The query of which came first, the chicken or the egg, is a popular riddle, used to illustrate our inability to understand the relationship between two associated events. However, from a scientific point of view, the answer is clear: the egg came first.
In nature, unique species arise when mistakes in the genetic code of an individual lead to traits that offer a competitive advantage; the process of natural selection then assures that these errors are retained in future generations and, over time, a new species, possessing these traits, will emerge. The mistakes may occur due to gene mutations, the insertion of foreign genetic material (e.g. from a virus) or duplication errors during cell division; natural cross-breeding of similar species may also lead to a new species (assuming that the offspring are viable and able to reproduce). Of course, any changes that are detrimental to the survival of an organism are soon removed from the gene pool. This basic process, recurring over billions of years, has governed the evolution of all natural life forms on our planet, including humans. Having learned to manipulate genes and select traits via artificial pollination and cross-breeding, man has dramatically accelerated the production of unnatural species and subspecies.
In contrast to the simplified view of creationists, who believe that a micro-managing deity created two parents for each species, evolution is a gradual process, unfolding over hundreds or thousands of generations. The point at which a chicken emerged on the ever-expanding tree of evolution is open to debate but, without doubt, that first individual came from a fertilized egg.
