1610s, "to indicate specially," from special + -ize. Sense of "engage in a special study or line of business" is first attested 1881; biological sense is from 1851. Related: Specialized; specializing.
specialize spe·cial·ize (spěsh'ə-līz')v. spe·cial·ized, spe·cial·iz·ing, spe·cial·iz·es
To limit one's profession to a particular specialty or subject area for study, research, or treatment.
To adapt to a particular function or environment.