CALIFORNIA sea lions may have the best memory of all non-human creatures. A female called Rio that learned a trick involving letters and numbers could still perform it 10 years later - even though she hadn't performed the trick in the intervening period.
Learning concepts such as "sameness" - when one letter or number matches another, for example - is thought to require sophisticated brain processing. So scientists expect animals to have trouble retaining the ability over long periods unless they are given repeated reminders of the rules. Primates like the rhesus macaque have been found to have impressive long-term memories, but Rio trumped them all.
Colleen Kastak and Ronald Schusterman, marine biologists at the University of California, Santa Cruz, began training her in 1991. They started by holding up a card with a number or letter on. Rio was then shown a card bearing the same symbol and another ...
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