Caring for placebo - an evolutionary view

The placebo effect is a fascinating phenomenon that appears in many forms, but its most familiar example is simple: give someone a sugar pill with no active ingredients, and yet, they often experience real improvements. The usual explanation is that “the placebo activates the body’s natural healing ability.” But this leads to a curious question—why does the body require a sugar pill to begin healing? Why doesn't it just heal on its own?

There are many possible explanations, but the ones I’d like to explore focus on the idea that Homo sapiens are inherently social and deeply responsive to care and connection.

Music for today: Ndikhokhele Bawa

Resource allocation: the Health Governor

Healing and activating the immune system are energetically expensive processes. It makes sense, then, for the body to engage them only when the necessary resources are available. Humphrey and Skoyles describe a metaphorical ‘Health Governor’—a system that allocates energy where it's most needed. This internal regulator weighs a wide range of current signals and past experiences to make the best decision possible.

One of the key factors in this process is the sense of safety. If the environment feels unsafe, energy is diverted toward dealing with the perceived threat or stressor. But when safety is sensed, the body can afford to redirect resources toward healing and recovery.

see footnote for image credit and story

Social Baseline Theory

For humans, the most important cues of safety often come from other people—especially when those people show genuine care and concern. The human brain assumes the presence of ‘social resources’—it expects access to supportive relationships and cooperative individuals. When this expectation is violated, it increases both cognitive and physiological effort, leading to distress. This idea lies at the heart of Social Baseline Theory.

In this light, healing and recovery can be activated by positive social signals. Broadly speaking, three types of social cues may contribute—often in combination: physical signals (like touch), verbal communication, and environmental context.

This helps explain why the body may require a kind of ‘placebo trigger’ to initiate its healing capabilities. In the face of injury or illness, the presence of a caring person can signal safety, allowing the body to redirect energy toward recovery.

Socially elevated grooming

This idea posits grooming and attention as elements of prototypical medicine, and socially elevated groomers as prototypical clinicians. I find that phrasing particularly compelling. As a physical therapist, I see myself as a kind of socially elevated groomer—through caring touch, intentional verbal and non-verbal communication, and a healing-oriented environment, we can already achieve a great deal.

It also helps explain why some so-called "alternative" practitioners often report positive outcomes. Compared to the overwhelmed doctor in a busy hospital—focused more on lab results and imaging than on the person in front of them—the alternative practitioner may offer something essential: time, presence, empathy, reassurance, and a sense of meaning.

Signal Theory of Symptoms

Here's another twist in the story—one that adds complexity, but also depth. Many of the symptoms that lead someone to seek medical help aren’t the root cause of the problem, but rather its consequences: pain, fever, vomiting, nausea, diarrhea, swelling, apathy, and so on. These symptoms don’t just support defense and healing; they also function as signals, alerting others to the need for care.

This idea forms the basis of the Signal Theory of Symptoms, which proposes that symptoms serve a dual signaling function: they guide the individual to adjust their own behavior for recovery, and they also communicate to others that help is needed.

The intensity of symptoms increases their signaling power. As a result, symptoms may be unconsciously exaggerated to improve the chances of attracting support and treatment. Once that support is provided—whether through care, attention, or medical intervention—the signaling purpose is fulfilled, and the symptoms can recede.

Of course, this raises the issue of free riders: people who might fake symptoms to gain assistance. However, many symptoms are energetically costly and hard to fake convincingly, making them reliable, or “honest,” signals.

One particularly compelling thought is this: Just as symptoms may persist when the underlying physical cause remains untreated, they might also linger when that cause is resolved but the evolutionarily shaped need for interpersonal care and attention is left unmet. 

symptoms signal the need for help

Supressing versus activating the immune system

You may have noticed an apparent paradox between two theories: the "health governor" suggests that the immune system is activated in the presence of care, while the "signal theory of symptoms" proposes that the immune system is suppressed when care is present.

It's important to remember that humans are complex biological systems, so it doesn't have to be one or the other.

One theory focuses on symptoms, while the other encompasses the entire healing process, including symptoms. This suggests that the signal theory could actually be a part of the health governor concept. The "governor" (remember, it's just a metaphor) can decide, based on all available information, whether social signaling is necessary. In certain situations, social signals may not be needed—such as when you're alone or when signaling would be counterproductive.

