Doctor Science Knows

Friday, June 02, 2006

Housework and Fleas: How to do Evolutionary Psychology properly

If you spend much time on feminist blogs, you'll notice a bunch of people (most of whom seem to be males) talking about Evolutionary Psychology, and claiming that this or that human behavior may have an evolutionary cause.

They're usually wrong, and they've given EvPsych a really, really bad name. I'm going to show how it's done *right*.

Over at Alas, a Blog Ampersand has been going through the Male Privilege Checklist, discussing and explaining the entries. In Amp's post on Harassment, Car Sales, Housecleaning, and Weight, a commenter said:
it’s entirely possible that women have to one degree or another been selected during evolution for better hygiene than men.

Here's what I wrote:
I am putting on my Actual Degree in Evolutionary Biology Hat here, to say:

"back that puppy up with studies of non-human species or take it back."

Your argument is based on issues of personal hygiene, which in my experience is a completely different issue than house cleanliness, which we biologists call "nest site maintenance". Nest site maintenance is about parasite control. Most primates do not have regular nest sites, but move around every few days. This means that as an order primates tend to be messy, because why bother when you're not going to be there when the flea eggs hatch (2-3 weeks).

The human flea (Pulex irritans) is not human-specific, but is a pig flea that expanded its range. I was actually surprised to find this out, because as a rule animal parasites (& diseases) move to humans after domestication, so I expected human fleas would be related to dog fleas, since dogs were domesticated 100,000 years ago, pigs no more than 10,000 ya. The flea evidence suggests that most humans did not have semi-permanent nest sites -- and the need to keep them clean -- before the Agricultural Revolution.

(side note: this means that when we say someone's messy home is "a pig sty", we are being accurate. fleas included!)

So, we've got: a) chimpanzees don't do housekeeping, so evolution wouldn't have much genetic material to "work with", b) humans have needed "housekeeping genes" for only about 500 generations (remember, humans don't have a distinctive flea species even though we've had fleas for at least 300,000 flea generations), and c) housekeeping normally has to be taught, and with difficulty.

Conclusion with Actual Science Content™: there is no scientific need to suppose that humans have evolved "housecleaning genes", much less that they differ by sex.

So why does Nathaniel immediately suggest them as a possibility? Because he hates housekeeping (see above, under "primates"), and he can't believe that the women he knows are willing to do it unless they feel biologically compelled, and so he lets them. And then he doesn't have to keep his own parasites at bay.

Sorry Nathaniel, I'm a woman (*waves XX chromosomes, offspring*) and I'm a typical primate, too, i.e. a slob. You gotta learn to clean your own nest site -- and both you and the women in your life have to learn when you really need to just let the mess go, and say "it's clean enough, really".

later, I added (or tried to add, except the posting interface hates me):
Science update:

While getting ready to post an expansion of my comment above to my blog, I set out to fact-check my assertions about flea evolution, some of which I had pulled out of my knowledge of biology aka my butt (e.g. that apes don't have fleas because they move around too much, which is true), and some of which I got by googling.

I now find out that the "human" flea, Pulex irritans, seems to be a native of the New World, and though at one time the original host was thought to be the peccary (a wild pig, though never domesticated), flea biologists now think it may have hopped over to humans from *guinea* pigs, when they were domesticated in the Andes. It then would have had to migrate to the Old World over the Bering Strait, in what you might call the opposite direction to the usual, fast enough to be found in Egyptian homes at the time of King Tut (from Antiquity, Volume: 75 Number: 289 Page: 499–500, "Fleas From Pharaonic Amarna", E. Panagiotakopulu).

The moral of this story:

1. Don't make up EvPsych theories unless you know a lot about human biology *and* about the biology of other species.

2. Check your facts; some will be surprising.

Evolutionary psychology doesn't have to be bad, any more than it has to conclude that any current social pattern is "natural". For instance, I've concluded that humans are *naturally* slobs, that by settling down and having fixed abodes we're practicing a behavior for which we are ill-adapted, and *naturally* trouble will come of it (plague, typhus, bedbugs, my study).

In conclusion, two book recs:

Mother Nature : Maternal Instincts and How They Shape the Human Species by Sarah Blaffer Hrdy. This is what feminist evolutionary psychology looks like.

More Work for Mother: The Ironies of Household Technology from the Open Hearth to the Microwave by Ruth Schwartz Cowan. Or, how come all these labor-saving household devices don't mean less time spent on housework?