Something for those who have been asking questions like, “Did they decide to . . .” to remember is that no one decided anything at all. These features of language develop organically, which is to say that there’s about as much planning involved as with a riot.
Did people in the 80s decide to start using “bitchin’” and “gnarly” as their (soon to be outdated) buzzwords? Nope, just happened. Someone thought it would sound cool, others picked it up, still others emulated them, and before you know it the Madonna look-alikes were spouting, like, totally bitchin’ speech patterns. There are people who are old enough to not only remember when the word “party” was only used as a noun, but that using it as a verb would get them verbally spanked with only slightly less vigorousness than someone who used “ain’t” without a trace of irony.
Language change happens in spite of language authorities, proscriptive grammars, indoctrination through education, and the disapproval of elders. There’s no planning and no deciding involved. One of the things that continues to fascinate linguists is that while there do seem to be some predictable things about how languages change, and while there are similarities between many languages, there are still so many things about language that show the chaotic and primally creative aspects of our brains.
But why call the difference between *pur- and *egnis a difference in gender? They are two different words, but I don’t see any clear relation between the difference between these two words and the general difference between words of different genders.
You seem to be saying people literally sat around and made decisions about this stuff. Is that what you mean to be saying?
Another example of “unnecessary” complexity in English and many other languages is in verb conjugation and verb-noun agreement (I’m not a linguist, so I probably used the wrong words there). For instance, why do we say:
“I am a linguist”
“You are a linguist”
“He is a linguist?”
When we could just use “am” or “all” or “be” for all those forms? Are we just doing it to pass the time and add complexity? Why do we say:
“The man runs” but “The men run?” Running’s not any different if more than one person is doing it - why do we add an -s on the end of the verb? I don’t mean to pick on your argument, Ombre, because it’s a fascinating question and I’m really enjoying listening to people’s suggestions, but I have the feeling that speakers of French and German use gendered nouns as naturally as we say "I am " but “they are” and are just as unaware of how exactly that complexity came about.
Danish is the outstanding example of a European language that does not inflect verbs for person and number at all. In that one regard, at least, it has surpassed even English in simplification, though it does remain more inflected in some other ways. I wonder the period of the Danelaw in England saw Danish being influenced by English just as English was influenced by Danish.
I’d have to put Russian as one of the most simplified in this respect, for the well-known absence of the copula (is, are, am, etc.). Additionally there are no definite articles in Russian. Thus:
English: The man is here.
Russian: Человек здесь [Chelovek zdyes’]. (lit: Man here).