It's not really so much a matter of principle as just the genetic programming which turns on cell differentiation, in certain ways, of cells in certain (e.g., proximal) locations earlier than in other locations. And, obviously, you would want a child to develop cephalocaudally as opposed to caudocephalically, for one so that the more vital and complex organs and tissues have the most time to develop. You would not want the brain of a human child, for example, to be the last thing that begins substantive development . . . Or the skull which must accommodate that brain to fully develop late to the effect of limiting brains size, because if (hypothetically speaking) that were to happen, everyone would revert to beasts -- and severely incapable ones at that.
If there is any principle that could be associated with cephalocaudal developmental modality, I would offer that it goes to prove the Darwinian principle of natural selection: That cephalocaudal development, from early on, has conferred survival advantage. If we may imagine a time in which naturally occurring mutated genes giving rise to caudocephalic growth vied in more equal numbers with those giving rise to cephalocaudal, then the relative absense of the former gene type now strongly suggests their non-viability, even lethality. We have in fact living proofs in the person of those expressing the rare genetic condition, microcephaly, a condition which but for socializing influence could never survive; and without or without social influences can never compete. We could go on - more distally - and perhaps even draw a connection between such cephalo-caudal evolutionary advantage and the inception of bipedal locomotion. But perhaps another posting.
If there is any principle that could be associated with cephalocaudal developmental modality, I would offer that it goes to prove the Darwinian principle of natural selection: That cephalocaudal development, from early on, has conferred survival advantage. If we may imagine a time in which naturally occurring mutated genes giving rise to caudocephalic growth vied in more equal numbers with those giving rise to cephalocaudal, then the relative absense of the former gene type now strongly suggests their non-viability, even lethality. We have in fact living proofs in the person of those expressing the rare genetic condition, microcephaly, a condition which but for socializing influence could never survive; and without or without social influences can never compete. We could go on - more distally - and perhaps even draw a connection between such cephalo-caudal evolutionary advantage and the inception of bipedal locomotion. But perhaps another posting.