Monkey business

This is especially true for pain. In nature, pain behavior can signal the need for support, but it can also attract predators. There's a fascinating and notable difference in pain behavior among Japanese macaque mothers during childbirth. In some regions of Japan, births happen almost unnoticed. The mothers and the group remain quiet and serene, and the process seems to be virtually pain-free.

However, in other parts of the country, within the same species of monkeys, mothers vocalize loudly during birth, indicating significant pain. In these cases, many other females are present.

The explanation for this difference comes down to safety—once again. In the more hostile northern regions of Japan, it’s safer to remain quiet to avoid drawing the attention of predators. In contrast, in the safer, more relaxed southern areas, the expression of pain is more openly allowed, possibly even inviting care and support from others.

No healing

The connection between placebo, healing, and social cues has significant implications. The absence of a caring environment can severely hinder healing and recovery.

Even if you're the most compassionate clinician, if the patient's social environment signals danger or indifference, recovery can be seriously compromised. A toxic social environment itself can be a major source of health problems (just think of the social baseline theory).

Moreover, even with the best intentions, a clinician can unintentionally trigger the opposite of the placebo effect: the nocebo effect. This refers to a negative impact on a patient's health caused by a clinician’s words, tone, behavior, or communication.

Important Safety Cues for Clinicians

The following insights are inspired by trauma research, particularly the Polyvagal Theory. These are signals the brain interprets as cues of safety:

• Soft facial expressions and eye contact (especially from trusted individuals)

• Warm, prosodic vocal tone (gentle, melodic speech)

• Affectionate touch

• Being in the presence of calm, regulated people (supporting co-regulation via nervous system mirroring)

• A sense of connection to others (belonging, companionship, social bonding)

• Safe environments (predictable, familiar, and quiet surroundings)

Additional Implications

Safety cues aren’t limited to human interaction—they can be body-based or environmental. For instance: relaxed breathing, warmth, soothing music or nature sounds, meditation and mindfulness practices These signals can engage the parasympathetic nervous system and promote healing.

Interestingly, cues suggesting that resources are abundant can also trigger placebo-like responses. A fun example: when hamsters are injected with bacteria, their immune response differs depending on whether they believe it’s “summer” or “winter” (as determined by artificial day/night cycles). In "summer," when survival and reproduction seem viable, the hamster mounts a full immune response—fever, appetite suppression, and bacterial clearance. In "winter," it simply holds the line, conserving energy.

Health is important, but in biology, reproduction is even more important. Signals that suggest reproductive opportunity can have placebo like effects. Another fun example: sick male zebra finches show visible symptoms—until a female finch is nearby. In her presence, their symptoms vanish, likely because of increased mating chances.

Summary

The placebo effect, with all its complexity, has several possible explanations. From an evolutionary standpoint, those focusing on social and caring aspects make a great deal of sense, although they certainly don’t capture the entire picture.

The health governor regulates energy allocation between the healing process and symptom intensity. Based on all available information—particularly social cues of safety and care—the governor makes the most optimal decision. In most cases, a supportive environment and social safety promote healing and reduce symptoms.

Any thoughts?

Thanks for reading! Cheers,

Pieter

References:

• Humphrey & Skoyles (2005) The evolutionary psychology of healing: a human success story. Current Biology

• Steinkoph (2015) The signaling theory of symtoms: an evolutionary explanation of the placebo effect. Evolutionary Psychology

• Coan & Sbarra (2016) Social baseline theory: the social regulation of risk and effort. Curr Opin Psychol

• Hoogstad & van Wingerden (2024) Monkey business. Freshview

Image credit and note: For these African people, when someone does something harmful, they take the person to the center of the village where the whole tribe comes and surrounds them. For two days, they will say to the man all the good things that he has done.The tribe believes that each human being comes into the world as a good. Each one of us only desiring safety, love, peace and happiness. But sometimes, in the pursuit of these things, people make mistakes.The community sees those mistakes as a cry for help. https://www.facebook.com/EvolverSocialMovement/photos/laughing-treesin-this-african-tribe-when-someone-does-something-harmful-they-tak/10152864659007731/