From an article on biology
The discovery of horizontal gene transfer (HGT) can be traced to 1928 when Fred Griffith reported the transfer of genetic material from heat-killed virulent Streptococcus pneumoniae to an avirulent form of the bacterium by a process he described as transformation (Bushman, 2002). It wasn’t until 1946 that other forms of non-reproductive gene transfer between organisms were identified and variously described as conjugation, transduction, recombination, rearrangement, linkage disequilibrium, etc. (Bushman, 2002). Since the 1980s these different examples of gene transfer have become known collectively as either horizontal or lateral gene transfer (Gogarten et al., 2002; Koonin et al., 2001; Ochman et al., 2000; Syvanen, 1994).
When exactly did they become known as HGT? In early 1980s? Or at some undefined point between the 1980s and today? Were they known as such on 1 January, 1990?
The use of become for some reason seemed strange to me. I'm not sure though.
Why "become", and not "been"?
Since the 1980s these different examples of gene transfer have been known collectively as either horizontal or lateral gene transfer.