Tuesday Tunes: "There is nothing new under the sun..."

Heard this song on the radio for the first time the other day...

... and I noticed the first five notes of the verse sounded awfully familiar!
(Compare the first line of the song above, from 33 to 35 seconds, with the first line of the chorus from the song below, about 53 to 55 seconds.)

Spanish Gold is only like three years old, and they're ripping off a one-hit wonder from the 80s?? Seems desperate. Although, maybe they're banking on the fact that 1984 is now THIRTY-THREE YEARS AGO, and their audience is too young — and too uncultured! — to know this creepy classic?

Who knows.

I've also wondered about The Black Keys' "Fever" (2014) and Peggy Lee's "Fever," (1959, cover of the 1956 original by Little Willie John) but I can't actually put my finger on (or ear to) the similarity between those two, beyond the name(s) of the song(s).

ALSO...

I heard on the radio the other day that Portugal. The Man's new hit, which I referenced a few posts ago, apparently "borrowed" the melody from a much older song. At first, my love for that song totally deflated. Then I did some research (I mean, Googled it and read the Wikipedia entry, then went to YouTube), and found that the "borrowed" song — "Please Mr. Postman" by the Marvellettes — didn't really sound like "Feel it Still" at all. But the band said it! They're the ones that volunteered the information! Right?

Anyway. This has me wondering how many new songs are really just recycled old songs and what constitutes as copyright violation or plagiarism and what doesn't.

Anyone know the rules or have a philosophical opinion on that?