Brinedew

Unpublished draft

SCANDAL Hypothesis

The SCANDAL hypothesis — Speciated by CANcer Development AnimaL — proposes that a lineage of cancer cells can undergo speciation and become a new species of organism.

The idea

A cancer lineage already satisfies several requirements that a population of organisms normally needs for speciation: it is a population of cells with heritable variation, it reproduces, it evolves under selection, and in transmissible cancers it has a life cycle that is independent of the host’s reproduction. The hypothesis takes this seriously as a category question: if a cancer lineage transmits between hosts, evolves its own adaptations, and maintains its identity across generations of hosts, the lineage is a candidate for species status rather than a disease.

The suggestion has a long history. Julian Huxley proposed in 1956 that tumors, having escaped the developmental and evolutionary constraints of the body, might be regarded as new biological units. Transmissible cancers give the argument its strongest evidence: the canine transmissible venereal tumor has existed as an independently reproducing lineage for thousands of years, and devil facial tumor disease has persisted for decades.

The hypothesis remains a minority position. The main objection is that cancer lineages depend on their hosts for habitat and nutrients the way a parasite does, and parasitism has never required species status; the counterargument is that CTVT is a parasite whose genome is a cancer cell’s, which is the point the hypothesis is trying to establish.