Sexual reproduction is costly from evolutionary point of view as it involves the formation of gamete and also requires enormous energy. So, the existense of sexual reproduction surely give distinct benefit which compensate the cost. In this writing, I will discuss the fitness advantage of sex and its correlation with the evolutionary arm races that we face with pathogen.
The point consider is that we encounter millions of pathogen in our daily lives and mostly are inococcus for us. Thanks to the immune system, we have strong protection so that the pathogen cannot exploit our body. On other hand, parasites also continually develop to sneak out from our immune system. If our immune system did not keep pace with the parasite and being static all time, parasite would win and wreak havoc on our body. So, the changes in parasites will also stimulate the changes in host, or in both organism, their genetic make up will change simultaneously over time.
The next question is that if host are able to defeat the pathogen, they should be in one step ahead of the parasites. This means that they should develop faster and anticipate the changes that will occur on parasites. And, in this area is actually the sexual reproduction has role on. Sexual reproduction involves meiotic recombination and also the gamete will be stochastically joined with other gamete during fertilization so that the genetic diversity will diversify. Genetic diversity is essential in providing raw materials where natural selection acts on it to select the best individual to tackle the pathogen. Research in Drosophila shown that if the mother was infected with pathogen, their progeny would have a wide range of genetic make up. This termed as “Red Queen Hypotesis” and one of popular topics in evolutionary biology so far. The bottom line is that sexual selection, even though requires high expense, is evolutionary selected as it will diversify organism and become the arsenal for overcoming pathogen.