth—not as a result of environmental adaptation later in life. These specimens are assigned to different species—Homo habilis, Homo erectus, perhaps others—but the fact that they coexist in time and space suggests that they belong to overlapping populations that did not displace each other.

Meanwhile, a fossilised jawbone from Swartkrans, previously misclassified, has now been identified as belonging to a new species of Paranthropus—gracile and small-toothed, unlike the robust chewing machines that usually define the genus. This adds a second Paranthropus species in southern Africa and, once again, points to parallel lineages, not a tidy succession.

Taken together with other finds (e.g. Homo naledi, Homo floresiensis, Homo luzonensis), this growing list of coexisting species challenges the assumption that evolution within the Homo lineage followed a competitive, progressive logic. Instead of a single, gradually adapting lineage, we see a proliferation of forms—many of them apparently capable, bipedal, and tool-using—spreading not only across Africa but deep into Eurasia and Southeast Asia.

The Ecological Inconsistency

So how do palaeoanthropologists explain this? Most still turn to the logic of branching speciation. Populations become isolated by geography, adapt to local conditions, and evolve along separate paths. This model works reasonably well in ecology. But in this case, it begins to fall apart. Why? Because these groups were not isolated. Many shared the same environments. They used similar tools. They walked upright. Yet their differences persisted and deepened. Even as some lineages remained small-brained or retained arboreal traits, they were not eliminated. Diversity increased instead of narrowing.

This presents a deeper inconsistency. If hominins were already occupying a niche that rewarded bipedality and tool manipulation, then the proliferation of multiple distinct forms within that niche becomes biologically puzzling. In many other genera, physiological and behavioural competence tends to reduce diversity: the best-adapted form outcompetes the rest (see Hardin’s Competitive Exclusion Principle). This is arguably what happened among the Pan lineage, which may have been displaced by Homo across much of its former range. By contrast, the great apes that survive today—Gorilla, Pan, Pongo—are largely allopatric and maintain well-differentiated morphologies suited to distinct ecological roles. They do not blur into one another the way hominins do.

Moreover, many hominin species display a curious mosaic of features—a blend of arboreal adaptations (curved fingers, climbing shoulders) with terrestrial traits (bipedal legs, tool-use morphology)—even when they share the same habitat. If ecological adaptation were the dominant force, we’d expect functional streamlining over time, not persistent mosaicism.

Hominins, however, appear to have proliferated side by side, much like different human ethnicities do today, without consolidating into a single dominant form. We find Paranthropus and Homo sharing space, and multiple Homo forms persisting in parallel. That such morphologically capable beings coexisted rather than converged suggests that we are not looking at different species adapting to different ecological roles. Something else is preserving the variation.

Even leading paleoanthropologists have begun to acknowledge this puzzle. Chris Stringer, once a proponent of the linear ‘Out of Africa’ model, now speaks of a reticulated pattern—a ‘web of populations’—connected by gene flow yet morphologically divergent. While he does not discard the evolutionary framework, his model no longer treats speciation as a clear-cut outcome of ecological pressures. Instead, he concedes that what we are observing may not be traditional species, but something more fluid.

Domestication as an Alternative Explanation

The continued presence of multiple ‘species’ within the same environments suggests that we may not be looking at separate species in the classical sense, but rather breeds or varieties within a socially differentiated population. What we call Homo habilis or Paranthropus robustus may reflect lineages maintained through reproductive control, not ecological separation. The variation is not eliminated because social cohesion is maintained culturally—not by geography, but by group identity, possibly grounded in maternal lineage and early caregiving patterns.

I do not base this on direct evidence from early hominins, but on the way reproductive choices are culturally regulated in Homo sapiens today, and how this pattern produces morphological and behavioural difference today. If this pattern has deep evolutionary roots, then interbreeding among early hominins, while biologically possible, may have been shaped by similar social mechanisms. In this light, distinct lineages could have been created and persisted like specialised varieties in a shared system—diverse, yet maintained by social rather than ecological pressures.

