Is Darwinian Evolution Universal?
After a triumphant landing, the Curiosity rover is ready to search Mars for signs of past life or suitability for life. Several readers have raised concerns that NASA scientists might fail to recognize life if it isn't based on carbon or is otherwise radically different from our kind of life. That's been a concern for NASA, and so in the 1990s, the space agency convened a panel to try to define life. The panel put evolution front and center: Life, the panel decided, is self-sustaining chemical system capable of Darwinian evolution.
Is Darwinian Evolution Universal?
Here's my column for this week. It will also appear in Monday's health and science section of the Philadelphia Inquirer.
After a triumphant landing, the Curiosity rover is ready to search Mars for signs of past life or suitability for life. Several readers have raised concerns that NASA scientists might fail to recognize life if it isn't based on carbon or is otherwise radically different from our kind of life.
It’s true that biologists don't have a single agreed-upon definition of life, and often end up with a laundry list of characteristics instead.
That’s been a concern for NASA, and so in the 1990s, the space agency convened a panel to try to define life, said Steve Benner, a biologist from the Foundation for Applied Molecular Evolution(Ffame). The panel put evolution front and center: Life, the panel decided, is self-sustaining chemical system capable of Darwinian evolution. Benner said Carl Sagan had some pull on the panel. “This definition is very Saganesque.”
Creationists aren’t too happy with this, but biologists for the most part say it’s a reasonable guess as to what would tie together life through the cosmos.
It’s something of a guess because we only have one example of life. All life here on Earth is related, and all organisms share same system of carbon-based molecules - DNA and RNA - to carry assembly instructions and other key information.
It’s not hard to image that some other type of life might use an alternative system. In recent years scientists have synthesized alternative molecules that act like DNA. There's TNA, PNA, and FNA, for example, and while DNA uses a four-character code, scientists have made alternatives that use more. (In the movie ET, the alien had a six-character genetic code).
Asking earthlings to define life is a little like asking a group of born and raised on a deserted island to define animals when they’ve never seen another animal. How would they know what’s possible?
Some creationists worry that the NASA panel’s definition will force scientists to ignore or cover up findings of life forms that didn’t evolve. Take the creationist website, "Uncommon Descent," which accused me of "getting it wrong" in a previous column for mentioning NASA's Darwinian definition without saying it’s controversial because a post-doc at Michigan State University criticized it in a blog post.
The blogging post-doc post in question proposed a "thought" experiment: "Suppose we go to another planet and find one being there, looking exactly like a human being. Everything we can measure about this being confirms that it is just as much alive as you and me. It eats, moves, heals, replenishes, communicates, feels, defecates. Learning more about this being, though, we find that it has no ancestors, and that it does not age. It does not reproduce, and it is the only such being on the planet. Thus, there is no lineage of descent and no population that can evolve. So this being is then not alive? Of course it is. This definition does not work."
Ffame's Benner said this type of criticism rests on a semantic misunderstanding between life and being alive.
One isolated person isn’t capable of Darwinian evolution - we can’t reproduce without a partner. We’re alive but we’re part of a larger system that would be considered life.
NASA's Darwinian definition does indeed embody the theory of evolution, he said. And if the theory applies universally, it predicts that you won't find parentless humanoid beings popping into existence. You might find life like robots, but these, he are what he calls biosignatures - products of a living world.
While NASA needs to think broadly about life, they can't very well go around declaring clouds and flames and crystals alive. One critical distinction, said Benner, is that living things copy themselves imperfectly and pass on the flaws to the next generation. Crystals grow and reproduce themselves with flaws, but the flaws aren’t passed down to offspring. They don’t evolve.
In looking for signs of past life, a general definition of life is not as important as a set of search criteria, said Harvard biologist Andrew Knoll.
Whether looking for signs of past life on Mars or ancient rocks here Earth, scientists look for patterns that can't be explained by physics and chemistry alone, he said.
