The Nature of Penis Duels, Mouse CPR and Evolution's Most Paradoxical Weapon.
On the behavior, neurobiology and selfish genetics of love, caring and altruism in the animal kingdom.
Nature is definitely a savage theatre of survival.
Probably one of the most quoted phrases in all of biology is «survival of the fittest». This is the term many people associate with evolution, natural selection, and Darwin.
First to be noted: Darwin never coined this term of “survival of the fittest”. It was this other dude, Herbert Spencer, who first introduced it in 1864.
Spencer was very much influenced by social and economic philosophy. He used “survival of the fittest” in a more general sense to describe how competition in various systems (including human societies) leads to the persistence of the most "fit" elements.
On the rare occasions I open instagram, I like to go to the «Nature Is Metal» account to have a look. And you can probably guess at what kind of content is posted to that account (if you are not familiar with it)?
A lot of stuff that easily reinforces the idea that the natural world is relentless, blood-soaked, and a place where only the truly fit wins.
And this is often a compelling narrative. Perhaps, keeping this perspective of nature makes it easier for us to justify all the crazy stuff we humans do. Both among our selves and towards nature. If nature truly is so brutal, it's okay to treat it brutally back, right?
But sometimes we get those small friendly reminders that it's not always so. Because sometimes, nature is tender, loving and full of hugs.
It recently happened to me, when I saw this recent study published in Science.
What they investigated here was how fellow mice responded when their mates were distressed, drugged and unconscious.
And it turns out, that they cared for each other. They increased the time they spent grooming and tending to these poor familiar individuals that were having a hard time. And when this didn’t help, and the condition of these poor lads worsened and they became more unresponsive — the mice turned to first aid to help!
Similar to how us humans get trained in CPR, they open the mouth and pull out the tongue to clear the airways. And it helped, as this actually sped up the recovery of their friends!
Love and Care in Fur, Feathers, and Scales
If you go looking for love in the animal kingdom, you’ll find it.
Evolution may have favored survival and self-preservation, but it has also shaped caregiving, love and compassion.
It is often very beautiful.
Also, it's occasionally very horny.
Take bonobos. They kiss, groom, and console each other. When one is upset, others step in with the gentlest embraces. And yes, bonobos are also the undisputed champions of recreational sex.
They use sexual behavior in just about every social context imaginable. They go male on female, female on female, male on male, male on rock, two guys on rock with four lads watching. Female bonobos do a lot of what primatologists delicately call genito-genital rubbing, or GG-rubbing: two squatting females rhythmically rubbing their swollen vulvas together, face to face, making intense eye contact, arousal levels fucking high.
The boys know how to get down too. It is observed that males might – when discreetly standing back to back – rub their scrotum against the butt cheeks of the other. They also engage in penis-fencing, something I remember a teacher of mine strictly forbid two of my classmates to do in the elementary school showers way back.
This is love that’s not just about reproduction.
Obviously.
It's social bonding.
They are known for resolving disputes by banging it out. Which sounds fantastic. The bonobos are our closest relatives. I wonder how human history would have gone down if mother- and father-in laws had not been so awkward about sex. Just imagine Adolf going about dealing with his problems and insecurities this way. Way more satisfying than genocide most likely. That lonely testicle was probably screaming for some proper ball-scratching.
A true lesson in biology to be sure: a couple million years of evolutionary divergence is enough to screw up even the best of ape practices.
But affection extends beyond orgies and sexual experimentation.
Grief is also present.
Elephants slow down when passing the bones of their dead, gently touching skulls with their trunks. They form tight herds led by wise, older females who help raise calves that are not even their own. Juveniles are basically babysat by allomothers, who aren't biologically required to give a damn, but do so anyway. Dolphins have been observed keeping ill or dying individuals afloat, swimming under them to push them to the surface so they can breathe. They’ve also been seen forming protective circles around vulnerable group members. This includes human swimmers in some rare encounters.
Dolphins also do gang rape of course, but you can’t expect all niceness either.
There are plenty of examples of animals helping each other out.
Blood sucking vampire bats might be the last ones you think of as caring and tender, but these guys are surprisingly generous. If one fails to feed, others who successfully dined that night may share their earlier meals by puking it back up for them. A favor that is remembered of course, and likely to be returned.
This type of behavior is even present when there is no clear reciprocal advantage too.
In a classic experiment, rhesus monkeys were taught to press a lever for food. But if pressing it shocked another monkey, many of them chose to go hungry rather than cause harm. In one famous study, rats learned to open a door to release a trapped peer. They did it even if they had no social contact afterwards.
