In their 2003 book "Crossroads to Islam", Yehuda D. Nevo and Judith Koren advanced a thesis, based on an extensive examination of archaeological evidence from the early Islamic period, that Muhammad may never have existed, with monotheistic Islam only coming into existence some time after he is supposed to have lived. This has been described as "plausible or at least arguable" and employing a "very rigorous historical methodology" by David Cook of Rice University, but has also been compared to Holocaust denial by historian Colin Wells, who suggests that the authors deal with some of the evidence illogically.