Is it Good to Share? The Parallel between Information Transfer and Horizontal Gene Transfer
Abstract
| Click on the arrow to start the video. | Video by Enam Huque |
Analysis of bacterial genomes has shown that a significant number of genes have been acquired horizontally from unrelated organisms rather than vertically by cell reproduction. A horizontally acquired gene could allow an organism to use a new metabolic pathway or exploit a new environment. However, it might disrupt the function of the other genes, or it might be parasitic or non-functional DNA. In a population of cells, there may be variability in the tendency to accept genes horizontally (e.g. differences in cell walls or membranes or in systems for import of DNA into cells or for breaking down DNA fragments inside cells). Therefore we ask whether it is good to share genes: will selection favour cells with a higher or lower rate of horizontal transfer? A similar question is relevant for the acquisition of culturally transmitted information (memes) in humans. Memes may be acquired vertically from parents, or horizontally from unrelated individuals. Vertically-acquired memes are subject to natural selection. Memes that increase the fitness of individuals will allow them to reproduce more frequently and pass those memes on to their offspring. Horizontally acquired memes did not necessarily increase the fitness of the donor individuals and have the potential to be harmful. Nevertheless, by learning from a wide range of sources we pick up much useful information that was not known by our parents. Therefore we ask whether it is good to share memes: will selection favour learning strategies with a higher or lower proportion of horizontally acquired memes? We will discuss simple mathematical models to address these questions, and to investigate the similarities and differences between horizontal transfer of genes and memes. In both cases there is a tendency for a population to split into groups such that horizontal transfer is frequent within groups and rare between groups. It has been suggested that horizontal gene transfer in the earliest stages of life was extremely frequent and that separate lineages of organisms emerged when the rate of horizontal transfer fell. Transfer between distantly related organisms is less likely to be successful than between similar organisms, hence there is a tendency for genetic isolation between groups to arise. In the case of cultural evolution, it is possible that selection favours strategies where learning occurs preferentially from individuals whose memes are similar to one’s own. This leads to the emergence of separate cultural groups that possess widely differing memes and that do not share information with one another.