  All life on Earth must find a way to manage the continuous perturbation of
gravity. From birth, and even before, humans exhibit effortful antigravity work
to enact bodily, postural and behavioural form despite gravity. Indeed,
observable antigravity behaviour is a standard diagnostic indicator of neonatal
sensorimotor health. Antigravity behaviour has been investigated extensively in
its biomechanical details. Yet its motivational structure has not been a focus
of research. What drives the human body to expend energy on this effortful
behaviour? It is widely understood that thermic homeostasis in humans is
organised around conserving core body temperature at a set-point of
36.5-37.5oC. There is currently no equivalent concept of a general homeostatic
set-point driving antigravity effort. In this theoretical paper, we aim to
establish such a concept. We make the case that the core developmental
set-point for human antigravity homeostasis is neutral buoyancy (gravity and
buoyant force are balanced), which is afforded to the foetus by its
approximately equi-dense amniotic fluid medium in utero. We argue that
postnatally, the general task of human antigravity balance is to emulate the
conditions of neutral buoyancy, based upon prenatal experience thereof. Our aim
in this paper is to sketch a high-level outline of a novel characterisation of
antigravity balance as conservative homeostasis, and lay out some implications
and predictions of this model, with the intention of spurring wider research
and discussion on this hitherto little explored topic.
  Keywords: antigravity, posture, homeostasis, prenatal, buoyancy, density,
fetus, foetus
