Letters to Nature

Nature 420, 810-812 (19 December 2002) | doi:10.1038/nature01151; Received 14 June 2002; Accepted 9 September 2002

Macroevolution simulated with autonomously replicating computer programs

Gabriel Yedid1,2 & Graham Bell1

  1. Biology Department, McGill University, 1205 avenue Dr Penfield, Montreal, Quebec, Canada H3A 1B1
  2. The Center for Microbial Ecology, 540 Plant and Soil Sciences Building, Michigan State University, East Lansing, Michigan 48824-1325, USA

Correspondence to: Graham Bell1 Correspondence and requests for materials should be addressed to G.B. (e-mail: Email: graham.bell@mcgill.ca).

The process of adaptation occurs on two timescales. In the short term, natural selection merely sorts the variation already present in a population, whereas in the longer term genotypes quite different from any that were initially present evolve through the cumulation of new mutations. The first process is described by the mathematical theory of population genetics. However, this theory begins by defining a fixed set of genotypes and cannot provide a satisfactory analysis of the second process because it does not permit any genuinely new type to arise. The evolutionary outcome of selection acting on novel variation arising over long periods is therefore difficult to predict. The classical problem of this kind is whether 'replaying the tape of life' would invariably lead to the familiar organisms of the modern biota1, 2. Here we study the long-term behaviour of populations of autonomously replicating computer programs and find that the same type, introduced into the same simple environment, evolves on any given occasion along a unique trajectory towards one of many well-adapted end points.