Scientists have discovered a gene which helps our bodies withstand gravity and take on their 3D shape - solving a century-old mystery.
A team of international researchers found the same mechanism lies behind proper alignment of tissues in the developing embryo to make complex organs.
It is now hoped that their breakthrough, published in the journal Nature, could help tissue engineers produce complex organs for transplant patients.
In 1915, mathematical biologist D'Arcy Thompson suggested that body shape was conditioned by gravity and most animals would resemble lizard-like creatures without it.
He wrote: "Were the force of gravity to be doubled, our bipedal form would be a failure, and the majority of terrestrial animals would resemble short-legged saurians."
His theory has been impossible to test until now as there has been no suitable experimental animal in which to study how bodies resist gravity and the effect of this on shape.
The researchers, led by the University of Bath, were able to identify a gene - called YAP - which helps the body resist gravity and demonstrated what happens when it is disrupted.
They found that when YAP is disrupted in medaka fish, tissues are distorted in the direction of gravity and are not aligned correctly - resulting in a flattened, almost 2D body.
Dr Makoto Furutani-Seiki of the University of Bath led the research team, along with Professor Hiroshi Nishina in Japan and Professor Carl-Philipp Heisenberg in Austria.
"The YAP system works a bit like one of those push-puppet toy figures that collapses when you push with your thumb," Dr Furutani-Seiki said.
"By identifying this new function for YAP, we have demonstrated a key mechanism underlying how our bodies take on their 3D shape.
"Put simply, without YAP we would all look very different inside and out - perhaps more like short-legged lizards, as D'Arcy Thompson wrote.
"What excites us is where this discovery may lead, particularly in the field of regenerative medicine."
The team discovered that disruption of the YAP gene in human cells also stops the cells forming 3D clusters. YAP is known to regulate organ size and is over-active in many human cancers.
It is hoped the research, funded by the Medical Research Council and Japanese Science and Technology Agency, will help grow organs for transplantation.
Dr Stefan Bagby, also from the University of Bath and co-author of YAP Is Essential For Tissue Tension To Ensure Vertebrate 3D Body Shape, said: "At the moment, we can grow 3D clusters of cells in the lab but cannot reproduce the precise structures of individual tissues and alignment of multiple tissues required to make complex organs such as an eye or heart.
"We hope to build on our discovery of the important role of YAP in tissue alignment to contribute to the goal of producing complex organs in the lab for transplantation."