The origin of primogeniture: a hypothesis Capital, productivity and inequality in traditional societies Summary: The economy structures the family. The family is a unit of production, reproduction and consumption. Its organization is linked to the first of the three terms, which conditions the other two. When natural capital is productive but scarce, scattered and attached to the ground, complex hunter-gatherers or early farmers prefer to inherit the cadets rather than eliminate the excess mouths to feed as do conventional hunter-gatherers. On the contrary, when capital is superabundant, concentrated and, or mobile, the egalitarian sharing of inheritance is necessary. Primogeniture is quite ignored in terms of history and anthropology. It is mentioned especially when it comes to royal estates, but for the rest, it is the subject of relatively little research. These are even often incomplete. Georges Peter Murdock himself admitted that his Atlas of Cultures fished extensively on this point. It will in fact be necessary to wait for the recasting of the work of Leplay by Emmanuel Todd to relaunch the debate. The French anthropologist thus highlighted the specificity of the nations with primogeniture, Germany, Japan, Korea, their industrial, military and technical capacity, their tendency to decline in birth rate or their propensity to sink into the most extreme violence. The trait is not limited to nation-states but also to ethnic groups within countries with a predominantly egalitarian heritage. The Bamikélés in Cameroon are distinguished by their commercial brilliance; In Europe, Catalonia and the Basque Country are the industrial heartland of Spain, while in France the Midi-Pyrénées region has almost as many researchers per inhabitant as the Ile de France region. In India, Sikhs are another minority known for their taste for arms and trade. In the strict sense, primogeniture is a variant of unigeniture; it is to favour the eldest son or daughter over other siblings. Nevertheless, the definition varies, depending on whether one considers the property transmitted, movable or not, for example, the share attributed to the heir, total or not, and whether it is the eldest of children, boys or girls, or its place in the siblings – we will thus speak of ultimogenesis when the privileged heir is the last to arrive – or of knowing whether this practice is systematic or not. Murdock dans son Atlas of World Cultures privilégie une définition souple ; It does not require a complete bequest to a single child. Emmanuel Todd is stricter but, he confines the notion within the family strain, putting notably aside the absolute nuclear family and the family to temporary co-residence (children leave their parents after a few years of cohabitation). He was thus led to reject the Anglo-Saxons and the majority of the Bantu and Niger-Congos of the group of societies with unequal successions. For our part, we will follow in Murdock’s footsteps, taking into account the peoples where the inequality of successions is neither systematic nor complete, despite the self-criticism he may have made of them - self-criticism moreover relativized by research 1 . We distinguish three levels of inequality between men, keeping in mind that women generally remain excluded from the field of inheritance.  Level 1. Non-egalitarian nuclear family (or absolute nuclear family) – indifference to equality, only circumstantial inequality. Anglo-Saxons, conventional hunter-collectors 2 .  Level 2. Unequal nuclear family (or sometimes with temporary co-residency). Polynesians, Nilotes, Couchites, Bantu (in part)  Level 3. Complete or incomplete strain family (coredence + partial or exclusive inequality) – Germans, Japanese, Koreans, Tibetans, Catalans, Occitans, Basques, Bantu (partial)... In the societies of the world I, defined by Alain Testart as not practicing neither agriculture, nor livestock, nor the storage of foodstuffs, roughly those of mesolithic, no inheritance rule is detectable. Indeed, the rules for sharing inheritance exist only as long as there are assets to share. From this point of view, economically, 1 Auke Rijpma & Sarah G. Carmichael (2016) Testing Todd and Matching Murdock: Global Data on Historical Family Characteristics, Economic History of Developing Regions, 31:1, 10-46, DOI: 10.1080 /20780389.2015.1114415 2 We integrate in this first level the conventional hunter-collectors of Testart World I by specifying that wealth does not exist in these societies, inequality does not translate into the deprivation of goods, via primogeniture, but by the deprivation of life, by murder or infanticide. On the contrary, the rich societies of the world II substitute a financial regulation for infanticide, for example by the wergled (a fine that allows to pay his crime or his crime).