Research coauthorship is useful to combine different skill sets, especially for applied problems. While it has increased over the last century, it is unclear whether this increase is universal across academic fields and which fields coauthor the most and least. In response, we assess changes in the rate of journal article coauthorship 1900–2020 for all 27 Scopus broad fields and all 332 Scopus narrow fields. Although all broad fields have experienced reasonably continuous growth in coauthorship, in 2020, there were substantial disciplinary differences, from Arts and Humanities (1.3 authors) to Immunology and Microbiology (6 authors). All 332 Scopus narrow fields also experienced an increase in the average number of authors. Immunology and Classics are extreme Scopus narrow fields, as exemplified by 9.6 authors per Journal for ImmunoTherapy of Cancer article, whereas 93% of Trends in Classics articles were solo in 2020. The reason for this large difference seems to be the need for multiple complementary methods in Immunology, making it fundamentally a team science. Finally, the reasonably steady and universal increases in academic coauthorship over 121 years show no sign of slowing, suggesting that ever-expanding teams are a central part of current professional science.

Information about the relative strengths of scholars is needed for the efficient running of knowledge systems. Because academic research requires many skills, more experienced researchers might produce better research and attract more citations. This article assesses career citation impact changes 2001–2016 for domestic researchers (definition: first and last Scopus journal article in the same country) from the 12 nations with most Scopus documents. Careers are analyzed longitudinally, so that changes are not due to personnel evolution, such as researchers leaving or entering a country. The results show that long-term domestic researchers do not tend to improve their citation impact over time but tend to achieve their average citation impact by their first or second Scopus journal article. In some countries, this citation impact subsequently declines. These longer-term domestic researchers have higher citation impact than the national average in all countries, however, whereas scholars publishing only one journal article have substantially lower citation impact in all countries. The results are consistent with an efficiently functioning researcher selection system but cast slight doubt on the long-term citation impact potential of long-term domestic researchers. Research and funding policies may need to accommodate these patterns when citation impact is a relevant indicator.