And of course, mice turn out to be more proficient in CPR than most human citizens.
But it's fair to ask whether this was a true act of kindness, or just some deranged case of tongue-pulling torture. And the same did the researchers investigating this. Thats why they looked into the brain of these mice, to uncover the actual neurobiological foundation behind this heroism.
The authors demonstrated the origin of this behavior to be oxytocin.
The “love hormone” behind so much of the world’s beauty — from scrotum rubbing and penis fencing to tiny, CPR-performing mice.
Nature hasn’t only weird animals to be brutal competitors, it has also made a brain capable of love. Behind every tender trunk-touch and chocolate-sharing rat is a molecular cascade of signals, receptors, and neural feedback loops.
The Neurobiology of Love and Care
The authors demonstrated the origin of the CPR behavior to be the oxytocin-producing paraventricular nucleus (PVN). In the context of the brain, a nucleus (plural: nuclei) refers to a collection of neurons (nerve cells) that are clustered and grouped together both anatomically and functionally.
This is a neat way of organizing things, as you then have things that work together on the same stuff sitting at the same place. It also helps researchers piece together the relationship between behavior (like CPR) and its «purpose», based on what the activity of that brain region is typically associated with.
Aggression or affection for example.
The PVN is a nucleus within the hypothalamus, a brain region that links the nervous system to the endocrine system (the hormone system). It’s a command center with many functions, and is involved in commanding things both in the brain and the rest of the body. For controlling stuff in the body, it collaborates with the pituitary gland, which is the one actually releasing hormones like oxytocin into the bloodstream.
And what these hormones do, is to act as messengers.
It travels the blood, so it can reach a designated destination elsewhere where it delivers a message for some other cell, tissue or organ to do its job.
Oxytocin is involved in regulating many different behaviors and brain functions.
It is used as a messenger in brain circuitry and on tissues involved in how mammals care for their young for instance. It puts together a lot of the stuff that drives the loving physiology of maternal behavior.
When a baby suckles at the tits, sensory receptors in the nipple send signals to the hypothalamus, which then triggers neurons in the PVN to release oxytocin from the pituitary into the bloodstream. That oxytocin then travels to the mammary glands, where it acts on special muscle cells to cause milk to squirt.
And it isn't just physical touch that causes this release of oxytocin — it can also be triggered psychologically.
Hearing a baby cry for instance, just thinking about nursing, or even just seeing your baby can cause the oxytocin messengers to be utilized. This can prompt squirts of milk even involuntarily. It's from this the term crybaby originates, referring to very un-masculine men causing involuntary milk ejection by their crying. That’s why men are told not to cry. Unnecessarily clean up and all that.
Oxytocin isn't just about the milk either.
It also enhances maternal bonding and protective behavior, it reduces stress and anxiety by chilling the HPA (stress) axis. In animal studies, blocking oxytocin can prevent maternal behaviors like licking, nuzzling, and retrieving pups. The classic science of producing bad mothers.
Studies like the CPR-in-mice experiment show that helping behavior can be modulated by oxytocin signaling in the PVN too. Or that these behaviors are associated with it, and is related to the brain regulation we typically see in individuals that are friendly towards each other.
Because oxytocin is also highly involved in regulating social bonding.
This plays out beautifully in voles. And here you can start to see the larger complexity at play. It's not all about the specific brain chemicals, it's about how certain brain regions interacts and use these chemicals.
In monogamous prairie voles, oxytocin activity follows a distinct pattern that helps form strong partner preferences — which is a completely different pattern than that you see in polygamous vole species, where oxytocin acts differently and in entirely different brain regions.
Furthermore, social behavior isn’t dictated by a single brain chemical either.
Vasopressin is yet another messenger involved in social behaviors. It works together with oxytocin, and is more associated with territoriality, aggression, and male-typical social behavior (which of course is its own kind of love, protect thy homie and all of that).
Everyone's favorite dopamine is also a key player here. It modulates reward, motivation, and is involved together with oxytocin in reinforcement of social bonds. Dopamine helps in making the parts of the brain that make love and social bonding happen, more likely to be happen again.
love is complicated.
But despite this complexity, and everything we don’t know yet: Love, empathy, sex, and social bonding — they all have neural footprints. You can trace at least part of it back to the brain.
And knowledge about these footprints can help us discover the origins of new and cute behaviors, as the one we see in these first aiding mice.
Which is not trivial, because with knowledge about this, we can start to break down what type of behavior this really is.
It's not tongue torture. It's not molestation.
