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Context: The evolution of solar active regions is still not fully understood.The growth and decay of active regions have mostly been studied in case-by-casestudies.  Aims: Instead of studying the evolution of active regions case by case, weperformed a large-scale statistical study to find indications for thestatistically most frequent scenario.  Methods: We studied a large sample of active regions recorded by theHelioseismic and Magnetic Imager instrument. The sample was split into twogroups: forming (367 members) and decaying (679 members) active regions. Wetracked individual dark features (i.e. those that are assumed to be intensitycounterparts of magnetised fragments from small objects to proper sunspots) andfollowed their evolution. We investigated the statistically most oftenlocations of fragment merging and splitting as well as their properties.  Results: Our results confirm that statistically, sunspots form by mergingevents of smaller fragments. The coalescence process is driven by turbulentdiffusion in a process similar to random-walk, where supergranular flows seemto play an important role. The number of appearing fragments does not seem tosignificantly correlate with the number of sunspots formed. The formation seemsto be consistent with the magnetic field accumulation. Statistically, themerging occurs most often between a large and a much smaller object. The decayof the active region seems to take place preferably by a process similar to theerosion.

Evolution and motions of magnetic fragments during the active region formation and decay: A statistical study