Science Corner: Only They Know the Difference

Maybe you remember the old Far Side cartoon with two jellyfish outhouses featuring (apparently) identical icons on their doors, the caption reading “Only they know the difference.” I was reminded of that strip reading this paper about two closely-related goby species. As the paper details, humans can face challenges differentiating them without genetic analysis. The most diagnostic visual difference only emerges once the fish reach a certain size, making the identity of smaller fish more ambiguous. Yet the genetic analysis reveals clearly distinct populations; when it’s time to find a mate of the same species, clearly the goby know who’s who.

An ongoing area of research involves questions of how species boundaries form and how they are maintained. How does a population that behaved as one become two? We’ve discussed this topic before; sometimes it is simply a matter of becoming separated or isolated and then accumulating differences which introduce or increase incompatibility. Plants or animals which arrive at different islands and then adapt to different conditions there, or even adapt to similar conditions in different ways, represent a fairly straightforward model to understand called allopatric speciation. But sometimes the genetic differences come before or without geographic separation; that’s know as sympatric speciation. These goby species apparently underwent that kind of divergence. They occupy the same coral reef, and to all but the most careful observers they appear to be one species. Yet two distinct populations can be identified.

So how do the two goby species stay separated? One possibility is that they just swim in different circles. Like the Capulets and Montagues, the Hatfields and the McCoys, or the Sharks and the Jets, the two species could just keep to their own kind. But that doesn’t appear to be the case. Researchers sampled a number of different shoals of fish, and in each one they found both species, typically in the same proportions. That suggests the two species swim together, eat together, and deter predators together. So the fish are likely using some kind of cue from other individual fish and being choosy about mates. (Although the genetic data also indicate that every once in a while a cross-population pairing occurs, also like those feuding human clans.)

I found myself thinking about those fish reading this article by Tim Keller about trends in American Christian communities. I don’t think I’m plugged in enough to the relevant scholarship to have meaningful commentary about the bulk of it, but the summary remarks resonated for me. He writes about how progressive Christians and fundamental Christians see fellow believers as either part of their own group, or part of the other. That’s a dynamic I’ve lately been more aware of. Because of how I talk about science topics, conservative Christians increasingly identify me as liberal or progressive, making assumptions about my theology in areas I would consider unrelated. So while anecdotal, my personal experience aligns with Keller’s model of how the distinctions between different Christian traditions are maintained.

This dynamic creates a kind of pressure, a feeling of being pushed away from one kind of theology and towards another. Or maybe more relevantly, away from one community and towards another. That’s a distinctly different sensation from being pulled or attracted towards that other community. If I were being drawn to a particular community, then that would provide direction and a plan. But a push away towards a diffuse, abstract idea of a community is directionless, more of a “you don’t have to go home but you can’t stay here” sentiment. If other people are experiencing similar pressures, that might go some way towards explaining why deconstruction is in the water.

Unfortunately, I don’t think the goby have any solutions for us. The idea of mutually beneficial shoals in which both groups participate even while maintaining their distinctiveness is an attractive endpoint, but we don’t know how the goby came to that arrangement and the particulars may not translate anyway. Sometimes those kinds of analogies help me find a launching point and some language for my thoughts, but they don’t line up well enough for a complete solution. When that happens, it’s best not to force something. Keller promises a path to renewal, but it remains to be seen whether that path has an on-ramp from where I find myself. In the mean time, I guess there’s not much else to do but to just keep swimming, just keep swimming.