Nice question, I'll answer it in parts:
Is it necessary for our body?
Well, there can be many perspectives for why humans like singing. Let's talk about the evolutionary perspective first. I found three theories about why singing was evolutionarily beneficial for humans.
The Shakespearean theory, that music is at least one of the foods of love, has a strong claim to be true. The more mellifluous the singer, the more dexterous the harpist, the more mates he attracts. In simple words, whom would you like to marry: a singer + hunter or just a hunter?
A second idea that is widely touted is that music binds groups of people together. The resulting solidarity, its supporters suggest, might have helped bands of early humans to thrive at the expense of those that were less musical.
The third hypothesis, however, is that music is a cross between an accident and an invention. It is an accident because it is the consequence of abilities that evolved for other purposes. And it is an invention because, having thus come into existence, people have bent it to their will and made something they like from it.
Anither perspective is the biological one. According to a Chicago Tribune article people who sing live longer than those who do not. Why? Singing stimulates better blood flow by increasing the efficiency of chest wall muscles in air exchange. Whenever you'd have tried to sing a nice song, you must have felt that you need to regulate your breathing in order to get nice tones. At one moment, have a huge breath-in, and the very next moment, release it slowly. All these help in increasing blood flow and thus, if you keep singing when you grow old, you would live longer!
If it is so, then why isn't everyone able to sing?
This has a very simple answer. The element that makes people sing poorly is problems with pitch accuracy, which is also called intonation. (Pitch can be understood as the ‘sharpness’ of a voice; female voices are typically higher pitched than male voices.)
Why Does This Happen?
It all comes down to those tricky activities of the brain. The problem with the brain lies in not being able to adjust its activities against a particular target (which, in this case, is a particular tone). That may be a bit confusing, so let’s break it down a little further.
When you hear a tone, your brain has a perception of its various parameters, such as loudness, pitch, tone and so on. It turns out that human brains are pretty good at perceiving the right tone, which means that the possibility of an error in our brain’s perception of the tone is ruled out. Hence, the ‘input’ component in this case is alright; the problem occurs at the ‘output’. After hearing the tone, the brain maps out an output tone to match the one it heard, but sadly, it’s not in tune.
It’s not that you don’t realize when you are singing off-key; ears do register that you’re not quite producing the tone that you intended to, so the vocal cords ask for instructions from the brain. However, the brain still sends the same instructions, and you simply can’t get the tone right. It’s almost as though the vocal cords have locked themselves in a particular position to produce the same erroneous tone every time, even after knowing better!
Is it in direct relation with neurotransmitter secretion like adrenaline?
Let me clear out some things here first. First of all, adrenaline is not a neurotransmitter, its a hormone (unless you're talking about adrenergic neurons). You can see the differences between neurotransmitters and hormones here.
Second, singing is a complex process and cannot be totally dependent on neurotransmitter (though singing isn't even possible without neurotransmitters!).
Back to the question, serotonin might have an effect on singing. Serotonin is regarded by some researchers as a chemical that is responsible for maintaining mood balance, and that a deficit of serotonin leads to depression. However, its effect on singing is not known yet (at least I can't find a reference for such a study).
EDIT: Another neurotransmitter (which I forgot to mention ;) that plays some (if not all) role here is dopamine. Dopamine is considered as reward and pleasure chemical because it is released in areas of brain (like nucleus accumbens) to give a feeling of reward and pleasure. It has been suggested that dopamine, through the mesocorticolimbic pathway, gives a feeling of pleasure after singing. That is probably why we feel so nice when we hit the perfect tone in a song.
Mesocorticolimbic pathway: a dopaminergic pathway in the brain consisting of the mesolimbic and mesocortical pathways. The mesolimbic dopaminergic pathway originates in the ventral tegmental area (VTA) of the midbrain and connects to the limbic system via the nucleus accumbens (NAc), amygdala, the hippocampus, and medial prefrontal cortex; it plays a critical role in reward related behaviors and reinforcement learning. The closely related mesocortical dopaminergic pathway connects the VTA to the frontal lobes.
- Human evolution: why music?
- Why do we sing?
- Why some people just can't sing well, no matter how hard they try!
- Neurotransmitters vs hormones
- Serotonin: facts, what does serotonin do?
- The neurochemistry of music; Mona Lisa Chanda and Daniel J. Levitin