Question

As a rule, the more basic the process under investigation, the more distant can be the evolutionary relationship with humans. Thus,
experiments aimed at understanding the molecular basis of nerve impulse conduction can be carried out on a distantly related species, such as the squid.

I don't get it...

Answer 1

Evolution is the process by which species become specialised for a particular environment. The functions they perform reflect that. For example, barnacles make a substance much like cement which glues them onto rocks in pounding surf. Humans don't need to do that.

Other functions are not specialised. The example given to you is nerve impulses. Almost all animals have to sense their environment and respond to it so almost all animals have neurons which are somehow organised into nerves, a brain, etc.

If you want to study a specialised function, you have to study it in the small group of species or even single species which has it. To study conditions under which barnacles make their cement, you'd have to study barnacles, not apes or mice or pea plants. But if you want to study something general, which all or most species have, you can study it in anything - to study nerve impulses, you can study humans or squids or whatever you like within the animal kingdom.