Chimpanzees and bonobos both show strong maternal bonds. In bonobos, mothers remain closely attached to their sons and even influence their sons’ mating success. In humans, these relationships go further: grandmothers and others begin to play roles in managing reproduction. This can only happen when offspring remain in the group, when dispersal is suppressed. And to suppress dispersal, you need attachment (love?).

Attachment between mother and adult child is not a biological necessity. It is a social innovation. The original dependency is turned into an asset—not just for survival, but for recognition, bonding, and group continuity. Over time, this asset becomes a powerful selective force. In such a system, children are not merely tolerated; they are encouraged to remain children. This social pressure selects for individuals who remain juvenile longer—both in form and in behaviour. This helps explain why neotenous traits appear in the fossil findings as stable, heritable features. They are hallmarks of a system where care, recognition, and inclusion become selective forces in their own right.

This is why we must take seriously the symbolic potential of early hominin behaviour. When Homo naledi buries its dead deep in a cave, without tools or fire, we are not seeing instinctual hygiene or shelter behaviour. We are seeing the extension of attachment. The dead body resembles the dependent infant: motionless, helpless, inert. If mothers carried pebbles that resembled babies, as the Makapansgat cobble suggests, then the face of the infant was already being seen as meaningful. And when the infant dies, the bond does not vanish. It finds form—in burial, in ritual, in memory.

Conclusion

All of this—bipedality, neoteny, mosaic traits, suppressed dispersal, symbolic behaviour—forms a coherent trajectory. It is not a trajectory well explained by ecological adaptation. It is explained by active self-domestication—not in the narrow sense of reduced aggression, but as the domestication of the child by the parent, and of the group by itself, through patterns of care, recognition, and exclusion. In this light, what we call speciation may simply be social sorting over time. Morphological variation is preserved and reinforced because it matters to the group, not because it increases survival per se. That is why the fossil record keeps multiplying—not because nature is confused, but because we are still reading social processes as biological divergence.

Domestication of Humans: Abduction

Recent observations of white-faced capuchin monkeys on Jicarón Island in Panama have documented a particularly telling case of a broader behavioural theme. Over a 15-month period, juvenile male capuchins were seen abducting infant howler monkeys. They carried them for days, sometimes until the infants died.

This behaviour does not resemble caregiving, nor does it fit the patterns of hunting or play. It appears instead as a deliberate act of taking and keeping, with no clear purpose beyond the act itself. The howler infants resisted. They cried out to their mothers, who remained nearby. Some capuchins actively chased howler mothers to seize new infants. Over time, the infants stopped struggling—from exhaustion or resignation. But the abduction never became parenting. The capuchins did not feed them; they did not appear to know how.

AI generated image of capuchin monkey holding two juvenile howler monkeys with possessive body language

Even more striking: the behavior spread. This was not an isolated anomaly. Other juvenile males began to imitate the behaviour, suggesting that it became what researchers called a ‘social tradition.’ That is, it propagated through social learning, despite having no adaptive benefit. The infants died. No reproductive or survival advantage was gained. Yet the abductions multiplied.

And crucially, these monkeys had no contact with humans.

Abduction in the Primate Imagination

Primates are known not only for nurturing their young, but also for engaging in possessive behaviours, including abduction. In species ranging from chimpanzees to macaques, individuals have been observed snatching infants from their mothers, sometimes with fatal outcomes. These behaviours can be violent or tender, spontaneous or strategic. They do not always serve an obvious adaptive purpose. And yet, they exist.

