dissecting the body’s battle to keep selfish genes in check

The Paradox of the Organism: Adaptation and Internal Conflict J. Arvid Ågren and Manus M. Patten (eds) Harvard Univ. Press (2025)

Some thirty-five years ago, biologist Richard Dawkins coined the phrase “paradox of the organism” to encapsulate a conundrum. If genes are ‘selfish’ — driven to increase their own chances of being transmitted to the next generation — some of them might act in ways that harm the organism as a whole.

For example, sections of DNA can ‘jump’ to different parts of the genome, copying themselves into other locations and, thus, shuffling genetic material. Such ‘jumping genes’ constitute nearly half of the human genome and are crucial for driving evolution and increasing genetic diversity. But they can also cause harmful mutations, and even cancer, when their insertion disrupts key genes that regulate cell growth.

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In The Paradox of the Organism, leading evolutionary theorists and philosophers explore such conflicts in a series of essays. They consider how a body made of myriad competing constituents can function as a coherent system, finely tuned towards one goal: maximizing the chances of surviving and reproducing. The book, edited by evolutionary biologists J. Arvid Ågren and Manus M. Patten, succeeds at making a challenging subject digestible.

The overall message is that internal conflict is a central, not peripheral, feature of organismal biology, and should be considered in studies of development, evolution, cancer and beyond.

Checks and balances on genes

The whole body is set up to help keep selfish genes in check, argues evolutionary theorist David Haig. This works through the separation of a small group of germline cells (eggs, sperm and their predecessors) from the somatic cells that make up the rest of the body.

Somatic cells will never give rise to a new organism, so there is no need for selfish elements to propagate in them. By contrast, the cell division that gives rise to sperm or eggs (called meiosis) is fertile ground for transmitting selfish elements. Because meiosis involves shuffling DNA and separating chromosomes, opportunities are ripe for genes to try to ensure that they are passed on to the next generation.

To combat the threat from selfish elements, specialized somatic cells actively police germline behaviour, sending signals that cause the death of abnormal germ cells. Furthermore, developing germ cells themselves limit transmission of selfish elements by tightly regulating or silencing their own gene expression.

The genome can be thought of as a “parliament” of sequences, an essay by evolutionary theorists Thomas Scott and Stuart West notes. Similarly to a parliament passing laws that the majority agree on, most parts of the genome act together to ensure an organism’s fitness, including by stopping selfish elements from causing harm.

Patten examines this balance. The organism can live with some selfish elements, he notes. Most jumping genes, for example, have little effect on health, and so there is little danger in letting them propagate. But others are more insidious — the genome has to counter them to prevent harm to the organism.

Take elements called X drivers, which skew the sex ratio of descendants towards females. Found on the X chromosome, these genes harm or kill sperm that carry a Y chromosome and so would otherwise produce male offspring. The genes might, for example, yield molecules that stop the Y chromosome from expressing crucial genes. Thus, a disproportionate fraction of surviving sperm carry only X chromosomes, and transmit the element to the next generation.

Genetic interventions such as this could threaten the species as a whole, Patten notes. Natural selection therefore favours the evolution of ‘suppressor’ sequences that inhibit their expression — the parliament maintains order.