This is probably a silly question. But, **Why do large turbulent eddies break up into smaller ones?**

##A possible argument##
Why can't they (large eddies) retain their size and gradually diffuse instead of breaking up. Does something make these large eddies unstable (similar to instability of laminar streamlines which causes transition to turbulence), forcing them to break up.?

What is it that determines the break up instant of an eddy?

In separated flows, a vortex is shed when "enough" vorticity is accumulated. Does this argument hold true for turbulent eddies too? i.e.; Do turbulent eddies break up due to accumulation of vorticity?