¿Por qué existe el sexo como mecanismo y no sólo la reproducción asexual, la cual tiene, también, sus beneficios?
Intro:
Sex might be biology’s most difficult enigma. The downsides of relying on sex to reproduce are undeniable: It takes two individuals, each of whom gets to pass on only part of their genome. Because these individuals generally have to get fairly intimate, they make themselves vulnerable to physical harm or infections from their partner. Asexual reproduction, or self-cloning, has none of these disadvantages. Clones can be made anywhere and anytime, and they receive the full complement of an individual’s genes.
Yet despite all its benefits, asexual reproduction is the exception, not the norm, among organisms that have compartmentalized cells (eukaryotes). In plants, for example — which are somewhat known for their genetic flexibility — less than 1% of species are thought to reproduce asexually often. Among animals, only one out of every thousand known species is exclusively asexual. For centuries, biologists have pondered this apparent paradox.
Gemas:
• Even the idea that sex is for reproduction doesn’t hold across the entire swath of eukaryotes. For the algae studied by Aurora Nedelcu, a biologist at the University of New Brunswick in Canada, sex isn’t about making more offspring. “They reproduce better asexually,” she said. The Volvox species she works with are facultatively sexual, meaning that they choose whether to clone themselves or have sex. When they opt for sex, it’s to improve their odds of survival.
• Scientists have known about the DNA-repair benefit of meiosis for decades, and some earlier work has also suggested that it might explain why harmful mutations are less common than might be expected. But Nedelcu’s research calls attention to why it might have been significant in the initial evolution of sex. The fact that these algae belong to some of the oldest lineages of eukaryotes, Nedelcu said, might suggest that “the ancestral role of sex was not for reproduction.” Instead, “sex appears to have evolved as a means to respond adaptively to stress.”
• Amy Worthington, a biology researcher who studies reproductive physiology and behavioral ecology at Creighton University, has seen something similar in field crickets. A female field cricket might be expected to become more vulnerable to infection after mating, when she’s presumably routing most of her energy to making eggs, but instead she becomes more resilient.
Conclusión:
It may even be that, if the fitness costs of the sexual act are low enough and the benefits are high enough, it’s not always worth searching for a suitable mate of another sex. Individuals might ultimately live longer and pass on more of their genes by having sex early and often with any member of their species they come across, or even by frequently engaging in masturbation. Such hypotheses have likely gone unexplored because our views on sex in other species are shaped by our views on sex in our own.