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Why is a graviton expected to have a spin of 2?

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What is string theory? — string theory Brian Greene explains the basic idea of string theory in under three minutes.

In the context of physics, the graviton is expected to have a spin of 2 because this value is required for the particle to be consistent with general relativity.

While other fundamental forces are mediated by carrier particles with a spin of 1—such as the photon for electromagnetism—gravity is uniquely linked to the curvature of space-time. To describe the gravitational force as a quantum field theory that aligns with the geometric principles of general relativity, the graviton must possess an intrinsic angular momentum, or spin, of 2 units.1

This requirement is naturally satisfied in certain theories based on supersymmetry, such as supergravity, which incorporate gravity by treating supersymmetry as a local symmetry that varies over space-time.1