1) Write down two of the main challenges related with studying ancient DNA?
2) Give two key insights into the evolutionary history of Neandertals which have been derived from the analysis of mitochondrial DNA (mtDNA). In what manners might the use of mtDNA be misleading or limiting?
3) Who were the Denisovans? From an anthropological prospective, what is remarkable regarding their discovery?
4) Based on the recent publication of the Neandertal and Denisova genomes, explain the present model for putative hybridization and gene flow between these lineages and modern humans. Comprise in your answer the historical time, approximate geographic location of inferred hybridization events and the genomic extent of introgression.