How do we find love?
It may feel like I am jumping the gun a bit, coming back after two years
and jumping straight to such a big question, but those two years have been
spent doing the experiments for my PhD thesis on the evolution and ecology of
species coexistence. While I generally consider my thesis work and my emotions
work as two separate bodies, this series of posts on romantic love is the most
natural launching point as it represents the overlap of the two. It is a great
transition from my pure science to thinking about more applied questions.
And anyways, people don’t really want to know what love is. What they
really want is to know how to find it! People’s drive to find love (I will
focus on romantic love as that is the most complete case) is a huge industry.
Actually, multiple industries, fueling match-making websites and consulting
services, countless books and talk shows, therapists, speed-dating events, and billions
of man-hours of gossip and conversation.
So what do I add to this conversation? I don’t feel that being a happily
married man or an evolutionary biologist give me a special view, many people
with those credentials have already chimed in. This may seem odd, but I come to
you as an ecologist. We are the people that study populations and communities
looking at how species interact with each other. It’s actually very similar to
economics and it probably has some insights since economists have already chimed
in plenty on romantic love, looking at it as an economic transaction.
How unromantic is that? An economic transaction!?! Romance is much more
like a competition! Hmmm, well I guess that’s more intimate but it doesn’t
sound any more romantic. It does give us a different perspective, though. And
let’s be honest, love does feel like a competition sometimes. Just because you
love somebody does not mean you always, or even often, want the same thing as
them. The reason I am going down this path is that when people are looking for something
called romantic love, they are looking for a stable and sustained relationship;
two people intimately coexisting, sharing their possessions, knowledge, and
themselves. Economists are good at placing a value on a relationship but, along
with a rather limited notion of value, this approach doesn’t identify
“sufficient” value. It is the ecologists who have devoted themselves to the
much more pertinent question, “how do things coexist?”
So what is necessary for competitors (individuals or species with
overlapping resource needs) to coexist? To try to make this paragraph manageable, let me quickly set “Sames” to mean
individuals of the same species and “Others” to mean individuals of a competing
species. Then, the coexistence criterion is that individuals must negatively
impact Sames more than they negatively impact Others (Chesson
2000). This is pretty opaque because “impact” here has a very mathematical
meaning and hidden implications. We can clarify these complexities by
relativizing impact. The longer coexistence criterion is that the ratio of impact
from Sames versus Others must be larger than the ratio of the carrying capacity
of Others relative to Sames (Equation 1). For our purposes, carrying capacity
basically measures a species’ local quality. It is the maximum population size
of the species when the competitor isn’t there.
 |
| Equation 1 |
The relativized coexistence criterion tells us that coexistence is a
balance of two qualities: how different two species are in their needs and how similar
they are in their ability to meet those needs (in a given environment). In
other words, coexistence requires species to achieve a similar enough level of
quality in a different enough way. The more different they are in their
qualities, the more different they have to be in their needs.
I imagine it like a bridge over a chasm. The width of the chasm is how
different the two species are in their ability to thrive in this environment
(their fitnesses). The length of the bridge we have is how different they are
in the way that they thrive. If the bridge is too short the weaker species
falls into the chasm and we don’t get coexistence. If the bridge is longer than
the width of the chasm, both species will coexist. Any extra bridge length
provides a buffer against fluctuation in the size of the chasm, stabilizing
coexistence in the face of change and random events. The most equal and resilient
coexistence comes when we have a massively oversized bridge spanning a very
narrow chasm.
From this we can identify three broad mechanisms which promote coexistence.
First, species need to be as equal in their fitnesses as possible – they need
to have very similar levels of quality in the given environment. Second, species
need to compete as weakly as possible – they need to have complimentary needs. Third,
species should have shared enemies or friends – they should have shared goals.
The first two mechanisms are necessary and sufficient for coexistence: similarity
of quality leads to narrower chasms while complementarity leads to longer
bridges. We can imagine the third mechanism as maintaining the bridge. Having
shared friends or enemies doesn’t promote coexistence by itself but if species
have different friends or enemies that erodes their ability to coexist.
