In the new series, however, it is specifically mentioned that Adam was unable to kill a shark. Now it is my understanding that sharks are one of the least likely of animals to be considered sentient (with creatures such as primates and whales being the most likely.) Sharks are almost totally instinctive creatures, as I understand it - their actions are founded on instinct with nothing approaching a rational thought process existing. So the fact that Adam was unable to kill a shark suggested quite strongly that any prohibition could not be solely linked to the sentience of the target creature. But it is still apparent that the new series Tomorrow People can eat meat - references to bacon in Origin Story and to Peperoni Pizza in the Living Stones make that obvious, and so I was still not comfortable with the principle that the TP could absolutely not kill when they were still quite happy to garner benefits from the deaths of animals. And further, they are obviously quite able to kill mosquitoes in The Culex Experiment.
So I cast around looking for another idea and then I thought about Adamís healing abilities.
They are seen to be very powerful in Origin Story where they are used to actually save someoneís life - possibly even to bring someone back from the absolute brink of death. Now Iíve heard it suggested that maybe that use drained them to such an extent that they became useless, and I quite like that suggestion. But I offer an alternative which is linked to my opinion of why Adam could not kill that shark.
Perhaps the power of belief is the defining principle here. Adamís ability to heal is shown on two occasions. On the first of these, he has no knowledge of what he can do - it just happens. There is no possibility of doubting his ability and so he does it. On the second occasion, the knowledge of what he can do is still fresh in his mind and he doesnít even pause to think about what he is doing. He is quick and decisive and he just does it again. Again, there is no time for doubt.
At the start of The Culex Experiment, however, the situation could be slightly different. Lisa wasnít seriously injured in Origin Story and Adam, also healed her by instinct. In the case of Kevin, though, he is in a fairly serious condition. Maybe Adam develops some sort of performance anxiety - because he feels an emotional connection to Kevin, because the situation is so desperate, maybe he chokes - and so he canít heal Kevin. Or maybe to be fairer, the ability to heal Kevin is beyond him. This is not a purely physical injury, this is a toxin flowing through Kevinís body. Maybe Adamís healing powers simply to not extend to that type of problem.
Regardless of the situation, perhaps Adamís failure to heal Kevin sows so much doubt in his mind about the ability in general that he loses it - because he failed once, he can no longer create the correct mindset and focus himself in order to heal. Maybe he is too afraid to try and do it.
So the ability may still exist in theory - but Adam, consciously or unconsciously refuses to use it, because of a desire to avoid the chance of failure - rather than try and fail, he does not try at all.
What matters, therefore, is the power of belief. Because he believes he cannot heal, he is unable to do it.
And letís apply that to being a Tomorrow Person in general and to what is described as the Prime Barrier in the original series. Because a Tomorrow Person believes they cannot kill, they simply cannot do it. That belief may be accurate - but even if it is not, the result would be the same.
And that would also possibly explain why Adam could not kill the shark. Perhaps a Tomorrow Person can kill a non-sentient being. But if the power of belief is strong enough to affect their abilities, if Adam believed that the shark was sentient on any level, then maybe the prime barrier came into play. It makes sense to me. How can we know if a creature is sentient or not? Some obviously are - man is the prime example. But beyond that, no one can really agree. There are so many different camps, it gets very confusing.
So it comes down to an individuals belief and judgement. Perhaps Adam somehow decided in the moment that he was attacked by the shark that it was intelligent or sentient. Even if that perception was wrong, once he had thought about it, the mere power of his belief may have triggered to prime barrier and so he could not kill the shark. But Ami never believed that the mosquitoes were sentient and so she could, without compunction, kill them.
In this theory, the power of belief, becomes as important as the substance of reality, and in my opinion, when dealing with the matters of the human mind, that does make sense. There may still be an absolute limit on any TP ability, this theory doesnít preclude that. It merely suggests that other factors besides that limit may have a profound influence.