Scientists used search criteria, for example, when evaluating alleged fossils in a Martian meteorite called ALH84001. Back in the 1990s, scientists found tiny oval-shaped patterns that looked like fossil Martian bacteria. The features did look interesting, said Knoll, but over subsequent months, other scientists found ordinary physical and chemical processes that could explain them without the need for any biology.
There are, said Benner, beings on Star Trek that don’t fit the Darwinian definition of life. Q isn’t a chemical system, he said, and the Crystalline Entity didn’t have parents. In the unlikely event that we find such beings on Mars, “We’ll have to change our definition.”
Contact Faye Flam at 215-854-4977 215-854-4977 , fflam@phillynews.com, or follow on Twitter @fayeflam. Read her blog at philly.com/evolution.
"Creationists aren’t too happy with this..."
Who cares? Farmers and botanists don't care what people who believe in garden fairies think. HIstorians don't interview people who claim to talk to the dead. So it's time that biologists (and the general public) just dismiss the opinions of people who think species magically poofed into existence.
Like every question that's ever been answered, EVER, any questions raised by the Mars rover will not be answered by divine magic.— RickK- Farmers do very little interviewing, I would think. Historians interested in Native American Shamans get no help, either. Most of the general public have no interest in species at all.
No scientific discovery is likely to enlighten anyone when interpreted by someone who so easily dismisses other humans and does so with so little persuasive ability. Enjoy your one person party.— Jack Hughes - Could this be a simple and broad definition of life: An entity that uses energy. Would that work?— varsity
- Varsity,
Not unless you think thunderstorms and hurricanes are alive.— anaxyrus - Or a toaster.— anaxyrus
- I just finished reading The Origin of Species. It is so interesting to see how many of Darwin's carefully drawn insights remain exactly true, long before anyone knew about molecular biology or the genome. One recurring theme is how much evolution is driven by nearly all species reproducing at a geometric rate--leading to the struggle for survival. Whatever life forms we find on Mars or elsewhere, if they are evolving, they are reproducing rapidly and competing for resources.— Neil Gussman
@anaxyrus: the definition of entity: being or existence, especially when considered as distinct, independent, or self-contained. Thunderstorms and hurricanes don't fall under this definition of entity. I think my definition still works. Maybe.— varsity- I'm the "blogging postdoc at MSU", and it would be great if my name was used in the article.
I understand Benner's distinction, but I don't think it's a very pertinent one. We would definitely say a non-evolving entity is alive, so why not say it is an instance of "life"? Also, a population that reproduces but does not evolve is possible, for example if the mutation rate is zero.
Bjørn Østman— bjornostman - @varsity: I see thunderstorms and hurricanes being entities under this definition. Toasters too. What about a hurricane disqualifies it from being an entity in your mind?— anaxyrus
- Bjoern Oestman; your thought example, and the use the ID crowd make of it, confuses conceivable with actually possible. But it does raise the interesting question of what we demand from a definition; does it have to hold under every logically possible circumstance, or only under those that are physically plausible? You also make a shrewd point; we say that mules are alive. And I have my own problems with Benner's definition; we were able to classify things as living or non-living long before we knew of evolution. "[a] general definition of life is not as important as a set of search criteria"; Andy Knoll gets it right again.— PaulBraterman
- My example is both logically and physically possible, though. Not sure why you would imply it is not physically possible? — bjornostman
- On my 4th or fifth reading of "Origin of Species", I was struck by how he followed all the precepts of logical argument. As a past debater, I was amazed how Darwin wins all arguments, first knocking out all competitive theories and then presenting his own with multiple examples. He is worth reading on this basis alone, even apart from his prime issue.— cdarwin
- @varsity Need definitions of self-contained and being. I think organisms would fail self-containment if you think hurricanes do. Your definition of being would seem ad hoc. What besides an organism would be a being to you?— anaxyrus
- If you don't know the definitions of those words I can not help you anymore. I would like to now see your definition of life. — varsity
- @PaulBraterman, did you see the references on the caecilian post at WEIT?— anaxyrus
