Simon -  Absolutely brilliant
Of course

Marine life is preconceptional because all life sprang from it.

Right  from the beginning 3 billion years ago the primordial soup possessed the chemicals (call them nutrients if you like)  necessary for life to come into being. Then 600 million years ago the efforts of the previous 2.4 billion years laid the preconceptional grounds for the birth of multicellular life at the so -called Cambrian explosion when all 32 phyla we know to day enter the fossil record.

Then 100 million years ago or so, the collapse of the giant ginkos, ferns and their allies, led to the evolution of the gentler flowering plants with protected seeds containing concentrated packets of omega 6 fatty acids (linoleic mainly) needed to develop the vascular invasion and cell adhesion network that embedded the embryo to stick to the uterine wall instead of being laid as a clutch of shelled eggs. That focussed the nutrient supply on one instead of many offspring. It led to the placenta from which event mammal evolution took off.

Moreover, it filled the missing biochemical gap needed for brain evolution namely a balance of between 1 to 1 and 2 to 1 of omega 6 to omega 3 for cerebral expansion which up to that time there is no record
of any significant advancement of brain capacity. Then finally, the return of a primate to the waters edge to get the best of both worlds was the preconceptional stimulus for cerebral enhancement and ultimately H. sapiens.

That of course is backed by the previous return of land mammals to the sea which are now the dolphins and whales with massive brains and migrating huge distances to get their omega 6 fatty acids but at the same time benefiting from the wealth of DHA omega 3 and its allies which is difficult to obtain on land.