I'd like to add here an explanation, for how I view the two methods I see for creating hypotheses regarding the relationsips between similar things as equally justified, at the same time mutually exclusive. I'll call the first "causal", the second "conditional" . In a nutshell, one is the belief that shared traits imply an originar cause, in opposition to the other, which invokes separate conditions that can generate the same result.
Both methods are employed by humans to explain the emergence of the similarities (shared traits) between objectively unrelated things. But they have drawbacks and are prone to error:
- the causal method  is prone to create false causal or kinship relations between things, which may be understandable (like genealogic) or mysterious (like spiritual). Such possible failures end up in theories as the race theories of the Nazis, or the alien or Antlantic theories surrounding the pyramids.
- the conditional method  is prone as well to offer explanations that work formally (on paper), but may be not the real thing, pretty much the way a lawyer can detach one completely from an actual crime through a perfectly sensible, but factually baseless construct.
The main difference I notice between the two is that while the former assumes an existing effect as a cause to another, or an existing single common cause to both effects, through a possible but unproven interaction, the latter assumes possible but unproven similar, analogous or identical causes that can trigger the same effect through known and reasonable means. It should be noted that in the first case, "common cause" is one actual occurance, while in the latter the "common cause" is merely conceptual, regarding different phenomenae, connected only through the nature of their result. For instance when you say "the revolution made X and Y rich", it has two meanings:
- the same event (ie the French revolution) made them rich.
- different but identical/similar events (revolutions) made each of them rich.
To exemplify: the bow and arrows. Can we ever be sure whether it was inherited from the same source, or it was discovered/invented separately by different civilizations? Probably not; unless we find concrete evidence (which may never happen), all we have is different clues and hypotheses about how things evolved. Proximity, for example, is a strong argument for kinship, it is very likely that two civilisations geographically close to each other shared that knowledge. Simplicity to explain how that knowledge had emerged, on the other hand, is a strong argument to believe that the two civilisations discovered the said knowledge independently - ie. when it is demonstrated how easily the same knowledge can occur to different people or communities independently.
One may treat this case separately: whether the man, or certain groups (cultures, races) has in itself the program to create the bow. It is in fact, in my opinion, not a totally different case from the one claiming cultural interaction, since it again, assumes a common legacy (same cause) but which can actually not be there, and which again, can be alternatively explained by assuming the occurance of conditions that are independent and merely are either identical or have the same outcome.
 - purely conventional notations, because I have no time to check whether they are fully appropriate, or whether there exist more appropriate notions for them.
 - which I also call "the NF style".
 - which I call "the NT style". It remains to be seen if these "styles", which are based on my observations on people but rather statistical, I actually appropriately associate as such, and how do they work based on the IM. This matter is off-topic and it is left here as a reminder for a different ramification of the subject.