- NASA's definition is acceptable, as is the laundry list. There's no right or wrong with definitions, just utility. You do not have a workable/useful definition if you with to exclude accepted non-life on Earth. Instead of explanation, you provide assertions. I can't help you understand why your definition is useless if you are not willing to explain YOUR meanings of these words. The dictionary definitions of self-contained would either include the non-living (complete) or exclude animals (which are dependent on other forms of life). "Being" is either an organism (synonym, not definition) or a mushy philosophic abstraction.— anaxyrus
- Interesting: you throw "an entity that uses energy" into Google and you get pollution sources, angels, and cyborgs.— anaxyrus
- And to "throw" it "into Google" is supposed to mean what, exactly? Since all of the definitions of these words seem to be dependent on the user's interpretation, debating their meanings is a pointless exercise. I think my definition could work, I never said it was perfect or definitive. In my opinion NASA's definition is totally unacceptable and presumes that life forms that we are not aware of must undergo a process that works well in our world but may OR may not be necessary in another world. — varsity
- I agree with Knoll that what NASA needs is a list of search criteria; it doesn't have to be a rigorous definition. However, looking for things that evolve would not at all work well for such search criteria, because it takes too long to identify evolution. Instead, look for metabolism, growth, and reproduction.— bjornostman
- @varsity Chemistry is universal. To get to what we would call life would require substantial chemical evolution that would eventually become Darwinian. Darwinian evolution boils down to mathematics; it is not unique to life on Earth.— anaxyrus
- I understand where you are coming from, I really do. However, that is just an educated guess that we would have to see substantial evolution. You and I have no idea what we might find so it's a guess; a good one but a guess none-the-less. — varsity
- Oh, and throwing it in to Google shows that entity is used with a variety of definitions. Using "entity" in the definition of life subtracts rather than adds clarity.— anaxyrus
- Please, I'm assuming you are smarter than that. You could throw any number of words into google and find multiple definitions. You're better than that bro. — varsity
- Ok, so back to your definition of entity: a being or existence, especially when considered as distinct, independent, or self-contained.
Which one (or more) of these does a hurricane fail in your eyes?
That the laws of the Universe are homogenous is more than just a good guess at this point.— anaxyrus - Nevermind. Been over that. Led to nothing. I don't see how you see a mouse as being self-contained, but not a hurricane. Self-contained is an abstraction that doesn't help much in dealing with concrete reality.— anaxyrus
- cdarwin wrote: "As a past debater, I was amazed how Darwin wins all arguments, first knocking out all competitive theories and then presenting his own with multiple examples."
Darwin's "Origin of Species" doesn't actually discuss the origin of any species. Why do you suppose that is?
If Darwin couldn't list fossil evidence to support his ideas, where did his ideas come from? Pigeon breeding and observing the Galapagos finches?
If so, do evolutionists think pigeon breeding (which occurs as a result of intent and design) is a legitimate approximation of natural selection, and if so, how?
Do evolutionists think the Galapagos finches (which all still interbreed and none have evolved beyond being finches) legitimately exemplify Darwin's concepts, and if so, how?
— dab - I am robot... my name is dab... i just cut and paste statements that make me look like a dolt. I have no original ideas. I make it seem like I'm uncovering a conspiracy but I really just sound crazy. Abort... Abort... Abort — Aquanerd09
- dab,
Everything you wrote is fallacious.
1. Although speciation had not been documented, he did provide a mechanism through which species could multiply.
2. Darwin did have fossil evidence supporting his idea, as well as embryology, morphology, and biogeography. Read the book some day.
3. Artificial selection simply involves determining who mates and who does not. Darwin knew the environment would unintentionally do the same thing (at a slower pace, hence the need for an ancient Earth).
Not ALL species of Galapagos finch are interbreeding. They have evolved so much that they do not all appear to be finches superficially. The finches have shared common ancestry for more than 99.9% of history and have diverged quite remarkably in the last <0.1%. As we would predict from Darwin's scenario of colonization and adaptive radiation, the genetic sister group of the clade is a single South American finch species.— anaxyrus - Faye, did you mean "life-like robots"? And should it be "these are what he calls..."?