It is likely a sign of affection and care.
Something that we hope to see in human behavior, but don’t necessarily expect to see other animals being just as brilliant at. It breaks with this whole «nature is metal» and «survival of the fittest» thing that makes nature so hard, brutal and inspiring for those who need to comfort themselves with this as the reality of things.
Also, love and empathy is kind of weird. It comes at a cost, as you sacrifice yourself to the benefit of others.
Why are brains wired to allow for all these behaviors, if competition is the driving force of nature? Why does altruism even exist?
Frankly, because if you get down to it, it sometimes makes sense. Genetically speaking that is. And Herbert Spencer might still be true about his survival of the fittest.
However, It’s not about the fitness of individual organisms like you, me and some mice or other — but the fitness genes.
Altruism and the Fittest Genes
Altruism, or being nice to others at a cost to yourself, has several proposed evolutionary explanations.
Sometimes it's obviously beneficial, because it's reciprocal. You get something in return from the one you helped (direct reciprocity). Other times it might just be to boost your reputation and status, because that can also get you laid or some other returns in the future (indirect reciprocity). It's also important to remember that helping the group can enhance the survival of the individual.
And when on the topic of helping the group, that’s when we get to the interesting genetic stuff.
But first — to fully explain altruism — we might want to look at some core fundamentals in evolutionary biology. Namely fundamentals concerning selection.
Survival of the fittest is a cornerstone in many peoples assumptions of what natural selection is. Some individuals are better at surviving, and very good at banging and making more kids. Those kids inherit all the good stuff from their parents, and will thus in turn be good at survival and banging too — and so the genes of the fit and sexy pass down in many generations to come.
And that’s not too bad of an explanation. I would approve this as an explanation of natural selection from my 3 year old daughter if I asked her. But that’s mostly because that’s the version I have thought her (because you have to start somewhere). As you probably agree with, an explanation fit a 3 year old is not really an explanation sufficient to properly explain important biological phenomenon. But it doesn’t need to be that complicated either.
The important thing here is that it’s not about the individual, but rather the genes.
Natural selection is a force of nature, and that force works upon something, like gravity works on a body of mass. A replicator is that something. It is an entity that can copy it self, has some inherent variation to play with, and have some impact on its own success in this whole replication process.
Genes fit this description: It can copy self, it displays variation in the form of mutations and different alleles (versions of the same gene), and it impacts its own replication success (some variants replicate better than others). An organism, when it reproduces, doesn’t copy it self. It just helps in the copying of the replicators — its genes. Very good genes are really good making an organism that effectively helps them copying themselves.
Genes are the fundamental replicators on which selection is working.
Evolution is about the survival of the fittest genes. Genes get selected if they are able to get themselves copied faster than competing alleles.
And this is crucial if we are to understand altruistic behaviors among animals. It's only what the genes care about that is important. I am anthropomorphizing here of course. Just like whoever holds the papacy doesn’t really care about the ruined lives of a thousand deaf kids — genes don't really care.
But still, Its only they (meaning the genes), who needs to be passed on through generations. And the forces of nature has shaped a system where they are in control.
So to understand why love, care and altruism exist in a brutal world — we need tot think like a gene.
And this brings us to the theory of kin selection. And no, this isn’t about how evolution tells you that it is sometimes okay to fuck your cousin.
Its more that your genes sometimes allows you to enjoy and be psyched about your cousin fucking others.
Or as the evolutionary biologist J.B.S Haldane allegedly said after doing some calculations on the back of an envelope: «Im prepared to lay down my life for eight cousins or two brothers».
The theory of kin selection seeks to explain the altruistic behaviors in nature we had a brief look at earlier. Thus explaining the core question of why an individual would behave in a way that favors others but not themselves, or at a cost to themselves (like wasting energy and time doing CPR).
And the explanation for this can be summed up by this simple equation:
rB > C
It is known as Hamiltons rule. Again, here we need to remember: it's all about what the genes want. They want to replicate and conquer.
So, an allele (a specific variant of a gene), will spread through kin selection if this condition is met (referring back to the equation): If the benefit to the receiver (B), weighted by how genetically related they are to the altruist (r), is greater than the cost to the altruist (C).
The r is the coefficient of relatedness. It tells you the probability that you and another person share the same allele by descent. And for you and your cousin Becky (that you secretly got the hots for), this is 0,125 (se illustration below for further explanation).
