Sorry, biologists, a population is supposed to be composed of only humans. Sorry, cool kids, being popular is actually being like all other humans. Population is from the Latin nominative populatio, "a people", from populus "people". Popular (of which pop, "cool", is an abbreviation) originally meant "public" in Middle French as populier. This is a borrowing from Latin popularis, or "belonging to the people", which stems from populus. Likewise, the word people comes through French as peupel to go back to populus. Clearly a very popular word, populus is also the direct etymon of the now-ubiquitous term populist, which means "of the people", the Spanish word pueblo "town", and the Italian word popolo, or "people". However, for all that linguistic significancy, we don't know what comes next. The main theory traces it to Etruscan (which would go further back to Proto-Tyrsenian), but we have no clue about that. The word poplar, as in the tree type, also goes back to a Latin word populus, but it was a homonym with no semantic connection (the word went on to develop from Old French poplier and Anglo-French popler, and is supposedly from Proto-Italic poplo, "army", and also probably Etruscan. BUT IT HAS A TOTALLY DIFFERENT HISTORY).
Adam Aleksic, a rising sophomore studying linguistics and government at Harvard University, has been described as the internet's sixth most famous etymologist. He also has disturbing interests in politics, vexillology, geography, board games, conlanging, and law.