When does a tool become part of an individual?

A new paper argues that major evolutionary transitions may begin not only through mergers between existing organisms, but also when lineages generate new components from within.

To the point

• Major evolutionary transitions change what counts as an individual.
• Paul Rainey proposes a further route to such transitions: “autogenic transitions in individuality”.
• The paper uses transmissible cancers and human–AI systems to ask when internally generated entities might become part of new evolutionary individuals.

Evolutionary history has been shaped by moments when lower-level units became parts of something new. Genes became organised into chromosomes, cells became integrated into multicellular organisms, and some animals evolved societies in which individuals function as parts of a larger whole. Such events, known as major evolutionary transitions, are among the deepest transformations in the history of life.

In a new Perspective article in Comptes Rendus Biologies, Paul Rainey of the Max Planck Institute for Evolutionary Biology in Plön and ESPCI in Paris argues that these transitions may arise in a way that has received too little attention.

Most accounts focus on mergers between already existing evolutionary entities: separate genes, separate cells or separate organisms. Rainey draws attention to a different possibility. A lineage may generate, from within itself, a new component that later becomes incorporated into a higher-level individual. He refers to such possibilities as autogenic transitions in individuality.

The distinction matters because internally generated novelties are easily dismissed as products, tools or by-products of the systems that produce them. Yet, under the right conditions, such components could become part of a new parent–offspring system. At that point, variation, heredity and differential reproduction would operate not only on the original lineage, but on the composite entity itself.

The paper develops the idea through examples from biology and culture. Many internally generated novelties, including tools, language and genetic innovations, influence evolution while remaining embedded within existing systems. Transmissible cancers reveal a more striking boundary case. They originate as cells within an organism, escape normal regulation, and establish independent evolutionary lineages capable of transmission between hosts.

Artificial intelligence provides a contemporary and provocative thought experiment. AI is a human-made tool, but it is increasingly involved in human decision-making, education, communication and social organisation. Rainey asks what would be required for human–AI systems to move beyond tool use and become more deeply integrated evolutionary units.

The paper does not predict that this will happen. Instead, it uses evolutionary theory to clarify the conditions under which such a transition could be recognised. Human–AI systems would need to vary, reproduce and transmit their organisation in ways that allow selection to act at the level of the composite.

“AI is interesting not just because it is powerful,” says Rainey. “It is interesting because it is becoming entangled with human development, decision-making and social organisation. Evolutionary theory gives us a way to ask when something remains a tool, when it becomes a partner, and when it might become part of a new individual.”

The work extends earlier research published by Rainey in Philosophical Transactions of the Royal Society B in 2023, prior to the rapid rise of large language models, and by Rainey and Michel Hochberg in PNAS last year. The topic will also be discussed at a workshop in Plön in November of 2026.