Irregular Verbs and Evolution

Question

A few years ago, I have studied Spanish in high school, for two years, though I feel fit to confess that I remember very few things from those classes, and I am not able to maintain a conversation in Spanish.

1. Now I am taking a university course in Latin, and I am sure (as anybody who shares my experience probably likewise will be) there are direct correlations between the two languages. One thing that I did remember from my Spanish class is the irregular form of ten?re/tener; now that I realize that this verb is regular in Latin (1st p. sing. pres. indic. = tene?), is there a linguistic reason why this became tengo in Spanish, or is this just an idiosyncrasy, which like every language has? Or are ten?re/tener not related verbs?

Of course, I realize that this is not a Latin forum, but the question sort of traverses between the two, and there is no LATINDICT, so I thought fit to ask this question here. Verbs in the Romance family tend to become more regular, not less so, and this seems an exception.

1. Do all regular verbs take the same stem for all tenses? I've been told that there's only one principal part for most Spanish verbs, but I'm just checking to make sure.

Welcome to Spanishdict. Good question. - rac1, Dec 5, 2013