In the thought experiment, how did the writer determine that the being has no ancestors? The reasoning seems to be "no evidence for ancestors, therefore no ancestors." If so then surely the writer can also reason that "no evidence for god/creator, therefore no god/creator." Can't have it both ways.— mattfoley772 - anaxyrus wrote: "Not ALL species of Galapagos finch are interbreeding." So?
Jonathan Weiner ("The Beak of the Finch", 1994) says beak changes in Galapagos finches during a severe drought (1977) is "evolution in action", even though the changes were reversed after the drought ended, and no net evolution occurred.
The beak changes Weiner writes about can be more accurately described as "minor variation in action".— dab - anaxyrus wrote: "Darwin did have fossil evidence supporting his idea..."
What fossils did Darwin mention in "Origin of Species" as evidence for the origin of any species?— dab - So? Genetic evidence confirms that a single lineage split multiple times, filling an adaptive radiation that is represented today by multiple species. Just as Darwin had surmised. (That and apparently, you have no problems lying in trying to help your sad case.)
Feel free to learn about population genetics some time. This example shows beak length returning to its former size, but the population genetics have been permanently changed by the guidance of natural selection through two bottlenecks. The example in The Beak of the Finch is not a test of common ancestry or the proposition that populations can change (the facts of evolution no thinking scientist would dispute in this day and age), but rather examines evolutionary theory (is evolution led by natural selection or is it predominantly drift?)
What fossils did Darwin mention as evidence for common ancestry? Did you read On the Origin? I'll give you a hint. The fossils in question are from a clade of eutherians that prior to the late Pliocene were endemic to the continent on which Darwin spent the greatest amount of time during the Beagle voyage.— anaxyrus - dab, anaxyrus: I wonder if you two are talking past each other a little bit? My read on dab's comments is that he(?) wants to know how a species originates -- I'm guessing, what/where is the breakpoint from a previous species? Does Darwin's work specifically address that? To me, that sounds like determining when an individual from an older (ancestral) species would, perhaps, no longer be able to breed successfully with a newer (evolved) species. If that's dab's question (please confirm one way or other, dab), that would be a sort of bottom-up approach.
anaxyrus, what I'm reading from you seems more of a top-down approach, at least as far as speciation goes. Namely, here's the fossil record, note that if we arrange certain fossils in temporal order, we can see features appear/disappear/change in a progressive way that are linkable to mutations, thus over the course of time one species morphs/evolves into another. This explanation works for plenty of people, but if the questioner is wondering about the breakpoint (if such a discrete point even makes sense) between old and new species, then it may be unsatisfactory. I am kind of curious if evolution works in such a way that one generation cannot breed with the previous generation. Is breedability :) lost in bits and pieces or all at once?
Is that accurate for you two? Apologies if I've misconstrued anything. It may simply be that the definition of "species" is too fuzzy for everyone to settle happily on an explanation.— nerdyseahorse - Come on Nerdy... Giving credence to a known Creationalist. He doesnt care about the truth. Dab flings arguments that are rudimentary and insulting to the science of evolution. By you validating his "arguments" you perpetuate a debate where there is none. You're smarter than that. — Aquanerd09
- Gave him credence? How so? I was just trying to understand the impasse. I think I'm made it clear on here that I'm not an ID'er. But at the end of the day, we should look at the argument, not the person making the argument. I thought the point of a literal reading of "origin of species" was interesting. — nerdyseahorse
- You also have to remember that species isolated from one another contribute to this speciation. If one generation completely separates from the next over time, then yes, interbreeding would cease or at least viable unfertile offspring would occur. But an exact breakpoint like you said doesn't make sense in the timescale since at any point some of the species (those closest) would at one given time be able to breed successfully with their closer neighbor. — Aquanerd09
- I alwys thought this was a good synopsis on this subject
http://karmatics.com/docs/evolution-still-there-are-monkeys.html
— Aquanerd09 - It was a good read; thanks. Conjectural, of course, but plausible. — nerdyseahorse
- Nerdyseahorse,
The last thing David Buckna wants is to know how species originate. If he genuinely wanted to learn about evolution, he would start reading the recent literature, Coyne and Orr's Speciation would be one place to start. What dab wants is to spread his creationist manure. I answered his questions. South American fossils ARE relevant to the origins of modern South American species (more so than Darwin thought).
