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

310 | HOW THE MIND WORKSlogic, to derive some truths from others; arithmetic, to predict the effectsof aggregating; biology, to reason about living things and their powers;kinship, to reason about relatedness and inheritance; and a \ variety ofsocial and legal rule systems. The bulk of this chapter explores thoseintuitive theories. But first we must ask: when does the world allow theories(scientific or intuitive) to work, and when does it force us all to fallback on fuzzy categories defined by similarity and stereotypes?Where do our fuzzy similarity clusters come from? Are they just theparts of the world that we understand so poorly that the underlying lawsescape us? Or does the world really have fuzzy categories even in ourbest scientific understanding? The answer depends on what part of theworld we look at. Mathematics, physics, and chemistry trade in crisp categoriesthat obey theorems and laws, such as triangles and electrons. Butin any realm in which history plays a role, such as biology, members driftin and out of lawful categories over time, leaving their boundaries ragged.Some of the categories are definable, but others really are fuzzy.Most biologists consider species to be lawful categories: they are populationsthat have become reproductively isolated and adapted to theirlocal environment. Adaptation to a niche and inbreeding homogenize thepopulation, so a species at a given time is a real category in the worldthat taxonomists can identify using well-defined criteria. But a highertaxonomic category, representing the descendants of an ancestralspecies, is not as well behaved. When the ancestral organisms dispersedand their descendants lost touch and adopted new homelands, the originalpretty picture became a palimpsest. Robins, penguins, and ostrichesshare some features, like feathers, because they are great-great-grandchildrenof a single population adapted to flight. They differ becauseostriches are African and adapted to running and penguins are Antarcticand adapted to swimming. Flying, once a badge of all the birds, is nowmerely part of their stereotype.For birds, at least, there is a kind of crisp biological category intowhich they can be fitted: a clade, exactly one branch of the genealogicaltree of organisms. The branch represents the descendants of a singleancestral population. But not all of our familiar animal categories can bepegged onto one branch. Sometimes the descendants of a species