Get huge or be a plant

Par Divers Moyens On Arrive à Pareille Fin (Michalle de Montaigne)

Cancer seems to be a fact of (biological) life. From time to time, cells go rogue, breaking the discipline of the organism, so to speak, and multiplying without control. Setting aside the multiple inherited and environmental factor that can contribute to trigger such rogue behaviour, one woud say that the more cells in an organism, the higher the risk of developing cancer. Yet, that’s not the case.

Surprisingly, although cancer should be a body mass- and age-related disease, large and long-lived animals do not suffer higher cancer mortality rates than smaller, shorter-lived animals. This is a phenomenon known as Peto’s Paradox(1).

In fact, animal gigantism is a recurring phenomenon, and not only in the cinema. Large body size has evolved multiple times throughout the history of life, including in 10 out of 11 mammalian orders. Elephants has 100 times as many cells as human beings do, whales as many as 1000. They are not completely immune to cancer. However, elephants have a 5% lifetime risk of cancer mortality, far less than humans.

To the extent that there has been selection for large body size, there likely has also been selection for cancer suppression mechanisms that allow an organism to grow large and successfully reproduce.

Tollis, Marc, et al. ‘Return to the Sea, Get Huge, Beat Cancer: An Analysis of Cetacean Genomes Including an Assembly for the Humpback Whale (Megaptera Novaeangliae)’. Molecular Biology and Evolution, 2019.

Yet, “repression” is not the only strategy life has evolved to survive rebel cells. There is a completely different one which is to ignore and accommodate the insurrection.

In an animal each cell and organ has a place and purpose. All parts must work and cooperate for the individual to survive. A human cannot manage without a brain, heart or lungs. Cancer is often fatal in animals, because their cells and systems are highly specialised and inflexible. Plants, however, develop in a much more flexible and organic way.

Rather than having a defined structure as an animal does, plants make it up as they go along. Whether they grow deeper roots or a taller stem depends on the balance of chemical signals from other parts of the plant and the “wood wide web”, as well as light, temperature, water and nutrient conditions.

Critically, unlike animal cells, almost all plant cells are able to create new cells of whatever type the plant needs. This is why a gardener can grow new plants from cuttings, with roots sprouting from what was once a stem or leaf.

All of this means that plants can replace dead cells or tissues much more easily than animals, whether the damage is due to being attacked by an animal or to radiation.

Mutated cells are generally not able to spread from one part of the plant to another as cancers do, thanks to the rigid, interconnecting walls surrounding plant cells. Nor are such tumours fatal in the vast majority of cases, because the plant can find ways to work around the malfunctioning tissue.

As it happens, there are usually different means to come to a like end.

For the time being, we do not know how to escape our core biology, and therefore, suppression may seem a better strategy. However, if you could start from scratch and design a brand new living organism, which one would you choose? What are the implications for our global super-organism strategy?

____________________

(1) Peto, R., et al. ‘Cancer and Ageing in Mice and Men’. British Journal of Cancer, vol. 32, no. 4, 1975, p. 411.

Featured Image: The Asian Elephant and Conservation Project, Yod Yeam #069

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