Adaptation-Executers, not Fitness-Maximizers

“In­di­vi­d­ual or­ganisms are best thought of as adap­ta­tion-ex­e­cuters rather than as fit­ness-max­i­miz­ers.”
—John Tooby and Leda Cos­mides, The Psy­cholog­i­cal Foun­da­tions of Cul­ture.

Fifty thou­sand years ago, the taste buds of Homo sapi­ens di­rected their bear­ers to the scarcest, most crit­i­cal food re­sources—sugar and fat. Calories, in a word. To­day, the con­text of a taste bud’s func­tion has changed, but the taste buds them­selves have not. Calories, far from be­ing scarce (in First World coun­tries), are ac­tively harm­ful. Micronu­tri­ents that were re­li­ably abun­dant in leaves and nuts are ab­sent from bread, but our taste buds don’t com­plain. A scoop of ice cream is a su­per­stim­u­lus, con­tain­ing more sugar, fat, and salt than any­thing in the an­ces­tral en­vi­ron­ment.

No hu­man be­ing with the de­liber­ate goal of max­i­miz­ing their alle­les’ in­clu­sive ge­netic fit­ness, would ever eat a cookie un­less they were starv­ing. But in­di­vi­d­ual or­ganisms are best thought of as adap­ta­tion-ex­e­cuters, not fit­ness-max­i­miz­ers.

A toaster, though its de­signer in­tended it to make toast, does not bear within it the in­tel­li­gence of the de­signer—it won’t au­to­mat­i­cally re­design and re­shape it­self if you try to cram in an en­tire loaf of bread. A Phillips-head screw­driver won’t re­con­form it­self to a flat-head screw. We cre­ated these tools, but they ex­ist in­de­pen­dently of us, and they con­tinue in­de­pen­dently of us.

The atoms of a screw­driver don’t have tiny lit­tle XML tags in­side de­scribing their “ob­jec­tive” pur­pose. The de­signer had some­thing in mind, yes, but that’s not the same as what hap­pens in the real world. If you for­got that the de­signer is a sep­a­rate en­tity from the de­signed thing, you might think, “The pur­pose of the screw­driver is to drive screws”—as though this were an ex­plicit prop­erty of the screw­driver it­self, rather than a prop­erty of the de­signer’s state of mind. You might be sur­prised that the screw­driver didn’t re­con­figure it­self to the flat-head screw, since, af­ter all, the screw­driver’s pur­pose is to turn screws.

The cause of the screw­driver’s ex­is­tence is the de­signer’s mind, which imag­ined an imag­i­nary screw, and imag­ined an imag­i­nary han­dle turn­ing. The ac­tual op­er­a­tion of the screw­driver, its ac­tual fit to an ac­tual screw head, can­not be the ob­jec­tive cause of the screw­driver’s ex­is­tence: The fu­ture can­not cause the past. But the de­signer’s brain, as an ac­tu­ally ex­is­tent thing within the past, can in­deed be the cause of the screw­driver.

The con­se­quence of the screw­driver’s ex­is­tence, may not cor­re­spond to the imag­i­nary con­se­quences in the de­signer’s mind. The screw­driver blade could slip and cut the user’s hand.

And the mean­ing of the screw­driver—why, that’s some­thing that ex­ists in the mind of a user, not in tiny lit­tle la­bels on screw­driver atoms. The de­signer may in­tend it to turn screws. A mur­derer may buy it to use as a weapon. And then ac­ci­den­tally drop it, to be picked up by a child, who uses it as a chisel.

So the screw­driver’s cause, and its shape, and its con­se­quence, and its var­i­ous mean­ings, are all differ­ent things; and only one of these things is found within the screw­driver it­self.

Where do taste buds come from? Not from an in­tel­li­gent de­signer vi­su­al­iz­ing their con­se­quences, but from a frozen his­tory of an­ces­try: Adam liked sugar and ate an ap­ple and re­pro­duced, Bar­bara liked sugar and ate an ap­ple and re­pro­duced, Char­lie liked sugar and ate an ap­ple and re­pro­duced, and 2763 gen­er­a­tions later, the allele be­came fixed in the pop­u­la­tion. For con­ve­nience of thought, we some­times com­press this gi­ant his­tory and say: “Evolu­tion did it.” But it’s not a quick, lo­cal event like a hu­man de­signer vi­su­al­iz­ing a screw­driver. This is the ob­jec­tive cause of a taste bud.

What is the ob­jec­tive shape of a taste bud? Tech­ni­cally, it’s a molec­u­lar sen­sor con­nected to re­in­force­ment cir­cuitry. This adds an­other level of in­di­rec­tion, be­cause the taste bud isn’t di­rectly ac­quiring food. It’s in­fluenc­ing the or­ganism’s mind, mak­ing the or­ganism want to eat foods that are similar to the food just eaten.

What is the ob­jec­tive con­se­quence of a taste bud? In a mod­ern First World hu­man, it plays out in mul­ti­ple chains of causal­ity: from the de­sire to eat more choco­late, to the plan to eat more choco­late, to eat­ing choco­late, to get­ting fat, to get­ting fewer dates, to re­pro­duc­ing less suc­cess­fully. This con­se­quence is di­rectly op­po­site the key reg­u­lar­ity in the long chain of an­ces­tral suc­cesses which caused the taste bud’s shape. But, since overeat­ing has only re­cently be­come a prob­lem, no sig­nifi­cant evolu­tion (com­pressed reg­u­lar­ity of an­ces­try) has fur­ther in­fluenced the taste bud’s shape.

What is the mean­ing of eat­ing choco­late? That’s be­tween you and your moral philos­o­phy. Per­son­ally, I think choco­late tastes good, but I wish it were less harm­ful; ac­cept­able solu­tions would in­clude re­design­ing the choco­late or re­design­ing my bio­chem­istry.

Smush­ing sev­eral of the con­cepts to­gether, you could sort-of-say, “Modern hu­mans do to­day what would have prop­a­gated our genes in a hunter-gath­erer so­ciety, whether or not it helps our genes in a mod­ern so­ciety.” But this still isn’t quite right, be­cause we’re not ac­tu­ally ask­ing our­selves which be­hav­iors would max­i­mize our an­ces­tors’ in­clu­sive fit­ness. And many of our ac­tivi­ties to­day have no an­ces­tral analogue. In the hunter-gath­erer so­ciety there wasn’t any such thing as choco­late.

So it’s bet­ter to view our taste buds as an adap­ta­tion fit­ted to an­ces­tral con­di­tions that in­cluded near-star­va­tion and ap­ples and roast rab­bit, which mod­ern hu­mans ex­e­cute in a new con­text that in­cludes cheap choco­late and con­stant bom­bard­ment by ad­ver­tise­ments.

There­fore it is said: In­di­vi­d­ual or­ganisms are best thought of as adap­ta­tion-ex­e­cuters, not fit­ness-max­i­miz­ers.