Can we scientifically rate veganism?

1) It is claimed that DHA led to better functional brains. This would be important in the human developement. (is this correct?)

2) DHA is nowadays (what about before) most found in fish oils or fish, together with EPA.

3) LA can be transferred to DHA but has nowadays (what about before) a low conversion.

4) Can the amount of DHA needed, be gained from plant based products?

5) so could in the past the amount of DHA be to low in plant based foods, so without eating fish we would not have gained a growth in brains (not so much quantitative but qualitative)

6) if it can not be achieved from plant based foods, human beings would not have had the growth and MIGHT not became ethical in the first place.

7) So are animals in essence ethical???

8) So would ingesting fish have led to ethical thinking that would lead to veganism. Or would we never had veganism without growth of our brains through DHA and eating of fish?