Image by Martin Harvey via Getty Images (linked for reference only)

Captive and wild macaques have stolen puppies and carried them around for days. Chimpanzees have taken infants from rival groups or even from members of their own troop. In some cases, these abductions end in infanticide. In others, the infant is carried gently until death from neglect. And occasionally, a strange, uneasy bond may form between the abductor and the abducted—a one-sided intimacy that seems to resemble parenting, yet lacks the elements of functional care. Such cases may suggest a rudimentary form of attachment, not unlike what in human terms might be called a traumatic bond, though the motivations and perceptions of the nonhuman individuals involved remain open to interpretation.

It has often been assumed that these behaviors are rare outliers, or that they are provoked by human interference. But the recent capuchin observations show otherwise: these tendencies are not necessarily distortions—they are part of the primate repertoire.

Domestication as Abduction

The benefits of abduction may not be immediately apparent. However, such acts may create conditions in which something new can emerge. This is where the findings intersect with my broader thesis on the origins of humanity. In my post on dispersal and human society, I suggest that domestication is fundamentally opposed to the natural pattern of dispersal seen in primates. Where dispersal enables the offspring’s independence, domestication inhibits it. It arrests the movement of the young away from their natal group, drawing them into a structure of dependence that is no longer biological, but social, even symbolic.

In this way, abduction may have played a formative role in the emergence of our species. In my work on the ‘Behaviour of Language,’ I argue that humans are an intentionally self-domesticated species—a view that contrasts with mainstream approaches, which describe a passive, natural selection of traits like reduced aggression and increased prosociality. As I explore in ‘Who Domesticated Humans?’ this narrative overlooks the inherently intentional character of domestication—an act of controlling other individuals and their reproduction. These are not just evolutionary trends; they are decisions and actions embedded in interaction and amplified by learning.

In this light, the fact that primates are prone to ‘abduction fads’—even in interspecies cases—seems to support this argument: if abduction is part of the cultural range of primates, then the intentional retention of the offspring becomes not just likely, but evolutionarily grounded. Mothers and others may ‘abduct’ not with violence, but with emotional force. They may hold on to the child not merely to protect it, but to bind it, to keep it from forming bonds in foreign groups or with unacceptable partners. The mother may make herself indispensable. In doing so, she creates a new structure of dependence—a relation in which the child learns to respond to signals, to read her intention. This goes beyond instinct. It is the beginning of a new form of communication and cooperation.

All gender is male: An ethological perspective

When we observe humanity from a perspective of animal behaviour (ethology), we find something unusual: human females do not look or act like females in most other species. Instead, they exhibit behaviours and characteristics that, in the rest of the animal kingdom, are associated with males competing for mates. This might seem counterintuitive at first, but when we consider my hypothesis that human society has evolved around reproductive control, it makes perfect sense.

A male peacock

In most species, males are the ones who display elaborate fitness signals, competing for female choice. Think of peacocks with their extravagant tails, male deer with their antlers, or lions with their thick manes. These traits are costly, requiring energy and resources, and they exist because males must prove their fitness to gain mating access. Females, on the other hand, usually remain bland, passive, and cryptic in appearance and behaviour—because they don’t need to advertise themselves. They simply choose the best mate available.

A female human?

Humans, however, break this pattern completely. In our species, women also engage in fitness signalling, sometimes even more than men. This is evident in:

Ornamentation and beauty: Women tend to invest in personal appearance, makeup, jewelry, fashion—forms of display that in other species are typical of males.
Sexual signaling: Women, unlike most female mammals, develop permanent secondary sexual characteristics (such as enlarged breasts) that serve as constant reproductive signals, rather than just appearing during estrus.
Social grooming and competition: Women form complex social alliances, engage in status competition, and use indirect aggression—a pattern seen in male-male competition in many other species.

Why does this happen? As I mentioned, the answer may lie in our evolutionary origins: humanity is built on domestication—through the control of the offspring’s reproduction. And the ones who are naturally situated to have the most influence over this process are biological females—mothers.

This is particularly evident when we look at our hunter-gatherer past, which represents the vast majority of human evolutionary history. Unlike agricultural and industrial societies, which are recent and male-dominated in terms of formal political structures, hunter-gatherer societies were fundamentally built around maternal control.

