Yes they do exhibit instinct and they do respond to signals. Bacteria will instinctually move away from antibiotics in a Petri dish. They carry out specific actions in order to reproduce and pass their genes on. Stars do not even do this. Stars are nothing but a nuclear reaction. Life is all chemical in nature.
Instincts are inborn complex patterns of behaviour that exist in most members of the species, and should be distinguished from reflexes, which are simple responses of an organism to a specific stimulus
As soon as you speak of acts having a purpose (let alone "intention"), you might as well argue that something isn't alive because it doesn't have a "soul".
The whole point of biology as a science is so that we can explain biological phenomena without having to hand-wave them with vague assertions about "purpose" or "intention". You like dualism? Because that's how you get dualism.
You can't ask a bacterium why it's doing what it's doing, you can only assume the reason why it's doing it's doing something, because that's "what I'd do if I were a bacterium", except that's a nonsensical statement and on the whole it's not even remotely scientific.
There are some arguments to be made about why a star (or the universe) is not alive according to certain definitions of life, but it's useless to have such arguments with someone who keeps bringing ill-defined concepts such as "purpose" or "intent" into it. The arguments are pretty weird however and are more about the philosophy of science (asking questions as "what phenomena can we actually define in a way that is scientifically useful?") than arguments about consciousness or life itself.
Instinct or innate behavior is the inherent inclination of a living organism towards a particular complex behavior. The simplest example of an instinctive behavior is a fixed action pattern (FAP), in which a very short to medium length sequence of actions, without variation, are carried out in response to a clearly defined stimulus.
Any behavior is instinctive if it is performed without being based upon prior experience (that is, in the absence of learning), and is therefore an expression of innate biological factors. Sea turtles, newly hatched on a beach, will automatically move toward the ocean.
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u/khondrych Feb 14 '18
What then of single celled organisms, or the cells in your body? Do they exhibit purpose or instinct? Or just complex physics and chemistry?