Cultural Evolution from Mosquitos to Worm Grunting

A very good day of grunting worms. Credit: Ken Catania So-called Gene-Culture Co-Evolution can be very obvious and direct or it can be very subtle and complex. In almost all cases, the details defy the usual presumptions people make about the utility of culture, the nature of human-managed knowledge, race, and technology. I would like to examine two cases of gene-culture interaction: One of the earliest post-Darwinian Synthesis examples addressing malaria and sickle-cell disease, and the most recently published example, the worm-grunters of Florida, which it turns out is best explained by direct reference to the man (Darwin) himself.

Strictly speaking the worm grunters of Florida is not an example of gene-culture interaction, as far as I know. But this case study serves as a starting point for a discussion of how traits that "make sense" arise even though the rise of said traits does not necessarily "make sense."

First, let me tell you what worm-grunting is so you don't feel compelled to scroll down the page to find out. I know you want to know.

"grrunht. grrunht. grrunht." To grunt worms, you need to get a proper wooden stake and a rooping iron. You drive the stake into the ground, then rub the rooping iron (a piece of metal) back and forth on the top of the stake to make a grunting sound. The earthworms in the vicinity come out of the ground and you capture them. Why? For bait, of course.

It's all about bass fishing.

Worm grunters do not know why this works. However, Charles Darwin did. He explained the phenomenon in his famous monograph on earthworms. Darwin said, "It is often said that if the ground is beaten or otherwise made to tremble worms will believe that they are pursued by a mole and leave their burrows."

Funny thing, that. I promise you that the typical Florida Worm Grunter is a fundamentalist Christian who believes "Darwin was Wrong." But, of course, I suppose knowing something is not all that important. As long as you get the bait. And thus, the bass.

Anyway, Ken Catinia is a biologist who tested Darwin's hypothesis and the results of his work were published literally seconds ago in the journal PLoS ONE.

Here it is shown that a population of eastern American moles (Scalopus aquaticus) inhabits the area where worms are collected and that earthworms have a pronounced escape response from moles consisting of rapidly exiting their burrows to flee across the soil surface. Recordings of vibrations generated by bait collectors and moles suggest that "worm grunters" unknowingly mimic digging moles. An alternative possibility, that worms interpret vibrations as rain and surface to avoid drowning is not supported.

"grunt. grunt. grunt." The key word here is: Unknowingly. You see, these worm grunters do not have to know how or why grunting works, but you can bet your Aunt Tillie's dentures that over time the noises made by the human grunters become closer and closer to the noises made by the moles, because the better you are at imitating the stimulus, the more bait you get, and thus .... (all together now) ... the better the bass fishing. The bass fishing is the proxy for Darwinian fitness, but since most of these grunters actually earn their living collecting worms for bait, the number of worms that come flying out of the ground is more than a proxy. Them worms is RS in the makin' ...

That is all very interesting, but what about malaria and sickle cell? This is an old story, and I want to point out two versions of it. This all starts out with the discovery of the sickle cell allele. In the late 1940s, researchers tried to understand the distribution of this allele in relation to race. The previous several decades had seen an increasingly complex view of race emerge in Western, Central and especially East Africa, where your basic tribal black person refused to cooperate with older concepts. It turned out that almost every trait that was first defined to describe the "African" or the "Negro" failed to show up in one group or another, with some groups having nearly none. You have probably heard the story about how anthropologist started out with the idea that there were about five races, but as fieldwork progressed, it was quickly discovered (and reported in some summary paper somehwere) that there were realy 15 races. Then a later paper showed how there were 43 races. Then a later paper showed that there were 111 races. And so on and so forth. Finally, when the number of races was passing 500 or so and there was no sign of a letup, anthropologists figured out that they were doin' it wrong. Well, these days were the end time for the race concept, but people were still using sickle-cell trait as a racial feature.

In the 1950s a researcher named A.C. Allison suggested that sickle-cell heterozygotes had some protection against falciparum malaria (Plasmodium falciparum the deadliest of the malarias). Staring with Allison's work, and continuing with Frank Livingstone's work, it eventually became apparent that the sickle cell allele was a) one of several easy to get mutations conferring protection against malaria; and b) not a racial marker, but rather, an indicator of recent history and very rapid local adaptation.