Hunter-gatherers largely avoided material private property, owning no land and accumulating little stored wealth. However, they could hardly escape the need to own other humans, the basic resource necessary to produce descendants. In most other great apes, this is not possible, as individuals disperse from their natal groups upon reaching sexual maturity. So, maintaining cohesive and large breeding groups required some way to prevent dispersal, ensuring stability and cooperative child-rearing.

One way to achieve this is through sexual advertising. Females would have begun to compete to become the reproductive centre, to attract males and females towards them. Had males been the ones in this central position, they would have inevitably competed in a manner similar to hierarchical animal species such as gorillas or lions, where dominance is asserted through direct conflict instead. Such a system would have led—and eventually did lead—to instability, making social cohesion difficult to sustain. Instead, early human societies appear to have followed a different path—one where control over reproduction remained in maternal hands, not through brute force, but through a subtler, sexual form of influence.

This explains why our species is so exceptionally sexual. In a broad sense of animal behaviour, women are akin to males who compete symbolically to attract mates and cooperators who help them have more descendants. This did not simply shape early human societies—it laid the foundation of human civilization. Human societies likely emerged through maternal strategies of influence, fostering long-term stability, but the inherent maleness of this domesticating behaviour paved the way for the direct and aggressive strategies of their sons.

Where does this leave modern Western society? That is a question for another discussion. But if we are to make sense of contemporary conflicts over gender, power, and social organization, we must begin by recognizing the biological and anthropological realities that have shaped us as a species.

Culture and the Myth of Learning

A young chimpanzee, clinging to its mother, will stretch out its hand or make vocal requests for a bite of what the mother is eating. Sometimes, the mother obliges and offers the infant some food; other times, she remains focused on her own meal, leaving the infant to fend for itself. The infant must be persistent, begging repeatedly in hopes of securing nourishment.

This process, common among primates, emphasises that the responsibility for acquiring food falls on the infant. The same is the case with practical skills or knowledge. For example, when a young chimpanzee observes an adult cracking nuts with a stone, the infant is responsible for learning the technique through observation. The mother might facilitate the process a little, but she doesn?t stop to actively teach or guide. She cracks her nuts, and the infant must figure it out by watching and trying on its own.?

This stark contrast between primates and humans suggests that the origin of human culture is in the behaviour of teaching, not learning. Yet, modern scientists keep looking at social learning for clues. Why is that?

Culture

First of all, scientists define culture in terms of social learning, not teaching. This means that teaching cannot be the origin of human culture, by definition!?

Culture is a ?set of learned behaviors, beliefs, and customs that characterize a group, passed down through generations primarily through social learning and observation? (Richerson & Boyd, 2005). Culture is the ?collection of learned behaviors, values, and knowledge that are acquired through socialization and adaptive processes? (Henrich, 2016). Culture is the ?transmission of socially learned knowledge, behaviors, and values from one generation to the next, ensuring the continuity and evolution of group practices? (Mesoudi, 2011).?

The closest those definitions get even to a conservative notion of teaching?a change of behaviour in one individual to facilitate learning in another?is a vague, almost magical notion of ?transmitting? or ?passing down? something. The emphasis is clearly on psychological and theoretical notions such as learning and adaptation, not on behavioural observation.? Anthropologists, ironically, seem reluctant to acknowledge what goes on in the real world of humans, opting instead for an idealised view of human cooperation in which the offspring are always happy to learn.

Modern Myths II

In my previous post, I addressed the fact that humans evolved to prioritise kin cohesion over dispersal, breaking a pattern of primate behaviour that is 50 million years old. In primates, dispersal is the norm, with one sex typically leaving the natal group upon maturity. Humans, on the other hand, stay close to our parents, even into adulthood.?

