A new Marvel fan theory may have explained exactly why S.H.I.E.L.D have never been able to create another Captain America.
Reddit user 4DimensionalToilet shared their own theory recently, suggesting that Captain Americas super soldier powers may have come directly from the Heart Shaped Herb, the Vibranium-infused plant that gives the Black Panther their super strength, speed, and endurance as well.
Tony Starks father Howard Stark was famously behind helping scientist Dr. Abraham Erskine tweak the serum so that it worked successfully; the first time Erskine tried the serum on Johann Schmidt, Schdmidt turned into Red Skull.
We also know that Stark must have visited Wakanda – or had a source there – as Caps shield is made of vibranium, a super metal also only found in Wakanda. So it makes sense that Stark would also know about the Heart Shaped Herb.
The Heart Shaped Herb was incorporated into the Serum by Howard Stark, who somehow got a sample of the Herb from Wakanda, where he also obtained the vibranium used to make Caps famous shield, argues the theory.
The Herb contains a key ingredient that prevents the enhanced individual from getting fucked up like the Red Skull, the Hulk, and the Abomination did.
This theory also explains why Bruce Banner and Emil Blonsky failed to turn into super soldiers when they were injected with the serum after Steve Rogers – because the key ingredient was missing.
How this may affect Avengers 4 is an intriguing question though, as at the end of Black Panther, TChalla decided to reveal the extent of Wakandas power to the rest of the world which means there is scope for the Herb to help create more super soldiers.
(Remember, although Killmonger burned down TChallas garden, Nakia stole one Heart Shaped Herb – and as it was vibranium which gave the plant its power, there is always room for the metal to give another plant the same powers.)