How can an animal get "upgrades" at different stages of its life?

Question

I want an animal that gets harder to kill as it grows older, biologically immortal.

Every time the animal passes different stages of its potentially endless life, it can choose to "upgrade" its own DNA. Children born from older animals are already born upgraded but can choose more upgrades if they manage to survive. This mechanism makes the animal harder to kill as it grows older.

The upgrades can be anything from decorative displays, higher conscious and subconscious intelligence or various health and strength factors like thicker skin muscle tissue, looser skin to resist bites and scratches or more stiff tendons and cartilage to increase strength at the cost of flexibility or vice versa.

Thought process

There's no doubt that the children you have in your youth will be different to the offspring produced in more mature ages, not only because of the degradatory process of aging but also because genes change and mutate as time passes. Virus immunity is nothing but evolution of your body, often instantly.

So evolving in one lifetime is not impossible, after all evolution merely means change and growth, development.

In video games sometimes there are infinite randomly generated dungeons that get harder and harder as one explores more, and the playable character will find powerups to keep up with the difficulty. This is not done to make the game eventually be impossibly harder but to force the player to continuously adapt to new environments and ever changing challenges; it's made to kill boredom, not to kill the player.

Often the player finds more than one powerup and has to choose between them to make play styles variable. Maybe this round you choose 3 bonuses for speed, agility and intelligence but the next you want to try toughness, vitality and stamina. In this way, the dungeon feels unique every time.

I want this game's mechanism to be part of an animal's biology.

Question

How would this be possible? By that I mean how would the mechanism work and what would enable it to function correctly?

Answer 1

Unless it’s already programmed in the creatures DNA it won’t spontaneously “evolve”.

There’s a fine line between adaptation and evolution, the latter mostly applies to the immune system. Everything about a living thing is preprogrammed in DNA with different responses to different stimuli; if A this response and if B other response. A creatures form doesn’t just change unless it’s already programmed to do so, like in metamorphosis. These programmed responses are how creatures adapt; muscles worn down = muscle growth, manual labor = thicker skin, bright sun = tanning and so on...

However the immune system can not only adapt but can also evolve. Normally immune cells have specific receptor proteins and create specific antibodies. But some immune cells can create new combinations at random to fight off potential unknown enemies. This is the closest thing to evolution you’ll find. But please note that this doesn’t create anything “new”, it just recombines existing features (a locksmith that makes different locks but can’t start making doors).

Other than that there’s natural selection, which you already know of so no point in repeating. You want your creature to change during its lifetime. What you need is a creature capable of as much variety as a dog if not more. You also need it to go through partial metamorphosis multiple times during its lifetime, with different forms depending on the environment. If you want the changes to be conscious choices then you’ll want to go the hormonal route. Changes in brain activity during stress causes a change in hormones, which in turn causes your creature to adapt. Simple.

In short: your video game creature can pick multiple classes during its life that stack together but can’t create new classes. That would require actual evolution, natural selection and trials and errors with the offspring.”

Sorry for the long answer, have a potato.