Most of the time, I try to convince myself that this is nothing more than a touch of healthy neuroticism. Perhaps this is what it’s like for everyone—maybe this is what it means to really care about something, to commit one’s convictions and beliefs to the page and to offer them up for scrutiny by others. Who wouldn’t feel a little concern at this prospect?

But sometimes reality bites back, when the thing I’m worried about actually comes to pass. That happened this month, with the publication of a paper showing that bumblebees (bees FFS!) can solve a problem they have never previously encountered. The capacity to innovate is suggestive of genuine intelligence, something that is generally reserved for other species, like parrots, primates and (of course) us.

Why do I care? Well, the book I’ve just finished writing— THE THINKING ANIMAL—is on exactly this topic. It is a book that showcases the diversity of animal minds, asking what intelligence is and where we find it. I’ve spent years, and missed several submission deadlines, trying to craft a coherent narrative, one that explains why we see intelligent behaviour in some species but not in others. And now I have bumblebees and their shenanigans to consider. It is most inconvenient.

I jest (sort of). It can be useful to having one’s assumptions challenged—and the bees have definitely done that. To see how, we need to first consider what intelligence actually is. Although it can be tricky to define, many researchers now agree that it presents as behavioural flexibility—the ability to stop failing approaches, try different ones, and intuit novel solutions. Until the bumblebees came along, compelling evidence in insects was scarce. We knew they were capable of impressive feats but these were typically explained as the product of simple learning mechanisms, not raw ingenuity. That meant, when it came to the question of intelligence, I could safely put bees to one side.

But what if they do belong in the intelligent club after all?

What did the bees do?

The bee study riffed on a well-known paradigm in animal cognition, known as the box-and-banana task, which was first run on chimpanzees. Chimps were placed in a room with some wooden boxes and food (e.g. a bunch of bananas) that dangled out of reach. The question was whether they would put 2 + 2 together, by stacking the boxes to reach the food. Chimpanzees can do this, and (in a modified version) so can elephants. But bees?

Apparently, yes.

The bee version of the task was pint-sized: a small, circular testing chamber with a food reward (a blue ‘flower’) and a small Styrofoam ball, like the ones you find inside a beanbag. In the first training phase, bees learned that they could obtain a sugary reward from the ‘flower’ and—separately—that they could roll the lightweight ball around the test chamber. In a second phase, they were trained to push the ball off the blue flower to access the sugary solution, helping to link the action of moving the ball with obtaining a reward.

Next came the intelligence test.

Now the researchers moved the blue flower from the floor of the testing chamber to the ceiling—out of reach for the bees, just like the bananas were for the chimps. They stuck the bees back in the chamber with the ball, and waited. In principle, bees could access the food by rolling the ball under the flower and climbing on top of it. But doing this required them to solve a problem they had never encountered. Astonishingly, however, this is exactly what they did1. And this behaviour was not only observed among a couple of individuals, but in the majority of the animals tested.

But before we get too excited, there are some simpler ‘killjoy’ explanations to rule out. Firstly, we know (from previous work) that bees enjoy playing with balls. This might conjure up an image of a bee having a great time, rolling a tiny football around, but this detail also introduces a problem for the ‘intelligent bees’ idea. It suggests that the bees could have simply been having fun with the ball, and only used it to access the food when they happened to roll it past the flower. This sounds less like insight and more like opportunism. If this was the only experiment they had run, I would have been able to relax.

But it wasn’t. In two subsequent experiments, the authors made the challenge progressively harder, aiming to rule out such deflationary explanations. In one, the flower was placed on one side of a barrier, and the ball on the other. Here, the bees had to retrieve the ball and guide it through a small opening to get the food. Once again, most succeeded. In a second and even more convincing task, the enclosure had two identical barriers at each end, and the flower was placed behind one of them. If bees were rolling the ball at random, we’d expect them to roll the ball in both directions. Instead, they overwhelmingly directed it to the side where the flower was located. Together, these experiments are difficult to dismiss.

