Sexual Reproduction Removes Harmful Mutations From an organism's point of view, the goal of reproduction is to continue the species and produce the most successful offspring. The question is: what is the most effective way to do that? Is is more effective to spend less energy producing a copy of an organism, or should that organism share genetic material even though it will expend more energy? Over millions of years of evolution, sexual reproduction has become the preferred method to produce the next generation. Obviously there is some advantage that sexual reproduction has over asexual. Biologists have been puzzling over the question of why sexual reproduction evolved if it is so costly for an individual. One theory suggests that sexueal reporduction removes harmful mutations from the genetic material of organisms. This theory has become popular recently because new technologies have enabled biologists to test whether it is plausible. Mutations happen, and most changes in genetic material cause harmful effects on the individual. Mutations are suprisingly frequent; biologists conservatively estimate that there is a mutation rate of one per zygote per generation (Crow "Mutation Rate" 8385). That means almost every individual has at least one mutation. Furthermore, mutations will always happen. There is no way, in the course of normal life, to stop mutations from occuring. According to the proposed theory, sexual reproduction brings together then removes the bad mutations, so the population as a whole will retain fewer mutations. The idea behind this theory is simple: sexual reproduction produces good offspring and bad offspring by resorting the genetic material, and consequently the mutations, of two individuals. The good offspring will have fewer mutations just by chance sorting of chromosomes, and the bad offspring will have more mutations for the same reason. In the course of natural selection, the bad offspring will be removed from the population because they are less fit to survive in their environment. Therefore, the individuals with fewer mutations will tend to survive to reproductive age. Asexual reproduction produces offspring that are copies of the parent, thus there is no resorting of genetic material. When an organism reproduces asexually, the offspring has all the bad genes of the parent and may only get new genetic material through mutation. Thus, mutations will accumulate in individuals and in populations. If these mutations are randomly eliminated for whatever reason, there is still an overall loss of fitness to the species. Sexual reproduction is advantageous because many mutations can be eliminated from the gene pool at once when a bad offspring doen't reproduce. When an individual with many mutations doesn't survive, the individual's mutations are not passed to the next generation. Thus, sexual reproduction is advantageous for species with high mutation rates. Unlike other theories that explain why sexual reporduction evolved, this theory can be tested. Biologists can measure the average mutation rate in a species, then raise many generations of organisms and test the fitness of the organisms after many mutations. The data that has been presented so far is not entirely conclusive (Wuethrich 1982). It suggests that the theory is valid, but more work needs to be done to provide definite answers. This theory is even stronger when combined with the Red Queen theory. Together the theories suggest that sexual reproduction both collects the few good mutations and eliminates the bad ones. Although biologists have not come up with a definite answer to why sexual reproduction evolved, there are good theories that explain most of the observed data.