"the gradual development" is correct and usable in written English
You can use it to refer to a process that occurs slowly over time. For example, "The gradual development of new technology has made many tasks easier."
As the endosymbiotic origin of eukaryotic flagella was never widely accepted by the scientific community, models of the gradual development of eukaryotic cytoskeleton in a stepwise manner were developed.
It is even possible to follow the gradual development of his ideas in this direction.
However, the gradual development of other mini-clusters is already being overshadowed by something much bigger: the Internet.
Sanctions remained and took a severe toll until Iraq accepted the Oil for Food Program and the gradual development of that program mitigated the effects of the sanctions.
Since the summer, NOAA's Climate Prediction Center had been favoring the gradual development of El Niño conditions; it even issued an El Niño watch in recent months.
Elsewhere, the charming doubt of "Perhaps I am wrong to seek the flywheel of human progress in the gradual development of exchange and specialization.
However, it stemmed primarily from the populace's ingrained and instinctive conservatism, which only the gradual development of a grassroots opposition movement was later able to overcome.
Neil's illness — a gift to Apted, if a trial to Neil — shows the limitations of the original show's simplistic sociopolitical premise, and it underscores the series' actual accomplishment: revealing the gradual development of ordinary lives in all their extraordinary complexity.
Both exiles from Austria, they saw social democracy, exemplified by Franklin Roosevelt's New Deal and the gradual development of Britain's welfare state, as manifestations of a collectivism that occupied the same spectrum as nazism and communism.
The era that followed witnessed the collapse of the Roman breeds and the gradual development—especially during the era of Charlemagne in the late 8th and early 9th centuries of improved types, owing largely to the importation of Arabian stock.
Although the actual nature and size of the historical settlement remain matters of scholarly debate, the ruins of Troy at Hisarlık, Turkey, are a key archaeological site whose many layers illustrate the gradual development of civilization in northwestern Asia Minor.
