ape language latest issue journal nih research vol jan pp contain short review article pat shipman human evolution cover article refer fade line between ape human actually title climb family tree hominid hominid discussion linguistic ability interest subscriber linguist list author discuss kanzus sue savage rumbaugh s book kanzus ape brink human mind john wiley son ny accord savage rumbaugh kanzus rudimentary grammar displace referent arbitrary symbol case icon lexigram computer s r ability equal old child later section work derek bickerton language specy university chicago press summarize bickerton admit kanzus ape young child protolanguage full language lack grammatical element most rest section language devote broca s area cortical specialization john 