Livingstone wrote a number of papers on this, but two were key: One in the British Medical Journal in 1957, and the other in American Anthropologist in 1959. While the latter is more comprehensive and provides a richer version of the story, the former is accessible and can be found at this link.

Where Allison had recognized the malaria-sickle cell connection, Livingstone added the historical particulars. Looking in West Africa (where Allison had worked in East Africa) Livingstone proposed that fulciparum malaria was not a human disease until recent encroachment into a forest habitat by agriculturalists. Foragers living previously in the rain forest would have had very little contact with the progenitors of this mosquito, because of the physical layout of the forest and the nature of drainage. But agriculture removed the canopy and created myriad breeding locations for the mosquito vector (Anopheles), bringing the vector into greater frequency and into more direct contact with the humans.

Just to be sure that we understand the story here, you may have to remember back to Bio 101 or high school for the details of this classic case. If you are a homozygote for the S allele (no sickling) then you are very likely to die of malaria because you are not protected against this deadly form at all. It may or may not kill you before you reproduce, but on average, homozygotes for S have fewer offspring than they otherwise might have. If you are homozygotic for s (the sickling allele) then you will die before you reproduce (in the absence of medical intervention, not available in the African "Neolithic" and "Iron Age" during which all this was happening). But, if you were heterozygotic for s (if your genotype was "Ss") then you would not die of the sickle cell disease, and you you would have protection against the extra deadly form of malaria.

Proving that evolution sucks, and that if there is an intelligent designer, s/he is a moron.

That was Livingstone. But later, others, in particular Bill Durham, developed this idea even further (I'm oversimplifying here). In some parts of West Africa, there is a tradition of eating yams, which contain a chemical that actually reduces the effects of sickle cell. However, that also reduces the effectiveness of sickle cell in fighting malaria. To make matters worse, the time of year that the yams are harvested is the time of year when the malaria-carrying mosquitoes are most common, and one is most likely to get malaria. Abundant yams would mean severely curtailing the effects of sickle cell in heterozygotes, making this dumb adaptation even dumber.

However, in these traditional cultures, a cultural trait emerged that fixes this. There is a yam festival, during which the idea is to NOT eat any yams. For several weeks. The yams are harvested, put into yam storage bins, and they start to rot ... but you can't eat them. Eventually, the festival ends and you can eat the yams that have not rotten yet. The festival tends to end at about the same time that the malaria threat is reduced. And, just like the worm grunters of Florida, the people participating in this behavior do not know what is happening. There is supposedly no connection made in the West African case between yams and reduction of protection against malaria. I'm not sure that I believe that, but that is what is said.

But how does such a trait emerge?

Who knows? But the worm grunters may provide a clue. With worm grunting, it must not be too difficult to see the connection between a particular procedure and combiantion of tools and success, even given that there would be background variation in worm recruitment owing to factors unconnected to the act of grunting. Over time, observation and possibly experimentation calibrate the method, and the calibrated, improved method becomes part of the relevant folklore. I strongly suspect that something like this happened in West Africa, and was missed by the researchers who assumed the natives would not have figured out a gene-culture connection. But just like the Florida worm grunters do not know how or why gruinting works, the West Africans many have also not known how the festival interacted with illness (or lack of it) in the villages.

You often hear about how culture is "adaptive." This is usually part of the "evolution has stopped for humans" song and dance. It is often presumed that culture is in some way smarter than biology. Thoughts, symbols, communication of accumulated information of methods via our wonderful linguistic capacity 'override' biology.

Well, no. Culture tend to be dumb, indirect, unscientific, and often a matter of luck. Practices may be developed because they work, but more often than not "working" is measured only indirectly, if at all. And, as in the case of malaria, cultural change and technological innovation are not always improvements. Agriculture and the rain forest did not mix: Malaria is only one of many very nasty diseases that have emerged because of this association. And sickle cell is only one example of a barely effective, painful, and utterly annoying adaptation to deal with the problems culture caused.

Kenneth C. Catania (2008). Worm Grunting, Fiddling, and Charming--Humans Unknowingly Mimic a Predator to Harvest Bait PLoS ONE, 3 (10) DOI: 10.1371/journal.pone.0003472

Linvingstone, Frank (1959). Anthropological Implications of Sickle Cell Gene Distribution in West AFrica American Anthropologist, 60 (3), 533-562