  Observations in the Hubble Deep Fields have been used to study the evolution
of galaxy morphology over time. The majority of galaxies with z < 1 are seen to
be disk like, whereas most objects with z > 2 appear to be either chaotic or
centrally concentrated ``blobs''. Such blobs might be the ancestral objects of
ellipticals or of galaxy bulges. About 1/3 of objects with z > 2 appear to be
in the process of merging. The region with 1 < z < 2 marks an important
transition in the global history of star formation from a merger dominated
regime at z > 2, to one at z < 1 in which most star formation takes place in
galactic disks. It is speculated that the break in the Madau plot at z sim 1.5
might be related to the transition from merger-dominated star formation at z >
2 to disk-dominated star formation at at z < 1.
