"The Love Hormone: The Key to Canine Evolution?"

How a single molecule created the pack instinct!

Originally published on April 22, 2009 at PsychologyToday.com.

Wolves Are an Anomaly

Wolves are an anomaly in the natural world. They’re one of only two species of land mammals who have a history of hunting animals that are larger and more dangerous than themselves, and who do so by working together in a socially sophisticated manner. The other species is homo sapiens. (Members of the dolphin family, especially orcas, also hunt large prey as a team.)

So how did the wolf become the wolf? Where did the pack instinct—the behavioral template for this unique style of hunting—originate?

The common, broad-stroke evolutionary explanation is that certain species form groups as part of an adaptive strategy that changes the selection pressures felt by the individuals so that those who align themselves socially rather than decide go it alone” have better odds of passing on their genes to the next generation, and to the next, etc, etc.

The thing is, individual animals don’t have strategies, they don’t feel selection pressures, and they certainly don’t have any awareness of what it means to pass on their genes to the next generation, let alone the next and the next. On a certain level we all know this.

But according to some theorists, evolution does take place in real time, it just does so on a molecular level, which then transmigrates upwards into changes in morphology, which influence changes in behavior, etc. And if this is true then adaptation has nothing to do with an animal’s behavioral choices in response to environmental changes, it’s part of a simple energy exchange, taking place on a molecular level, one that doesn’t put selection pressures on the organism but does put some kind of energetic pressure (probably thermodynamic) on the nuclei of certain cells.

Of course I’m a dog trainer, not an evolutionary biologist. So what do I know? I’m probably oversimplifying this. But hear me out...

In most mammalian predators, the offspring are kicked out of the “nest” once they reach adolescence. The parents don’t continue nurturing them, and with good reason: nature doesn’t want a group of “bloodthirsty” types living in close proximity; if food is scarce you run the risk that they’ll vent some of their aggression on one another. But unlike what we see with the big cats (with the exception of female lions), wolf offspring aren’t kicked out of their nests (or don’t decide on their own to leave) until they’re at least 2 years old. That’s a substantial divergence from the norm.

Why the difference? Oxytocin.

It might sound improbable that a simple neuropeptide, even though it has some pretty fancy tricks up its sleeve (for one thing it acts as both a hormone and a pheromone) could be responsible for such complex changes in behavior. But recent research by Insel & Young, 2002, shows that in monogamous prairie voles, when the effects of both oxytocin and vasopressin (which are closely related), were disrupted—by derailing their connections to the “reward pathways”1 in the nucleus accumbens—the formerly monogamous voles quickly became promiscuous.

This was a huge reversal, and it took place immediately.

In contrast, Lim et al, 2004, did a study with promiscuous meadow voles, and found that the addition of oxytocin and vasopressin (again, in direct connection with the “reward circuits” in the brain), produced long term pair bonding where no such behavior had previously existed. And again, the results took place immediately, in real time. [2], [3].

“A change in the expression of a single gene in the larger context of pre-existing genetic and neural circuits can profoundly alter social behavior, providing a potential molecular mechanism for the rapid evolution of complex social behavior.” (Lim et al, 2004.)

See that? “A molecular mechanism for the rapid evolution of complex social behavior.” So I think it’s quite probable that at some point in the wolf’s evolutionary history, certain wolf pups, or certain wolf parents, or possibly both, kept producing these intriguing neuropeptides long past the time frame that their feline “rivals” did.

Over countless generations the cats became more and more fearsome (yet still solitary) predators. Wolves, meanwhile, took a different path. They didn’t become more fearsome; they became more social. And they became more successful at hunting. This could’ve happened fairly quickly, possibly within the span of a few generations. Add to this the way intricate social behaviors—particularly when used for hunting large prey—require enormous intelligence and emotional flexibility, and it starts to become clear that the wolf’s social metamorphosis may also be part of what enabled wolves to become much more adaptable to living and thriving in various habitats, environments, and eco-systems, far more so than any feline species has ever been capable of.

Why does hunting large prey require more intelligence?

Intelligence is perhaps the wrong word. Think of it as the number of computations necessary to successfully hunt large, dangerous prey as part of a group, as opposed to the number required to either hunt small prey by yourself or, if you’re a big cat, to hunt the type of animal, large or small, that you can take down fairly easily on your own.

If you’re a cheetah chasing a gazelle your focus is fairly simple compared to that a wolf chasing an elk as part of a group dynamic. The cheetah is focused primarily on 3 things: 1) the changing movement, energy, and emotions of the prey, 2) changes in the terrain, and 3) the changes in his own movements, levels of energy, intensity, drive, etc.

But for a wolf, he’s doing all that while focusing on the changing positions, energies, intensities, emotions, and movements of each of his pack mates as well. If he’s hunted with them before he’s also got a backlog of data about their preferences and behavioral tendencies in similar situations. The larger the pack, the larger the database, and the larger the number of computations necessary.

So as soon as wolves started hunting in concert, they automatically became more “intelligent” and more adaptable. [4]

Then, when wolves began their long relationship with human beings and eventually became domesticated by us (or vice versa), and began their new incarnation as dogs, they expanded on the wolf’s adaptability, so much so that the modern dog’s natural habitat now includes every corner of the globe, including Antarctica. (Since a dog’s natural habitat is anywhere that involves living and working alongside human beings, Antarctica should clearly be on the list.)

To sum up: wolves probably didn’t invent the “strategy” of hunting large prey as a way of adapting to their environment. Their innovative pack hunting dynamic may have just been an outgrowth of a simple molecular change in their brain chemistry. And it’s why they were subsequently able to evolve so quickly into the most social, the most adaptable, and most diverse species on earth: our best friend, the dog.

Anyway, that’s what this dog trainer thinks might’ve happened.


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1) “Reward circuits” refers to dopaminergic (and other neurotransmitter) circuits in the brain, even though more and more research shows that these are not reward pathways, per se, (dopamine is released when negative things happen, or when an animal senses a change in the pattern of reward). They should probably be called attentional, or mnemonic pathways, since dopamine’s purpose seems to be to make us pay attention to and remember salient environmental patterns, both positive and negative.

2) Oxytocin has more of an effect on females while vasopressin influences male behavior more directly. An interesting side note is that when men and women kiss, the levels of oxytocin go down in the female but go way up in their partners. Another interesting point is that vasopressin also controls kidney and urinary function, primarily through regulating how much sodium is in the blood. It’s also tied, in inverse proportion, to production of the stress hormone cortisol; the more stressed an animal is, the more sodium there is in its bloodstream, hence the more the animal needs to urinate. I find this interesting because for years I’ve noticed that most male dogs who are overly focused on “marking” also tend to exhibit symptoms of emotional stress and anxiety, and marking seems to be a way for them to reduce those feelings. But when you give these dogs an outlet for their internal stress, they generally stop marking quite so much.

3) Baumgartner et al 2008 then did a study on human beings which showed that the reason oxytocin creates feelings of love, nurturing, trust, generosity, and perhaps even altruism, is that it selectively deactivates neural activity in the amygdalla and midbrain regions, switching off some of the brain’s fear circuitry. Oxytocin doesn’t prevent people from responding to imminent danger, but it does influence people to have feelings of deep trust toward members of their families and social groups

4) In terms of adaptability, wolves were once the most widely-distributed land mammal on earth except for human beings, and we were primarily responsible for reducing their range by killing them whenever and wherever we could. (At the same time we were doing this we were inviting the wolf’s brother, the dog, into our homes.) By the way: the most widely-distributed marine mammal is the orca. It can’t be an accident that these three species are all group predators.

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