A slime study has turned basic assumptions about intelligence on their head.
Definitions of intelligence all infer the use of grey matter to learn from experience. But now a slime made up of independent, single cells appears to have "learned" to avoid irritants despite lacking a central nervous system.
Researchers from Belgium and France studied physarum polycephalum, also known as "many-headed slime".
The slime can often be found on decaying leaves and tree trunks in moist areas, and it slowly travels from place to place by extending finger-like protrusions called pseudopods.
The scientists placed a sample near another petri dish containing a meal of oats, separated by an agar gel "bridge" for the slime to "crawl" across.
It typically managed to do this within two hours.
Then the team marked part of the bridge with an irritant of quinine or caffeine.
The researchers watched as the slime "showed a clear aversive behaviour", taking about three times as long to cross the bridge and avoiding the substance.
But in the days that followed the crossings became quicker, which researchers say show that the slime may have been learning how to cross the bridge more efficiently.
The organism preceded humans on Earth by around 500 million years, suggesting that what we understand as learning may predate recognised nervous systems.
The study was carried out by the Research Centre on Animal Cognition at Toulouse University and published in the Proceedings of the Royal Society B.
The report said: "Our results point to the diversity of organisms lacking neurons, which likely display a hitherto unrecognised capacity for learning."
The discovery may help scientists to understand the behaviour of other simple organisms like viruses.
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