The existence of this genetic basis for being a Tomorrow Person can be extrapolated from three facts in particular. The first is that the Tomorrow People have been identified a distinct species, Homo superior, by advanced alien races (The Visitor). The second is the identification of the Tomorrow People as members of the species Homo novis by Rabowski (The Medusa Strain). The third and most telling fact is a definite statement by John that a gene makes the Tomorrow People what they are (Hitler’s Last Secret). The combination of these facts suggest beyond all reasonable doubt in my opinion that the abilities of the Tomorrow People are at least partly genetic.
It can also be determined that the mere existence of this gene (or gene complex) is not enough for the abilities of a Tomorrow Person to manifest themselves. A case in point is that of Patricia Conway who despite having the requisite genes to break out was somehow retarded in her abilities well beyond the normal time of breakout (Secret Weapon, The Revenge of Jedikiah). It appears that break out is somehow related to adolescence. With the exception of Patricia and possibly Elizabeth all known break outs have occurred during presumed physical adolescence. Certainly these break outs have occurred at opposite ends of puberty (with Kenny and Kevin in early adolescence, while Adam was in late adolescence (Elizabeth as well, possibly - she is very difficult to classify precisely in this way).
With the acceptance of the facts that a genetic predisposition towards break out does not guarantee break out and the fact that a very large proportion of Tomorrow People are from the British Isles and that the genetic complex is not solely limited to one race or to one country we are faced with attempting to define theories to explain the phenomenon of break out.
I have developed a theory of break out that may help serve to explain this phenomenon. (Note: I am not the only person to have come up with this theory or a similar one).
As evidence of this possible attraction, we can offer a few cases. The most apparent is the friendship between Megabyte and Kevin. Despite an age difference they are drawn to each other as friends. However, some other possible cases do exist. Ami definitely seems to have been drawn to the other Tomorrow People - to Kevin in particular (a possibility - perhaps a Tomorrow Person in danger may instinctively call out to other Tomorrow People in the vicinity. Examples of this may include Hsui Tai's contact with Mike). Jade also obviously feels a strong attraction to other Tomorrow People - although this may be merely a result of her knowledge of what they are, or her apparent infatuation with Megabyte.
This theory (Theory of Attraction) may be coupled with the Theory of Proximity very easily - if proximity serves to increase the chance of break out, it is not inconceivable that some mechanism may exist in nature that makes two Tomorrow People coming into proximity more likely - a mechanism such as a force of attraction.