I want to go into this idea of shared friends or enemies a little more
since there is less information on the subject available and I had to do my own
modeling to check it out. The first thing to note is that species don’t
interact simply as species-pairs, they exist in a larger community. That means
that while they are competing with each other, they are also competing, and
potentially cooperating, with other species. Complementarity works by each
species’ success making the environment worse for them, relative to the other
species, making future success more difficult (e.g., less prey, more predators):
when two species consume and are consumed by different species, these negative
feedbacks allow them to coexist. Interactions with mutualists (species which
cooperate with, and mutually support, the focal species) and other competitors
work in the opposite direction. As a species becomes more abundant its
mutualists become more abundant and its competitors become less abundant,
actually making the environment more desirable. When two species compete with
and cooperate with different species, these positive feedbacks will make it
harder for them to coexist. If, on the other hand, they share friends and
enemies, any advantages gained by one species will be shared by the other,
allowing the bridge to stay strong [1].
So, what does ecological coexistence tell us about romantic
relationships?
Well, quite simply it formalizes what is already common wisdom: both individuals
should perceive their partner as being more valuable than themselves. They
should both feel “lucky” to be in the relationship. This doesn’t mean anything
as extreme as actually valuing the other more than yourself (“I would die for
you”). It just means that if both individuals were to direct all of their
energy into the relationship, towards maximizing their shared wellbeing, they
would both be better off.
The new insight from ecological coexistence is what is necessary for this
to be true.
We can translate the ecological criterion into relationship terms by
replacing species with people, population size with wellbeing, and new
individuals with benefits received from contributions. Also, it makes more
sense to frame the relationship in the positive so we can replace “more
negative” with “less positive”. Thus, for two people to coexist in a
relationship, each contribution must
positively impact the other partner more than it would have impacted the
contributor (at least on average). The net effect of this is that both individuals
must value their partner’s total contributions higher than their own.
From Eq. 1, we see that for a relationship to achieve this, the couple’s
contributions need to be more complimentary than the relative difference in
their abilities to provide those contributions. In other words, the amount each
individual values what the other person brings to the table, relative to what
they themselves bring to the table, has to be greater than the relative
difference in the sheer amount they are able to bring to the table. Just as
with species, they need to achieve a similar enough level of quality in a
different enough way. It’s not enough for two people to be equal (e.g., prom
king and queen) and it’s not enough for both to be complimentary and humble (value
themselves less than they are valued by the other). You need at least some of
both. The latter is necessary for any positive relationship, no matter how big,
while the former is necessary for the relationship to be as substantial as a
romantic one.
A lot of what I am saying has already been said. From psychology and
neuroscience, we know that successful romances are a mix of similar and
different (I am getting my neuroscience info from an interview
of Helen Fisher of Rutgers University on her book, “Why We Love: The Nature and
Chemistry of Romantic Love”). Successful partners tend to be similar in
many ways. They tend to have equal attractiveness, social and economic status,
intelligence, as well as being equal in other qualities by which we tend to
rank people. They also tend to be similar in their major goals and values. Both
partners tend to share religious, political, and social goals but more
importantly both partners tend to be the same in whether they favour long-term
or short-term goals, whether they are more concerned in investing in their
future or making the most of their present. The best relationships also have
differences though, while the couple should share many goals, they should be
different in how they go about achieving them. In the most simplified metric,
one is usually a dominant personality while the other is a more subordinate
personality. More generally, the couple should agree which partner is stronger
in each area such that one is always dominant while the other is subordinate,
though who is dominant changes between situations or tasks.
While I have to admit that I only went to the effort of working out the
effect of shared friends and enemies for species coexistence because I knew
shared value was thought to be important for relationships, I think you will
still agree that the three mechanisms above fit well with what relationship
science has to say. First, species need to have similar carrying capacities
while couples need to have similar levels of quality (as measured not by each
other but by themselves, which should be a product of how much their present
society/environment values them). Second, couples, just like species, need to
be complementary in their needs and abilities. Finally, couples need to have
shared goals and values such that they succeed and fail together.
What coexistence theory really adds to this picture is a general
framework under which we can unify all this information. Psychologists have a
whole bunch of regressions that say which relationships are more likely to
succeed but these relationships are messy, there are a whole bunch of
relationships which don’t seem to fit. There are successful couples where both
are very dominant, where they are very different in terms of social and
economic status, where they have different religions, etc. Coexistence theory tells
us that a successful relationship results from the whole picture.
