- Where in the embryo does the person reside? Morphogenesis – the formation of the body from an embryo – once seemed so mystifying that scholars presumed the body must somehow already exist in tiny form at conception.
- This idea finds modern expression in the notion that the body plan is encoded in our DNA. But the more we come to understand how cells produce shape and form, the more inadequate the idea of a genomic blueprint looks, too. What cells follow is not a blueprint; if they can be considered programmed at all, it’s not with a plan of what to make, but with a set of rules to guide construction. One implication is that humans and other complex organisms are not the unique result of cells’ behaviour, but only one of many possible outcomes.
- This view of the cell as a contingent, constructional entity challenges our traditional idea of what a body is, and what it can be. It also opens up some remarkable and even disconcerting possibilities about the prospects of redirecting biology into new shapes and structures. Life suddenly seems more plastic and amenable to being reconfigured by design. Understanding the contingency and malleability of multicellular form also connects us to our deep evolutionary past, when single-celled organisms first discovered the potential benefits of becoming multicellular. ‘The cell may be the focus of evolution, more than genes or even than the organism,’ says Iñaki Ruiz-Trillo of the Institute of Evolutionary Biology in Barcelona. Far from the pinnacle of the tree of life, humans become just one of the many things our cells are capable of doing.
- Acknowledging that the human form is a contingent outcome of the way our cells are programmed for construction raises some mind-bending questions. Are there, for example, human xenobots (perhaps we might call them anthrobots)? If so, are they truly ‘human’? Might there be a kind of organ or tissue that our cells could make but don’t normally get the chance to? Might our still cells ‘remember’ older evolutionary body shapes?
- Perhaps at least some of the attractors that AI algorithms could help identify in xenobot-type assemblies ‘are echoes of past targets of natural selection’, says Bongard. ‘At least some of these new configurations may tell us things about the environments and selection pressures that acted on these organisms in their distant past, and how they responded evolutionarily. In a way, these attractors are like fossils: they might be giving us partial glimpses into the past.’
- They also raise questions about how much we can reshape biological forms – including our own. In one sense, we already know that the human body has considerable ‘plasticity’. No genetic signal tells an embryo to split into identical twins, for example: it’s just one way the assembly rules happen to play out. And even relatively modest genetic tweaks to the rules can generate markedly different bodies. The heritable condition called Kartagener’s syndrome, for example, which leads to respiratory problems in early childhood, can sometimes be accompanied by complete mirror-image reversal of the internal organs – the heart lying to the right, say – which leads to health complications. It’s as if one key step in the early formation of the body plan went awry but then the cells accommodated it as best they could. Developmental problems such as spina bifida, in which the neural tube that will become the spinal cord fails to close, have many complex and imperfectly understood causes that may all lead to the ‘wrong’ outcome of the assembly rules.
- ‘Wrong’, that is, for the health of the baby. But sometimes the rules result in a morphological outcome only a little different from the most common one: an extra finger, a shorter limb or overall stature, a cleft palate. These are only ‘errors’ if we choose to make them so; sometimes, a non-standard body shape is only a problem because, as a society, we don’t make adequate allowance for it, physically, aesthetically or socially. There are many ways that humans can look, because the result isn’t written into our genome. What cells get are guidelines for assembly, and the result is not prescribed. Nature has realised that there are better and more versatile ways to build than that.
- Philip Ball is a British science writer, whose work appears in Nature, New Scientist and Prospect, among others. His latest book is The Book of Minds (2022). He lives in London.
- I’m not quite sure what to make of this.
- The description of the science of ‘xenobots’ – termed rather unhelpfully after a kind of frog (the African clawed frog, Xenopus laevis) from which the cells are cultured – is a little OTT in its claims.
- The fact that various somatic outcomes are possible by tweaking the environment doesn’t mean that viable ones – let alone great leaps forward – will be forthcoming even with the assistance of AI. As we’re all aware, minor variations usually lead to catastrophe.
- But the general idea – that there’s more to foetal development than the ‘blueprint in the genome’ is (it seems) generally correct; the environment in which the cells develop has a lot to do with how they develop. For more, see the author’s book: "Ball (Philip) - How to Grow a Human: Reprogramming Cells and Redesigning Life".
- But, I didn’t like the relativist suggestion that body-plans are rather arbitrary. As the paper points out, the Cambrian explosion created very many body plans that natural selection weeded out as sub-optimal and which no longer occur. No doubt indefinitely more ‘failed experiments’ left no fossil record.
- The final few paragraphs suggest– rightly – that some ‘errors’ in the human body-plan are clearly detrimental, and just that – ‘errors’ (such as spina bifida). But it denies that what are less serious ‘errors’ are other than unfashionable variations that ‘society’ doesn’t make adequate provision for. Well, this is absurd. And whether or not something is an ‘error’ is orthogonal to society’s response to – and accommodation of – such ‘variations’. Six fingers may not be much of a handicap, and might occasionally be an advantage. But two fingers would stop you doing a lot of things, both in modern and pre-modern societies, and is just as much a deviation. Cleft palates – as well as being disfiguring – are a right nuisance until ‘corrected’. It isn’t just an unfashionable variation to have your food coming out of your nose. More could be said.
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