Gravity as a Boundary Condition for the Evolution of Three-Dimensional Multicellularity

Area of Science:

• Evolutionary Biology
• Mechanobiology
• Genomics

Background:

• Life evolved under a constant 1g gravitational field.
• Gravity provides a continuous, ubiquitous, and directional mechanical force.
• This force may have influenced the development of complex multicellularity.

Purpose of the Study:

• To propose gravity as a mechanical boundary condition influencing the evolution of complex multicellularity.
• To synthesize evidence from evolutionary biology, mechanobiology, and genome architecture.
• To investigate gravity's role in genome organization and cell differentiation.

Main Methods:

• Order-of-magnitude calculations of hydrostatic loads.
• Comparative genomic and imaging analyses.
• Integration of altered-gravity (microgravity and hypergravity) experiments.

Main Results:

• Gravity-derived hydrostatic loads are relevant to nuclear and chromatin mechanosensitivity.
• Complex animals utilize volumetric genome organization for stable cell identities.
• Microgravity and hypergravity rapidly and reversibly alter chromatin topology and transcription.

Conclusions:

• Gravity serves as a stable mechanical reference point in evolution.
• It likely contributed to the evolvability of mechanogenomic architectures.
• Gravity is essential for high-dimensional differentiation and tissue homeostasis.