Abstract: Reproductive division of labour (RDL), where specialised 'reproducers' assist sterile 'helpers' in transmitting genetic information, has evolved repeatedly and at vastly different biological scales. Examples include eusocial insects (queens and workers), multicellular organisms (germ and soma cells), ciliates (micro- and macro-nuclei), and cells (genes and enzymes). For over half a century, the standard theory has been that RDL evolves only if relatedness is sufficiently high (Hamilton's rule). Here, we challenge this theory by presenting a model that demonstrates that RDL can evolve if relatedness is sufficiently low. Our model, which represents the evolution of multicellular organisms, considers both the population dynamics of organisms and the developmental dynamics of cells within an organism. Thereby, the model allows for the fact that the evolution of RDL can increase relatedness between cells within an organism. Our results show that low relatedness can induce the evolution of RDL as follows: low relatedness promotes the evolution of cheaters; in response, RDL becomes advantageous for organisms because RDL can increase relatedness, thus keeping cheaters at bay. Therefore, our results indicate that the evolution of RDL can be a cause, rather than a consequence, of high relatedness, offering a fundamentally new perspective on the evolution of RDL.