Obino, amazingly enough, some things in Nature arise by sheer chance and have no functional meaning that anyone can discover. Other times researchers may kind of guess at a reason or cause but yet still be unsure. Sometimes something of a general nature may be said, based on Bergmann's and Allen's rules, for example; sometimes parallels can be drawn with other species, i.e. the enlarged frontal sinuses of gerbils and some other desert-adapted animals, and donkeys (and to some degree Arabian horses) which also have enlarged frontal sinuses.
Note also in my previous reply how I slyly slip in the plural -- several times, as in "head shape or head shapes". This is because there is not one single head shape in Arabians, nor in Thoroughbreds, nor Draft horses, nor Barbs, nor any other breed; there is always an array or spectrum or range.
This is the purpose of morphometrics, to discover and document that range; and as a biologist, I am certainly a morphometrician, with many papers published on that subject with respect to both horses and dogs. So while you're sitting around in a state of ennui contemplating the state of the universe, my advice to you is -- don't oversimplify. Nature is complex and that's what merits "much thought". Cheers -- Dr. Deb
So, Obino, if you're on the road like an interstate trucker, best advice I can give you is this:
(1) Get interested in geology and learn how much there is to discover by looking at the shape of rocks exposed in roadcuts. Get a textbook of geology or geomorphology that discusses mainly the United States, and read up on where the glaciers once were, and what the signs of their presence are that can still be seen everywhere.
(2) Get interested in grasses and/or toxic weeds, and learn how much there is to discover at every rest stop or truck stop....go around the back where the weeds are, and you will find a veritable garden of wonders.
(3) Stop at the Kentucky Horse Park in Lexington and tour the Museum of the Horse there.
(4) Stop at the Page Museum/La Brea Tar Pit Museum in Los Angeles, and spend time learning from the excellent skeletal mounts that can be seen there, of Equus occidentalis the Pleistocene horse that occurred at that locality, plus the saber-toothed cats, short-faced bears, and dire wolves.
(5) Stop at Morrill Hall at the University of Nebraska at Lincoln and spend time learning from the Hall of Mastodons as well as many, many other excellent mounts of animals from the Tertiary and Pleistocene periods.
.... and I could give you more, but that's a pretty good start. There's no excuse for self-deprecation and there's no excuse for ever being "bored". Cheers -- Dr. Deb