How can the animals actually evolve in chapter 10 with random mutation?

[Rickert]

In order to evolve, the animals have to go through a long period of
time, such as 5 million days. In the book, it is written that the
animals evolve because of the surrounding environment. Meanwhile, the
inheritance and mutation are determined by random function:

(defun reproduce (animal)
(let ((e (animal-energy animal)))
(when (>= e *reproduction-energy*)
(setf (animal-energy animal) (ash e -1))
(let ((animal-nu (copy-structure animal))
(genes (copy-list (animal-genes animal)))
(mutation (random 8)))
(setf (nth mutation genes) (max 1 (+ (nth mutation genes)
(random 3) -1)))
(setf (animal-genes animal-nu) genes)
(push animal-nu *animals*)))))

How can this randomness correlate with the evolution of the animals,
which involves the environment surrounding it? Genes generation and
mutation are completely random, and has nothing to do with the jungle
or the plants. Or am I missing something?

[Purity Control]

No I don't think you are missing anything, and I think this is exactly the point.

I don't like the word evolution. It gives us the impression that we are somehow really clever and adapt to our surroundings.

I prefer the term evolution through natural selection. This suggests we mutate randomly and nature / environment picks the winners and losers.

The evidence of the game supports the latter theory rather than the first.

[Tu Hoang Do]

Ohh Thanks a lot. I get it now. So that's how the randomness correlates to the evolution, by natural selection.