Posts Tagged ‘Life’
“Man tends to define in terms of the familiar. But the fundamental truths may not be familiar.”*…
Most of us probably do not need to think too hard to distinguish living things from the “non-living”. A human is alive; a rock is not. Easy!
Scientists and philosophers do not see things quite this clearly. They have spent millennia pondering what it is that makes something alive. Great minds from Aristotle to Carl Sagan have given it some thought – and they still have not come up with a definition that pleases everyone. In a very literal sense, we do not yet have a “meaning” for life.
If anything, the problem of defining life has become even more difficult over the last 100 years or so. Until the 19th Century one prevalent idea was that life is special thanks to the presence of an intangible soul or “vital spark”. This idea has now fallen out of favour in scientific circles. It has since been superseded by more scientific approaches. Nasa, for instance, has described life as “a self-sustaining chemical system capable of Darwinian evolution”.
But Nasa’s is just one of many attempts to pin down all life with a simple description. In fact, over 100 definitions of life have been proposed, with most focusing on a handful of key attributes such as replication and metabolism.
To make matters worse, different kinds of scientist have different ideas about what is truly necessary to define something as alive. While a chemist might say life boils down to certain molecules, a physicist might want to discuss thermodynamics…
A comparative survey of the definitions that currently exist concludes…
To properly define life, we might need to find some aliens.
The irony is that attempts to pin down a definition of life before we discover those aliens might actually make them more difficult to find. What a tragedy it would be if in the 2020s the new Mars rover trundles straight past a Martian, simply because it does not recognise it as being alive.
“The definition can actually hinder the search for novel life,” says [Carol] Cleland. “We need to get away from our current concept, so that we are open to discovering life as we don’t know it.”
It is surprisingly difficult to pin down the difference between living and non-living things: “There are over 100 definitions of ‘life’ and all are wrong.“
* Carl Sagan
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As we strive for beginner’s mind, we might send exploratory birthday greetings to John Theophilus Desaguliers; he was born on this date in 1683. A natural philosopher, clergyman, and engineer, he is best remembered as the experimental assistant to Isaac Newton, who went on to popularize Newton’s work in public lectures and publications. On the strength of that work, Desaguliers was elected to the Royal Society and ultimately became its curator.
In his own work he coined the terms conductor and insulator. He repeated and extended the work of Stephen Gray in electricity. He proposed a scheme for heating vessels such as salt-boilers by steam instead of fire. And he made inventions of his own (e.g., a planetarium), and material improvements to others’ machines, such as Thomas Savery’s steam engine (by adding a safety valve and using an internal water jet to condense the steam in the displacement chambers) and a ventilator at the House of Commons.
“We are what we pretend to be, so we must be careful about what we pretend to be”*…
There is just something obviously reasonable about the following notion: If all life is built from atoms that obey precise equations we know—which seems to be true—then the existence of life might just be some downstream consequence of these laws that we haven’t yet gotten around to calculating. This is essentially a physicist’s way of thinking, and to its credit, it has already done a great deal to help us understand how living things work…
But approaching the subject of life with this attitude will fail us, for at least two reasons. The first reason we might call the fallacy of reductionism. Reductionism is the presumption that any piece of the universe we might choose to study works like some specimen of antique, windup clockwork, so that it is easy (or at least eminently possible) to predict the behavior of the whole once you know the rules governing how each of its parts pushes on and moves with the others…
The second mistake in how people have viewed the boundary between life and non-life is still rampant in the present day and originates in the way we use language. A great many people imagine that if we understand physics well enough, we will eventually comprehend what life is as a physical phenomenon in the same way we now understand how and why water freezes or boils. Indeed, it often seems people expect that a good enough physical theory could become the new gold standard for saying what is alive and what is not.
However, this approach fails to acknowledge that our own role in giving names to the phenomena of the world precedes our ability to say with any clarity what it means to even call something alive. A physicist who wants to devise theories of how living things behave or emerge has to start by making intuitive choices about how to translate the characteristics of the examples of life we know into a physical language. After one has done so, it quickly becomes clear that the boundary between what is alive and what is not is something that already got drawn at the outset, through a different way of talking than physics provides…
Physics is an approach to science that roots itself in the measurement of particular quantities: distance, mass, duration, charge, temperature, and the like. Whether we are talking about making empirical observations or developing theories to make predictions, the language of physics is inherently metrical and mathematical. The phenomena of physics are always expressed in terms of how one set of measurable numbers behaves when other sets of measurable numbers are held fixed or varied. This is why the genius of Newton’s Second Law, F = ma, was not merely that it proposed a successful equation relating force (F), mass (m), and acceleration (a), but rather that it realized that these were all quantities in the world that could be independently measured and compared in order to discover such a general relationship.
