Sitat Opprinnelig skrevet av Mod Vis post
Thyroid hormone, iodine and human brain evolution.
Thyroid hormone, iodine and human brain evolution.
Venturi S. and Bégin M. E.
Chapter of book: "Environmental Influences on Human Brain Evolution"
by: Cunnane S. and Stewart K. Publisher: John Wiley, 2010. ISBN: 9780470452684

INTRODUCTION: Evolution of the hominin lineage is marked by progressive brain expansion and complexity concomitant with coordinated changes in other morphological and behavioral traits that characterize speciation events. In addition to gene variation, changes in climate, habitat, and diet are well-recognized environmental stimuli for evolutionary change. Iodine is an
environmental stimulus to which living organisms react, a point particularly evident in amphibian metamorphosis and potentially also in hominin evolution.

In toto, selection pressures effecting evolutionary change involve biological mechanisms permitting adaptation and evolution under changing environmental conditions. A common biological control mechanism could potentially coordinate a suite of physiological, morphological, and behavioral changes as important as brain evolution. We contend here that such a mechanism was hormonal and that thyroid hormone and iodine were pivotal components of such a mechanism.

The principal fossil sites of hominins correlated in space and time with volcanic and fissural local or nearby iodine sources (Borensztejn, 2005). In vertebrates, iodine is incorporated into thyroid hormone in the thyroid gland. Crockford (2003, 2008) provided solid evidence that changing thyroid function, specifically rhythms of thyroid hormone secretion, is crucial for speciation events taking place over decades.

The same thyroid hormone mechanism can be applied to the process of humanizing australopithecines. Here, we postulate a link between thyroid function, iodine, and evolutionary changes as they apply to the evolution of hominins and, more specifically, the large brain of Homo sapiens.

We emphasize changes in habitat and the connection between enhanced dietary availability of iodine, selenium, and polyunsaturated fatty acids (ikke flerumættede vegetabilske olier man spiser, men dem kroppen selv syntetiserer af fortrinsvis kostens animalske - æg, fuldfede mælkeprodukter, fisk m.v. - Omega-3'er/red.) as brain-selective nutrients necessary for thyroid function and hominin brain expansion.

Source: Environmental Influences on Human Brain Evolution (Book)

Read more / les mer... (PDF redirect Sites.google.com)