What are "vos" and "-eis" conjugations?
They're mostly seen in Castilian Spanish or European Spanish. "-eis" is sort of like writing the British "ou" in words. Unless you want to travel to Spain, you'll be hard-pressed to use that conjugation. "Vos" on the other hand is a bit more common, appearing in some dialects in Latin American (Such as Argentinian, some Venezuelan and Colombian accents, etc), Castilian Spanish and Ladino. Technically, the English equivalent would be "ye" as it is very archaic Spanish, but nowadays it´s simply used as "You."
What is convergent evolution?
Convergent evolution is Mother Nature tracing its previous work. Now, seriously. It happens between two completely different species who develop similar characteristics in order to adapt to an environment. One example would be sharks and dolphins; although they are from distinct species, they have roughly the same aerodynamic body shape, because they are both predators that depend on speed and maneuverability to hunt.
What's the difference between Past Perfect and Present Perfect? Why bother using Perfect?
Perfect tenses tell us that an action has been completed fully, unlike the Simple tenses, which simply state the moment in time the action takes place. We use Past Perfect to tell that the action happened in the past and has been completed. Present Perfect is a bit tougher because it has many uses, but simply put, the action started at some point and continues to the present, where it will be finished.