Steven Pinker -- How the Mind Works - Hampshire High Italian ...

Revenge of the Nerds 159tance of acquired characteristics—are also not up to the job. The problemgoes beyond the many demonstrations that Lamarck was wrong infact. (For example, if acquired traits really could be inherited, severalhundred generations of circumcision should have caused Jewish boystoday to be born without foreskins.) The deeper problem is that the theorywould not be able to explain adaptive complexity even if it had turnedout to be correct. First, using an organ does not, by itself, make the organfunction better. The photons passing through a lens do not somehowwash it clear, and using a machine does not improve it but wears it out.Now, many parts of organisms do adjust adaptively to use: exercisedmuscle bulks up, rubbed skin thickens, sunlit skin darkens, rewardedacts increase and punished ones decrease. But these responses arethemselves part of the evolved design of the organism, and we need toexplain how they arose: no law of physics or chemistry makes rubbedthings thicken or illuminated surfaces darken. The inheritance ofacquired characteristics is even worse, for most acquired characteristicsare cuts, scrapes, scars, decay, weathering, and other assaults by the pitilessworld, not improvements. And even if a blow did lead to an improvement,it is mysterious how the size and shape of the helpful wound couldbe read off the affected flesh and encoded back into DNA instructionsin the sperm or egg.Yet another failed theory is the one that invokes the macromutation: amammoth copying error that begets a new kind of adapted organism inone fell swoop. The problem here is that the laws of probability astronomicallymilitate against a large random copying error creating a complexfunctioning organ like the eye out of homogeneous flesh. Smallrandom errors, in contrast, can make an organ a hit more like an eye, asin our example where an imaginable mutation might make a lens a tinybit clearer or an eyeball a tiny bit rounder. Indeed, way before our scenariobegins, a long sequence of small mutations must have accumulatedto give the organism an eye at all. By looking at organisms with simplereyes, Darwin reconstructed how that could have happened. A few mutationsmade a patch of skin cells light-sensitive, a few more made theunderlying tissue opaque, others deepened it into a cup and then aspherical hollow. Subsequent mutations added a thin translucent cover,which subsequently was thickened into a lens, and so on. Each stepoffered a small improvement in vision. Each mutation was improbable,but not astronomically so. The entire sequence was not astronomicallyimpossible because the mutations were not dealt all at once like a big gin