Like most people, I hate having a cold or the flu.
But being sick gets slightly better when a friend drops off some classic movies or goes out for a snack and comes back to throw it up all over me.
Wait, that’s bats.
Feeling cared for makes me feel better, even if I’m still sick.
And vampire bats cheer up their sick friends by going out, drinking some blood, coming back, and barfing it all over them.
You know, so the sick bat doesn’t have to go out!
We humans and bats are pretty social creatures.
But -- like you might’ve noticed with pretty much everything we talk about in this course -- there’s a whole range of ways that animals work and live together.
Social behavior like caring for our young, fighting off rivals, joining a pack, or even fusing together into a huge super animal like the Power Rangers, adds a whole other layer of complexity to the lives of animals.
And even raises questions about being, culture, and what it means to be an individual.
It’s time to put the “meta” in metazoan.
I’m Hank Green, and this is Crash Course Philosophy.
Just kidding, I’m way younger than Hank -- I’m Rae Wynn-Grant, and this is Crash Course Zoology... with a hint of philosophy.
All animals -- not just butterflies!
-- have some level of social-ness that influences how they interact with other animals in their species.
Formally, sociality is how much individual animals tend to associate with other individuals in groups where they cooperate together towards a shared goal, like raising young or hunting down food.
We can think of sociality like another layer of multicellularity, or being made up of many different cells, which is one of the four key animal traits.
Having more than one cell enables specialized tissues and organs, like a brain, and opens up new ways of life that bacteria can only dream of.
Well, if they could dream, because you know, no brain.
Except in sociality, instead of individual cells working together, there are individual animals.
Many insects, a few crustaceans, and exactly 2 mammals practice the most extreme form of sociality.
They’re eusocial, which is a term first used by American entomologist Suzanne Batra who’s known for her work on bees.
Eusocial societies have three essential characteristics: many generations are alive at the same time, there’s an extreme division of labor where individuals focus on just one specialized task, and older animals cooperatively raise younger ones.
Termites might actually have been the first eusocial animals to evolve.
They’re also an example of eusocial animals so highly organized that the entire society functions like a single superorganism, where groups of individuals function more like different systems in the body that work together to keep the overall organism alive.
But eusociality isn’t the only way animals work together.
Presocial animals maintain close family relationships, and maybe live together or cooperate to raise young, but not as dramatically as truly eusocial animals.
Presociality is pretty common and covers a huge range of behaviors, so scientists divide animals further into categories and subcategories, two of which are subsocial and parasocial -- which are the ones most other animals fall into.
In subsocial animals, parents take care of their young for at least a little bit.
This includes a fair number of animals: fish, many arthropods, and, yes, even some annelids, like leeches.
All mammals are at the very least subsocial, since mothers feed their young milk, but often mammals have more complex social lives.
Mammals can be parasocial animals that live together in a single place and take care of their kids for some amount of time.
Sometimes they’ll help their buddies out with their kids, or show mild versions of some eusocial traits.
Lions might be a familiar example, but there are also social millipedes, and even spiders.
And at the other end of the spectrum we’ve got solitary animals, which live alone except for times when they have to be around another animal to mate or raise their own young.
A lot of solitary animals will wander a vast territory, and have young that grow up pretty quickly.
But remember, we humans use all these categories to understand how non-human animals interact with each other, but they’re pretty fuzzy.
Many animals have complicated social lives, or change how they interact with others in the species as they grow, and we’re still working on understanding what all those complexities are!
Including how and why social behavior evolved in the first place.
In the 1960s and 70s, evolutionary biologists, who study how animals change over time and how those changes resulted in the diversity we have today, connected altruism with the evolution of social behaviors.
Altruism is when an animal does something that benefits another at its own expense.
Like donating to a charity, or our vampire bat puking up blood.
In particular we believe animals engage in reciprocal altruism, meaning that when they do something nice, they expect something in return.
Our vampire bat was nice to the sick bat not out of friendship, but in case it got sick and needed blood-vomit one day too.
Specifically, it could be that some animals are driven by inclusive fitness, which is when an individual can increase its evolutionary fitness by supporting its non-offspring relatives.
Like in this case, it makes sense to give up a small cost, like sharing your lunch, for a bigger benefit to relatives.
