Posts Tagged ‘Lewis Thomas’
“The past lives within the present, and our ancestors breathe through our children”*…
Indeed, that’s true all the way back. And as Jonathan Lambert explains, we now have more visibility on that distant past. The emerging understanding of our “last universal common ancestor” suggests it was a relatively complex organism living 4.2 billion years ago, a time long considered too harsh for life to flourish…
If you follow any path of ancestry back far enough, you’ll reach the same single point. Whether you begin with gorillas or ginkgo trees or bacteria that live deep in the bowels of the Earth — or yourself, for that matter — all roads lead to LUCA, the “last universal common ancestor.” This ancient, single-celled organism (or, possibly, population of single-celled organisms) was the progenitor of every varied form that makes a life for itself on our planet today.
LUCA does not represent the origin of life, the instance whereby some chemical alchemy snapped molecules into a form that allowed self-replication and all the mechanisms of evolution. Rather, it’s the moment when life as we know it took off. LUCA is the furthest point in evolutionary history that we can glimpse by working backward from what’s alive today. It’s the most recent ancestor shared by all modern life‚ our collective lineage traced back to a single ancient cellular population or organism.
“It’s not the first cell, it’s not the first microbe, it’s not the first anything, really,” said Greg Fournier, an evolutionary biologist at the Massachusetts Institute of Technology. “In a way, it is the end of the story of the origin of life.”
Still, understanding LUCA — whether it was simple or complex, and how quickly it emerged after life’s origin — could help answer some of our deepest questions about where we come from and whether we’re alone in the universe.
“[LUCA] tells our own story,” said Edmund Moody (opens a new tab), an evolutionary biologist at the University of Bristol. “It gives us a point from which we can look even further back.”
For half a century, biologists have focused on different kinds of physiological, genomic and fossil evidence to paint portraits of LUCA that sometimes clash dramatically. In 2024, Moody and a team of interdisciplinary researchers, including geologists, paleontologists, system modelers and phylogeneticists, combined their knowledge to build a probabilistic model that reconstructs modern life’s shared ancestor and estimates when it lived.
The analysis, published in Nature Ecology and Evolution in July, sketched a surprisingly complex picture of the cell. LUCA lived off hydrogen gas and carbon dioxide, boasted a genome as large as that of some modern bacteria, and already had a rudimentary immune system, according to the study. Its genomic complexity, the authors argue, suggests that LUCA was one of many lineages — the rest now extinct — living about 4.2 billion years ago, a turbulent time relatively early in Earth’s history and long thought too harsh for life to flourish.
The analysis reaches two conclusions that seem in conflict with each other, according to Aaron Goldman, who studies the molecular evolution of early life at Oberlin College and wasn’t involved in the new research. “The first is that LUCA was a complex cellular organism that likely lived in a complex ecological setting,” he said. “The second is that LUCA dates to a time that is pretty early in the history of Earth.” The results could mean that life evolved from a simple replicator into something resembling modern microbes remarkably quickly, he said. “That’s really exciting.”
“Our work suggests that those early steps of evolution weren’t hard; they’re pretty easy,” said co-author Phil Donoghue, an evolutionary biologist at the University of Bristol. “If you’re concerned with the origin of microbial-grade life, then that’s apparently very easy, and it should be quite common in the universe.”
Not all experts in the field agree, however. Some argue that a few hundred million years is not enough time for complex life to have evolved. The authors stress that their analysis is a first attempt to paint a fuller, admittedly fuzzy, picture of LUCA. “I fully expect and hope people prove us wrong in certain aspects,” said Moody, the paper’s lead author, especially if those new results offer a clearer view of the ancient ancestor of all life we know…
Eminently worth reading in full: “All Life on Earth Today Descended From a Single Cell. Meet LUCA,” from @evolambert in @QuantaMagazine.
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As we look back, we might send microscopic birthday greetings to Lewis Thomas; he was born on this date in 1913. A physician, poet, etymologist, essayist, administrator, educator, policy advisor, and researcher, he distinguished himself in medicine and microbiology both for his suggestion that an immunosurveillance mechanism protects us from the possible ravages of mutant cells (an idea later championed by Macfarlane Burnett) and for his proposal that viruses have played a major role in the evolution of species by their ability to move pieces of DNA from one individual or species to another.
