Here is another post from Gary Jackson:

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There is a book that I have never seen mentioned here that has
relevance to the discussion about EFA's and other nutrients. The book
is titled "Nutrition and Evolution" by Crawford and Marsh[Keats], and
was published in 1988. The book is very well referenced. The main
theme, is a look at certain micro-nutrients and different species
ability, or lack thereof, to synthesize them. By using this method
they argue for the existence of the food chain and its evolution. To
precis the book , and probably not do it justice, the argument is as
follows.

The premise is that total DNA is the same for all cells in the same
animal and from one mammal to the other. Lower forms of life have less
DNA. As some mammals become more complex than others in one area or
another, the % of DNA devoted to that specialization is greater. This
leaves a deficit of DNA for other tasks (because total DNA is
constant). Nutrient synthesis is the expression of one of DNA's tasks.
If nutrients can be obtained from food and not synthsized, then
valuable DNA space is saved. The second premise is that EFA
composition(the types of EFA's) of the brain and neural system is the
same for all mammals. What does differ is the ratios of the EFA's and
the totals, and the size of the brain. eg. The predatory cats have a
more highly developed neural system than their prey. Their requirement
of sythesized EFA's are greater than their prey. The prey has less
neural EFA requirement and has more sythesized EFA stored in the
flesh. Cats cannot synthesize neural EFA's from vegetation, but they
can from the partially synthesized EFA's from herbivore's flesh. Hence
the food chain. A similar argument is made for predators eysight
(especially night vision) and Vitamin A synthesis.

On the same theme there is an argument made for the relative brain
sizes and omega3 and omega6 ratios. It goes something like this. The
larger the brain relative to body size, the lower the ratio of omega6
to omega3 and the larger the total quantity. So humans have a 1:1
ratio, as have dolphins. Most land mammals have a 6:1 ratio, while sea
animals have up 1:40 ratio as expected. Expression of this is claimed
to be reflected in the respective milk compositions of the mammals.eg.
Rhino milk is skewed towards greater protein and minerals and less
EFA's while human milk is the opposite. I did often wonder about the
seemingly absurdly low amount of protein in human milk and the high
fat content. Many supporting studies are cited. eg. Babies on
parenteral nutrition lacking in omega3 display neurological problems
until omega3 is added. There is a striking inference made from all
this. The sea-land interface contains the most abundant sources of
both omega3 and omega6 EFA's. This reflects in the EFA ratios of
savannah mammals and deep sea fish. Man and dolphins have ratios that
suggest they both evolved on or near the coast. As a personal
speculative aside, it did occur to me that the calcium requirements in
dairy free diets, can only be realistically met by eating sea
vegetables and fish. Many of these are extremely rich in calcium. This
is assuming the RDA's for calcium are vaguely correct.

So to cut a long story short. By analysing nutrients and their
requirements and synthesis among lifeforms, we may be able to figure
how and why they evolved. I have not done this book justice in my
attempt at summary. There is so much else that is discussed that I
have not even mentioned.

PS.
1.I apologise for the length of the post.
2.I have no interest whatsoever in proceeds from the book, other than
its relevance to the discussion.

Gary