What I have tried to convey is that coexistence is a balance and this has
both positive and negative implications. Biologists study coexistence because
lots of species can coexist but also because lots of species can’t. No matter
how much equality or shared values a couple have, a successful relationship
requires at least some complementarity. The amount of complementarity required
only goes up with couples that are less equal or more independent in their
goals and different in their values. This means that people need to be
realistic in what they are looking for because a relationship requires that
both parties be satisfied. This lack of realism is most clearly seen in hoping
that a little bit of complementarity will cover for a substantial difference in
how much they are valued by society. Basically, you should probably stop
swooning over that celebrity (unless you are one yourself, at least in your own
way) because it is unlikely you are that really, ridiculously complimentary.
On the positive note, a rewarding romantic relationship only requires
that the balance be met, which can happen in many ways. Maybe there is just one
person out there who will maximize this balance for each of us, a soul mate,
but the opportunity cost of waiting for that one perfect relationship far
outweighs any additional benefits relative to finding a great relationship that
works. Coexistence, not just perfection, will lead to a rewarding romantic
relationship. When looking for a match we should seek equality,
complementarity, and shared goals, but successful relationships are born of
unexciting amounts of each, as long as we have all three, and we can even get
away with little of one, or even two, provided we have enough of the others.
You only need species to be as different in lifestyle as they are in ability
and you only need couples to be as complimentary as they are different in
quality [2]. Shared values and goals are only as important as those values and goals
are to the individuals, and if couples are well matched enough in the other two
areas they can overcome even important differences in what they value.
Now go forth and nerd up the dating scene (either yourself or with unsolicited
advice)!
In the next part of this series I will take this analogy one step
further, exploring what we can learn about the evolution of a relationship
(from initial attraction to old married couple) by looking at how species
coevolve with their competitors.
[1]
For the sake of the analogy I am simplifying how species interact with
predators and mutualists. In nature, shared predators can actually stabilize
coexistence if the predators are limited in how many types of species an
individual can efficiently hunt (due to learning, spatial separation of prey,
etc.). In that case, predators are known to switch between prey depending on
which one is more abundant, punishing success and supporting failure.
For mutualists, much of the ecological literature
focuses on competition for mutualists. Basically, mutualists are limited in how
many individuals they can interact with and mutually benefit. This leads to
species competing with each other to be more desirable to the mutualist. For my
purposes, I have assumed that the mutualist benefits each species proportional
to how much they benefit the mutualist and that the mutualist is only limited
by the number of individuals interacting with it. Thus, species don’t get
biased gains from or compete over mutualists but, if shared, they can benefit
from mutualists supported by the other species. This more accurately reflects
the relationship analogy of a shared goal or value, where the personal value of
a success is generally negligibly reduced by sharing that success with a small
number of others (e.g., raising a child, supporting a political cause).
[2] One aspect that this analogy misses is that species can have populations in multiple habitats while individuals have to be in a single environment (including place, career, social network, etc.). The first filter for species coexistence is that they have to survive in the same habitat. Equally, a major factor in finding a suitable partner is finding someone who thrives in the same environment you do (I feel comfortable leaving this in a footnote as people tend to interact primarily with others who chose the same environment). Equation 1 takes effect within the environment but if the relationship requires that one partner be in a environment for which they are not well suited, they will calculate equality based on their potential (in the environment they would choose otherwise) and the complementarity gains would have to cover the lost potential to justify them staying (I think this second part is true, should probably do the math to confirm).
[2] One aspect that this analogy misses is that species can have populations in multiple habitats while individuals have to be in a single environment (including place, career, social network, etc.). The first filter for species coexistence is that they have to survive in the same habitat. Equally, a major factor in finding a suitable partner is finding someone who thrives in the same environment you do (I feel comfortable leaving this in a footnote as people tend to interact primarily with others who chose the same environment). Equation 1 takes effect within the environment but if the relationship requires that one partner be in a environment for which they are not well suited, they will calculate equality based on their potential (in the environment they would choose otherwise) and the complementarity gains would have to cover the lost potential to justify them staying (I think this second part is true, should probably do the math to confirm).
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