A Good Saturday Evening Flick
by BradfordStephen Jay Gould wrote Wonderful Life, a book in which he imagined the possibility of going back in time and replaying the evolution of life to see how closely it would resemble the original. Genetic changes are thought of as containing a stochastic element sifted by natural selection. The effects of natural selection would be influenced by environmental conditions. If the tape were run again with altered environmental conditions different results would be expected. A different set of random genetic events would change the tape. The logic is readily apparent.
Re-running scenes could be fun so if the tape of life were rerun what might we expect to see and is there anything we can do to in some small way simulate a forward/backward tape replay? Perhaps Henrique Teotnio and colleagues did replays of something much less gradiose but nevertheless useful as revealed in a Nature Genetics paper. But this is a contemporary movie and cites changes in the fruit fly (Drosophila melanogaster). The study was discussed in a blog entry titled Reverse evolution in real-time. Incidentally, this is an excellent blog IMO. Quoting from the linked piece:
The scientists used laboratory-grown populations of fruit fly (Drosophila melanogaster), derived from an original group of flies, harvested from the wild back in 1975. These ancestral flies were grown in the laboratory, for two decades, under different environmental conditions, (such as starvation and longer life-cycles) so that each population was selected for specific characteristics. Henrique Teotnio and colleagues placed these populations back in the ancestral environment, for 50 generations, to impose reverse evolution on the flies, and then looked at the genetic changes in certain areas of chromosome 3 of these flies.
Says Henrique, 'In 2001 we showed that evolution is reversible in as far as phenotypes are concerned, but even then, only to a point. Indeed, not all the characteristics evolved back to the ancestral state. Furthermore, some characteristics reverse-evolved rapidly, while others took longer. Reverse evolution seems to stop when the populations of flies achieve adaptation to the ancestral environment, which may not coincide with the ancestral state. In this study, we have shown that underlying these phenomena is the fact that, at the genetic level, convergence to the ancestral state is on the order of 50%, that is, on average, only half of the gene frequencies revert to the ancestral gene frequencies evolution is contingent upon history at the genetic level too'.
These findings provide further insights into the basic understanding of how evolution and diversity are generated and maintained. On the one hand, it provides evidence for evolution happening through changes in the distribution of alleles in a population (so-called standing genetic variation), from generation to generation, rather than the appearance of mutations, from one generation to the next. Conversely, as Henrique notes, 'It has implications for the definition of biodiversity: some of the 'reversed' flies appears to be phenotypically identical to the ancestral flies, but they are genetically different. How then do we define biodiversity?'.
Good question. Perhaps forward and reverse evolution can be engineered through adjustments of regulatory mechanisms. Constructing complex physical structures implies a logical sequence to the placement of physical components. For example, one would think a regulatory element would be preceeded by that which is regulated.
TP asked some questions recently in a comment.
Assuming scientists will be able to successfully reverse evolution in chickens, could the same techniques be used to fast-forward evolution?
Could such an effort provide evidence of front-loaded traits?
Fast-forwarding would be more problematic but rich in possibilities. My answer to TP's second question is yes. Genes that are indispensible in different pathways would be candidates.
March 8th, 2009 at 4:51 pm
I think you misunderstand Gould's position. He argued that if you could "rewind the tape" of evolution to the Precambrian, and then "run it forward" again, you wouldn't get the same biosphere we have now, even if the selective pressures were not altered. In other words, there are so many moments in the entire run that depend fundamentally on "accidents" that, as a result of historical contingency, getting the exact same outcome would be extremely improbable. In some sense, Gould's position is already the reductio ad absurdam of the "accident/contingency" school of thought, and as such is a relatively strong argument, especially when contrasted with the alternative.
The opposite position to Gould's is the one taken by Simon Conway Morris, who has argued that there is so little "accidental-ness" and historical contingency in macroevolution that we would still appear near the end of each run, regardless of what environmental changes occurred in each run. The reductio ad absurdam of this position is, of course, the idea that if the history of life on Earth were re-run, I would still chose to have a grilled gouda sandwich for lunch today. Clearly absurd, and so Morris's position can be judged inferior to Gould's on both logical and evidenciary grounds.
However, even if Gould is right, this doesn't necessarily rule out the concept of "front-loading", so long as such front-loading is not considered to bring about exactly the same outcome if repeated. In other words, God might "play dice", but at a craps table that was already rigged in His favor (by Him) in the long run.
Comment by Allen_MacNeill — March 8, 2009 @ 4:51 pm
March 8th, 2009 at 5:05 pm
Allen Mac_Neill:
I take it then that there are so many chance contingencies in the environment (including the genomic ones) that outcomes would inevitably vary with reruns. Is that accurate?
