It is not altogether clear why sex exists

Surprisingly, it is not at all clear why sex exists. Requiring the contribution of two parents in the production of offspring is remarkably inefficient.

 

Think of a mutant female – a hermaphrodite – who can reproduce without male input, and whose offspring have the same ability.

 

Each one of the hermaphroditic offspring of our original hermaphrodite is capable of reproducing by itself, however, so that in this case 100 per cent of the original reproductive effort will contribute offspring to the next generation.

 

In evolutionary terms, hermaphroditism is thus twice as efficient a reproductive strategy as sex.

 

Why, then, isn’t the natural world dominated by male-less species?

 

And in the face of this insect evidence why is sex so prevlent?

 

So sex must have an evolutionary advantage powerful enough to counteract the impulse to eliminate it.

One suggestion is that disease – carried by parasites – may be the critical factor.

For when a population of sexless clones is attacked by a parasite that has breached their immune defences, the population is devastated. The immune system does not have enough variation.

However as opposed to the clone state of hermaphroditism which foists the same (clonal) version of the immune system on their offspring 

the femal/male coupling will pass on new versions of the system courtesy of the reshuffling of genes that is part of the sexual process. And it is in these new variant therein, some argue, that holds the key to overcoming the parasite.

 

 Sex then, on this theory is all all about reconfiguring genetic variation to combat the latest challenge to the immune system.

 

Because the interaction between parasite and host is essentially an arms race – as soon as the host population has cracked the puzzle posed by the parasite, the onus is on the parasite to evolve a new and more devious means of defeating the host’s immunity – the evolutionary interplay between parasite and host is a non-stop cycle of evolutionary thrust and parry.

Sex is the runner (immune system)  who never stops running as the parasite tsunami advances. No wonder sex is so breathless.

"It takes takes all the running you can do,’the Red Queen explains to Alice, ‘to stay in the same place.’