To the Editors:   

 

Evolutionary  psychology  is  the attempt to understand our mental faculties in   light of the evolutionary processes that shaped them.  Stephen Jay Gould  calls   its  ideas  and their proponents "foolish," "fatuous," "pathetic," "egregiously   simplistic," and some twenty-five synonyms for "fanatical."  Such  language  is   not  just  discourteous;  it  is  misguided,  for  the  ideas  of  evolutionary  psychology are not as stupid as Gould makes them out to be.  Indeed,  they  are   nothing like what Gould makes them out to be.   

 

Evolutionary  psychology often investigates the adaptive functions of cognitive   and emotional systems -- how natural selection "engineered" them to  solve  the   kinds  of  problems  faced  by  our  ancestors in their struggle to survive and   reproduce. The rationale follows from two premises Gould himself states nicely:   

 

    (1) "I ... do not deny either the existence and central  importance  of     adaptation,  or the production of adaptation by natural selection. Yes,     eyes are for seeing and feet are for moving.  And, yes again, I know of     no  scientific  mechanism  other than natural selection with the proven     power to build structures for such eminently workable design."   

 

    (2) "The human brain is the most complicated device for  reasoning  and     calculating ...  ever evolved on earth."   

 

 Quite  so.  First,  adaptive  design  must  be  a product of natural selection.   Complex organs like eyes have many precise parts in exacting arrangements,  and   the  odds  are  astronomically stacked against their having arisen fortuitously   from random genetic drift or as a by-product of  something  else.  Second,  the   brain,  like  the  eyes  and the feet, shows signs of good design. The adaptive   problems it solves, such as perceiving  depth  and  color,  grasping,  walking,   reasoning, communicating, avoiding hazards, recognizing people and their mental   states, and juggling  competing  demands  in  real  time  are  among  the  most   challenging   engineering  tasks  ever  stated,  far  beyond  the  capacity  of   foreseeable computers and robots.  Put the premises together -- complex  design   comes  from  natural  selection, and the brain shows signs of complex design --   and we conclude  that  much  of  the  brain  should  be  explained  by  natural   selection.   

 

 So  where's  the  controversy?    Gould  claims his targets invoke selection to   explain everything. They don't. Everyone agrees  that  aspects  of  the  living   world   without  adaptive  complexity  --  numbers  of  species,  nonfunctional   features, trends in  the  fossil  record  --  often  need  different  kinds  of   explanations,  from  genetic  drift to wayward asteroids. So yes, we all should   be, and are, pluralists. But we should not be indiscriminate pluralists.  Gould   blurs his own distinction when he writes,   

 

    We  live  in  a  world  of  enormous  complexity  in organic design and     diversity -- a world where some features of  organisms  evolved  by  an     algorithmic  form  of natural selection, some by an equally algorithmic     theory of unselected neutrality, some  by  the  vagaries  of  history's     contingency, and some as byproducts of other processes. Why should such     a complex and various world yield to one narrowly construed cause?   

 

 It shouldn't, of course, but then most researchers aren't trying to explain the   entire  "complex  and  various  world."    Many  of  them are trying to explain   "complexity in organic design" -- the remarkable natural engineering behind the   ability  of  creatures to fly, swim, move, see, and think.  Now, complex design   should yield to one "narrowly construed cause" -- Gould knows of no  scientific   mechanism  other  than  natural  selection  with  the proven power to build it,   remember? Those blinkered, narrow, rigid,  miserly,  uncompromising  ultra-pan-   selectionists  whom Gould attacks are simply explaining complex design in terms   of its only known cause.   

 

 In the case of the human brain, Gould  accuses  evolutionary  psychologists  of   ignoring an alternative:   

 

    Natural  selection  made  the  human  brain big, but most of our mental     properties and potentials may be spandrels -- that is, nonadaptive side     consequences of building a device with such structural complexity.   

 

 Evolutionary  psychologists  are  not  ignorant  of  this hypothesis. They have   considered it and found it to be unhelpful.   

 

 First, it  is  rooted  in  a  false  dichotomy  between  "conventional  natural   selection  working  in  the  engineering mode" and "spandrels," the nonadaptive   by-products that are "sources for later and  fruitful  reuse"  and  which  "may   later  be co-opted" for useful purposes.  What is missing from these phrases is   the subject of the verb. Reuse by whom?  Co-opted by what?  Most snails have  a   spandrel  formed by the space around their shell axis; what allows some species   to use it to brood their eggs?  Are they generally more  clever  and  dextrous?   No;  their  anatomy and nervous systems have been altered in an adaptive way to   take advantage of the spandrel. So the re-user  and  co-opter  are  none  other   than:  natural  selection.  Not only do co-opted spandrels implicate selection,   but selection implicates spandrels.  We evolved from  organisms  without  eyes,   feet,  and  other complex organs. The organs must have originated in precursors   that were spandrels for some ancestral organism.    The  distinction  in  which   spandrels  work "in addition (and sometimes even opposed to)" natural selection   is spurious.   

