The Uniqueness of Mammals

In 2017, I presented a paper at the Florida Academy of Sciences entitled “The Importance of Being a Mammal.” Its thesis was threefold. First, a number of behaviours appear to be characteristic of mammals. Those behaviours can be used as taxonomic markers alongside physical traits—a suggestion Konrad Lorenz made long ago, but which has been largely ignored. Second, some of those behaviours have heretofore been thought of as characteristic of human beings, but can now be seen as an extension of evolution.

I call these behaviours “the mammalian factor.” These behaviours have been overlooked by both ethologists and comparative psychologists and there is scant, if any, formal documentation of them in the professional literature. But they can be observed and anecdotal stories and videos could be used as a starting point for research. There is historical precedent for using anecdotes as the basis for scientific investigation, as in reports of a snow-capped mountain in central Africa (Mt. Kilimanjaro), an aquatic mammal with a duck’s bill that lays eggs and injects poison (the platypus) and a huge, hairy, human-like monster from central Africa (the gorilla).

The behaviours that appear to be characteristic of mammals include the following.

Kissing

To my knowledge, there has been no formal study of kissing in non-human animals, although a perusal of Google Images reveals a plethora of mammals kissing each other. Usually, at least one of the participants closes its eyes as it is being kissed and, if bipeds are involved, one of them will hold the face of the other kisser. In elephants, the trunks intertwine.

Epimeletic Interspecies Behaviour

There have been several instances of an animal of one species helping an animal of a different species. For example, a hippopotamus was recorded lifting up a duckling that was unsuccessfully trying to get out of a pond, a bear rescued a crow from drowning, a cat attacked a dog that was trying to maul a toddler, a dog saved a cat from drowning, humans have saved various wild animals in distress, a dolphin helped a beached pygmy sperm whale, a rabbit dug out a trapped cat and a rhinoceros freed a zebra foal that was immobilized by mud. The hippopotamus and rhinoceros examples are particularly interesting, since those species are notorious for being highly aggressive.

There have been many anecdotal accounts of similar behaviours. A child that had been lost in Africa was found, guarded from hyenas by a pride of lions. Once the human rescuers arrived, the lions calmly got up and walked away. Last year, a toddler who spent the night alone in a wintry forest reported that a bear had stayed with him to keep him warm. For centuries, there have been reports of dolphins keeping capsized sailors afloat. These anecdotes, of course, do not qualify as scientific proof, but they do provide a starting point for further investigation.

Dreaming

REM sleep has been found in dogs, primates, cattle, cetaceans, platypuses, moles, sloths, giraffes, opossums, rats, humans and cats. Some birds have also been shown to have REM sleep, though it appears to be minimal.

Killing Prey before Eating It

With the exception of insectivorous mammals, mammalian predators—unlike fish, reptiles, amphibians and invertebrates—generally prefer to kill their prey before eating it. For humans, the thought of swallowing a living organism generally arouses disgust.

Hygiene

There is very little data on mammalian defecation. Nonetheless, there is isolated documentation that mammals may practice rudimentary hygiene when defecating: house cats bury their faeces, dogs wipe their hind legs, horses lift their tails. Jane Goodall reported chimpanzees using leaves as toilet paper. Approximately once a week, arboreal sloths will descend from the trees where they live to defecate and bury their faeces; during such times they are very vulnerable to predation. Several species use a latrine: that is, a specific location for defecation. It is also possible that faeces may be aversive to some species. However, this is complicated because some animals have anal scent glands and the chemicals produced by these glands may intermix with waste matter. These chemicals relay a message to conspecifics, who may therefore inspect the waste.

Non-mammalian species, such as reptiles, insects, fish, amphibians, echinoderms and crustaceans display no unusual behaviours after defecating vis a vis the faeces, although some species of birds do lift their tails to defecate and some remove scat from their nests. The usual behaviour, however, is simply to ignore the faeces. On the other hand, I have observed several fish species (foxheads, groupers, puffer fish, yellow tangs and damsel fish) turn around immediately after defecating to ingest and then spit out the faeces, repeating this behaviour two to four times before finally ignoring the faeces.

This is another behaviour that appears to have been overlooked by comparative psychologists and ethologists.

Interspecies Bonding

Mammalian species will often bond with other species, including humans.

Although interspecies bonding does not appear to exist in reptiles, insects, echinoderms, fish or amphibians, a few species of birds do exhibit interspecies bonding through the imprinting that occurs immediately upon hatching. Aside from the phenomenon of imprinting, there have been no formal studies of interspecies bonding.

