Recent media article about vampire bats and friendship

Sapiens Magazine just put out an article about vampire bats and friendship.

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The author Leah Shaffer did a great job, probably the most accurate media story on the vampire bats I can remember. Usually, journalists get a lot wrong, but they did a great job fact-checking this one.

Also, below is an edited transcript of some of the email interviews connected to this article which don’t make it into the article. I paraphrased the questions I was asked, and re-arranged or deleted some of them.

Does your research tell us about cooperation in general or in humans?

I do think the vampire bats can give us general insights into how cooperation works in a network of social relationships. Mostly this is due to their cooperative behaviors being easier to measure and manipulate compared with say people and other primates. They are small like lab rats, and cooperative behaviors like grooming and food sharing take place in a small dark corner of a cave or tree, so you can simulate that in captivity.

But clearly, human social networks are quite different and more complex than vampire bat food-sharing networks!

One issue in human cooperation is that between-tribe competition can mask the nuances of within-tribe competition. People focus on in-group vs out-group behavior. But clearly, people have differing relationships also within their in-groups.

You should contact Robin Dunbar. He is a prolific and influential author on the topic of the evolution of human social networks.

Where do you study the bats in Panama?

I captured them in Tole, Panama (at a roost on a cattle pasture) and brought them to the Smithsonian Tropical Research Station in Gamboa where I keep them in captivity.

Why do you not consider the food-sharing to be “communal”?  

“Communal” implies that something is shared (roughly equally) throughout a community. The bats share exclusively with their family and friends–with specific individuals more than others within a roosting group. They are more nepotistic than communal. The bat’s social network is not the same as the group it roosts with.

Are scientists trying to find the friendship gene?

It is very silly to say that there might be a “friendship gene”. So I think that sounds bad, simplistic. Some science writers will say someone found, say, a “vision gene” but what that really means is that there’s a gene that turns on another gene that encodes a protein (one of many) that the eyes need to function properly. So if you mutate that gene, the individual is blind. But calling that a “gene for vision” is misleading.

There are no genes for complex traits or behaviors. Like, say you need say 10,000 different chemicals to bake a chocolate cake, and if you discover just one of them (like sucrose), it makes no sense to say “we found the chocolate cake molecule”. The whole idea of a “cake molecule” doesn’t even make sense. Even the whole list of molecules should not be called “cake molecules” because you can make many other things with those same molecules. Same is true for “vision gene” or “friendship gene”.

Friendship is even more complex than the chocolate cake example, because friendship is not a physiological structure or even a trait of a single individual; it is an emergent outcome of the behavior of two individuals (or more). Differences in behavior are also influenced by differences in the brains among multiple individuals.

I’m not doing anything with genetics or brain differences underlying cooperative traits at the moment. Hopefully, someday in the future we will see the brain work linking hormones and neurotransmitters and their receptors to the behaviors. After that, we might then look at changes in the genetic sequences that build the receptors. That would be more than 5 years away I think. It’s not happening in the next 2 years (unless someone gives me a giant pile of money after reading your article). I’ve decided I would also rather collaborate with a neuroscientist and have them do the work.

What I’m hoping to do next is to work on how food-sharing bonds might extend to other kinds of behaviors outside the roost, like feeding from the same wound. I plan to work with a German team (a guy named Dr. Simon Ripperger) to put tiny computers (smaller than 2 gram) on the backs of vampire bats. The computer backpacks communicate with each other wirelessly, and with a wifi base station, and log the distance and time of social encounters. All the data can be collected remotely. That way, we can study captive bats and then keep tracking their social interactions after we release them into the wild. We hope to gain insights into social foraging in vampire bats. Social foraging and wound-sharing outside the roost should help explain social grooming and food-sharing relationships within the roost. Stuff like that.

Can you briefly explain what “social grooming” is?
Social grooming is when one animal grooms another. Social grooming is rare in most bats.

I did a study showing that non-vampire bats kept in the same situation spent no time or very little time (under 1% of their awake time) licking the fur of other bats, even when they were stuck together in captivity for their whole lives. That fur licking might just be bats licking food off another bat’s fur if they are messy eaters. Social grooming was 14 times higher in vampire bats and  it serves a social function.

In the the prairie vole research, did the researchers find all the genes for monogamy?
No, they found a key genetic sequence that will turn on and off the expression of receptors for brain chemicals that influence pair-bonding. So by adding or subtracting the  receptors (or the genes for it) they could turn monogamous behavior in males on or off. It’s amazing. That is simplifying it a bit. But that’s the gist.

You can study monogamous pair bonding at many levels in biology. Monogamous behavior differs between species, but also between populations. Across individuals, it depends on brain differences– the number and location of receptors on brain cells, which depend on gene expression, which depend on regulatory genes. They described that whole process from the species level to the genes. It is complicated, but let me try and break it down.

So DNA, genes, that encodes the proteins which link together to form a “receptor”– the receptor is on the membrane of a neuron. It is like a lock and molecules like oxytocin and vasopressin are neurotransmitters– the “keys” that fit into those “locks”. If the cell has the right lock and you put the right key into the lock, then you make that brain cell do something different. So a monogamous vole has those locks on cells in different amounts and in different regions of the brain. Having more locks on those brain cells makes those neurons more responsive to the chemical signals (hormones and neurotransmitters). This basic mechanism is very common in biology. For example, having different receptors for hormones throughout various body parts is what makes a male and female bodies develop differently. So this the same kind of thing, but inside the brain.

What does this all mean? It’s exciting. It means that we are beginning to understand how specific neural mechanisms (the key-lock stuff) lead to many of the differences in behavior between individuals–what we call “personality traits”. I think it’s truly transformational science, capable of changing the way we understand human nature. Eventually, in the distant future, personality will be largely understood as differences in the brain in just the same way that differences in running ability are understood as physical differences in lungs, blood, muscles, etc. I imagine a world where we would never say something like “this person is an evil person” and that’s the end of the story; we would instead say something like “this person lacks empathy for others because they lack oxytocin receptors throughout this region of their brain” or “this person had this traumatic childhood experience which led to these exact changes in their brain”. And maybe in the future we will treat such brain/behavior disorders more precisely, rather than what we do now, which is more like hitting your TV and seeing if the screen stops flickering.

Who did this research with the voles?
I can give you a list of names off the top of my head and you can dig further: Sue Carter, Larry Young, Steve Phelps, Alex Ophir, Tom Insel

Was the author wrong in distinguishing between “reciprocity, reciprocal altruism and “pro-social” behavior”?
Reciprocity and reciprocal altruism (I use these interchangeably) are not really examples or types of prosocial behavior. To me, they are hypotheses to explain why ‘prosocial’ traits are favored by natural selection. In other words, prosocial behavior can be explained by reciprocity, but not vice versa.

Prosocial behavior means you’re just helping another individual for whatever evolutionary reason. Authors start using the term “prosocial” to describe a behavior in an agnostic way without assuming an evolutionary explanation. Terms like “altruism” have a technical definition in the evolutionary literature that involves a decrease in lifetime reproductive success. So a behavior researcher can’t use that to describe a mere observation of helping without evolutionary biologists complaining. You could say “psychological altruism” but that suggests you know something about how the animal is thinking. So “prosocial behavior” makes no assumptions about evolution or psychology. It’s very confusing because different authors sometimes use these terms a bit differently. But I imagine that Joan Silk (or other leading experts on this topic) would agree with what I’ve written above.



About Gerry Carter

I study the behavioral, sensory, and social ecology of vampire bats.
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