Would you risk your life to save someone else? Probably – for your child, your spouse, or another close family member. But how about for a stranger – someone quite different from you – would you do it for a thousand strangers? Would you at least endure a papercut if it made life easier for others unlike you?
These are the types of questions explored in mutualism, the arena of ecology and evolutionary biology that looks at how and why unrelated species cooperate.
Mutualism is distinct from cooperation within species – wherein one individual might sacrifice herself for the benefit of the obvious, similar whole. Mutualism is, instead, an activity that takes place between species. It includes mutually beneficial symbiotic relationships, such as the friendly microbes that live in our gut. Both parties get something out of the association, but at some personal cost. It is this cost that has perplexed evolutionary biologists, going back to at least Darwin: why should one party endure harm for the benefit of a very different party?
And this is the question that initially got me interested in studying mutualism.
The field has not been studied very much compared to interactions involving predation, competition, and exploitation. Yet we are learning that every organism on Earth is involved in at least one mutualistic relationship. Some might label the cost one endures to benefit another as “altruism”, but researchers in our field, like many people outside it, are haunted by doubts that there is any such thing as true – unqualified – altruism.
My grandmother always said she tried to do something every day for someone who could never return the favour. I am sure she was sincere and meant what she said. But now when I think about it, I don’t know how she could find such people in her small village of Bobcaygeon, Ontario. First, she would soon run out of people to help, and second, she would have had a hard time not running into those she had helped. In fact, anyone who tries to help someone without an expectation of benefit learns this: it is hard - because no matter how much you try, good deeds seem to come back to you in some way. This could be just the warm feeling you get from helping others.
So how does this anecdote relate back to the initial question: how can a mutualism evolve if it is costly to provide another individual with a benefit? The answer is that most, if not all traits, are associated with some cost, and so there must be a net benefit of possessing a trait for it evolve. To illustrate such a trait using a non-mutualism example, consider a male peacock's feathers. Such an elaborate display is obviously associated with a cost - it makes the male more conspicuous to predators and hinders their ability to escape quickly. Yet, an elaborate display is more attractive to females, increasing the male peacock's reproductive success. Therefore, a mutualistic trait evolves not to benefit another party, but because it leads to a net benefit for the bearer of the trait; the plant doesn't produce nectar for the good of the bee, it produces nectar to attract the bee that then provides the plant with a reproductive service, namely pollination. Taking advantage of another's unique abilities is often an effective strategy, perhaps explaining why mutualism frequently pays-off in nature.
This not only speaks to the value of research in this field, but again reminds us that whether we are the same species or not, we are all part of a greater whole; how we interact with each other, as well as other organisms, can come-back to affect our own well-being. By studying mutualism, we hope to understand how – despite varying interests and needs - entire ecosystems are built upon the cooperative efforts of its members.
If organisms as distantly related as plants and bacteria can recognize this, I'd like to think, so can we.