The Olmec theory came from Andrzej Wiercinski and historian Frederick Peterson, not from Dr. Van Sertima.
“These regions include the Gulf Coast and Oaxaca. The Gulf Coast was initially peopled by the Olmecs (the earliest known major Mesoamerican civilisation) and was later home to the city of El Tajín.”
(Xavier Roca-Rada, NLM provides access to scientific literature. Inclusion in an NLM database does not imply endorsement of, or agreement with, the contents by NLM or the National Institutes of Health. Learn more: | 2020 Nov; 11(11): 1346.)
Ancient DNA Studies in Pre-Columbian Mesoamerica - PMC
“The pioneering study of ADNMT carried out on Olmec individuals, one from San Lorenzo and the other from Loma del Zapote, resulted,
in both cases, in the unequivocal presence of the distinctive mutations of the “A” maternal lineage.
That is, the origin of the Olmecs is not in Africa but in America, since they share the most abundant of the five mitochondrial haplogroups characteristic of the indigenous populations of our continent: A, B, C, D and X.”
[…]
Enrique Villamar Becerril. Physical anthropologist from ENAH. Candidate for a doctor in Mesoamerican studies (UNAM), with an analysis of ADNMT in bone remains from various sites of the Preclassic period.”
(Villamar Becerril Enrique, "DNA Studies and the Origin of the Olmecs", Mexican Archeology, no. 150, pp. 40-41.)