The sequence of steps leading to citrate metabolism in the LTEE. In the Lenski Long-Term Evolution Experiment (LTEE), the complex innovation of citrate metabolism gradually evolved by natural selection through steps 1–6, and was naturally rewarded in the 7th step for exploiting a new resource zone (see text for references).

  Part of: Gilbert OM (2020) Natural reward drives the advancement of life. Rethinking Ecology 5: 1-35.