Comment by Bradford — March 8, 2009 @ 5:05 pm
March 8th, 2009 at 5:59 pm
Allen:
At the risk of sounding pedantic, it's almost certainly impossible to keep the selective pressures constant while varying the biosphere, since the biosphere itself produces many if not most of the selection pressures Red Queen).
Comment by Raevmo — March 8, 2009 @ 5:59 pm
March 8th, 2009 at 9:47 pm
Bradford:
Yes, you've got it. There have been so many events, and so many of them depend on when they occur in the time sequence, and so many of them are effectively "random" (i.e. uncorrelated) with respect to each other, that the probability of getting the same outcome with each iteration of the Phanerozoic asymptotically approaches zero.
In other words, according to the mainstream view of macroevolution, we (and everything around us) are an accident of history, never to be repeated. Which is, of course, exactly what each one of us is, from a genetic point of view: unique, irreplaceable, but not "special", if by that term one means "the ultimate goal of all creation".
Which means, of course, if we mess it up this time, there won't be a next time, and there won't be anyplace for the "elect" to find refuge, and (unless there is some currently unknown and unimaginable form of space travel) there won't be any way to escape the consequences of our failure…ever.
Comment by Allen_MacNeill — March 8, 2009 @ 9:47 pm
March 8th, 2009 at 10:36 pm
It's not reasonable to expect the "exact same outcome". But we might expect to see similar outcomes; cells, intercellular communication, multicellular structures, bilaterialism, appendages, bones, light sensing with lensing, sexual reproduction, respiration, predation, etc. The question is the relative importance of contingency and determinism.
If you reran the tape of life, it's doubtful you would see hominids, or even primates. But you might very well see terrestrial craniates.
Comment by Zachriel — March 8, 2009 @ 10:36 pm
March 8th, 2009 at 11:31 pm
Why would cells be expected?
Comment by chunkdz — March 8, 2009 @ 11:31 pm
March 9th, 2009 at 8:04 am
"Might" be expected due to the chemistry of fragile replicators, the requirement of segregation, the simplicity of membrane formation.
Comment by Zachriel — March 9, 2009 @ 8:04 am
March 9th, 2009 at 1:15 pm
Zach,
And when you say "We might expect…"
who is the "we" you are talking about?
Comment by chunkdz — March 9, 2009 @ 1:15 pm
March 9th, 2009 at 1:50 pm
Those who understand that exo-solar planets are not made of quintessence but matter, and that similar molecules will form under similar conditions.
Comment by Zachriel — March 9, 2009 @ 1:50 pm
March 9th, 2009 at 4:11 pm
We would also expect life to be cellular because all of the living things we have ever encountered are composed of cells (either just one or many of them stuck together). This observation is, of course, subject to the "problem of induction", but until we find non-cellular forms of life, that's the only assumption warranted by the evidence.
Furthermore, we know (as the result of two centuries of experimentation on cells) that:
• If the plasma membrane (the outer boundary of the cell) is compromised, the cells stops working (i.e. it dies). Ergo, an outer boundary that has properties similar to those of the plasma membranes of living cells is apparently necessary for life (as far as we can tell, given the evidence available to date = AFAWCTGTETD).
• Things that don't have an outer boundary that has properties similar to those of the plasma membranes of living cells can't do the things that living organisms do (AFAWCTGTETD). For example, viruses can't reproduce on their own and can't carry out the metabolic processes necessary to combat the ravages of entropy. Ergo, viruses are not alive, and one of the reasons for this is that they lack plasma membranes.
As Zachriel has pointed out, there are certain molecules that are always found in living organisms, either as structural material or carrying out particular functions (AFAWCTGTETD). These molecules (I like to call them "biomolecules") form spontaneously from the most common elements synthesized in the big bang and in red giant stars: hydrogen, oxygen, nitrogen, carbon, phosphorus, sulfur, calcium, sodium, potassium, chorine, magnesium, zinc, iron, and the rest. And when they form spontaneously, they form the same kinds of molecules we see in living organisms: monosaccharides, amino acids, and nitrogenous bases (note that here the qualification AFAWCTGTETD does not necessarily apply). Polymerize and rearrange these and you have all of the "stuff" necessary for life.
Ergo, we don't know for sure that living organisms exist anywhere else, and we don't know for sure that, if they do, they will be composed of hydrogen, oxygen, nitrogen, carbon, etc. arranged into polymers composed of monosaccharides, amino acids, and nitrogenous bases. However, since all of these things can be shown to be produced spontaneously (i.e. without "intelligent" guidance), then it seems reasonable to think that if life exists anywhere else, it will have all of these properties.
