'has been gradually evolving' is correct and usable in written English.
You can use it to indicate that a situation or process has been changing over time. For example, "The technology industry has been gradually evolving since the inception of the personal computer."
Alas, something does, something that last week was pried out from the obscurity where for four billion years it has been gradually evolving its present shape.
For over a year now, the site has been gradually evolving to leverage its data beyond Facebook proper so that it could better compete against Twitter and Google.
Interfaces between solid and aqueous solution have been studied for well over a century but during the period under review the model used to describe this interface has been gradually evolving from one based on a macroscopic viewpoint to one based on a microscopic bond valence picture.
Our live sets have been gradually evolving since our first live show together a few years ago and is something we are constantly looking to better.
So, machine tools have been gradually evolved out over the past few decades to meet the increasing demand of manufacturing complicated components with high degree of accuracy in large volume.
By this doctrine, anything and everything can be equally well explained; and it has proved as pernicious with respect to Expression as to every other branch of natural history.…He who admits on general grounds that the structure and habits of all animals have been gradually evolved, will look at the whole subject of Expression in a new and interesting light" (Darwin 1872b, p. 12).
Relations have been gradually improving since then.
Genetic and antigenic analyses of subtype H9N2 isolates from the past 2 decades have shown that these viruses are gradually evolving from the Eurasian lineage into several distinct sublineages and are becoming established in domestic poultry (7 – 18 ).
The startup's apps have become platforms for musicians, but are gradually evolving into augmented reality mobile apps.
While it has been successfully implemented in medical, dental and nursing schools, outcome based education is gradually evolving in the complementary and alternative medicine professions.
Big Phil's smirk is gradually evolving into a quivering lip - where's wife Amy when he needs a hug?
