The wandering Fulani: children of the Green Sahara
Unsupervised Learning Journal Club #6
This year I’m trying out an occasional feature for paying subscribers, the Unsupervised Learning Journal Club where I offer a brisk review and consideration of an interesting paper in human population genomics.
In the spirit of a conventional journal club, after each post, interested subscribers can vote on papers for future editions. I’m open both to covering the latest papers/preprints and reflecting back on seminal publications from across these first decades of the genomic era.
If your lab has work we might like or you otherwise want to suggest a paper for me to cover, feel free to respond to this email or comment on this post.
The previous editions were:.
Wealth, war and worse: plague’s ubiquity across millennia of human conquest
Where Queens Ruled: ancient DNA confirms legendary Matrilineal Celts were no exception
Eternally Illyrian: How Albanians resisted Rome and outlasted a Slavic onslaught
Homo with a side of sapiens: the brainy silent partner we co-opted 300,000 years ago
Brave new human: counting up the de novo mutations you alone carry
Free subscribers can get a sense of the format from my ungated coverage of two favorite 2024 papers:
The other man: Neanderthal findings test our power of imagination
We were selected: tracing what humans were made for
Unsupervised Learning Journal Club #6
This time we’re reviewing a recent paper some readers have been requesting I cover since it came out: Population history and admixture of the Fulani people from the Sahel (2025). It comes out of Carina M. Schlebusch’’s group at Uppsala University, and appeared in The American Journal of Human Genetics on February 6th, 2025. The first author is Cesar A. Fortes-Lima, whom I interviewed about his paper on the Bantu expansion in 2023.
The Sword of Jihad
In March 1903, in the market square of Sokoto, capital city of an empire approaching its centenary, the last vizier of the improbable Sokoto Caliphate officially submitted to British rule. This act came in the wake of a series of brutal defeats by the European colonial power as it pushed northward from its coastal redoubts, bristling with modern weapons to which the locals had no answer. British forces promptly elevated a new puppet caliph to the role, but the more momentous event was the end of an audacious African imperial project that had been materially and permanently reshaping the Sahel for the previous century. The dawning age of European colonialism would unceremoniously carve up the entire continent, but the chapter closing at that moment had indelibly marked the Sahel alone. A century earlier, the fist of conquest came not from a far off continent, but from the arid wastes to the north; armies marched under the banner of a self-proclaimed caliph, and his fanatical followers swept across the Sahel’s sun-baked plains. The waves of conquest and conversion they unleashed would leave a legacy of eventually binding together much of modern Nigeria, Mali, Niger and Cameroon, uniting disparate kingdoms and tribes ostensibly under the domineering aegis of a strict Islamic faith, helmed by a preeminent ruler, the Caliph, or “Commander of the Faithful.”
The Sokoto Caliphate’s origins were modest, its spark an 1804 rebellion against a petty tyrant that would trigger an efflorescence of Muslim revivalism and unleash a jihad against pagan peoples all across West Africa. But the fanatics also brought to heel many already Muslim peoples whom they judged lax in their commitment to the faith, expanding the empire by the 1830s so that its frontiers ranged from the deserts of Mali in the northwest to the edges of the Cameroon’s tropical forests in the southeast, a vast network of peripheral territories around a locus of power on northern Nigeria’s plains, centered on the city of Sokoto.
