Primate evolution is a central topic in biology and much information can be obtained from DNA sequence data. A key parameter is the time "when we became human," i.e., the time in the past when descendents of the human–chimp ancestor split into human and chimpanzee. Other important parameters are the time in the past when descendents of the human–chimp–gorilla ancestor split into descendents of the human–chimp ancestor and the gorilla ancestor, and population sizes of the human–chimp and human–chimp–gorilla ancestors. To estimate speciation times and ancestral population sizes we have developed a new methodology that explicitly utilizes the spatial information in contiguous genome alignments. Furthermore, we have applied this methodology to four long autosomal human–chimp–gorilla–orangutan alignments and estimated a very recent speciation time of human and chimp (around 4 million years) and ancestral population sizes much larger than the present-day human effective population size. We also analyzed X-chromosome sequence data and found that the X chromosome has experienced a different history from that of autosomes, possibly because of selection.