Because their success, as far as your genes are concerned, is still your success.
So as long as altruistic or inclusive fitness behaviors are a net benefit for the genes involved, they’d show up more and more often in a population.
And they could eventually lead to the evolution of complex societies and social behaviors!
But evolution has actually given the world a social lifestyle so extreme it gets its own concept beyond sociality.
Let’s live a Day in the Life of a colonial organism, the Portugeuse Man O’War.
Allow me to introduce Physalia physalis, the Man O’War.
It floats across the Atlantic, Indian, and Pacific oceans, sailing on the winds and currents and dragging its long, stinging tentacles behind it like a net, snatching up prey as it goes.
The Man O’War is?
made up of physically connected, interdependent clones.
Basically the individual building blocks that make it up are actually mini-animals called zooids or ramets instead of just individual cells, so we call it a colonial organism.
Like there are zooids that make up the gas bladder that the Man O’War uses to float around.
The zooids even pump out their own carbon monoxide gas to inflate it!
Other zooids form the tentacles with little venomous barbs to paralyze prey.
With their meal trapped, the tentacles pull the prey upward, delivering the prey to other zooids that secrete digestive proteins.
There are also zooids responsible for making sperm or eggs.
And some zooids, called jelly polyps, probably do something, we just don’t know what yet.
All the zooids look and act differently because even though they all have the same genes, some have turned different ones on or off.
It’s like when you skip certain steps in a recipe -- even if you have the exact same instructions and ingredients, you can get very different results.
We call the whole Man O’War the zoon or genet, and for it to work as one unit, the zooids have to communicate with each other.
We know nerves help coordinate movement, but exactly how colonial organisms work on a day to day basis, remains mysterious.
Have a nice day… or days, Man O’ War!
Corals and Man O’Wars are the most well known colonial organisms, but there are others like salps and pyrosomes.
Coloniality is such an extreme form of sociality we even consider it its own thing.
And it’s evolved independently multiple times, with some lineages having more intense modularity, or division of labor between the individual animals that make them up, than others.
Some scientists hypothesize that colonality is like an evolutionary “if you can’t beat em, join em.” Super intense competition for space made an extreme division of resources and cooperation a good strategy.
And being able to grow and adapt indefinitely because each piece of a colonial organism acts like it’s own independent subsection is a plus.
It’s urban sprawl, but in animal form!
But even at the extremes, evolution makes no commitments.
Some previously colonial organisms, like some hard corals and one group of the otherwise colonial-to-the-core phyla of Bryozoan, have returned to the single-ish life over time.
Though why they quit on coloniality is something that scientists are trying to figure out.
But maybe it’s a similar explanation as to why evolution reverts to something simpler in other traits: being colonial just wasn’t benfical enough to keep doing.
Regardless of how extreme the lifestyle, from our human perspective, animals forming what looks like societies or colonies brings up some big, philosophical questions that we really don’t have good answers for...yet.
Like take beehives and ant societies that form superorganisms, or any colonial organism.
What exactly counts as the “individual” animal, and who is evolving here -- the individual or the whole society, or both?
And it gets more complicated.
Some colonial organisms like Bryozoans reproduce in two different ways.
They sexually reproduce between zoons, but the individual zooids are produced by assexual reproduction, which is why they’re clones.
And a 2020 paper by researchers from the US and Panama found that only traits passed between zoons, and not individual zooids, could be inherited.
Which means natural selection and evolution like we see in other animals only applies to the superorganism and not the individuals making it up.
So is the zooid or the zoon the animal?
The lines really are that murky.
The other big question is whether animals have culture, or the collection of behaviors, customs, and knowledge of a group that has something in common, like an ethnic origin or location where they live.
Culture is passed down not by genetics, but through learning.
Culture seems like a human thing, but animals like orcas speak different dialects and use different hunting techniques depending on what part of the world they’re from...which looks like a culture to me!
So there’s so much more to learn in zoology.
Animals live far richer social lives than us humans give them credit for.
They consider if it’s worth their trouble to help each other out, hold specific jobs within their society, and some work so closely together that it’s impossible to tell where one animal ends and another begins.
Their complex social behaviors can even go way beyond anything us humans are capable of!
Next week we’ll talk about a very different type of interaction between animals that’s