Confronting Friends and Family

[Kirbmarc]

But of course they are. Why are two parents with brown eyes able to produce a child with blue eyes? If their genes have the "evolutionary advantage", how come the blue-eye gene is simply not passed on genetically to their children? That would make more evolutionary sense.

There is no evidence of a disadvantage or an advantage in having blue or brown eyes. Both blue-eyed and brown eyed individuals have children and their children are likely to reach sexual maturity and have other children.

Moreover, the fact that "evolutionary neutral" genes are still passed is evidence against design in evolution. Natural selection only weeds out genes whose expression lead to either premature death or a smaller number of offsprings. Every other gene is still passed.

You also have to take into account sexual selection. If blue-eyed people are not rejected as mates, they will have offsprings. Statistics show that blue-eyed people aren't usually rejected as possible mates, so the "blue eyes" genes aren't a disavantage.

You can make arguments as to survivability rates, etc, but the fact remains that an sexual reproduction has the cost to the species of a 50% reduction in the rate of reproduction. We know some species literally produce thousands of offspring to give them the "best chance" of survival.

If for some reason the survivability rate of individuals who carry a certain gene is zero (for example a parasite or a change in the environment) while the survivability of individuals who don't carry it is more than zero, reproduction rates don't matter anymore, what matters is genetic diversity.

Asexual reproduction doesn't allow for genetic variability. One parasite can easily end an asexual species in a very brief time (geologically speaking).

No one has successfully demonstrated that robust genes cover the full cost of the price of sexual reproduction. It may go some way, it may go a long way, but it can't cover the cost - let alone end up into benefit on its own.

In 1975, George C.Williams showed that there are species capable of both sexual and asexual reproduction. They reproduce sexually when the environment is changing, and asexually when it isn't.

This shows that there are situations when sexual reproduction is highly beneficial, and others when it isn't. Most species which reproduces sexually live in environments which change quickly and frequently and are extremely rich in parasites, and therefore gives a huge advantage to sexual reproduction.

So bdelloid rotifers share this ancestor too, but haven't used sexual reproduction for 80 million years. Doesn't that mean that sexual reproduction can be beneficial, but that it isn't always beneficial?

Of course. Nothing is always beneficial, or always detrimental. It depends on the ecological context (environment, predators, parasites, sexual selection...)

Bdelloid rotifers, however, are also able to incorporate foreign DNA from their food, increasing genetic diversity in their species through means other than sexual reproduction. This means that genetic diversity is a clear advantage, no matter how you achieve it.