Evolution is, essentially, the passing on of desirable genes from one generation to the next through natural selection. External conditions such as climate, environment and the availability of food sources determine which traits are the most desirable to possess in order for a species to survive and thrive. A percentage of the population of a species will carry those traits and thus survive the prevailing conditions of the time, passing their genes on to the next generation. As external conditions change, so too do the traits required for survival. Over many generations these gradual shifts in survival requirements have led to the development of completely new species.
There are two ways in which genes are transferred to ensure evolution continues. The better known of these is vertical or linear transfer; the passing of genes directly from parent to offspring. Vertical gene transfer is a long, slow process which powers evolution over thousands of years. Horizontal or lateral gene transfer, first discovered in the laboratory during the mid 1900’s, allows species which don’t reproduce sexually such as bacteria to quickly mutate or evolve by sharing desirable genes on contact. Wide scale antibiotic resistance in bacteria is achieved through this method of exchange. Genetic material is shared between individuals via direct cell to cell contact, infection with common bacteriophages (viruses), and/or uptake of available segments of DNA in their environment.
Broader study of molecular genetics, spurred by advances in genome sequencing has led to the discovery of a wide range of conditions in which horizontal gene transfer can take place. In turn these discoveries prompted further study into the possible range of conditions in which horizontal transfer may have occurred naturally throughout the process of evolution, particularly in the early stages. The question of whether more complex multi-celled life forms may have shared genetic information in this way has also been raised.
The implications of a wider occurrence of horizontal gene transfer than was previously thought are creating much controversy amongst evolution theorists. For instance, phylogenetic trees, popularized by Charles Darwin in his major work “The Origin of Species” illustrate the genetic relationships between species. They are, however, based on the premise that vertical gene transfer is and always has been the critical factor in speciation and that all forms of life on Earth derived from one single common ancestor. Darwinian evolution theory also necessitates isolation of species in order for new species to develop. Horizontal gene transfer challenges the foundations of these long held beliefs, presenting a plethora of scenarios from which new, often conflicting theories have arisen.
Did all forms of life originate from one common ancestor, or did the primordial soup consist of several genetically unique organisms exchanging codes in some form of “intelligent” conversation? Is the almost identical genetic coding present in all life forms simply a remnant of common descent, or is it a result of the continuance of conversations such as these? Could prolific horizontal gene transfer provide the missing link in the chain of human evolution?
These are just a few of the questions that may ultimately be answered as the role of horizontal gene transfer in evolution is further studied and understood. Currently they remain very much open for debate. A growing body of evidence does suggest though that genetic exchanges of this type played more than just a small part in the evolution of life on Earth.
