Until the discovery of Neanderthal admixture in all non-African populations by the Max Planck Institute for Evolutionary Anthropology, the most publicly popular narrative of human evolution and settlement around the globe was the Out of Africa model, which posited that all humans descended from a single population of humans originating in Africa approximately 200,000 years ago who proceeded to settle the globe in the subsequent years, completely replacing whatever archaic hominids may have been occupying the lands that they settled. The model received a further blow after the sequencing of DNA from a fossil finger bone found in Denisova revealed that Melanesian populations had further admixture with the population to which the individual whose finger was found belonged.
The notion that all humans were completely descended from a single population living in Africa 200,000 years ago appealed to the ideological framework of some on the secular left who saw it both as a rebuke to the Creationist narratives that were held by scriptural literalists as well as a possible means of arguing that race itself was a meaningless concept. Ironically, just as this worldview was disintegrating, Richard Dawkins placed this T-shirt for sale at his site’s store:
But Dawkin’s design is certainly not the only “We are all Africans” T-shirt design. Here’s one that is cataloged with a set of “Atheist Designs” at Spreadshirt:
Here is one version from Squidoo that actually directly incorporates the Out of Africa model: