Hanging in there: Prenatal origins of antigravity homeostasis in humans

Abstract: 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