Box 1.

Protocells

Created through human artifice but not merely by manipulating a natural living organism (such as a bacterium), a protocell is a self-assembling and self-reproducing chemical system, with the following three properties:

1. It maintains its identity over time by spatially localizing its components in some form of container.

2. It utilizes free energy from its environment and digests environmental resources in order to maintain itself, grow, and ultimately reproduce. This use of energy and materials is a form of metabolism.

3. The containment and metabolism are under the control of replicable and inheritable chemical information that can be “mutated” when the protocell reproduces. This informational chemistry functions as a programmable genetic system.

The proper chemical integration of these three properties enables protocells to reproduce themselves, and a population of them could adapt and evolve by natural selection.