Can somebody please explain the evolution bit.

The book is a lot clearer about this than the movie. It turns out that on Kaspak, human beings follow the course of evolution during their lifetimes.

They start as eggs, which hatch into fish.
The fish become amphibians and crawl onto land.
The amphibians develop into reptiles.
The reptiles become mammals.
The mammals become apes.
The apes become pre-humans.
The pre-humans become humans.

And at each stage, at least each stage once they become mammals, the females will expel eggs into the river, and these eggs will be carried downstream to start the whole process over again.

However, there are rare humans known as Cos-ata-lo and Cos-ata-lu who are born in the regular way, without recapitulating the evolutionary history.

Den Valdron has his own ideas about this, which you can read here: http://www.erbzine.com/mag14/1490.html

It's good. He does leave one loose string, which I manage to tie up here: http://www.erbzine.com/mag23/2306.html





- Aging is a physical problem, and physical problems are amenable to engineering solutions.