The bees look, and behave, as if they know exactly what they are doing.

So what does this all mean?

Well, it definitely means I have some edits to make. More fundamentally, it challenges our notions of where we might find intelligence in species other than our own. For too long, intelligence has been associated with big brains, or assumed to be restricted to species that sit closer to us on the evolutionary tree. The bee study shows that both of these assumptions are incorrect. Resemblance to humans and brain size are unreliable predictors for intelligent behaviour.

What is going on in the minds of the bees is less clear, however. It is unlikely that bees and humans solve novel problems in the same way, or have the same subjective experience while doing so. For us, the realisation of how to solve a problem—the moment of insight—is often characterised as “abrupt” and “unexpected”. Insight is associated with mental restructuring, where we see things in a new way (a bit like the perceptual shift we experience when staring at a Necker Cube).

Stare at this Necker Cube for a while and you will see it flip orientation.

Finally, insight is also subjectively rewarding–the A-ha! moment when we see the solution feels good.

It is uncertain and (for now) unknowable whether bees experience anything like this when they solve a novel problem2, though my hunch would be that they do not. It seems noteworthy that bees only succeeded in the experiment if they had previously learned to move the ball to get a food reward. Bees in a control group, that did not perform this training step, never worked out to get the food. To my mind, this suggests that their problem-solving success depends critically on a learnt association (move ball=get food), and that they cannot ‘reason’ their way to the solution without it.

Problem-solving in bees and problem-solving in humans might therefore be very different experiences. But why should we expect anything else? An animal need not have a mind like ours to display intelligence. Just as electric cars and petrol ones can both drive despite having very different ‘engines’, problem-solving behaviours that look similar on the surface can be generated by different cognitive machinery.

Our brand of cognition has evolved in response to the specific selection pressures that we have faced, just as that of bees has evolved in response to theirs. And while we can justifiably marvel at behavioural similarities—they like balls! they solve problems! they’re like us!—more marvellous still is to consider how we might differ. Intelligence may be more widespread than we have imagined, but perhaps it is also more diverse than we can imagine.

The Social Instinct (2021) is available to buy here (US) and here (UK).

The Thinking Animal: What Other Intelligence Reveals About Our Own will be published in 2027 and is available for pre-order now.

Lasius psammophilus queen and worker (© Volker Borovsky, Wikimedia Commons)

But from an evolutionary point of view, workers are a puzzle. An individual that cannot reproduce, by definition, leaves no descendants. Sterile workers therefore seem to flout the basic tenet of Natural Selection, by putting the queen’s reproductive interests before their own. Though Darwin saw this as the “one special difficulty” that threatened his whole theory, the apparent paradox can, in fact, be explained by evolution itself.1 Related individuals share copies of the same genes, meaning that it can be adaptive to sacrifice your own reproductive success if, by doing so, you help a relative to reproduce.

But sterile workers are not just confined to the ant world. It might surprise you to learn that we also have them in our societies.

We call them grandmothers.

In mid life, human females undergo a sharp transition from fertility to infertility. To see just how unusual this is, check out the figure below, which shows the reproductive lifespans of 52 mammal species. The green part is where females are alive and still breeding; any post-reproductive lifespan is shown in yellow.

You don’t need to look too closely to get the point. For most species, the bar is entirely green indicating that females continue breeding, or at least try to, until they drop dead. There are just a handful of species that have any semblance of yellow, indicating a post-reproductive lifespan where females are alive, but no longer reproducing. In the middle of the plot, we find a handful of toothed whale species, also known to experience menopause.

And, down at the bottom, there’s us.

Figure adapted from Ellis et al. 2018 Postreproductive lifespans are rare in mammals. Ecology & Evolution, 8, 2482-2494.

The average human female can expect to spend more than 40% of her adult life in a post-reproductive state. But, in doing so, they appear to be forfeiting the currency of evolutionary success. The existence of menopause therefore poses the same evolutionary puzzle as sterile workers. But is it shaped by the same logic, or is there something else going on?