Oh, and it will almost certainly require liquid water, both inside and outside.
Beyond that, however, (and if one follows Gould's logic) all bets are off. There may, for example, be planets on which things like cephalopods are the "highest" form of intelligent life. There may be others on which things like insects are the dominant form of life on land (just the way they are here), but without competition from things like vertebrates. And it is very likely that most of the planets that have life are populated almost entirely by things like bacteria (based on how long our planet fit this description).
Speaking of vertebrates, it seems to me that they are the least likely form of life we will find elsewhere, if indeed we find any at all. As Gould takes pains to show (using mostly fossil evidence) vertebrates have always been a very "unlikely" group, and fully bipedal primates are among the most unlikely of all.
In other words, finding multiple races of four-legged bipedal highly social humanoids who have developed non-biological technology, but who differ only in the surface architecture of their foreheads (and who can interbreed with each other to boot) is so unlikely as to be virtually impossible…unless, of course, they are descended from a common ancestor and were dispersed among several widely separated planets a lonnng time ago (from a galaxy far, far away)…
Comment by Allen_MacNeill — March 9, 2009 @ 4:11 pm
March 9th, 2009 at 6:24 pm
Ok. Lack of quintessence, and universal chemical properties = life will come from sterile environment.
I can see where you're coming from.
Comment by chunkdz — March 9, 2009 @ 6:24 pm
March 9th, 2009 at 6:46 pm
The question is not what kind of life, but why would one expect a sterile environment to spontaneously generate life – cell or not.
Your answer unfortunately assumes the necessity of life a priori. Popper understood the human need to have expectations, and that a "horizon of expectation" was a component of pre-science or proto-science. It is therefore reasonable for humans to "expect" that cells should arise, just as it is reasonable for humans to "expect" that cells can be designed. Popper would admonish both sides that the lack of falsifiability excludes either expectation from the realm of science.
In answering the question of why cells would be expected if the tape were replayed your answer is because that's the only choice. But if we're learning anything from the lab it's that we are much closer to making a cell than ever getting one to form on it's own. I say whoever gets there first – design or self-assembly – the winner gets to lay claim to the more reasonable "expectation". So far the trend is that the self-assembly paradigm gets more convoluted and improbable as the search continues, and the design paradigm gets more and more plausible.
May the best expectation win.
Comment by chunkdz — March 9, 2009 @ 6:46 pm
March 9th, 2009 at 9:28 pm
That wasn't the question. The thread topic concerned the relationship between determinism and contingency in evolution, a question that presupposes the existence of life.
Comment by Zachriel — March 9, 2009 @ 9:28 pm
March 9th, 2009 at 9:44 pm
Vertebrates as a clade might not exist, but motile bilaterally symmetrical organisms seem plausible, perhaps even with sensory organs housed in a bony head.
It is a very interesting question. Of course, there is not yet enough evidence to reach any definitive conclusions.
Comment by Zachriel — March 9, 2009 @ 9:44 pm
March 9th, 2009 at 11:21 pm
And I was content to explore that until you decided to rewind the tape all the way back to before the first cell. If you "expect" a cell to emerge from a puddle, I dare say you are treading way beyond Popper's horizon of expectation and into the realm of subjective guessing. No better than ID really. Worse, considering the lack of any plausible pathway or observed spontaneous generation. At least ID is approaching a demonstration of cell construction.
Comment by chunkdz — March 9, 2009 @ 11:21 pm
March 9th, 2009 at 11:28 pm
Really? I think that fire-breathing telepathic unicorns are the least likely lifeform.
Come on, Allen. You sound like an ID'er making a complexity argument.
Vertebrates kick ass. You can bet your's that if vertebrates are within the algorithmic search space that vertebrates will be favored for survival.
Comment by chunkdz — March 9, 2009 @ 11:28 pm
March 10th, 2009 at 6:16 am
Which is why Zachriel always sounds like a Discovery Channel documentary. Low on substance, fat on air.
Comment by Jean — March 10, 2009 @ 6:16 am
March 10th, 2009 at 7:58 am
Jean:
That's still many orders of magnitude higher on substance than you, Jean.
Comment by Raevmo — March 10, 2009 @ 7:58 am
March 10th, 2009 at 8:04 am
We have the chemistry of replicators and the physics of membrane formation. This doesn't go away because you wave your hands.
