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Blood Buddies

Tuesday, December 28, 2010 - 12:29 PM

In this new short, a tree full of blood-sucking bats lends a startling twist to our understanding of altruism and natural selection.

In our recent episode The Good Show, we grappled with a troubling question: how can goodness and self-sacrifice thrive in a world that Darwin tells us ought to favor selfishness? We follow up on that idea with Jerry Wilkinson, chair of biology at the University of Maryland-College Park, who describes an amazing discovery he made in 1977 that revealed an entirely new way of explaining selflessness.





Professor Gerald S. Wilkinson


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Comments [28]

Peter Griffith

After listening to this discussion on the Vampire bats, I believe that this compels one to believe that the altruistic behavior in animals is almost certain. There are many traits seen in these bats that are very similar to humans. Although, the one that is most prevalent is sharing. It is amazing how bats are able to share blood with another starving bat. This is something that can provide a stepping stone into the complex world of how animals are able to interact and understand each other.

Sep. 02 2013 03:23 PM
Matt from Atlanta

I'm a tad disappointed, because I feel like this is one of those episodes that flat out ignores the most likely explanations in order to preserve some sensationalist conclusion in the spirit of the show. I'm very much a layman when it comes to evolutionary biology, but even just reading "The Selfish Gene" by Dawkins (the very man to open your previous show), presents several similar accounts of altruism outside of the family, all of which are explained by the same mechanism of the selfish gene.

Jul. 23 2013 09:47 AM
Aaron Rice from Burlington, VT

just a note:

"always; without exception"


Interesting piece though.

Jun. 05 2012 11:05 AM
Corey Roberts from CANADA

I'm thinking that 40,00 years ago when the large mammals with all the blood disappeared, maybe a single family of bats began sharing blood meals. Subsequently all other vampire bat colonies became extinct except this single family, which of course left offspring and whose genes and behaviour came to represent the entire species as we see it today.

And as the large mammals have not returned, the behaviour persists, because each member of the colony gains from in terms of producing more future offspring. I suggest that if a greater source of blood became available, the incentive to cheat may become greater, and we may see the behaviour switch away from feeding each other. Perhaps the introduction of cattle is changing bat behaviour today.

Basically I can in-vision that it started as strictly kin based thing then became a hard-wired species trait, because maybe only a single bat family or population survived the decrease in blood supply. A genetic analysis would tell us how closely related all vampire bats are as a species.

Apr. 29 2011 11:29 PM
Isabel from NH

That is so cool! I love bats. And Vampire bats too!

Mar. 29 2011 05:40 PM

There is a possible logic gap in this claim of altruistic behavior towards non-relatives. To put it simply, the bats in the test are "known to not be related", but do the bats know that?

I don't know much about bats, but if the following statements (all plausible, I think) are true:
1) The bats normally fly back to the same hollow tree each day (eg, if they're territorial).
2) The colony of bats within a given tree are normally closely related to each other.
3) The sharing is normally only between bats within the same tree.

then the sharing behavior could have evolved as a form of altruism between relatives, without the bats needing to distinguish between relatives and non-relatives, as long as they limit the sharing to other bats within the same tree. So putting several non-related bats together to form a colony was an artificial situation that the bats would not normally experience, and they would have no reason to have evolved the ability to distinguish between relatives and non-relatives when sharing food.

Feb. 20 2011 12:13 AM
Michael from Texas

i must agree with most in this comments section: this is not proof of selflessness. It is a classic example of reciprocal altruism. It would have, i think, made for an even more interesting episode if it would have delved into the reciprocal altruism aspect and cheater detection systems that these bats have inevitably evolved. Really disappointing episode. Really a mass media treatment of science.


invariably - on every occasion : always

Feb. 08 2011 06:25 PM
Stevezy from Kentucky

idk bout this hypothesis yall, selection acts on indies not for the good of the species yo. Still interesting tho, feel like deej knows whats up, kin selection spread 2 tha max. Plus just cause altruism evolved from a form of selfishness it doesn't mean that our individual decisions to be kind are not truly selfless. idk cool stuff though, thanks

Feb. 02 2011 05:00 PM

This is so nice! I'm gonna go out now and throw up into few homeless people's mouths.

Jan. 31 2011 04:52 AM
Morris from Indiana

Sharing food so that your genes, along with everyone else's, don't go down the the proverbial flusher is not exactly altruism.

Jan. 19 2011 04:13 PM
Lindsey from IL

Maybe these bats would have eaten each other's blood if they didn't share. Maybe they were each just looking out for themselves.

Jan. 06 2011 01:44 PM

I start thinking about "friend over kin". I think the case is that your friend becomes kin therefore you ware willing to help him more. I know it from military experience. when you serve in a unit, your buddies become your brother. you can get killed trying to save your mate. and you will not hesitate to do so.

Jan. 06 2011 04:36 AM

I agree with what others have said...this is not really a form of altruism. It's more like mutualism where each partner is benefiting from the exchange (albeit one benefits immediately and one benefits in the future). It would also be interesting if the researchers had determined the amount of relatedness within the study group (and perhaps the did). Kin selection can still account for the evolution of this type of behavior providing the relatedness within the group is higher than between groups.

Jan. 05 2011 03:40 PM
Chisa from NY, NY

What an interesting story!

