Pur Autre Vie

I'm not wrong, I'm just an asshole

Wednesday, August 09, 2017

Dogs and Bacteria

Zed retweeted this tweet, with the obligatory comment that it is the story of Alan's life:
I am obsessed with the video. Of course it is a short clip and the surface interpretation—that the dog thinks the swimmer is drowning—could be wrong. But I'm prepared to take the clip at face value.

One deeper question is what is going on in the dog's head. That is to say, even if the dog "believes" that the swimmer is drowning, is that a subjective belief, or is it a description of a mechanical process? (In other words, does the dog "believe" the human is drowning in the same way that a computer might "believe" a shape resembles a butterfly?) But these sorts of philosophical questions are pretty much unanswerable, I think. I want to believe that the dog is experiencing urgent concern for the swimmer, but it's hard to say.

The video reminds me, though, that humans and dogs co-evolved very early on. Long before cats were domesticated, long before humans started practicing agriculture, our fates had become interwoven with the fates of dogs. Putting aside what is "really" going on inside their heads, it is easy to see why dogs would evolve to display tremendous loyalty, and why we would evolve to recognize and reward it. And this, I think, is why the video makes such an impression on me. It is the vivid playing out of a dynamic that is built into our genes, and the genes of dogs.

It reminds me of a theory that occurred to me years ago. One striking fact about the human sense of taste is that ascorbic acid (vitamin C) is virtually tasteless. This is odd given that it is a necessary nutrient. What I think it indicates is that until we created highly artificial environments like ocean-going ships, we seldom faced scarcity of ascorbic acid, and so there was little or no selective pressure to detect it.

By contrast, it is very easy to taste lactic acid and acetic acid, neither of which is (so far as I know) nutritionally necessary or even helpful. Not nutritionally helpful, but still quite valuable in food, because for reasons that I don't fully understand, there aren't any pathogens that can survive sufficiently low pH levels. So lactic and acetic acids are preservatives and indicators of safety, and being able to detect sourness in food and drink was probably very valuable in our evolutionary environment. More valuable than detecting ascorbic acid, it would seem!

And so it appears that, just as with dogs, acid-producing bacteria probably co-evolved with us, and our response to them has been built into our genes through long-running selective pressure. I like to think about this when I'm enjoying a sour beer. That is the taste of human history! That is a signal from my ancestral environment reverberating in my brain.

(Alcohol might be subject to the same dynamic—like acid, alcohol is effective at killing pathogens, and certainly humans are inclined to seek it out. Caffeine, by contrast, seems as though its effects must be serendipitous, because why would we evolve to respond positively to it? Coffee is healthy but it's not that healthy. Also, I don't think most humans had access to coffee or tea for most of human history.)

I should note a few boring possibilities. Maybe lactic acid and acetic acid are simply easier to detect than ascorbic acid for chemical reasons. Maybe we developed a taste for tart foods precisely because tart fruits are often (though not always) high in ascorbic acid, and not because lactic acid protects food from pathogens. (In this theory, lactic acid is detectable to us because it bears some chemical resemblance to citric acid and malic acid, I guess.)

But I prefer to believe that lactic acid tastes strong because it was so valuable to our ancestors. And I prefer to believe that dogs have a subjective feeling of loyalty and affection, and I'm certainly not going to stop enjoying videos of them displaying it.

3 Comments:

Anonymous Anonymous said...

I'm not convinced that ascorbic acid is tasteless. I'm pretty sure I could recognize it.

8:04 AM  
Blogger James said...

I have pure ascorbic acid, which I use in brewing beer (ascorbic acid is effective at removing chlorine from water). It is not truly tasteless, but its taste is mild enough that in typical concentrations it is not noticeable. It certainly doesn't taste nearly as strong as the other acids that are typically found in fruits (citric and malic).

Consider that there is considerably more ascorbic acid in green bell peppers than there is in oranges (pound for pound). Do green bell peppers taste like ascorbic acid to you? Not to me.

Just on an evolutionary level, it's hard to imagine humans would have known to eat green bell pepper (high in vitamin C) and not, say, grapes (quite low in vitamin C), in order to avoid scurvy.

11:05 AM  
Blogger James said...

Or to be more precise, it's not that I think ancestral humans understood the link between nutrition and scurvy. What's hard for me to imagine is that an anatomically modern human would detect the ascorbic acid flavor in green bell pepper and be drawn to it. By contrast, I believe our ancestors probably were drawn to malic acid, citric acid, etc., which are easily detectable by taste and which, while being nutritionally unimportant in themselves (as far as I know), are often found in fruits that contain all sorts of helpful nutrients.

11:13 AM  

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