Is sex important?

In the chapter Wholly Virgin from the book Dr. Tatiana's Sex Advice to All Creation, the Philodina and the narrator discussed about whether sex or asexual reproduction was more efficient and why. I think that sex is important because as it said in this chapter, "...sex may be an advantage is because the shuffling of genes gives an edge in the perennial battle against disease."(228) Also we can adapt to our environment because gradually organisms would need to change to be able to survive. One of the costs of reproducing sexually is that females need to have more than two children in order for the population to stay the same or grow, when asexual reproduction needs only one child for the population to stay the same. But the costs of reproducing asexually is that the organisms genes don't change and they stay the same which can be bad because they wouldn't be able to survive if their environment changed. Some arguments in the chapter were, "...what is sex for..."(213). Another one was, "Or, to get back to the central question, if they can do without sex, why can't the rest of us?"(216) The next one was, "In the long run we're all going extinct," said Miss Philodina tartly. "Sex won't save you from extinction! The dinosaurs had rampant sex, and look what happened to them. You can have sex till you're blue in the face, but if your habitat vanishes, it's you and the dodo."(224) Finally another one was, "The pocket mouse bravely interrupted: "But surely if you don't have sex, you can't adapt to the future? If you can't adapt to the future, you haven't got a future."(224) A question I have is, which organisms be both asexual and sexual?