Farmers plant soybeans in a crop rotation because soybeans take nitrogen out of the air and fix it into the soil, so that other plants (which cannot take nitrogen from the air) can use it. (Stick with me, I promise it gets interesting). The alternative is to use ammonia that is produced artificially using the Haber–Bosch process. This takes a lot of energy. Like, a LOT. Around 2% of ALL the energy produced every year goes to making ammonia! We only know how to do it using high heat and pressure. But legumes perform this process at normal atmospheric pressure and temperatures.
But…how do they do it? St. Thomas would say that there is a design here (his 5th proof for the existence of God). I assume the evolutionary biologist would say that the plant evolved to be able to do this. I think we can all intuitively see how, say, the bears with the sharpest fingernails are the ones that survive and pass on their genes to their offspring, eventually resulting in claws, etc. We can kind of see how that makes sense. Darwin calls this survival of the fittest. OK. Sure. Thing is, claws, teeth, feathers, wings, etc. are able to be spoken of as being more or less “fit” for their task. Survival of the “fittest” implies a gradation of fitness. But, being able to take nitrogen from the air is a completely binary proposition. Either this physical/chemical process happens or it doesn’t.
Now, perhaps you’re thinking: “Well, who needs evolution in a case as simple as this. We’re talking about a stupid plant. Why did it need to evolve at all? Maybe some plants just worked that way and so they’re still around. Throw enough things against the wall over billions of years and something’s bound to stick!” Fair point! Except…if this process is so simple, why haven’t we replicated it? Remember how I said it takes a TON of energy to generate ammonia for fertilizer? This is a problem that humanity is trying to figure out, but we haven’t been able to. Because it turns out the humble soybean solved an INCREDIBLY complex problem using 170 electrons and 2 catalysts. What “arrangement” of the electrons makes this work? We have no clue. Oh, we could run the simulation through a computer and actually discover what works…except there’s one problem. The number of combinations that define the problem. The number is 2^170. If you’re thinking, “OK, that’s big, but how big? Like, I couldn’t use my iPhone and we’d need a couple super computers kind of big?” Well, bigger than that. As in, the number of atoms on planet earth is 2^150. So, to define problem space, you would need every atom on earth, and then a million more earths and every one of their atoms too. Yeah…that’s gonna take some time. I dunno, let’s say you’re checking a BILLION combinations every microsecond, it’d still take you 10^19 millennia. Read: way longer than the universe has been in existence. Pretty lucky soybean.
Perhaps the atheist evolutionary biologist would then claim that “look, it didn’t evolve, this is just the way that the universe works physically and chemically. It’s just a basic first principle.” I would simply counter by saying, “Oh, you mean this is an example of the universe acting ‘always, or nearly always, in the same way, so as to obtain the best result?’ Why, that’s exactly what Aquinas says too. Welcome to theism friend! Try the bean dip.”