Here, again, most scientists posit that this happened because we were naturally selected to remain close to kin. This beautiful story of a very special evolutionary process makes us feel more connected to the animal kingdom. Yet, as it occurs today, it was probably our parents?and their parents?who actively wanted us to stay close and help out, just as Homo sapiens did with dogs and other domestic animals, not natural selection.?

This shift to ensuring close family ties allowed for the rise of multigenerational households, something virtually unseen in other animals. The presence of grandparents and extended kin is an exceptional feature of human societies. Indeed, if we lived longer, we would likely see great-grandparents and beyond as integral parts of the family unit. However, it makes little evolutionary sense that an ape?our evolutionary ancestor?would be naturally selected for such deep devotion to its cultural ancestors, their signs, symbols, and abstract ideas.?

A more plausible explanation is that human culture has less to do with learning by innocent animals and far more to do with teaching them. Humans have an aptitude for learning, and we are keen to observe and imitate, but this is a consequence of human domestication and teaching. What we learn is often irrelevant to the survival and reproductive needs of the organism, just as food and sex are irrelevant when you are not hungry or fertile. As members of a society, we have to learn abstract ideas, rituals, moral codes and gratitude to the dead.

Conclusion

Life is hard. It is always comforting to imagine that our children desire to eat whenever we want them to; or that they ?go to school? to ?learn?, when they are in fact taken there by us so that they may be taught. In the past, the idea that parents forcibly teach or feed their children would not be controversial because these behaviours were regarded as necessary, even morally good. The prevailing view of human uniqueness then was centred around spirituality. However, there is clearly a sense in which the current materialistic focus on animal culture remains spiritual, a projection of human ideals onto nature.

?

Richerson, P. J., & Boyd, R. (2005). Not by Genes Alone: How Culture Transformed Human Evolution. University of Chicago Press.

Henrich, J. (2016). The Secret of Our Success: How Culture is Driving Human Evolution, Domesticating Our Species, and Making Us Smarter. Princeton University Press.

Mesoudi, A. (2011). Cultural Evolution: How Darwinian Theory Can Explain Human Culture and Synthesize the Social Sciences. University of Chicago Press.

Language and human uniqueness

Paleoanthropology, the study of ancient humans, continually revises our understanding of what makes Homo sapiens unique. Initially, the faculty of ‘language’ was thought to be exclusive to modern humans. This view expanded to include Neanderthals as new evidence came to light. Now, even Homo erectus, our ancient ancestor, is considered to have had this capacity. This progressive reevaluation suggests a fundamental shift in how we understand language, a trait that might set our entire genus apart from other apes.

Traditional perspectives have often portrayed language as a precursor to, and facilitator of, complex social cooperation, suggesting that the ability to communicate complex ideas was what allowed human societies to flourish. However, the attribution of language to ever more ancient types of humans—who lived an arguably more isolated existence for very long periods of time—questions the transformative powers of this communicative trait.

Indeed, the ability to produce speech or other elaborate signals cannot, by itself, produce a human society. There is nothing in those signals that causes receivers to come together around them. As I have explained, the key to the evolution of language, and human evolution generally, is in the human ability to motivate receivers to engage with signallers, rather than letting them go about the environment, away from ‘society’.

The Prescriptive Nature of Language

Prescription, in the context of human communication, refers to the intentional and purposeful act of making others respond to our signals.

Human-dog interactions offer a compelling illustration of this concept. Consider a scenario where a dog communicates its desire for food through barking and gazing between you and the desired item. The dog does not have an intention that we respond to its signals; its focus is merely on obtaining the food and the fact that you can help. In contrast, humans motivate the receiver (in this case, the dog) through incentives or consequences for not responding. As a result, dogs appear very keen and receptive to our signs and commands.