Do we only experience menopause because we live for longer now?

In short, no. But, as this is a common misconception, it’s worth explaining why it is wrong. It hinges on the assumption that, thanks to modern medicine and sanitation, we now live much longer lives than we used to. As females are born with all the eggs they will ever have, maybe these effectively “run out” in mid life, at around the time our ancestors would have typically died.

This idea feels intuitive but is unlikely to be true. Although we are living a bit longer nowadays, studies of contemporary forager groups show that people who survive childhood can typically expect to survive into their 60s2 — well past the point at which women typically go through menopause.

And looking at the rate of follicle loss over a woman’s lifespan also indicates that the body is not running out of eggs so much as actively discarding them. Human females are born with around 1 million follicles, each capable of producing an egg. This supply declines exponentially throughout life,3 but even with this loss rate, the average woman should remain fertile into her 60s and maybe even 70s (see the dotted line on the figure below).

Adapted from Cant & Johnstone (2008) Reproductive conflict and the separation of reproductive generations in humans. PNAS, 105, 5332-5336

Instead, something strange happens in the mid 30s: the rate of follicle loss suddenly accelerates, and their number plummets. By around age 50, follicle levels drop below the minimum threshold required for regular menstrual cycles, and menopause begins.

This highlights the mechanics of menopause. But it doesn’t answer the question of why.

Why do women experience this sharp decrease in fertility in their 30s? And why do they then persist as sterile vessels, when it would seem that they have become reproductive dead ends?

Why do we experience the menopause?

To answer these questions, we need to take an evolutionary perspective. Through this lens, we come to realise that menopause is the outcome of an evolutionary battle, played out over millennia, between grandmothers and their daughters-in-law.

We sometimes bemoan the menopause as signifying the start of old age, perhaps feeling as though we are becoming decrepit and defunct. But I want to offer an alternative perspective.

It starts with dispersal. Our best guess is that, in ancestral societies, reproductive-age females tended to leave their home to live with their ‘husband’ and his family, rather than the other way around. An important consequence is that younger females were competing with their mothers-in-law over the resources needed to raise children.

Historical data sets can help us get a feel for the effects of this competition. In Finland, the Lutheran church kept meticulous records of marriages, births and deaths from the 1700s until the early 1950s. These records show that when a grandmother bred alongside her daughter-in-law, children were less than half as likely to survive.

But this scenario was also exceedingly uncommon, with just 30 or so grandmothers (out of more than 500) having babies at the same time as their daughters-in-law. Instead, most of the time, we see a case of what looks like altruism: the older females concede to the younger ones in these reproductive battles. They stop breeding.

To see why, consider how each female is related to the other’s children. The grandmother is related to the younger female’s children, but the reverse is not true. This means that the younger female’s genes don’t ‘care’ about the older female’s children at all.

This is what’s known as a relatedness asymmetry – and it weakens the mother-in-law’s hand.

A grandmother is selected against breeding if doing so harms her grandchildren. She is therefore more likely to concede in any battle over reproduction, with her genetic pay-off coming in the form of grandchildren. This does not involve any conscious decision-making, but is the outcome of an evolutionary process which prioritises her genetic success. Crucially, data from whales tells a similar story. There, too, older females stop breeding because doing so means that they avoid harming their grandoffspring. In the long run, this can be a more successful strategy than continuing to breed themselves.

Once females are committed physiologically to sterility, they can give their genes an additional boost by investing in their grandoffspring. In humans, for example, the presence of a grandmother increases the number of grandchildren that are born and the number that survive; and in whales, post-reproductive females improve calf survival, perhaps because they remember migration routes, or know where the best fishing grounds are. These benefits provide the selective impetus for extended lifespans.

Menopause, then, is borne of conflict: it is the resolution to a battle between females over who gets to breed. But ultimately it is also a form of cooperation—one generation stepping aside so that the next can thrive.

This is adapted from The Social Instinct (2021), which is available to buy here (US) and here (UK).

