"...Applying a molecular clock to extrapolate times of origin of more divergent HCV variants, such as subtypes and genotypes, is clearly pointless, as the number of neutral sites or the limitations on sequence change at variable sites is not known, so there is no denominator with which to calculate and correct for multiple substitutions. The constriction of sequence space of viruses such as HCV with GORS implies that many of the branches that are evident on phylogenetic analysis of contemporary sequences that define virus species, genotypes or genera occurred at remote times in the past. In making the molecular clock-based estimates above of 350–1000 years for the time of divergence of genotypes, we are therefore in danger of telescoping a much longer period of virus evolution into an unrealistically short time-frame.
A much longer time perspective on HCV evolution, provided by our understanding of GORS constraints, fits much better with the globally distributed nature of HCV and the concentration of specific genotypes with historically relatively isolated populations in sub-Saharan Africa and south Asia. As a potential comparison, GORS in the widely distributed human virus hepatitis G virus/GB virus C appears to have restricted sequence drift to 11–13 % nucleotide sequence divergence over the course of evolution of modern humans over the last 100 000–150 000 years (González-Pérez et al., 1997; Pavesi, 2001; Simmonds, 2001). The greater sequence diversity between HCV genotypes implies times of origin that occurred even further back in the evolution of humans..."
So, probably during a mammoth hunt.
I'm thinking it passed from mosquitoes to humans.
No! the evidences of passing from mosquitoes to humans are not known
That's really a great question. And like with so many other great questions there are only theories offered as answers. The one theory that I find the most compelling is the theory of descension or de-evolution to use another term. I've posted on this a few times in the past. This holds that a virus such as HCV may have first been an organism such as a parasite, or even an antibody. Whatever the answer there is one thing known for sure---HCV in its evolutionary past had to have been self-replicating on its own without using intracellular mechanisms. Here is a link with alot of useful information on the topic.