One human-like ability may be the key to 14 animals' survival

You may think the calculus you learn in high school never comes in handy in real life, but across the animal kingdom, creatures as diverse as fish and apes show that the classroom isn’t where the number-crunching really counts.

Numerical competency means the ability to estimate and process numbers of things or events, in order. This incredible cognitive skill is one of the reasons we humans have had the edge over other animals, but while we like to think of ourselves as uniquely gifted, we are not alone in our abilities.

Numerical competency isn't quite the same as doing arithmetic, but having a basic grasp of counting things in sequence is crucial to other animals' existence, too.

"The surprising thing is that this seems to be presented across the entire animal tree of life."

That's the take-away from a review published Monday in the journal Trends in Ecology & Evolution. As the researchers argue, for some animals, understanding numbers has become a vital, adaptive trait that gives them an evolutionary edge and improving their chances of survival, generation after generation.

“From a biological point of view, an individual has to reproduce to pass on his genes to the next generation. And second, it has to stay alive long enough to do so,” Andreas Nieder, director of the Institute of Neurobiology at the University of Tübingen, and author of the review, tells Inverse.

“Numerical competence is both necessary for the survival of an individual and for reproduction.”

And far from being a rare skill, Nieder explains that we likely just don't know how common numeracy is among our fellow fauna because we haven't been looking for it.

“The surprising thing is that this seems to be presented across the entire animal tree of life. Almost every animal that has been investigated for numerical competence shows some rudimentary type," he says.

These five crucial strategies to survival demonstrate just how precious numerical competence is for 14 species across the animal kingdom.

5. To gather and hunt

Whether you are a wolf or a snail, the more food available, the more food animals tend to go for.

Take the fire-bellied toad. These animals reliably choose six items of food over three, but they are less picky when it comes to choosing between two or three food items. Researchers aren't sure whether the toads count the items or judge how large the food stash is, but that they understand quantity is apparent, Nieder explains.

Wolves take a slightly different tack when it comes to numbers and food. When they are hunting, the clever canines count how many of them there are in the pack available to hunt, and then decide what animal they can prey on. Essentially, wolves calculate the optimal number of peers they need to take down an elk versus a bison, for example. That skill enables them to hold individuals back if they think it'd be a waste of energy.

Another creature that counts to make its meals is the spider-eating, jumping spider. This creepy crawly waits specifically for only one other spider to be near its prey before attacking.

One spider is better than none, or course, but it is also safer than two or three spiders.

4. To defend themselves

Elks try to use math to avoid getting eaten by wolves by counting their herd members, according to a 2011 study. These herbivores either choose to live in smaller herds, because they’re less likely to attract wolves, or they choose to live in larger herds because there’s a lower chance that any one particular elk will be preyed on. High numbers also mean a higher chance of spotting the predator because there are more eyes on the ground.

Black-capped chickadees, one of Nieder’s favorite examples, communicate to each other how dangerous an upcoming predator is by counting out their cries. The more dangerous the prey, the more times they sing a “dee” note. Other birds listen alongside the chickadees and count the "dees," planning their escapes accordingly, a 2005 study shows.

Chimpanzees are garrulous apes which happily travel into other chimps' territories in search of food. But whether the rival chimp groups get into an aggressive fight with each other doesn’t actually depend on the food at stake. Instead, the chimps assess which group has the more adult males, and makes its moves accordingly, the review explains.

3. To know where to go

Honeybees, apis mellifera, count the landmarks they pass to establish how far they’ve travelled. According to this 1995 study, if a bee has been trained to collect nutrition from a base between landmark three and four, say, it will count the landmarks rather than measure the distance to orient themselves. Similar results were obtained in another bee study in 2008.

Bees aren't the only inset to do this. According to a paper in Science from 2008, the desert ant counts its steps to measure distance from the nest. The way researchers found this out is pretty interesting in itself: They put the ants on stilts, establishing that ants that took longer steps misgauged their travel distances, as if they were operating on a “step counter” mechanism.

2. To make group decisions

A solo-swimming, three-spined stickleback fish decides its travel direction according to the direction most other fishes go in, according to a 2008 study.

This is an example of sensing a quorum — the minimum number of individuals supporting a group decision. This strategy also decreases their chances of being eaten.

The same goes for ants. When they have to decide where to relocate their nest, they have a voting system, by which they pick the new nest containing the most number of ants. A similar process occurs among honeybees, according to a 2004 study.

African wild dogs also vote by counting how many of them sneeze in favor of something, according to a 2017 “Sneeze to Leave” study. Baboons do something similar too, according to a 2018 Science report.