Homo sapiens also experienced a time of great famine...I wonder if we also developed this 'niceness' strategy when our species dwindled to the hundreds...?

It's interesting to think about how this kind of 'niceness' also depends on 'fairness' or 'justice' - the expectation of reciprocal action.

I wonder if examples of animal 'niceness' that arose in species that didn't have times of starvation are different...and do not depend on 'fairness'?

Bonobos, for example, are thought to wage 'love, not war' because, unlike their Chimpanzee cousins, they evolved in an environment where food was plentiful.

Do animals who evolve where food is plentiful develop 'niceness' (or peace-keeping) strategies based on 'love' (sex, grooming etc for Bonobos)..while animals who evolve where food is scarce develop niceness based on 'justice' or 'fairness' (like humans and bats who only give if there's an expectation of getting back)?

Just musing...

Jan. 05 2011 03:19 PM
claudia intama from Chiang Mai

Was the picture taken from Stelllaluna? It looks really familiar

Jan. 04 2011 08:59 PM
Jeff from Edmonton, Canada

Yeah I think some people here are hitting on what I am thinking too.
So they shared food which they had plenty of in expectation that they would be given food if they were in trouble. Thats pretty selfish, maybe not as much as not sharing in the first place, but selfish none the less. Sort of like investing my money, its more planning than going without.
Examples of Animals saving other species (Thomas pointed out the Dolphins and Chimps) Thats a much better example of non selfish caring in the wild.

Jan. 04 2011 01:08 PM
Emma from Toronto

I really don't think this case is an explanation of 'why there is nice-ness in the world'. Feeding strategies are much more than a choice whether or not to be “nice”: reciprocal altruism is ultimately a survival strategy.
Call me a reductionist, but no matter how ostensibly altruistic a relationship may seem to be, the basis for the relationship is a survival strategy. And aren't survival strategies inherently self-serving? If so, I think the bigger question is "what does it mean to be nice in a world where everyone's just trying to survive?"

Jan. 04 2011 12:09 PM
Michael Griffin from Tokyo

Every vampire bat is more closely related to any other vampire bat than it is to a member of some other species, so when vampire bats act generously toward each other, they are looking after "family," relative to the population of animals generally.

The existence of a famine situation in the evoluationary past of these animals is intriguing. Might the definition of "family" become broader the more difficult the circumstances? A moment of extreme challenge to survival is the worst time to go it alone. Better would be to team up with anyone or anything that is willing to work with you. The more extreme the challenge, the more cooperating partners you should consider helping / being helped by.

Consider the opposite scenario. When food and water are abundant and free for the taking, the temperature is in a survivable or comfortable range, who needs anyone or anything else, except for purposes that are essentially optional?

Jan. 04 2011 11:32 AM
Sean Michael Robinson from Seattle, WA

When the going gets tough, the tough nicely vomit blood into each other's mouths...

Jan. 03 2011 06:15 PM
amberlight from California

I'm sorry mh. For everytime I saved you and you saved me...can't we work this small problem out? I miss you my friend.

Jan. 03 2011 05:58 AM
gail from cape may nj

quid pro quo

Dec. 30 2010 02:47 PM

Thinking about it more, it occurs to me that we might not have learned anything new about animal behavior through the vampire bats. It could be that the altruistic behavior evolved through the mechanisms of kin selection normally, but, because evolution is imperfect, it evolved in a way that is exploitable--either because the mechanisms that detect kinship are imperfect or for some other reason. Maybe not enough time has passed to refine the trigger for the altruistic behavior. But still, it's an intriguing example.

Dec. 30 2010 08:15 AM

I understand that there are some examples where kin selection would at least have a hard time explaining the altruism observed (it's hard to respond not knowing the examples you have in mind). But what I was trying to suggest was maybe "kin" can mean "conspecifics". So, I guess I'm thinking of "species selection" (call it what you will)--just the same mechanism as kin selection, where an individual works against their own fitness to increase the fitness of a conspecific because there is a high concentration of genes in common (compared to non-conspecifics). Obviously (or potentially obviously), the prevalence of such behavior should be low because of the low (compared to relatives) overlap of genes between any 2 unrelated conspecifics, but it might still happen. Do we know of species that reduce their fitness to increase the fitness of other species? That would definitely run counter to the conjecture I'm putting forward here.

Dec. 30 2010 08:08 AM
Reginald P from Webzone

Episode was great was always but....I'm going to make this really brief having that 2 minute speech edited into every episode/podcast is pretty annoying and makes listening to episodes back to back a pain. First Wikipedia now this..

Dec. 30 2010 01:43 AM
Thomas from New Jersey

DJ, Human acts of altruism often run counter to kin selection, as do a few amazing examples we have of dolphins and chimps saving drowning humans.

Dec. 29 2010 10:37 PM
DJ from MA, USA

Interesting show, and at least a provocative (potential) counterexample to kin selection as the mechanism of the evolution of altruism. I wonder, though, if vampire bats sharing with "friends" isn't all that different from kin selection, though: vampire bats are likely to have more genes in common with each other than, say, any other species. Could this be an example of "kin" selection at a larger scale?

Dec. 29 2010 12:21 PM
Jose from Queens

Sharing is Caring! :)

Dec. 29 2010 10:22 AM
lea from montana

Thank you

Dec. 28 2010 11:20 PM

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