But Lewis is more widely known for his writing, perhaps most especially for his first two books– The Lives of a Cell: Notes of a Biology Watcher (which won National Book Awards in two categories) and The Medusa and the Snail: More Notes of a Biology Watcher (which won another National Book Award)– which underscored the interconnectedness of life by sketching the ways that what is seen under the microscope is similar to the way human beings live.
“Biology gives you a brain. Life turns it into a mind.”*…
I have a confession. As a physicist and psychiatrist, I find it difficult to engage with conversations about consciousness. My biggest gripe is that the philosophers and cognitive scientists who tend to pose the questions often assume that the mind is a thing, whose existence can be identified by the attributes it has or the purposes it fulfils.
But in physics, it’s dangerous to assume that things ‘exist’ in any conventional sense. Instead, the deeper question is: what sorts of processes give rise to the notion (or illusion) that something exists? For example, Isaac Newton explained the physical world in terms of massive bodies that respond to forces. However, with the advent of quantum physics, the real question turned out to be the very nature and meaning of the measurements upon which the notions of mass and force depend – a question that’s still debated today.
As a consequence, I’m compelled to treat consciousness as a process to be understood, not as a thing to be defined. Simply put, my argument is that consciousness is nothing more and nothing less than a natural process such as evolution or the weather. My favourite trick to illustrate the notion of consciousness as a process is to replace the word ‘consciousness’ with ‘evolution’ – and see if the question still makes sense. For example, the question What is consciousness for? becomes What is evolution for? Scientifically speaking, of course, we know that evolution is not for anything. It doesn’t perform a function or have reasons for doing what it does – it’s an unfolding process that can be understood only on its own terms. Since we are all the product of evolution, the same would seem to hold for consciousness and the self.
My view on consciousness resonates with that of the philosopher Daniel Dennett, who has spent his career trying to understand the origin of the mind. Dennett is concerned with how mindless, mere ‘causes’ (A leads to B) can give rise to the species of mindful ‘reasons’ as we know them (A happens so that B can happen). Dennett’s solution is what he calls ‘Darwin’s dangerous idea’: the insight that it’s possible to have design in the absence of a designer, competence in the absence of comprehension, and reasons (or ‘free-floating rationales’) in the absence of reasoners. A population of beetles that has outstripped another has probably done so for some ‘reason’ we can identify – a favourable mutation which produces a more camouflaging colour, for example. ‘Natural selection is thus an automatic reason-finder, which “discovers” and “endorses” and “focuses” reasons over many generations,’ Dennett writes in From Bacteria to Bach and Back: The Evolution of Minds (2017). ‘The scare quotes are to remind us that natural selection doesn’t have a mind, doesn’t itself have reasons, but is nevertheless competent to perform this “task” of design refinement.’
I hope to show you that nature can drum up reasons without actually having them for herself. In what follows, I’m going to argue that things don’t exist for reasons, but certain processes can nonetheless be cast as engaged in reasoning…
Distinguished neuroscientist and psychiatrist Karl Friston argues that the special trick of consciousness is being able to project action and time into a range of possible futures: “The mathematics of mind-time.”
See also: “How the Brain Creates a Timeline of the Past” (source of the image above).
* Middlesex
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As we get our minds around our minds, we might spare a thought for Oliver Wolf Sacks; he died on this date in 2015. A neurologist, naturalist, historian of science, and author, he had an active clinical practice, but is more widely-remembered for his writing, mostly case studies from his clinical experience and memoir in which which he treats himself as a clinical subject. Awakenings, for example, recounted his experience treating post-encephalitic patients with a new drug (levodopa); it was a best seller that served as the basis of a BBC Discovery documentary and was adapted into a feature film. Widely honored for his prolific work, Sacks was the recipient of the 2001 Lewis Thomas Prize for excellence in scientific writing.
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