Heme binding to albuminoid proteins is the result of recent evolution. 
We hypothesize that the structure of the heme binding site of paralogous albuminoids alpha-fetoprotein and serum albumin has evolved from the ancestor vitamin D binding protein through the 'phylogenetic intermediate' afamin, the most recently discovered albuminoid.  Heme binding to plasma proteins should serve not only as a buffer for heme homeostasis, avoiding heme binding to lipoproteins with the consequent oxidative stress, but also for heme transfer to the liver, complementing the function of hemopexin.