Evolution was originally released in 1971 as a greatest-hits collection culled from the band's first four records, easily their strongest work. While the Black Sabbaths and Led Zeppelins of the day were singing, quite convincingly, about Vikings, devils and all sorts of heavy fare, Iron Butterfly came off like the cartoonish kid brother of the early pre-metal days of the late '60s. Existing at their prime in the hazy moment between acid rock and the genus of what would become metal, the group never quite committed to either. Never heavy enough to really be menacing or scary, the group's metal ties were mostly based in rhetoric. Likewise, they were never quite pop enough to breakthrough in the post-Sgt. Pepper's era. Minor hit "Flowers & Beads" sounds like a far gooey-er take on the Lovin' Spoonful's stony love songs, and while the organ-heavy riff rock of "Unconscious Power" is all kinds of groovy, it's a far cry from even less heavy proto-metal. The heaviest the band gets on Evolution is probably their biggest hit, stoner classic "In-A-Gadda-Da-Vida," presented here in a drastically edited three-minute form, down from the side-long jam that was the original version. Separated from the legacy of that huge hit, Iron Butterfly boils down to the perfect caricature of a late-'60s hippie band: corny, dumb, ham-fisted but also colorful, silly, and fun. Quite possibly in over their heads at the time, Evolution gives the sense that the Iron Butterfly crew was cluelessly enjoying every second of their 15 minutes of fame, and making some spirited (if poorly aging) rock music for the time.
AllMusic Review by Fred Thomas