This is not how the science of biology works. It is true that doing excellent research in biology involves trafficking in numbers, especially these days: For example, statistical methods help one gain confidence in trends discovered through repeated observations (such as a significant but small increase in the rate of cell death when a drug is introduced). Nonetheless, there is nothing fundamentally quantitative about the scientific study of life. Instead, biology takes the categories of living and nonliving things for granted as a starting point, and then uses the scientific method to investigate what is predictable about the behavior and qualities of life. Biologists did not have to go around convincing humanity that the world actually divides into things that are alive and things that are not; instead, in much the same way that it is quite popular across the length and breadth of human language to coin terms for commonplace things like stars, rivers, and trees, the difference between being alive and not being alive gets denoted with vocabulary.
In short, biology could not have been invented without the preexisting concept of life to inspire it, and all it needed to get going was for someone to realize that there were things to be discovered by reasoning scientifically about things that were alive. This means, though, that biology most certainly is not founded on mathematics in the way that physics is. Discovering that plants need sunlight to grow, or that fish will suffocate when taken out of water, requires no quantification of anything whatsoever. Of course, we could learn more by measuring how much sunlight the plant got, or timing how long it takes for the fish-out-of-water to expire. But the basic empirical law in biological terms only concerns itself with what conditions will enable or prevent thriving, and what it means to thrive comes from our qualitative and holistic judgment of what it looks like to succeed at being alive. If we are honest with ourselves, the ability to make this judgment was not taught to us by scientists, but comes from a more common kind of knowledge: We are alive ourselves, and constantly mete out life and death to bugs and flowers in our surroundings. Science may help us to discover new ways to make things live or die, but only once we tell the scientists how to use those words. We did not know any physics when we invented the word “life,” and it would be strange if physics only now began suddenly to start dictating to us what the word means.
The origin of life can’t be explained by first principles: “Why Physics Can’t Tell Us What Life Is.”
See also this interview with Jeremy England, the author of the article linked above (and of the book from which it is excerpted): “The Physicist’s New Book of Life.”
- Kurt Vonnegut, Mother Night
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As we live and let live, we might spare a thought for Ernest Everett Just; he died on this date in 1941. A pioneering biologist, academic, and science writer, he contributed mightily to the understanding of cell division, the fertilization of egg cells, experimental parthenogenesis, hydration, cell division, dehydration in living cells, and the effect of ultra violet rays on egg cells.
An African-American, he had limited academic prospects on his graduation from Dartmouth, but was able to land a teaching spot at Howard University. Just met Frank R. Lillie, the head of the Department of Zoology at the University of Chicago and director of the Marine Biological Laboratory (MBL) at Woods Hole, Mass. In 1909 Lillie invited Just to spend first one, then several summers at Woods Hole, where Just pioneered the study of whole cells under normal conditions (rather than simply breaking them apart in a laboratory setting). In 1915, Just was awarded the first Spingarn Medal, the highest honor given by the NAACP.
But outside MBL, Just experienced discrimination. Seeking more opportunity he spent most of the 1930s in various European universities– until the outbreak of WW II hostilities caused him to return to the U.S. in late 1940. He died of pancreatic cancer on this date the next year.
“I’m sure the universe is full of intelligent life. It’s just been too intelligent to come here.”*…
The Fermi paradox, named for physicist Enrico Fermi, is the apparent contradiction between the lack of evidence for extraterrestrial civilizations and various high estimates for their probability (e.g., some of the optimistic estimates for the Drake equation). Fermi wondered, “where are they?”
By way of context, Tim Urban in his wonderful Wait But Why?:
As many stars as there are in our galaxy (100 – 400 billion), there are roughly an equal number of galaxies in the observable universe—so for every star in the colossal Milky Way, there’s a whole galaxy out there. All together, that comes out to the typically quoted range of between 1022 and 1024 total stars, which means that for every grain of sand on every beach on Earth, there are 10,000 stars out there.