Tickling

Tickling has been recorded in humans, rats and some apes. It remains to be seen how widespread it is among other mammals, since research has been scarce. Care must be employed to avoid misinterpreting grooming and scratching as tickling.

Reaction to Death

There is a dearth of formal studies of this. Whereas non-mammals often fail to react to the discovery of the corpse of a conspecific, or may even cannibalise it, some mammals react with stress. Documented, anecdotal instances of dogs mourning the death of their owners or of a conspecific are legion. Some chimpanzee mothers have been observed carrying the corpses of their offspring and some cetaceans have tried to keep their dead offspring afloat and have kept vigil over a dying or dead conspecific. There has also been one documented instance of a cat meticulously burying its dead offspring and another of a cat trying to revive an unresponsive dead conspecific. Of particular interest are the accounts of elephants coming across the bones of familiar elephants and carefully examining them; there are some reports of elephants “burying” dead conspecifics by covering the body with dirt and vegetation. One avenue of possible formal research would be to ascertain whether similar behaviours can observed among solitary mammals.

Tactile Drive

In mammals living in herds, packs, pods, etc., such as bottlenose dolphins, chimpanzees, baboons and sperm whales, touch appears to be very important. Sometimes an individual will appear to request another animal’s touch and an animal that seems to be experiencing fear, agitation or anger will often appear to calm down if touched by others, whether the touch is cursory or more intense (such as hugging in primates). Adult humans who sleep alone will often hug a large pillow. Human infants who sleep with a parent may fall asleep on one side of the bed, but while they sleep they will rotate their bodies until one of their extremities comes into contact with the parent, whereupon they cease movement.

In several famous experiments conducted by Harry Harlow, some monkeys who had previously experienced touching were later deprived of touching by conspecifics. They appeared stressed while isolated. Others, who had reared without ever being touched by a conspecific, exhibited permanent maladaptive behavioural aberrations (they were unable to socialize or mate).

Personality

Individual mammals have unique personalities. Both researchers and laymen have often remarked that animals like dogs, cats, wolves, cetaceans, apes, pigs, horses and elephants display behavioural idiosyncrasies. Anyone who has owned several mammalian pets or livestock of the same species can attest that, like human children, each individual behaves differently from its conspecifics even though they are in the same environment and exposed to the same stimuli. Dogs and cats often seem almost human in their behaviours. I have never come across a crab, snake or trout that appeared to have a personality. It is highly significant that most animals we keep as pets and feel emotionally attached to are mammals, as opposed to crustaceans, insects, amphibians, fish or reptiles.

By personality here, I mean a pattern involving behaviours that are part of the repertoire of a specific animal and are not only not the result of learning or conditioning but are resistant to alteration through learning or conditioning. Some researchers are of the opinion that individual differences in an inborn behaviour—for example, differences in ability to learn navigation in mazes in different strains of rats—are synonymous with personality. They have broadened the term to include even insects and nematodes because of differences in their degree of, for example, aggression. I believe that personality-defining behaviours are distinct from the core behaviours of a particular species (such as duration and speed of flight in birds or insects, maze navigation in rats, length and intricacy of courtship, degree of aggression towards conspecifics etc.). Most behaviours follow a bell curve distribution, just as physical traits do. Personality refers to consistent behaviours unique to a particular organism.

Behavioural Mimicry and Culture

This is well documented in the literature. Some juvenile mammalian predators often have difficulty killing prey so the adults will often bring helpless prey to them, presumably to demonstrate killing or for the juveniles to practise on. Other instances of modelling have been recorded in bottlenose dolphins, meerkats, monkeys, dogs, golden hamsters and apes. Interspecies behavioural mimicry has also been observed.

Some mammals that live in groups also create a rudimentary culture: defined as learned behaviours that are copied by other members of the group and transmitted to offspring. This has been witnessed in banded mongooses, orangutans, dolphins, orcas, monkeys and apes.

Play

This has also been thoroughly documented in the formal literature, though the formal definition of play remains elusive. Play is much more frequent in juveniles than adults (although in some species, such as otters, bonobos and ferrets, there seems to be little quantitative difference). Animals often engage in spurts of aimless energetic activity. Juveniles tend to exhibit excessive, occasionally non-functional activity: the play behaviour is not goal-directed. Juvenile carnivores engage in wrestling or mock fighting with each other and occasionally with adults and sometimes chase each other. Juvenile herbivores tend to have spurts of running and chasing each other; sometimes they will abruptly jump straight up into a standing position and begin to run energetically. Mock fighting between juvenile herbivores is infrequent, except in horned species.

These are not the only behaviours that can be classified as play (a panda bear cub has been recorded rolling back and forth on a snow bank and putting snow on its face). Dolphins and beluga whales in captivity and whales in the wild have been observed to create air bubbles in the shape of a ring—a toroidal vortex—and swim through it or push it around, like humans blowing smoke rings. Humans occasionally introduce floating toys to the tanks of captive dolphins and beluga whales, which they either grab or push around. These stimuli will not elicit similar behaviour when introduced into the shark tank. Bubble bursting by beluga whales may also be a play activity.

Interspecies play takes place when there is no possibility of aggression or predation, even on the part of animals that would ordinarily be hostile towards each other. YouTube has a plethora of videos documenting this. For example, wild polar bears have been filmed playing with dogs. When a member of one species initiates play with a member of another, the latter often appears confused or apprehensive because of the differences between the typical play behaviours of their respective species. Occasionally, this confusion dissipates and play ensues. Dolphins have been observed playing with whales, pinnipeds and humans (a New Zealand dolphin named Moko often played with humans). One cetacean was filmed gently pulling a snorkeler down into the water by the leg and then bringing her back up to the surface. This could have been an instance of play.

Some investigators insist that non-mammals, such as reptiles, cephalopods and spiders, also engage in play. However, they may be anthropomorphizing.

The best stimulus to elicit play behaviour, whether in humans or animals, is probably a ball. This could be used as the basis of comparative studies across species. Rabbits, horses, bears, cows, dogs, emus, tigers, lions, monkeys, cats and moose ferrets have all been recorded playing with a ball (a moose was recorded invading a football game and seemingly trying to imitate the humans kicking the ball around).

A ball introduced to reptiles, insects, echinoderms, fish, amphibians, crustaceans or most birds will not result in play behaviour.

Intelligence and Plasticity of Behaviour

Lower animals, such as fish, crustaceans, amphibians, reptiles, insects and some birds, exhibit stereotypical behaviours: when presented with certain stimuli, they will behave in a specific, undeviating manner. A century ago, Jacques Loeb pointed out that insects can exhibit behaviours that resemble the tropisms of plants. A ladybird, for instance, will exhibit negative geotropism; if put on a blade of grass it will climb up and if the blade is reversed, it will turn and climb up again and this can be repeated numerous times. Once the insect reaches the top, it will open its carapace and fly away.

Mammals rarely engage in repeated stereotypical behaviour when presented with a task wherein they cannot directly obtain their goal, but will change their behaviour and attempt different strategies. This could provide one possible definition of intelligence in animals: the more complex the improvised strategy, the more intelligent the animal. Other behaviours can also be used as markers of intelligence and there are gradations in intelligence.

Fairness

Morality did not occur in humans spontaneously. It must have had animal precedents. Ethologists such as Frans de Waal have discovered that some mammals, particularly monkeys and apes, show a rudimentary sense of fairness and inequity aversion. Similar studies have been carried out with dogs and humans. Only species that are habitually gregarious and cooperative appear to demonstrate inequity aversion. Some studies have raised doubts as to whether the phenomenon exists and, if so, is confined to primates, or is an aspect of mammalian behaviour more generally. Further research on this is necessary.

Exceptions

At times, nature defies the human desire for orderly taxonomy. For example, there are mammalian monotremes that lay eggs (e.g. echidnas), flowering plants that lack chlorophyll and cold-blooded naked mole rats.

The Psittacidae (parrots) appear to have some mammalian behaviours. They exhibit play, learning through modelling, interspecies bonding and kissing and certain species are highly regarded for their intelligence. Some humans reciprocally bond with them, carrying them on their shoulders. This is never done with other avian species.

Corvids have also demonstrated intelligence in several replicated experiments.

Humans

Humans have always asked what differentiates mankind from the other animals—by which they generally mean what makes mankind superior to other animals. Plato proclaimed that man was a featherless biped; hearing this, Diogenes of Sinope plucked the feathers off a chicken and threw it over the wall of Plato’s academy, forcing the philosopher to amend his definition. He added “with broad, flat nails.” When Niko Tinbergen, the Nobel prizewinning ethologist, was asked how human beings differ from animals he responded, “I wish I knew.”

For millennia, people have recognized that humans are related to animals and have often felt shame at the connection, believing that we should transcend our animal nature.

In the past, it was believed that what makes mankind unique is our use of tools, or of language, our opposable thumbs or our large brains.

I would suggest that what makes us unique is that we are mammals—only more so. The mammalian characteristics have been amplified in human beings. This echoes Darwin’s supposition in The Descent of Man that humans differ mentally from animals in degree rather than in kind and that, as Giovanni Boniolo put it, it is only logical to suppose that human behaviour evolved from that of our non-human ancestors. Some people may not like this idea.

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