TWO chimps have broken down another barrier separating human and animal minds. Lana and Mercury can remember how to count three years after they last performed the task.
Animals have proved themselves able to remember abstract concepts for longer periods. Rio the seal, for example, showed he could apply the concept of 鈥渟ameness鈥� after 12 years (New 杏吧原创, 26 October 2002, p 25), while 33-year-old Lana has shown she can still use a lexicon 20 years after she was first taught it. But the two chimps鈥� counting feat is unique.
Michael Beran at Georgia State University in Decatur trained the chimps to use a computer screen and joystick. The screen flashed up a numeral and then a series of dots, and the chimps had to match the two.
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Seventeen-year-old Mercury learned numerals one to seven, while Lana managed to count to six. The chimps found the task progressively harder with larger numbers. 鈥淭he meaning of the numbers for the chimps becomes 鈥榝uzzier鈥� as the numerals get larger,鈥� Beran says.
When Beran tested the chimps again after a gap of three years, Lana and Mercury were still able to match the numbers, although their error rate had roughly doubled (Animal Cognition, DOI: 10.1007/s10071-003-191-x). But they avoided basic mistakes like confusing 鈥渙ne鈥� with 鈥渇ive鈥�.