1. To reproduce

Mealworm beetles are very prolific maters, gathering in groups to maximize their chances of finding a partner. But numbers are important after mating, too.

The male beetle will hang around their female for extended periods of time according to how many rivals it encountered in the past. The more the rivals it met, the more it’ll stick around, according to the new review.

Pseudoscorpions are similar, but they take it to a new level: They actually regulate how much to ejaculate during copulation according to the number of rival mates. The first male scorpions to copulate with a female has a higher chance of fertilization, so by counting how many others went before them, male pseudoscorpions avoid wasting too much of their sperm.

How do animals count?

As these fourteen incredible species demonstrate, having some sense of number is almost a ubiquitous, innate characteristic, shared across invertebrates to primates, on varying different levels. The reason why is down to neurology, Nieder says.

“Part of this capability is present based on the way our brain is wired,” he says.

“So it seems that our visual system is spontaneously wired with the capability to extract numerical information when we look at something.”

In fact, researchers believe that there are specialized cells in the brain geared towards making sense of numbers, known as "number neurons," or numerosity-selective neurons. These neurons have been found in humans, macaque monkeys, and crows.

That’s why, even as babies, we can estimate the size of a set, Nieder says. This ability precedes language skills, and can be seen in other animals, too.

“There is something I would even say innately present in our brain that has these biological roots," he says.

There are some key differences between us and our fellow creatures, however. Unlike humans, animals estimate numerosity in approximates. The more similar the number of things, the harder it is for animals to tell them apart, Nieder explains.

This gap may be down to the fact that, to a fish or a crow, things that are more different in number or size have greater impact on their lives. Two versus three pieces of food doesn't seem to alter their behavior as much as two versus six pieces, for example.

Animals' abilities also suffer from something called the "numerical size effect." That refers to the fact that, past a certain threshold, the number doesn't really matter in terms of gain or loss to the animal. If there is lots of food to eat, for example, it doesn't matter to the animal how much more food there is beyond their point of satiety, Nieder says.

Evolving to count

Researchers still don't know exactly how or why these animals do math.

Animals, like us, use a vast array of signals and techniques to regulate their behavior.

“What is, however, still missing is the big question: Why can they discriminate?” Nieder says.

“What's the survival and the reproduction benefit? The adaptive value? And is this real? We are actually lacking dedicated studies.”

More tests in the field will enable scientists to better understand whether all these animals are truly counting, or doing something else.

"This basic understanding of what numerical quantity means… this is already present in our cousins in the animal kingdom.”

But the research so far suggests that, across the animal kingdom, understanding numbers evolved independently in different species as a beneficial trait.

“This strongly indicates that that is a huge survival benefit, huge adaptive value for probably any animal to be able to discriminate the number of objectives,” Nieder says.

The evidence also belies our own belief in our human uniqueness. If wolves and spiders can count, to at least some extent, then it suggests our own mathematical abilities are rather more innate to our biology.

“It was previously thought that these symbolic accounting capabilities emerge in our species based on our language skills,” Nieder says.

“Now it turns out that this is not the case. There are these precursors, this basic understanding of what numerical quantity means. This is already present in our cousins in the animal kingdom.”

“Homo sapiens arrived here and took numerical competence to a whole different level, by employing real number symbols,” Nieder says.

“But there are already these precursors on which our brain can build on. And that's one of the fascinating issues.”

Highlights: Numerical competence, the ability to estimate and process the number of objects and events, is of adaptive value.

It enhances an animal’s ability to survive by exploiting food sources, hunting prey, avoiding predation, navigating, and persisting in social interactions. It also plays a major role in successful reproduction, from monopolizing receptive mates to increasing the chances of fertilizing an egg and promoting the survival chances of offspring.

In these ecologically relevant scenarios, animals exhibit a specific way of internally representing numbers that follows the Weber-Fechner law.

A framework is provided for more dedicated and quantitative analyses of the adaptive value of numerical competence.

Evolution selects for traits that are of adaptive value and increase the fitness of an individual or population. Numerical competence, the ability to estimate and process the number of objects and events, is a cognitive capacity that also influences an individual’s survival and reproduction success. Numerical assessments are ubiquitous in a broad range of ecological contexts. Animals benefit from numerical competence during foraging, navigating, hunting, predation avoidance, social interactions, and reproductive activities. The internal number representations determine how animals perceive stimulus magnitude, which, in turn, constrains an animal’s spontaneous decisions. These findings are placed in a framework to provide for a more quantitative analysis of the adaptive value and selection pressures of numerical competence.