The science world isn’t in total agreement about what percentage of those stars are “sun-like” (similar in size, temperature, and luminosity)—opinions typically range from 5% to 20%. Going with the most conservative side of that (5%), and the lower end for the number of total stars (1022), gives us 500 quintillion, or 500 billion billion sun-like stars.
There’s also a debate over what percentage of those sun-like stars might be orbited by an Earth-like planet (one with similar temperature conditions that could have liquid water and potentially support life similar to that on Earth). Some say it’s as high as 50%, but let’s go with the more conservative 22% that came out of a recent PNAS study. That suggests that there’s a potentially-habitable Earth-like planet orbiting at least 1% of the total stars in the universe—a total of 100 billion billion Earth-like planets.
So there are 100 Earth-like planets for every grain of sand in the world. Think about that next time you’re on the beach.
Moving forward, we have no choice but to get completely speculative. Let’s imagine that after billions of years in existence, 1% of Earth-like planets develop life (if that’s true, every grain of sand would represent one planet with life on it). And imagine that on 1% of those planets, the life advances to an intelligent level like it did here on Earth. That would mean there were 10 quadrillion, or 10 million billion intelligent civilizations in the observable universe.
Moving back to just our galaxy, and doing the same math on the lowest estimate for stars in the Milky Way (100 billion), we’d estimate that there are 1 billion Earth-like planets and 100,000 intelligent civilizations in our galaxy.1
SETI (Search for Extraterrestrial Intelligence) is an organization dedicated to listening for signals from other intelligent life. If we’re right that there are 100,000 or more intelligent civilizations in our galaxy, and even a fraction of them are sending out radio waves or laser beams or other modes of attempting to contact others, shouldn’t SETI’s satellite dish array pick up all kinds of signals?
But it hasn’t. Not one. Ever…
Perhaps. as we’ve mused here at (R)D before, life is there, but we’re not seeing it because it isn’t a form of life that we recognize: c.f., “Two possibilities exist: Either we are alone in the Universe or we are not. Both are equally terrifying” and “That is a very Earthling question to ask, Mr. Pilgrim.”
But there are some who’ve refused to give up on the search for more traditionally-defined life; indeed, a new study quantifies the “fraction” (to which Urban alludes, above) of civilizations that could (should?) be communicating around our galaxy:
One of the biggest and longest-standing questions in the history of human thought is whether there are other intelligent life forms within our Universe. Obtaining good estimates of the number of possible extraterrestrial civilizations has however been very challenging.
A new study led by the University of Nottingham and published [earlier this month] in The Astrophysical Journal has taken a new approach to this problem. Using the assumption that intelligent life forms on other planets in a similar way as it does on Earth, researchers have obtained an estimate for the number of intelligent communicating civilizations within our own galaxy -the Milky Way. They calculate that there could be over 30 active communicating intelligent civilizations in our home Galaxy…
Details at (the slightly misleadingly-titled): “Research sheds new light on intelligent life existing across the galaxy.”
* Arthur C. Clarke
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As we stay tuned, we might send far-seeing birthday greeting to Fred Hoyle; he was born on this date in 1915. A prominent astronomer, he formulated the theory of stellar nucleosynthesis. But he is rather better remembered for his controversial stances on other scientific matters—in particular his rejection of the “Big Bang” theory (a term he coined, derisively, in one of his immensely-popular series The Nature of the Universe on BBC radio) and his promotion of panspermia as the source of life on Earth.
“That is a very Earthling question to ask, Mr. Pilgrim”*…
What does it mean to be alive? Science, shockingly, still doesn’t have a consensus. For example, is it fair to say that the novel coronavirus now sweeping the world is alive? The short answer is there isn’t one agreed-upon answer — for something so basic, you’d think life would be easier to define.
The first recorded definition of life came from Aristotle in ancient Greece, around 350 BC. He posited that to be alive, something must grow, maintain itself, and reproduce. In contrast, the most well-known modern definition is probably NASA’s, which says living things must be “a self-sustaining chemical system capable of Darwinian evolution.” Take, for example, great apes: given appropriate resources like food and water, the “machinery” of a great ape — its organs and nervous system — regulates itself, keeping the great ape functioning in most conditions. They are also capable of evolution — just look at us. But this isn’t the only accepted definition of life. There are actually over 100 published definitions!
