  Finding the formation mechanisms for bipolar configurations of strong local
magnetic field under control of the relatively weak global magnetic field of
the Sun is a key problem of the physics of solar activity. This study is aimed
at discriminating whether the magnetic field or fluid motion plays a primary,
active role in this process. The very origin and early development stage of
Active Region 12548 are investigated based on SDO/HMI observations of 2016 May
20--25. Full-vector magnetic and velocity fields are analyzed in parallel. The
leading and trailing magnetic polarities are found to grow asymmetrically in
terms of their amplitude, magnetic flux, and the time variation of these
quantities. The leading-polarity magnetic element originates as a compact
feature against the background of a distributed trailing-polarity field, with
an already existing trailing-polarity magnetic element. No signs of strong
horizontal magnetic fields are detected between the two magnetic poles. No
predominant upflow between their future locations precedes the origin of this
bipolar magnetic region (BMR); instead, upflows and downflows are mixed, with
some prevalence of downflows. Any signs of a large-scale horizontal divergent
flow from the area where the BMR develops are missing; in contrast, a normal
supergranulation and mesogranulation pattern is preserved. This scenario of
early BMR evolution is in strong contradiction with the expectations based on
the model of a rising $\Omega$-shaped loop of a flux tube of strong magnetic
field, and an \emph{in situ} mechanism of magnetic-field amplification and
structuring should operate in this case.