In other words, the specific gene or allele that you have — that really wants to replicate itself — has a probability of 0.125 or 12.5% of also being present in your cousin. So Haldane was correct it looks like, because 0.125 x 8 =1. Your gene can ditch you, and safely assume (based on probability) that 8 cousins is worth just as much as you. In other words, the benefit (B) for those genes to go reproduce with you or by having you helping your cousins to reproduce is equal.
But what’s even more heartbreaking, your mother Karen (really her genes tho, to be fair) can ditch you too. Because the fitness of her genes, equals the probability of the offspring she produces with those same genes, as well as those in her relatives that she helps produce. Meaning that 4 of your cousins are worth just as much as you — especially if they are as hot as Becky!
And that’s where the C comes in. The genes of your mother has to evaluate what it costs to be altruistic. If they give away the opportunity of having two kids (you included), to help raise 4 of your cousins — that’s not worth it.
Which finally concludes Hamiltons rule: r x B needs to be greater than C. So your mother's genes actually need 5 cousins or more to render you useless. There is some comfort in that at least.
From this we can see that selection is a little bit more complex than just survival of the fittest. Selection (at least if we listen to Hamilton), favors genes that maximizes inclusive fitness. This captures both direct fitness (the reproductive success your genes get from their own offspring), as well as indirect fitness (the reproductive success your genes have by helping kin or others with the same genes having offsprings).
It's the evolutionary score that matters for your genes.
It's about maximizing inclusive fitness.
But how does this relate back to the altruistic and loving behaviors of animals and humans?
Kin selection isn’t that bad at explaining that either. Because animals typically live in closer knit groups. Humans did too for most of our history. And groups in evolutionary contexts tends to be made up of individuals that are more or less related to each other. Or kin.
It might just be ancient instincts that makes your genes think they are doing themselves a favor when they make you behave nicely towards your wheelchair-using neighbor Jerry.
And we should also remember that most altruistic behaviors are not life sacrificing for the altruist. They are usually very low cost, which justifies your genes to help out those even more distantly related. You should obviously help wheelchair-Jerry, you lazy fuck.
Regardless, It’s all about the genes. A chicken is only the eggs way of making another chicken. The organism is only the DNAs way of making more DNA.
So what Herbert Spencer should have realized, is that it's all about the survival of the fittest genes. And in this regard nature truly is metal, because the fittest gene doesn't necessarily care if it is you who carries it.
Nature is hard and ruthless. It doesn’t really care for any of us, we (meaning organisms) are just reproductive machines in the world of genes.
As long as they survive and replicate, that’s all they care about.
But, the same ruthlessness that drives genes to survive by helping you, is what drives them to help you helping others. It's ruthlessness giving rise to the capacity for care, tenderness and friendship.
Because when selection only favors the fittest genes, and when the genes are all around you, they create love.
Leave a comment to update me on how things go with you and your cousin Becky would you? Or just subscribe to let me know you are on board with all of this 👌
References and further reading:
MASSERMAN, J. H., WECHKIN, S. & TERRIS, W. ‘altruistic’ behavior in rhesus monkeys. AJP 121, 584–585 (1964).
Waal, F. B. M. D. Bonobo Sex and Society. Scientific American https://www.scientificamerican.com/article/bonobo-sex-and-society-2006-06/.
Bartal, I. B.-A., Decety, J. & Mason, P. Empathy and Pro-Social Behavior in Rats. Science 334, 1427–1430 (2011).
Sætre, G.-P. & Ravinet, M. Evolutionary Genetics: Concepts, Analysis, and Practice. (University Press, Oxford, 2019).
Nowak, M. A. Five Rules for the Evolution of Cooperation. Science 314, 1560–1563 (2006).
Weinstein, D. Herbert Spencer. in The Stanford Encyclopedia of Philosophy (eds. Zalta, E. N. & Nodelman, U.) (Metaphysics Research Lab, Stanford University, 2024).
Dale Purves et al. Neuroscience. (Sinauer Associates, New York, 2018).
Staes, N. et al. Oxytocin and Vasopressin Receptor Gene Variation as a Proximate Base for Inter- and Intraspecific Behavioral Differences in Bonobos and Chimpanzees. PLoS One 9, e113364 (2014).
Carter, C. S. Oxytocin Pathways and the Evolution of Human Behavior. Annual Review of Psychology 65, 17–39 (2014).
Burkett, J. P. et al. Oxytocin-dependent consolation behavior in rodents. Science 351, 375–378 (2016).
Witteveen, A. B. et al. The oxytocinergic system in PTSD following traumatic childbirth: endogenous and exogenous oxytocin in the peripartum period. Arch Womens Ment Health 23, 317–329 (2020).