Vertebrates might be 'favored', but for evolution of vertebrate-like organisms to occur, each of the previous forms have to be adapted to their own environments. An alimentary tract could form the basis of further evolution, then the inevitable development of a head might be plausible. The commonality of various genetic structures lends support to such a scenario. But as Allen_MacNeill mentioned, it is an arguable point.
No, he doesn't. The question is the relative importance of determinism and contingency. We know evolution is highly contingent, but I think that we can find significant evidence that certain structures are more likely due to the geometry of space, and life on a small rocky planet covered mostly with liquid water.
Comment by Zachriel — March 10, 2009 @ 8:04 am
March 10th, 2009 at 8:26 am
Incorrect attribution in my previous comment.
Comment by Zachriel — March 10, 2009 @ 8:26 am
March 10th, 2009 at 1:23 pm
True. We have laboratory designed RNA's produced under stringent laboratory conditions. We also have fatty bubbles. One indirectly supports the ID paradigm, the other supports…soap.
If you think all this means sterile environments spontaneously produce life, well… Popper wouldn't begrudge your inherent need to do so. He would however admonish you to acknowledge that this is not scientific. It's just Zachriel wondering and exploring.
Comment by chunkdz — March 10, 2009 @ 1:23 pm
March 10th, 2009 at 2:36 pm
Under what heading should we place such questions? Under empirical science? Or, natural philosophy?
I would argue that Gould’s book, Wonderful Life: The Burgess Shale and the Nature of History, qualifies more as a work of natural philosophy than is does of empirical science.
The basic problem that we have is that at present we are limited to one data set– what we know from one planet, within one star system, within one enormous universe, at one particular point in cosmological history.
Questions about determinism, contingency, teleology and dysteleology are about that way Nature is constructed and functions as a whole. Answering such question require a top down holistic perspective. Empirical science, on the other hand, is a primarily a bottom up approach.
That puts us in the position of hypothetical intelligent creatures trapped at the bottom of the ocean. We are very limited by are circumstances to gain much perspective of the greater reality that might exist above and/or beyond us.
It seems to me that those with an a priori commitment to naturalism limit reality to what we do know, and we can know, from the bottom of our ocean. Those who have an ID perspective are willing to accept a mush broader range of possibilities. Those other possibilities may not presently qualify a “science” but given our limited knowledge of our present circumstances they are legitimate avenues of inquiry.
At present can we really settle such questions? I would argue that all we can do is speculate about the possible alternatives.
Comment by JOHN_A_DESIGNER — March 10, 2009 @ 2:36 pm
March 10th, 2009 at 7:38 pm
Science: We can test the balance between determinism and contingency (albeit tentatively).
Blount, Borland, and Lenski, Historical contingency and the evolution of a key innovation in an experimental population of Escherichia coli, PNAS 2008.
Losos, Jackman, Larson, de Queiroz and Rodríguez-Schettino, Contingency and Determinism in Replicated Adaptive Radiations of Island Lizards, Science 1998.
Natural history. However, Gould published many scientific papers. His books were primarily meant to communicate his excitement about science to a wider audience.
Comment by Zachriel — March 10, 2009 @ 7:38 pm
March 11th, 2009 at 5:35 pm
There is no doubt that Gould’s book, Wonderful Life, is a book of Natural history, but it is also a philosophical interpretation of Natural history guided by Gould own world view.
Here is how he concludes his book:
“And so, if you wish to ask the question of the ages– why do humans exist?– a major part of the answer, touching those aspects of the issue that science can treat at all, must be because the Pikaia [the first known chordate] survived the Burgess decimation. This response does cite a single law of nature; it embodies no statement about predictable evolutionary pathways, no calculation of probabilities based on general rules of anatomy or ecology. The survival of Pikaia was a contingency of “just history.” I do not think that any “higher answer” can be given, and I cannot imagine that any resolution could be more fascinating. We are offspring of history, and must establish our own paths in this most diverse and interesting of conceivable universe– one indifferent to our suffering, and therefore offering us maximal freedom to thrive and fail, in our own chosen way.”
What business is it of a paleontologist whether or not there some higher purpose or answer? What business is it of a paleontologist how I live my life?
Comment by JOHN_A_DESIGNER — March 11, 2009 @ 5:35 pm
March 11th, 2009 at 6:58 pm
It's a book written by a scientist, not a scientific paper. Such books are often personal stories. Hawking talks about knowing the mind of God. Darwin mentions the Creator. Einstein often peppered his remarks with mentions of God.
Certain highly contingent events had to occur for humans to evolve. You may choose to believe in a higher purpose anyway, but the evidence remains what it is.
Comment by Zachriel — March 11, 2009 @ 6:58 pm