Upfront: I am a computer science student trying to understand evolution and its implications.

I've been pondering the concepts of evolution for some time, especially related to neuroscience / how the brain works / how to emulate brains. I wonder how single-celled organisms evolved at all. I know, they don't "think"; but once their ATP levels get low, they know they must find food to sustain their system, aka staying alive. This is probably no active decision, more like: "The enzyme concentration tells me to find food".

Question: Was the entropy just high enough that at some point those organisms had the property that finding food somehow is preferable to death? Edit: How can an organism perform something without "knowing" it needs to perform it?

I hope, this isn't a terribly stupid question.

  • $\begingroup$ Do you think the following is a good reformulation of your question: Not all responses to environmental stimulus are performed consciously. How can unconscious responses be made? How can an organism perform something without "knowing" it needs to perform it? $\endgroup$
    – Remi.b
    Commented Nov 10, 2017 at 17:49
  • $\begingroup$ If the above is a good reformulation then note that 1) it is rather unrelated with the field of evolution (except by the extend that everything in biology is related to evolution) and 2) Any living organisms has unconscious responses to environmental stimuli (incl. humans). The question has no reason to be specific to unicellular organisms. $\endgroup$
    – Remi.b
    Commented Nov 10, 2017 at 17:51
  • $\begingroup$ @Remi.b Yes, especially the last part of your suggested reformulation is better than my own question. I will edit my question accordingly. $\endgroup$
    – thruun
    Commented Nov 10, 2017 at 17:53
  • $\begingroup$ @Remi.b I know, that this is not specific to single-celled organisms. I hoped, that by reasoning about simple life forms, one can deduce answers for more complex ones. If simple organisms "know" it is necessary to find food or procreate, more advanced organisms should know that too, right? $\endgroup$
    – thruun
    Commented Nov 10, 2017 at 17:56
  • $\begingroup$ "How can an organism perform something without "knowing" it needs to perform it?" -- physical & chemical laws coupled with biological stimuli & response; nothing more, nothing less. $\endgroup$
    – user22020
    Commented Nov 10, 2017 at 20:38

1 Answer 1


Nothing more than physics

Simple physics

If you drop a rock, the rock will fall to the ground. If there was a table underneath, the rock would stop its fall when reaching the table. Clearly the rock response to the environment but the rock does not need to be conscious (whatever you mean by "consciousness") of anything in order to response to the environment.

Explanations for a programmer

As you are a programmer, you will agree that when you do std::cout << 3+2 << std::endl;, nothing more than physics is happening so that the value 5 followed by a newline gets printed to the screen. It is relatively complex though. So complex as it may feel quite magical before having spend many hours learning about computer engineering.

You understand that if you write a, say, boids program, all that is happening is just a bunch of addition and multiplication (eventually a power). The program does not need to be "aware" of what it is doing (nor do the individual agent) in order to respond to the change of behaviour of a predator.

You could even write a self-learning algorithm and you would still accept that there is no consciousness involved but only very simple operations.


Living things are pretty much the same. They are relatively complex (more like a computer than like a rock) but essentially the same. Also, the response tot he stimulus is often (not always) adaptive as it has been selected. But at it's core there's nothing more than physics involved!

More info

If you want to learn more about the mechanism of living things in general, you might want to just open an intro book or have a look at an intro course such as Khan Academy > Biology for example.

You can as well pick a simple response to an environmental stimulus and study its mechanism. How about having a look at chemotaxis for example!

Note that you might also want to follow a short and introductory course to evolutionary biology such as Understanding Evolution for example.

  • $\begingroup$ Thank you for your answer and suggested readings! Maybe you are right with your first observation, that I concentrate too much on single-celled organisms. They are really just simple, biological state machines. As a computer scientist, it's just highly interesting to find out more about biological systems and how cognition evolved. $\endgroup$
    – thruun
    Commented Nov 10, 2017 at 20:06
  • $\begingroup$ I understand your point that "it's just physics", especially with lower life forms. However, how do things change with, say, mammals? Or probably anything that has a nervous system with a lump of neurons acting as a brain? Then, those stimuli certainly influence the behaviour of the organism, but based on experience or other internal assessments of the situation, the chosen behaviour may be different. $\endgroup$
    – thruun
    Commented Nov 10, 2017 at 20:13
  • $\begingroup$ Of course, the brain can also be seen as a very complex state machine, where neurons fire just differently after experiencing events ("learning"). Probably I should just do some reading to figure out how to better formulate my question about life and how the sum of these basic processes forms into something we call "intelligence" for higher life forms :) $\endgroup$
    – thruun
    Commented Nov 10, 2017 at 20:29

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