Transhumanity's understanding of humanity is virtually complete. From cells to societies, every aspect has its model. No single person can contain all of this knowledge at once, but the information is there for reference. Of course, transhumanity itself, by its nature, is in rapid flux, and a complete self-understanding is forever just over the horizon.
Most of this knowledge is directly useful, forming the foundations of transhuman tech from medichines to psychosurgery. One of the less practical but more popular areas of this research is in alternate-histories and counterfactuals, simulating Earth at points in history, making changes, and seeing what differs.
Of course, simulating the entire Earth with inhabitants even remotely approaching sentience is beyond the greatest of transhumanity's supercomputers. Adding to the problem, contingency simulations are typically run at accelerations of x10 or more. The simulations are therefore fundamentally statistical, populations existing only as elements of its economic and sociological models.
Contingency simulations receive grants for everything from sociological research, historical research, as well as refinement of models and simulations, but most of their funding is donated by individuals, who use the simulations for entertainment, inspiration, or just something interesting to learn about. Some of the more interesting alternative histories have also been licensed for entertainment, such as the Shattered Continents series of wargames based around worst-case scenarios, or High Impact Capitalism! competitive economic game based on a world without Karl Marx.