According to the paleontological record the last common ancestor of humans may have lived around 6 million years ago. Rates obtained by pedigree methods are about 10 times faster than those obtained by phylogenetic methods. Several factors acting together may be responsible for this difference. As pedigree methods record mutations in living subjects, the mutation rates from pedigree studies are closer to the germline mutation rate. Pedigree studies use genealogies that are only a few generations deep whereas phylogeny based methods use timescales that are thousands or millions of years deep. According to Henn et al. 2009, phylogeny based methods take into account events that occur over long time scales and are thus less affected by stochastic fluctuations. Howell et al. 2003 suggests that selection, saturation, parallel mutations and genetic drift are responsible for the differences observed between pedigree based methods and phylogeny based methods. Anatomical modern humans (AMH) spread out of Africa and over a large area of Eurasia and left artifacts along the northern coast of the Southwest, South, Southeast and East Asia. did not rely on a predicted TCHLCA to estimate single-nucleotide polymorphism (SNP) rates. Instead, they used evidence of colonization in Southeast Asia and Oceania to estimate mutation rates. In addition they used RFLP technology ("Restriction fragment length polymorphism") to examine differences between DNA. Using these techniques this group came up with a TMRCA of 140,000 to 290,000 years. Cann et al. (1987) estimated the TMRCA of humans to be approximately 210 ky and the most recent estimates Soares et al. 2009 (using 7 million year chimpanzee human mtDNA MRCA) differ by only 9%, which is relatively close considering the wide confidence range for both estimates and calls for more ancient TCHLCA. Because chimps and humans share a matrilineal ancestor, establishing the geological age of that last ancestor allows the estimation of the mutation rate. The chimp-human last common ancestor (CHLCA) is frequently applied as an anchor for mt-TMRCA studies with ranges between 4 and 13 million years cited in the literature. This is one source of variation in the time estimates. The other weakness is the non-clocklike accumulation of SNPs, would tend to make more recent branches look older than they actually are. These two sources may balance each other or amplify each other depending on the direction of the TCHLCA error. There are two major reasons why this method is widely employed.