And yet, none of this zeal or religious commitment is what truly underwrote the century-long Caliphate’s outsized success and long-term impact in the region. To understand the Sokoto Caliphate and its origins, it helps to recognize that its base of support was not purely religious, but ethnic and cultural. It began with intrigue at the royal court of a petty king. After a zealous and perhaps pedantic Fulani cleric in Northern Nigeria ran afoul of his ruler for remonstrating against that sovereign’s patently pagan practices, the vengeful king’s rage swelled into a full-brown genocidal persecution of the cleric’s people. But thus provoked, the Fulani swiftly transformed themselves into fearsome mounted cavalry. It was they who were the swords of what became a religious crusade against northern Nigeria’s corrupt rulers who continued to revere traditional idols while still demanding praise for their piety during Friday prayers. The same dynamics of lightning mobilization and seamless transition from pastoralism to mounted warfare that had long played out in Eurasia recurred little altered here in tropical Africa, right down to their outsized might in the face of far more numerous agriculturalist opponents. It was the military acumen of the Sahel’s mobile Fulani that powered the Sokoto Caliphate’s rise, whatever the merits of its stated Islamic revivalism. The Sokoto Caliphate’s raison d’être was orthodox Islam; its imperium was built in God’s name. But a Fulani ethnic core fought the battles that built an empire rivaling those of future European colonizers in size.
African nations, with their Western-imposed boundaries, can often feel uncomfortably packed with arbitrary assemblages of ethnicities, ancient enemies forced into a supposedly shared national identity. But the Fulani wholly defy this generalization; they are an ethnicity who flow across the borders of many nations. United by a common language, pastoralist lifestyle, and shared history, the Fulani tribes’ range spans the whole expanse of the Sahel, from the shores of the Atlantic to the highlands of Ethiopia. Today, the nearly 40 million Fulani people inhabit 20 nations across West, Central, and East Africa. The 15 million Fulani of Nigeria’s north make up some 6% of its population. But their cultural and historical influence in Nigeria is far out of proportion to these numbers. The Fulani-powered Caliphate’s 19th-century expansion saw the consolidation and conquest of northern Nigeria’s Hausa kingdoms, and a deeper penetration of Islam into the region that has carried on fueling conflict and conversion to this day. It was also the basis for the emergence of a synthetic “Hausa-Fulani” ethnolinguistic identity that would become the most powerful bloc both militarily and politically in modern Africa’s most populous nation.
But the Fulani are not just another nomadic people. They speak a western Niger-Congo language, which clearly situates them within the panoply of Sub-Saharan African peoples, in contrast to Hausa, which is Afro-Asiatic, and connects those savanna farmers to the Near East. And yet it is the Fulani who traditionally have struck physical anthropologists as exhibiting traits in keeping with a Eurasian origin; they are lighter-skinned than other peoples of the Sahel, and often have features like long, narrow noses and thinner lips more common among West Asians. Evolutionary psychologist Geoffrey Miller suggested in his 2001 The Mating Mind that these differences were driven by sexual selection alone, but preliminary work in 2009 using older genetic methods found that Fulani have admixture linking them to Eurasians.
Population history and admixture of the Fulani people from the Sahel is an important contribution and a leap forward in our understanding of these peoples’ population history because it applies genome-wide methods to 460 Fulani genomes drawn from across 18 regional populations. With well distributed sampling across many of the nations with Fulani populations, it is an excellent first stab at understanding the genetic variation of the Fulani as a whole; its balanced sampling choices minimize any risk of proving an unrepresentative subgroup, speaking for the Fulani of say Nigeria, or Mali alone.
The Green Sahara and West Africa
Using data across 633,000 single nucleotide polymorphisms (SNPs) per proband, the authors compared the Fulani samples to an assemblage of modern populations selected to represent the variation present across Sub-Saharan Africa, West Asia and Europe. In line with long-standing theories positing Eurasian admixture into the Fulani, the principal component analysis (PCA), which maps genetic variation of individuals along the two independent axes with the strongest explanatory power, shows that by heritage the Fulani samples sit at a distinct remove from the West African neighbors among whom most Fulani today live. Even in central and eastern African Fulani populations, the largest ancestry component resembles that of Sub-Saharan peoples resident west of Lake Chad, in a region stretching from Nigeria to the Atlantic and Senegal (although these Fulani do show some admixture from local populations). This result is in keeping with the Fulani’s linguistic affiliations; their native dialects hew closest to those of Senegal’s Wolof.