 

 Unlike snails, of course, we humans are clever enough to co-opt  our  spandrels   in  our lifetimes, as when we use our noses to hold up eyeglasses.  But how did   our brains get clever enough to do that? This is exactly what a theory of brain   evolution  must  explain.    Explaining the evolution of the human intellect in   terms of humans' ability to co-opt spandrels is circular.   

 

 Second, Gould casually slides from saying that natural selection made the brain   "big"  to  saying  that the brain was built with "structural complexity," as if   bigness and complexity were the same thing.    As  Gould  himself  has  argued,   bigger  brains  aren't  necessarily more complex or smarter brains.  Worse, the   suggestion that humans were selected for bigger brains is a perfect example  of   the  sin  Gould  attributes  to  others,  the confusion of a by-product with an   adaptation. If anything is a by-product, it is the size  of  the  human  brain,   which  guzzles  nutrients,  makes us vulnerable to blows and falls, compromises   the biomechanical design of the woman's pelvis, and makes childbirth dangerous.   Bigness  of  brain  is  surely  a by-product of selection for more complex (and   hence  hardware-demanding)  computational  abilities,  ones  that  allowed  our   ancestors to deal with tools, the natural world, and one another.   

 

 A  rejection  of Gould's theory does not put non-adaptive features "outside the   compass of evolutionary psychology"; nor was Gould the first to call  attention   to them. The original arguments for recognizing non-adaptive features came from   the founding document of evolutionary psychology, George  Williams'  Adaptation   and  Natural Selection, long before Gould and Lewontin reiterated them (without   attribution) in their "Spandrels" paper.  Nonadaptive  explanations  have  been   commonplace  in  the  field ever since, as Gould must be well aware, for in one   column he touted a non-adaptive explanation of the  female  orgasm  taken  from   another  founder  of  evolutionary psychology, Donald Symons.  According to the   most popular view in the field,  many  other  important  human  activities  are   spandrels,  including  art,  music,  religion,  science,  and  dreams.  Gould's   accusation is not even close to being accurate.   

 

 Evolutionary psychology  is  "even  more  fatuous,"  according  to  Gould,  for   thinking  seriously about the environment in which our ancestors evolved.  That   is "outside the primary definition of science," he says, because  claims  about   that  environment  "usually cannot be tested in principle but only subjected to   speculation."  Really? Then what makes Gould so  certain  that  our  ancestors'   environment  lacked written language -- the basis for his argument that reading   is a spandrel? Obviously it is  the  archeological  record,  which  shows  that   writing  is  a  recent invention, and the ethnographic record, which shows that   writing is absent from cultures not in contact with any of the inventors. It is   precisely such evidence that leads evolutionary psychologists to infer that the   ancestral environment lacked agriculture,  contraception,  high-tech  medicine,   mass   media,  mass-produced  goods,  money,  police,  armies,  communities  of   strangers, and other modern features -- absences with profound implications for   the minds that evolved in such an environment.   

 

 Gould  is  uninformed when he repeats the cliche that evolutionary reasoning is   just cocktail-party speculation. The standards of  the  field  require  a  good   empirical  fit  between  the engineering demands of an adaptive problem and the   facts of human psychology.  The former is grounded in game-theoretic and  other   optimality   analyses,   in   artificial   intelligence   and  artificial  life   simulations, and in relevant sciences such as genetics, physiology, optics,  or   ecology.    The  latter  is  based on converging evidence from experiments with   children, adults,  and  neurological  patients  and  from  survey,  historical,   ethnographic, paleoanthropological, archeological, and economic data.  Far from   being "barren," the adaptationist approach has, for over a century, driven  the   most  rigorous, elegant, and empirically rich branch of psychology, perception.   Today it is spawning new insights and intensive modeling and data-gathering  on   every  other  aspect  of the mind, including reasoning, mental imagery, memory,   language, beauty, sexual desire, autism, emotions such  as  fear  and  disgust,   violence,  the  numerical abilities of children and animals, and the shaping of   personality.(Note 1) Gould's hostility to  this  exciting  field  is  a  missed   opportunity for both.         

 

                               NOTES   (1)For  recent reviews, see The Adapted Mind, edited by J. Barkow, L. Cosmides,   & J. Tooby; The Moral Animal,  by  R.  Wright,  and  How  the  Mind  Works,  by   S. Pinker.