Trying to understand the formation of molecular clouds (MCs) and the generation of non-thermal motions a couple of groups found that, rather than being supported by turbulence against collapse over many free-fall times MCs form, collapse, form stars and disperse within a few free-fall times. In this scheme, turbulence is generated by the collapse itself, rather than a mechanism that supports the cloud. Although different observational features of MCs are reproduced by this model of cloud formation and evolution, also the turbulence-driven models have been able to reproduce some of these characteristics. Using Gaia EDR3, we have found what appears to be a distinctive feature that may allow us to determine which model of cloud formation and evolution is at play in MCs: the velocity dispersion of the newborn stars as a function of the mass of the stars. While turbulence models show that massive stars rapidly acquire high velocity dispersion, collapsing models show the distinctive signs of violent relaxation, where the velocity dispersion does not depend on the mass bin of the stars.