Wednesday, January 23, 2013

The unexamined walk is not worth taking

I've been reading Robert Macfarlane's beautiful book, The Old Ways: A Journey on Foot, about his travels in Britain and beyond, from walks around his home in Cambridge, England, to the bird islands of the north, to ancient seaways where he, no sailor, sails with friends, and on to Spain and even Palestine.  Macfarlane's is a deep, broad, poetic, idiosyncratic and haunting voice and there is much to take in.

His description of his barefoot walks is whimsical (his friend walks barefoot through nettles because it's chili for the feet), his walk across the Broomway, a path in Essex that only when the tide is out, where many a careless wanderer has met his end, shows a bit of a stubborn, defiant nature that I can't help but believe gets him far.  He travels alone, or enlists the aid of wizened sailors or lifelong inhabitants of the moors, he walks with friends.  But he is always observing.

It's an observation that he tosses off when writing of his travels between bird islands in northern Scotland that catches my attention today.  He is sailing from the Isle of Lewis with four experienced sailors on a 75 year old boat, the Jubilee.
I watched gangs of skua pursue single gannets: their method was to fly above a gannet, drop onto its back, force it down onto the sea, smash its skull with their beaks until the gannet was dizzied, then paddle its head underwater with their feet until it vomited up the contents of its stomach, which the skua then ate. 
This is curious indeed and raises many questions.  It's not the most straightforward way to catch fish, after all.  What else do skua eat, and how else do they procure it?  And are they always so brutal?  How on earth could they learn this rather exotic and complex way of dining?

Great Skua; Wikipedia
In my wanderings through what's written about skua, they are most frequently described as "avian pirates."  The fancy word for this is kleptoparasite, but as long as we're anthropomorphizing, "bully" or even "brute" might be more appropriate. Not only do they smash gannets' skulls, but they have been seen to grab them by the wing in mid-flight so that they stall and fall into the sea, whence the poor birds disgorge the fish they've just caught, freeing it for the skua to scavenge.  And it's not just gannets; they also steal from puffins or terns.

Most skua don't always steal what they eat, though.  They do fish themselves, usually splash diving for surface fish, and they often trail fishing boats and scavenge discards or innards.  But they don't live on only fish.  They eat a wide variety of things, including other seabirds; chicks, fledglings and adults, large and small. They also eat eggs, goose barnacles, tons and tons of goose barnacles, and sand eels when they are available, small mammals.

Gannet; Wikipedia
Skua are generalists, omnivores, but individuals also might specialize, preferring sand eels to barnacles, or whitefish to herring. And huge changes in what they eat over time have been documented, so they certainly can adapt to changes in the availability of foods.

Thieves, pirates, kleptoparasites.  Brutes.  Whatever you want to call them, they don't sound like very nice birds.  But are they worse than the gannet, who you might pity given how he is treated by his near-brethren?  The gannet is a hunter, too, hunting fish, that of course it eats alive, often swallowing the poor fish before surfacing after a dive.  And, people on the Isle of Lewis eat gannets, too (though Macfarlane writes: "I know a Lewisian crofter who, when I asked him whether he liked gannet meat, replied, "I gave a piece to the dog and it spent all week licking its arse to take away the taste.")  So we might just be pots calling the kettle black.

It could be, and surely is argued that kleptoparasitic behavior is innate: skua are born to harass gannets.  Not all seabirds treat each other this way, after all, so it must be something in the skua genome that makes them do this.

But, skua aren't only brutes.  Yes, they do treat gannets abominably, and they do dive bomb people who get too close to their nests, which from a person's perspective might seem brutish, but they are doing it to protect their young.  Which means that they do have some warm and fuzzy feelings. Indeed, like other seabirds, skua invest proportionately more in their young than do land birds.

What part of their behavior would be inborn, anyway?  They don't always smash the gannet's skull, they don't always grab their wing, they don't only eat by stealing, they don't only eat fish, indeed their diet can change from year to year, and they aren't always brutes.  So, exactly what kind of protein would a protein-coding gene be coding for to produce this kind of behavior?

Frigate bird; Wikipedia
Perhaps it's something that skua have been teaching their young for millennia, a behavior passed from generation to generation, not inborn at all. But if so, you'd think it might have caught on among other species of seabirds, so everyone would be dive bombing the poor gannet, a particularly skittish bird. Other seabirds are kleptoparasites, most notably the frigate bird, and many will steal another bird's food when the opportunity arises, but the skua version is not a generally shared behavior.  

So, of course what this all brings up is the question of whether there are genes for behavior or not. Or, is behavior an emergent property for which the groundwork is laid by genes that give us all the ability to scavenge and steal, care well for our young, and a whole host of things besides?  If so, we aren't going to find genes 'for' kleptoparasitism, just as we aren't going to find genes for good parenting -- or bad.

Life evolved depending on one creature living on the flesh of another, by and large.  It's a fundamental legacy of our common ancestry; we all share the building blocks of life, and get, or steal, them from others to survive.  No plant or animal likes being eaten alive, often in a cruel way (since other than humans, species haven't got abattoirs that are at least somewhat terror-free and quick in their killing).  It may be cruel for us to maim, kill, or torture one another for reasons other than food, as is so often what humans do.  But killing for food is what we have to do, whether we are eating plants or animals.  This was one of the observations that led Darwin to his theory that adaptations arise via harsh competition.  It's not the only fact of life, but it's a fundamental one.

Are there genes 'for' survival? 

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