Plants are intelligent too

EMBO Reports (2012) 13: 7, 591–595. doi:10.1038/embor.2012.83

EMBO Reports (2012) 13: 9, 773–773. doi:10.1038/embor.2012.122

Whilst welcoming Ken Richardson's argument that intelligent behaviour is present in all organisms [1], I draw attention to several omissions. First, many researchers have commented on the ubiquity of intelligent behaviour in the animal world. Commenting on protozoan behaviour, Alfred Binet, the creator of the first IQ test, wrote that “we find manifestations of an intelligence which greatly transcends the phenomenon of cellular irritability” [2]; Romanes stated that “no one can have watched the movements of certain infusoria without feeling that these little animals are not actuated by some amount of intelligence” [3].

Moving on from protozoa to multicellular organisms, Vertosick described “the intelligence of every living thing” including bacteria [4]. Similarly to Richardson, however, he omitted higher plants that form 99% of the eukaryotic biomass on Earth. Plant behaviour is not strikingly evident because it operates on a totally different timescale to our perception, but its visible aspect is phenotypic plasticity. Higher plants respond to an enormous variety of physical, chemical and biological signals in their environment to maximize foraging for resources in two distinct but unpredictable and variable environments: above and below ground. Optimizing this phenotype probably involves territoriality, self and alien recognition and competition, as described by game theory. Predictive assessments, decisions and trade-offs are all involved, as well as countering the threat of herbivores and disease. Mate selection is elaborate and underpinned by discriminating, complex conversations that precede and follow fertilization.

The goal of any individual plant is the same as that of any animal—the intelligent construction of behaviour to optimize life cycle fitness and maximize selection. To this end, nervous systems are not necessary; complex networks are sufficient to create intelligent behaviour. Higher plant cells are as complex as animal cells, and the individual plant coordinates its millions of cells into overall coherent and intelligent behaviour. Any discussion about the evolution of intelligence therefore has to include the behaviour of plants [5,6,7].