Chad populations show ancient African-Eurasian admixtures. Early Eurasian backflow hit southern Chad Laal speakers 4750-7200 years ago. R1b-V88 Y-chromosome from this backflow coalesced 5700-7300 years ago. Backflow originated from Near Eastern farmers in African Humid Period. Later Eurasian backflow around 3000 years ago reached northern Chad Toubou with 20-30% Eurasian ancestry. Admixed Africans exhibit heterozygosity decline. Eurasian admixture biases coalescent history inferences. Eurasian admixture confounds adaptation signals. Eurasian admixture masks archaic introgression signals. Vast African regions like Chad were genetically understudied until now.