Verb ending “e” in 1st person singular

Question

If we conjugate the verb of the 1st group in french, we will find, there is the -E ending in 1st point singular. (Je parlE, je trouvE).

So how did this -E appear? I know that during the period of Vulgar Latin in the French language the Latin sound -O, which used to be on this place, was reduced (so the verb sounded like "Je parl"). But what happened after it, making the ending -E appear?

By the way, the latin sound -O, which was reduced in french, is still alive in other roman languages (io amo (it))

Answer 1

The [o] did not "disappear", it eroded into a schwa sound which was still pronounced in Middle French. That vowel is what the e in those verb conjugation actually represents. You see, with the exception of various fixes that do not even necessarily reflect pronunciation better (like the plural of nouns in -nt, which until the early 18th century were spelled -ns in the plural), French spelling corresponds well to what was spoken around (if memory serves) 1600.

In any case, by the mid- to late 17th century, the schwa was dropped very frequently in the spoken language and now is dropped almost everywhere.

Answer 2

Almost all verbs ending in -er are conjugated the same, and parler is one of them. For many of them like écouter, danser, présenter, it would change the pronunciation significantly to drop the -e for "je" conjugation. It makes more sense to keep the -e on the "je" (and il/elle/on) conjugation for all regular -er verbs than to have so many "exceptions to the rule" for the pronunciation of what would be "j'écout" or "je dans"