In 'Goldilock and the Three Bears', Goldilock finds that only one bowl of porridge has the ''just right'' temperature, and in the same way within biology, you can find the 'just right' conditions -- called the Goldilocks principle. This a research team has done by demonstrating that in order to get the 'just right' amount of signalling for symbiosis in the roots of legumes, a specific enzyme called chitinase (CHIT5) must be present.