Contrary to many memes floating around perpetuated by those who haven't read the original or whom have forgotten, Darwin provided evidence for speciation (species origin) in the Galapagos finches and a model driven by differences in ecology and disruptive selection.
Contrary to what you wrote, speciation is not an event associated with a sterility barrier. With very few exceptions (mostly in plants), speciation is a process (which can take many thousands to a few million years) involving ongoing genetic divergence with reduced (eventually nonexistent) gene flow. Species are populations that do not regularly interbreed, not just those that physically cannot interbreed. Polar bears and brown bears are a good example. They occasionally interbreed, but this is not enough to keep both on the same genetic and morphological trajectory. They are "good" if fuzzy species.— anaxyrus - One of the informal definitions I've heard of species involved that members could (and would) breed within species, but not outside it, hence my question. It sounds like the oft-heard phrase "distinct species" is certainly wrongheaded in an absolute sense and probably wrongheaded in a relative sense as well. Thanks for the clarifications. — nerdyseahorse
- Nerdyseahorse,
If you wonder where sterility barriers come from, there are mutations that translocate genes from one chromosome to another. These types of mutations decrease fertility, but not by enough to disallow interbreeding. Over time, however, the number of these dislocations separating non-interbreeding populations becomes so great that sterile offspring result. Typically before that happens, we see that hybrids between the two have reduced fitness, or that females of one group are not receptive of males in the other group.— anaxyrus - An interesting digression there as well: why proximal species that can interbreed eventually don't. Do we have good evidence that they try their darnedest but weak offspring eventually lose the evolutionary lottery? (Don't answer that: way off topic, but might be worth exploring at some later post here. If Faye is reading this and feels so moved.) — nerdyseahorse
- I have to agree with the creationists on this one. Let's go back to that thought experiment with the human being. Let's say we drop a human being on Mars. Is he suddenly not alive because he's now incapable of evolution since he's isolated from his species?
Or, perhaps we create machine life forms that cannot reproduce. Are they suddenly non-alive because they are incapable of reproduction.
There's an inherent chauvinism in the definition. The implied assumptions are: 1) we'll find naturally occurring life and 2) that life will develop from the habitat in which we find it and 3) we will be able to recognize the systems act of evolution in the location and timeframe of observation. We cannot presume on these assumptions. Ammonites were around essentially unchanged for long periods of time. Were we there to observe them could we judge within our timeframe that they were capable of evolution or not?
While in all probability that is the sort of life we'd encounter it is a means by which we duck the question of what is life.
Life is that which evolves, we say, since that created us. Therefore, all things that evolve are therefore living. Are, then, evolution simulations in computers alive? Is an economy? Are internet viruses? Many of these sorts of things evolve after a fashion in that they can mutate, change, adapt to new surroundings. We can argue that to a computer virus a human being is a means of reproduction analogous to the way a cell would appear to a biochemical virus.
My own feelings is that we have a fair definition of life. It mediates energy (it is not an expression of energy as is a hurricane or tornado) for use. All of those definition of life things we saw in high school biology. Then some Dumb *$%(* would bring up viruses and ask if they're alive. Well, without something that *is* alive (i.e., a cell) they're not so it's a silly point.
We need to avoid semantic traps.— spopkes
In pursuit of her stories, writer Faye Flam has weathered storms in Greenland, gotten frost nip at the South Pole, and floated weightless aboard NASA’s zero-g plane. She has a degree in geophysics from the California Institute of Technology and started her writing career with the Economist. She later took on the particle physics and cosmology beat at Science Magazine before coming to the Inquirer in 1995. Her previous science column, “Carnal Knowledge,” ran from 2005 to 2008. Her new column and blog, Planet of the Apes, explores the topic of evolution and runs here and in the Inquirer’s health section each Monday. Email Faye at fflam@phillynews.com.
Reach Planet of the at fflam@phillynews.com.
