a bonobo humanity?

Nessa Carey’s book, The epigenetics revolution, was published in 2011, and discusses, and introduces, to many of us, gene methylation, histones, a number of different types of RNA, the names of specific genes, karyotypes, selective serotonin re-uptake inhibitors (SSRIs), phosphorylation, the Waddington epigenetic landscape and much else besides. Wikipedia’s account of epigenetics is no doubt more up-to-date, and is just about book-length (how long does a book have to be?), with over 200 references to scientific papers and such. Although the term was coined in the 1940s, the study of epigenetics is very much a 21st century thing, Our current knowledge of the area, like our knowledge of neurophysiology, has been one of the great developments in modern science. To read about it is exasperating, because there’s just too much to learn, to explore, to get your head around, and yet it’s vital to an understanding of who and what we are. When I think of SETI, for example, the Search for Extra-Terrestrial Intelligence, I wonder – how could such ineffable super-complexity have developed more than once in the universe, even given its incalculably massive extent?

I wish I was young and gifted with the opportunity to work in such a field, one which explains us, or tries to. How we manage to replenish all the cells in our bodies throughout our lives – not perfectly, for then we could live forever – but for a period extended enough for us to learn our own history, to fall in love, to learn from our many mistakes, to experience, delight in and suffer through all the stages of life, to observe all its amazing variety – the birds and the bees as they say, and the flowers and the trees, all of which have their genetic blueprints.

To think we had virtually no idea of this only a century ago, and we are 300,000 years old as a species, and DNA-driven creatures have existed for millions, maybe billions of years on this planet. We only worked out the structure of this molecule in the 1950s, and now we know for example that a spruce tree contains about six times more DNA than a human, and that it’s likely that our world was preceded by an RNA world, which still enlivens the viruses that plague us with influenza, hepatitis, polio, COVID-19 and so much else.

And all this epigenetic stuff – which is mainly about DNA methylation and histone modification – has been going on beneath our awareness, and certainly without our permission, since our life began as an embryo. That’s how our cells differentiate into some 200 different types. It has much to do with whether we’re tall or short, sickly or healthy, extroverted or introverted – even before we’ve ever met another soul. All of these goings-on in our growing bodies, as well as the inter-connections, disconnections and reconnections in our growing brains, in the time spent connected to a placenta and the subsequent years being buffeted by parents, relatives, strangers and frenemies, are what shape us for a lifetime.

So where am I going with all this? Those who know me might guess, and be much annoyed, or much heartened.

To return to Carey’s book, which explores, inter alia, how laboratory creatures like rats and mice show specific patterns of behaviour for a lifetime after early deprivation, stress and other conditions, I was struck by this passage:

The human brain possesses sufficient flexibility to generate adult outcomes in response to similar childhood experiences. Our brains contain one hundred billion nerve cells (neurons). Each neuron makes links with ten thousand others to form an incredible three dimensional grid. This grid therefore contains a thousand trillion connections – that’s 1,000,000,000,000,000 (a quadrillion). It’s hard to imagine this, so let’s visualise each connection as a disk that’s 1mm thick. Stack up the quadrillion disks on top of each other and they will reach to the sun (which is 93 million miles from the earth) and back, three times over.

That’s a lot of connections, so it’s perfectly possible to imagine that our brains have a lot of flexibility. But the connections are not random. There are networks of cells within the giant grid which are more likely to link to each other than to anywhere else. It’s this combination of huge flexibility, but constrained within certain groupings, that is compatible with a system that is mechanistic but not entirely deterministic.

Nessa Carey, The epigenetics revolution, pp 235-6

This is, I believe, the only passage in Carey’s 300-page book that refers to determinism, and of course it struck me enough to write one word in the margin.

‘Really?’

I don’t often write in the margins of my books these days. Decades ago I had a girlfriend who expressed shock and great disapproval at finding margin notes in some of my books. She apparently found this behaviour to be sacrilegious in some way. Texts were sacred even if they were reproduced in their thousands. So, though I respectfully disagreed, I’ve reduced my sacrilegious behaviour, maybe to honour her memory. But this time I couldn’t resist.

–  ‘mechanistic but not entirely deterministic’? What is the difference between these two terms? Aren’t these mechanisms determined by other mechanistic processes? Isn’t this what the book is all about? Isn’t this how we know about epigenetic processes, because they produce certain changes under certain specific conditions? Aren’t the determining factors precisely what we’re looking for, and what knowledge is all about. And yet there is, I find, a kind of fear or distrust of the word, even amongst those researchers who rely on mapping out the causal chain, often a complex and elusive one, to make good their discoveries. Whether we’re looking at the causes of cancer, or how one or two bees become queens while thousands more become workers, to mention just two topics explored in Carey’s book, we’re always trying to uncover and explain the determining conditions. It’s the sine qua non of all science.

Maybe I’m mis-representing Carey here. Maybe she meant, when she described  the ‘huge flexibility’ of our neuronal system, the impossibility of trying to pin things down, cause-and-effect-wise, with absolute certainty. But then, that’s not what she wrote. She wrote ‘not entirely deterministic’, and that was a red flag to me. So what was the part that escaped determinism? It doesn’t actually make sense.

The idea, it seems to me, and the argument that most people try to use against determinism, is that complexity trumps it (sorry to use the word ‘trump’ here). If complexity was infinite, that might be so, but complexity isn’t infinite, it’s just  complex.

So, that’s enough for now. Again, I wish I was fifty years younger, and a more disciplined person than I was in my youth, because I’d love to be working in the field of organic chemistry, or molecular biology, or neurophysiology, rather than peering at it over a vast stretch of ignorance, as I am today. But never mind…

References

Nessa Carey, The epigenetics revolution, 2011

https://en.wikipedia.org/wiki/Epigenetics