This conscious, strategic aspect of human signalling marks a critical divergence from the signalling behaviours of other species, besides explaining the seeming paradox of our “self-domestication”. Prescription challenges the notion that “language”—understood as speech or something like speech—led to human-style or large-scale cooperation. Instead, it suggests the complete opposite: language is a consequence, not a cause, of human cooperation, because increased cooperation must be established before more elaborate or sophisticated signals can evolve.

Communication is always a form of cooperation. In humans, the signaller needs to get the receiver especially interested in its signals, so that it will bother to interpret them, let alone respond appropriately. Only then, can signalling become more elaborate or sophisticated, and more meanings can be introduced. In other animals, this is not possible because receivers have no incentive to be receptive to new meanings. This explains the dramatic difference between the signalling repertoire of humans and that of other animals.

Biology, Not Philosophy

It’s a sunny spring day and the birds are busy. Some are flying about, perhaps foraging. I notice one staring at me from beneath a bush. What does it want? Suddenly, the bird returns with a little stick in its beak, flies away, and disappears into a tree. Ah—it’s probably building a nest.

I have chosen birds, but any organism could have played the protagonist in this opening scene. There are fish in the Pacific that crack open clams by tossing them repeatedly against hard surfaces. In the microscopic world, some amoebas carry bacteria when moving to a new location—in order to farm them. I could go on indefinitely. My point is simple: we distinguish what is alive from what is inert by its intentional behaviour. That is the essence of biology—the study of life.

This may sound naive, anthropomorphic, or unscientific. ‘Surely,’ you object, ‘organisms don’t really behave intentionally. They only appear to. Their behaviour results from natural selection, not from some life-spirit.’ Indeed, many take the essence of biology to be evolution. I do not mean to dismiss Darwin’s insight—God forbid! But biologists do not study rocks or molecules; that is the domain of physicists, geologists, and chemists. Biologists study material entities that move and interact as if with purpose.

So what do we mean by intention, if not this peculiar capacity for end-directed behaviour? And where did our mental intentions come from, if not from mindless animals without brains? Could we, in some sense, have mindless intentions too?

Reevaluating the Notion of Intention in Biology

Modern science is characterised by unabashed materialism, and yet intentions are conceptualised as mental states—alongside beliefs and desires. In this view, if a bird cannot think something like ‘I am going to build a nest,‘ it cannot have intentions. It is said to merely react to stimuli—like a robot, albeit a complex one.

This view descends from an old philosophical and theological tradition, which filters biological observation through the lens of our linguistic subjectivity. It actually runs counter to the Darwinian revolution, which was meant to bring humans into continuity with animals—not elevate them with metaphysical exceptions. It also reveals that scientists lack a biological definition of language, relying instead on philosophical notions that treat words and minds as something magical.

But biology, properly understood, need not take sides in metaphysical debates about matter and spirit. Biologists need not attribute minds to organisms, but they have every reason to attribute intentions. Indeed, the idea that living beings are evolved machines is a philosophical assumption, not a biological one. To make this clear, let me turn to a fundamental feature of life: communication.

Defining Signals in Animal Behavior: A Biological Perspective

Let’s go back to the beginning of this piece, where it’s a sunny spring day and I hear the birds singing. The purpose of these acoustic signals is not as obvious as the purpose of flying about or picking up little sticks. It takes a little more observation and inference to conclude what such a display is for.

According to biological observation, bird song is for attracting females and driving away competitors. Similarly, a bower bird’s flashy nest is not actually for laying eggs; rather, careful observation suggests that this structure is for attracting females. With the present text, I, as an animal, must be intending something similar. While I do not deny that my human intentions are more elaborate, I think that they are better explained through their relation to those of other animals.

Hence, in my view, bird song, the present text and other such signals reflect an intention to affect other organisms, to change their behaviour. Of course, animals act and develop in many ways that end up affecting others. However, signals are characterised by their dependence on the receivers’ intention to respond: The male bird sings or builds a flashy nest only because there are females around looking to maybe respond by choosing it as a mate. These females may be occupied with food or a predator. They must also decide which signals they will respond to, which signaller they will choose. Receivers cannot and won’t always respond to signals, however, they have an intention and interest in doing so; otherwise, there would not be any point in signalling.

