I've been experimenting with A and D intake for about 7 years. My D levels are maintained in the middle of the reference range, per labcorp or ZRT at 65 ng/mL. For me, this requires 6,000 IU D per day. I've experimented with A intakes from 3-4x my D intake per day, down to my current 1/6th. At 20-25,000 IU A per day, I over time developed symptoms of A toxicity, especially excessively dry skin, lips and mucous membranes. Over time, I tracked serum A levels and supplementation, finally settling where I am now, at 1,000 IU preformed (not beta arotene) A intake per day.
In an evolutionary environment, it seems highly unlikely that we could have acheived A intakes of 20,000 IU per day which is what Masterjohn and the WAPF recommend. Nor would we have had access to high vitamin cod liver oil. The liver is just one small part of an animal...one part that would have been shared among (likely) many people and would have been eaten in ratio to the rest of the animal, including the fat, muscle meat, other organs, bone marrow, brains and blood. My perception is that a daily high intake of retinol just wouldn't have been possible.