The Thinking Animal: What Other Intelligence Reveals About Our Own will be published in 2027 and is available for pre-order now.

First, a word about cycling itself. Cyclists1 are most definitely not cool (though, tragically, we all think we are). We are often a bit geeky, with a tendency to obsess over marginal gains, gear ratios and cadence. We abide by and sometimes even enforce an extremely arcane list of rules, that dictate the acceptable height of our socks and how our tan lines ought to appear. When one of our tribe is depicted in popular culture, he (and it is always a he) inevitably appears as a feckless husband, a wimpy male or a MAMIL.

But - and here’s where the science comes in - we are an intensely social species. We crave and in fact need meaningful interaction with our fellow humans. What if cycling could be a surprisingly effective way to achieve this? Read on for more….

Proposition: Cycling allows you to bond with people more quickly than, say, knitting2 - and there is a good scientific reason for this

Cycling is both physically and mentally demanding, often involving long periods in the saddle performing the Sisyphean task of hauling yourself up hills, only to then careen back down them again. 100km on a bike (a reasonably common distance for an amateur club ride) can take anywhere between 3 to 6 hours, depending on ability, mechanicals and cake stops, and will burn in the region of 2000 calories (i.e. basically all of your recommended daily energy intake). At the end of a ride like that, most of us are - to use the technical term - spanked.

But I think the shared adversity, if you can call it that, of a collective pursuit, like a difficult bike ride, is absolutely fundamental to the bonding that occurs so quickly among members of the same club. Shared suffering can bring us together: studies of football fans reveal that the ignominy of supporting a perenially losing team ignites stronger bonds among the team’s fans. West Bromwich fans report feeling a stronger kinship towards one another - and a greater willingness to sacrifice for their fellow fans - than their Manchester City or Arsenal counterparts. Decades of anthropological work has shown how intense collecive experiences can foster strong social bonds. Initiation ceremonies, hazing rituals and other so-called ‘rites of terror’ engender a strong sense of identity fusion, described by anthropologist Harvey Whitehouse as ‘a visceral sense of oneness with the group’. Identify fusion is thought to be stronger when people share dysphoric (psychologically or physically distressing) events, rather than euphoric experiences; and the more aversive the collective experience, the stronger the fusion that ensues. In extreme cases, individuals may feel such a strong sense of kinship and oneness with those they have experienced adversity with that they are even prepared to sacrifice themselves to protect their comrades.

Of course, I’m not claiming that a bike ride is akin to a rite of terror (though on some roads it comes close) but I do think that, so long as it is sufficiently difficult, cycling has some of the essential ingredients necessary for the social bonding effect to arise. And, perhaps more controversially, I think these ingredients are present in cycling to a greater degree than in other solo sports, such as running or swimming. Don’t forget that, unlike many solo sports, cycling is an intensely cooperative endeavour. Cyclists take turns to ride at the front of the line, making it anywhere from 30-50% easier for those who draft behind us. We rely on one another to point out hazards on the road, calling out potholes, cars, horses and anything else that might bring a ride to a premature end. In addition to helping one another out, I also wonder whether the shared experience of conflict with other social groups helps with this identity fusion. Without wanting to overegg the pudding here, there is a sense in which those who ride bikes can be thought of as systematically marginalised by those who drive cars - and even considerate motorists still pose a substantial danger to cyclists: in a collision between a bike and a car, a cyclist is typically going to come off worse. Many drivers (and cyclists!) are simply unaware of the road rules governing cycling; and when bikes and cars come into conflict, we find ourselves locked in intractable debates over who is at fault rather than considering the fundamental asymmetries in capacity to harm, or be harmed - and how we therefore ought to behave. The capacity for intergroup conflict is also thought to be an important driving force in sustaining identity fusion - and I suspect it is also part of the reason why we feel so bonded to our fellow cyclists.

So, there we have it. A scientifically motivated hypothesis for how and why cycling feeds a desire, deep within us, to connect with our fellow human beings. I also have several non-scientific points to make about why cycling is so great but I will save these for another post.