In 1997 academics in a "Journal of Current Anthropology" article criticised in detail many elements of "They Came Before Columbus" (1976). Except for a brief mention, the book had not previously been reviewed in an academic journal. The researchers wrote a systematic rebuttal of Van Sertima's claims, stating that Van Sertima's "proposal was without foundation" in claiming African diffusion as responsible for prehistoric Olmec culture (in present-day Mexico). They noted that no "genuine African artifact had been found in a controlled archaeological excavation in the New World." They noted that Olmec stone heads were carved hundreds of years prior to the claimed contact and only superficially appear to be African; the Nubians whom Van Sertima had claimed as their originators do not resemble these "portraits". They further noted that in the 1980s, Van Sertima had changed his timeline of African influence, suggesting that Africans made their way to the New World in the 10th century B.C., to account for more recent independent scholarship in the dating of Olmec culture.