Power, Sex, Suicide, by Nick Lane

Last updated on Dec 20, 2022

I was working through an intro biology course while reading this dense, fast-moving book, and it helped. Some quick background on organic chemistry, lipids and proteins, hydrophilia and amphiphilia and the structure of the cell membrane, different types of amino acids, the basics of aerobic and anaerobic cellular respiration and how enzymes facilitate it, glycolysis and the use of ATP as the "universal energetic currency" in the cell all helped; particularly the last as it is in chemiosmosis - the movement of protons across an electrochemical gradient to manage energy - where the book's main point is concentrated. This process was discovered by Peter Mitchell, a delightful eccentric who designed and built his own lab on his family farm and funded his research via a prize-winning herd of dairy cows. While this procedure is found in all branches of the living world - us eukaryotes, bacteria and archaea - eukaryotes have internalised it via a dedicated organelle, the mitochondrion, allowing us to grow much larger, and also leading to sexual dimorphism and, ultimately, cell death. (Hence the title.)

This is really, like Lane's previous book Oxygen, a grab bag of biological topics centred around a theme (in this case the mitochondria) with lots of corny jokes. Quite a bit of it is about theories of the origins of multicellular life, which actually interests me least; it all seems so speculative and unimportant. But I found the story of Lynn Margulis interesting. A lifelong maverick, her landmark paper suggesting that the mitochondria originated in a symbiotic relationship between two prokaryotes who decided to make it permanent (endosymbiosis) suffered ridicule for a decade before empirical evidence emerged to verify it. Her later career consisted in a quixotic war against the neo-Darwinian synthesis (claiming that genetic variation was mostly caused by symbiosis and lateral gene transfer rather than random mutations), and she ended up espousing AIDS denialism and 9/11 conspiracy theories.

Lavoisier (whose execution was the "gravest crime of the French Revolution" in the words of Bernard Jaffe) originally guessed that the poetic "flame of life" was literal, that food is fuel and is converted to heat in the body. It took a while for thermodynamics to develop and realise that heat was not a fluid (the "caloric theory") but energy that could be used for work. Cells don't produce energy, but convert potential energy, by taking apart and reassembling ATP. "Gram per gram, even when sitting comfortably, you are converting 10,000 times more energy than the sun every second."

Bacteria have many fewer genes. They also aggressively shed genes, and then pick them up from each other (lateral gene transfer). This is how antibiotic resistance spreads so quickly. So it is harder even to define a species, unlike in species who practice sexual reproduction and thus transfer genes vertically. Sex itself, and the division into two sexes, is a biological puzzle: it would be easier to have one sex, or tens of thousands (both of these configurations exist in nature). Some organisms, such as clownfish, change sex during their lifespan; sometimes sex is determined by the temperature at which eggs are incubated, or by a bacterial infection. Having two sexes cuts in half the number of prospective mates, but possibly mitochondria can explain it: since mitochondria-nucleus matching is delicate and not guaranteed, it is better to pass down one gamete that donates mitochondria (the egg, in humans) and one that doesn't (the sperm).

The internalisation of energy generation in the mitochondria has also enabled eukaryotes to grow much larger. Bacteria pump protons across their external membranes, and energy generation is limited by geometry: the declining curve of the surface-area-to-volume ratio. We keep it inside the cell, and thus can develop into large, multicellular organisms with much more DNA. Excess heat generation is another side effect, allowing endothermy (warm-bloodedness), and so "the colonization of the temperate and frigid regions, as well as an active nightlife". (Being an ectotherm is much more energy-efficient, but it makes you much less energetic and highly limited by the weather.) Kleiber's law states that the ratio between mass and metabolic rate is always around 3/4; no-one is sure why.

Cell death also seems to be related to the mitochondria, which bring it about when they sense the cell is damaged, which correlates with age but is not exactly determined by it, but rather by the rate of free radical leakage within the cell. Birds have a similar metabolic rate to mammals - the same "pace of life" - but can live ten times longer because they leak free radicals much more slowly. So it would seem that the key to life extension would lie in regulating this, although apparently consuming antioxidants is not an effective strategy. And here is a related quote I liked:

There are two main forms of cell death: the violent, unexpected, swift demise known as necrosis, in which the carpet is left stained with blood and gore; and the silent, premeditated swallow of a cyanide pill, apoptosis, in which all evidence of the deed is spirited away. This is the spooks’ end, and it seems appropriate in the Stalinist state of the body. In contrast, death by necrosis incites an unruly inflammatory reaction, equivalent to an incendiary police investigation, in which more bodies turn up, and the ructions take a long time to fade.

Last note: I found myself wondering why in biology there always has to be a reason for things - can't some of it just be a matter of chance? Apparently this way of thinking is known as "structuralism" (in contrast to "adaptationism") and has been much debated, most famously in Stephen Jay Gould's 1979 paper on "the spandrels of Saint Marco", the elegant forms in Renaissance buildings which were (ostensibly) not planned but emerge from broader architectural constraints.