This conceptualisation distinguishes signals from two other types of acts: coercion and cues. In coercion, an animal tries to change the behaviour of others who do not intend to behave that way. For example, the males of many species will harass females until they allow copulation; alternatively, they will punish them for refusing to mate with them, which increases the chances that they will accept the coercer. This behaviour is clearly not one of signalling, even though it succeeds at changing the other’s behaviour. In cues, the opposite happens. The female bird’s nest, for example, is not aimed at anyone; however, it is a cue for the cuckoo, who certainly seeks to lay eggs inside.

In sum, signals are acts or structures through which an organism (the signaller) intends to change other organisms’ behaviour, and which are effective because those organisms (the receivers) intend to respond to them. This (my) definition seems consistent with many observations of animal behaviour. It allows us to recognise signals in the same way that we recognise 1) acts and structures not aimed at others, such as nest building and nests, 2) acts and structures aimed at others who do not intend to respond (coercion), and 3) acts and structures that others react to but were not intended for them (cues).

In contrast, Maynard Smith and Harper (2003) define a signal as ‘any act or structure which alters the behaviour of other organisms, which evolved because of that effect, and which is effective because the receiver’s response has also evolved.’ Notice how this definition replaces intention – a concept describing observable phenomena – for the abstract notion of evolution, which refers to the ultimate origin of such phenomena. But before looking at the reasons for this terminological preference, let’s see how it impairs the definition of signal.

The Pitfalls of a Traditional Definition of Signals in Biology

Consider the way in which lions cooperate to hunt down big prey. Each organism reacts to the actions of others in a coordinated fashion, for example, one lion moves towards the back because another has moved to the front. Smith and Harper’s definition leads us to conclude that the first action is a signal: 1) the move has altered the other’s behaviour, 2) it has evolved because of that effect, without which the hunt would not be successful, and 3) the move is effective because the receiver’s reaction (its ‘response’) has similarly evolved. By contrast, in my definition, the lions’ actions cannot be signals because their aim is the prey. This is why I wrote that the lions react to each other’s behaviour in hunting, whereas they respond to each other’s signals.

The fact that responses (to signals) are intentionally cooperative, yet directed or aimed at receivers, sets them apart from other similar behaviours, such as group hunting. The same applies to conflicting interactions: males who retreat after hearing a mighty roar clearly intend to retreat, even though they will sometimes choose to fight.

But Smith and Harper do not see it this way: ‘If one stag pushes another stag backwards, that is not a signal but coercion. If it roars and the other stag retreats, it is a signal because the response depends on the evolved properties of the brain and sense organs of the receiver’ (Maynard Smith & Harper, 2003, emphasis mine). Here, the authors refer to a red deer contest in which males roar at each other. If the roars are not effective, the stags resort to pushing each other until the loser retreats. However, retreating is not a mechanical effect of being pushed backwards; it is a decision to abandon the fight, i.e. an evolved reaction that ‘depends on the evolved properties of the brain.’ The same is the case when females finally yield to a male’s aggression in sexual coercion, as I mentioned above. However, this makes coercion the same as a signal in the authors’ definition.

Conclusion

This post will continue. But for now, let me say this: despite decades of research, biology lacks a proper definition of signalling—one of its most basic and crucial concepts. This failure stems from a philosophical obsession with ultimate causes, rather than a commitment to empirical clarity. To be truly scientific, biology must set aside metaphysical anxieties about the origin of life. It must return to its proper task: observing and explaining the behaviour of living things.

References

Maanmieli, J. (2021). Prescription: A biological definition of language. Alethes.net, 1(2).

Maynard Smith, J. & Harper, D.G.C. 2003. Animal Signals. Oxford University Press, Oxford.