Views on Watson's scientific contributions while at Harvard are somewhat mixed. His most notable achievements in his two decades at Harvard may be what he wrote about science, rather than anything he discovered during that time. Watson's first textbook, "The Molecular Biology of the Gene", set a new standard for textbooks, particularly through the use of concept heads—brief declarative subheadings. His next textbook was "Molecular Biology of the Cell", in which he coordinated the work of a group of scientist-writers. His third textbook was "Recombinant DNA", which described the ways in which genetic engineering has brought much new information about how organisms function. The textbooks are still in print.