A lot of the debate comes down to the fact that the various fields of science approach the topic quite differently. A geneticist, whose focus is on known organisms and their genomes, will very likely have a different view on what constitutes life than an astrophysicist, who considers a more expansive, universal definition.
But beyond that, most of these definitions of life fall short in another, very subtle way: They are based on the origins of life on our planet. This means our hypotheses for what sentient and conscious aliens look like almost always reflect humankind. You only have to look at a Star Trek episode to see it — humanity likes to make the world in our image, which is partially why in sci-fi and fantasy a lot of the “aliens” look a lot like ourselves. (Okay, and because it’s easier to dress a human up as a humanoid alien)…
Cal Tech scientist (and published poet) Alison Koontz explains why none of the 100 definitions of life we have may be accurate away from “home”: “Our concept of life is too Earth-centric — alien life might look totally different.”
* Slaughterhouse-Five
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As we confront our chauvinism, we might send speculative birthday greetings to Harlan Jay Ellison; he was born on this date in 1934. A member (with Philip K. Dick, Samuel Delany, Thomas Disch, Ursula K. LeGuin, and Roger Zelazny) of the American “new wave” science fiction vanguard, Ellison wrote more than 1,700 short stories, novellas, screenplays, comic book scripts, teleplays, essays, and a wide range of criticism covering literature, film, television, and print media. Some of his best-known work includes the Star Trek episode “The City on the Edge of Forever“, his A Boy and His Dog cycle, and his short stories “I Have No Mouth, and I Must Scream” and “‘Repent, Harlequin!’ Said the Ticktockman“… for which he won many, many awards, including multiple Hugos, Nebulas, and Edgars.
Ellison is also remembered for his outspoken, sometimes combative personality, of which Robert Bloch (the author of Psycho) said “[Ellison is] the only living organism I know whose natural habitat is hot water.”
“It is a good day to study lichens”*…
Wolf lichen
Science is sometimes caricatured as a wholly objective pursuit that allows us to understand the world through the lens of neutral empiricism. But the conclusions that scientists draw from their data, and the very questions they choose to ask, depend on their assumptions about the world, the culture in which they work, and the vocabulary they use. The scientist Toby Spribille once said to me, “We can only ask questions that we have imagination for.” And he should know, because no group of organisms better exemplifies this principle than the one Spribille is obsessed with: lichens.
Lichens can be found growing on bark, rocks, or walls; in woodlands, deserts, or tundra; as coralline branches, tiny cups, or leaflike fronds. They look like plants or fungi, and for the longest time, biologists thought that they were. But 150 years ago, a Swiss botanist named Simon Schwendener suggested the radical hypothesis that lichens are composite organisms—fungi, living together with microscopic algae.
It was the right hypothesis at the wrong time. The very notion of different organisms living so closely with—or within—each other was unheard of. That they should coexist to their mutual benefit was more ludicrous still. This was a mere decade after Charles Darwin had published his masterpiece, On the Origin of Species, and many biologists were gripped by the idea of nature as a gladiatorial arena, shaped by conflict. Against this zeitgeist, the concept of cohabiting, cooperative organisms found little purchase. Lichenologists spent decades rejecting and ridiculing Schwendener’s “dual hypothesis.” And he himself wrongly argued that the fungus enslaved or imprisoned the alga, robbing it of nutrients. As others later showed, that’s not the case: Both partners provide nutrients to each other…
Gorgeous and weird, lichens have pushed the boundaries of our understanding of nature– and our way of studying it. Learn more at: “The Overlooked Organisms That Keep Challenging Our Assumptions About Life.”
A Year in Thoreau’s Journal: 1851
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As we contemplate cooperation, we might spare a thought for John James Audubon; he died on this date in 1851. An ornithologist, naturalist, and artist, Audubon documented all types of American birds with detailed illustrations depicting the birds in their natural habitats. His The Birds of America (1827–1839), in which he identified 25 new species, is considered one of the most important– and finest– ornithological works ever completed.
Book plate featuring Audubon’s print of the Greater Prairie Chicken
