My knowledge of Evolution is limited to the high school courses and subsequent features on TV.
If I understood clearly, evolution is a result of mutations - in which the mutations that jive better with the environment survive and go on to multiply. Also - mutations are totally random.
Q1. The italicized part is what I’d like to understand. Is there evidence to suggest that mutations are truly random? Instinctively, I feel that an organism in a new environment can provide the feedback to the genetic system (the genes) as to what might work better in the environment - so the genes as they mutate can try to produce those changes. Why is my instinct incorrect here ? Does the organism’s experience of the environment in no way effect what the genes do ? Or is there a feedback mechanism between the organism’s “senses” and the genetic system ?
Q2. Also - is there a simulation to show say how many random mutations (and generations) it took for a reptile to make it to a bird ? Sort of like a Monte Carlo simulation where the likelihood of all mutations is the same. If such were the case, does the most likely time (number of birth-lifetime-death time summed) look comparable to the historical timeline ?
I don’t think they are random in the way you seem to describe. There is currently a thread on cheetahs, and for a while there was a belief that cheetahs could be seperated into two species based on different back markings. But it turns out this is a result of a common mutation. So some mutations occur more frequently than others.
Changes (or damage) to genetic material happens randomly. There are of course, causes - some chemicals and other factors can interfere with the replication process and cause errors. Exactly what it causes is totally random; just remember, many genetic copying errors means the resulting embryo is not viable. There may be a miscarriage or the fertilized egg may simply fail to develop… so a significant weeding process has happened by the time a viable offspring emerges.
There is not feedback; other than only certain changes even make it to the next generation.
General theory nowadays suggests evolutionary changes can happen very quickly in response to significant stress in the environment - changed environment, different food sources available, etc. The though is much of evolution was in spurts, with significant pauses where the orgnaism did not change since a stable environment did not select for changes.
at a molecular level reactions are governed by thermodynamics and kinetics. lots of stuff is always happening. it all kind of goes through a sieve of what is useful to come out as an aggregate result.
There is absolutely no evidence whatsoever that any such mechanism exists, or ever has existed. The closest similarity I can offer is that in some very stressful situations, E. coli bacteria will activate an alternate DNA polymerase that has much lower fidelity of replication. That is, when things look bad, the cell begins replicating DNA imperfectly, introducing mutations into the genome. It’s thought that this is advantageous because if there are lots of cells introducing lots of mutations, perhaps a mutation may arise that will allow the cell to survive the stress. It’s important to note, however, that these mutations are still completely random - there are just more of them.
These sorts of simulations are done all the time, as a matter of routine. Such a simulation would no longer be considered the basis for an entire paper, but rather a figure within a paper. Or perhaps one panel within the figure. All the data check out.
I know I shouldn’t comment when I don’t know much about the situation, but here are my WAGs. First, AFAIK, there is no known feedback mechanism. It seems very unlikely there could be but the longer they look at genetics, the more complicated it seems. Second, just looking at the molecular structure (and sizes) of the base pairs, I would imagine that it is more likely that the single-ringed cytosine would be likelier to replace the single-ringed thymine than to replace either of the double-ringed bases, adenine and guanine. And vice versa. And similarly, adenine and guanine are likelier to replace each other than make any other replacement.
I just heard about a mutation for blond hair that affects about 25% of the population of the inhabitants of some Pacific island. No surprise there since apparently blondness has evolved a number of times mostly in places with less sun. But the surprise was that the particular mutation involved had never been seen before. I infer it was somehow unlikely. Perhaps it was not single nucleotide polymorphism (SNP) as described in my first paragraph. And yes, there are many more complicated kinds of mutation. A few years ago I heard about one that involves and entire sequence of DNA being reversed on the DNA and the mathematician (who happens to be a woman in Montreal whom I know) who figured out how to recognize such reversals.
We need to take a step back from this level to discuss randomness.
DNA is composed of millions or billions of bases of adenine (A), cytosine (C), guanine (G) and thymine (T), which pair into bonds. Mistakes can occur from a variety of mechanisms, including improper replication, mismatching, cross-linking, and intercalation, which is the insertion of material between base pairs. (All greatly simplified.) Some types of mistakes may be chemically or physically more likely to occur than other types of mistakes.
Going up a level, the consequences of a mistake can also vary greatly. It may not make a difference, it may stop something critical from happening, it may cause something to happen, or it may effect intensity or duration or anything else. How noticeable the consequence is and how deadly the consequence is will determine whether the animal reproduces successfully.
The sum total of all these consequences will determine whether new species develop over time. In strict mathematical terms, none of it is random because there are never equal likelihoods or equal outcomes. In a looser, more natural sense of speaking, everything along the line is random. It all just happens for no controlling reason that we’ve ever discovered. The mistakes are just random mistakes, the consequences are GIGO, the species survive or don’t because of outside environmental issues that work on the accumulated DNA in whatever form it’s taken. There is no feedback, except in the standard natural selection sense of some individuals reproducing in greater numbers than others.
There is something called paragenetics, which (as I understand it) is a way that individual genes can acquire ‘markers’ that independently affect the manner and frequency of their expression, so identical twins can experience different outcomes from one another, even though both outcomes are genetically driven.
As far as I understand it, these markers are altered by environmental conditions, and are somewhat heritable, but there’s no guarantee that a particular environmental condition will result in just the right change to the paragenetics to result in a coping mechanism arising, so it’s not a feedback mechanism
Reactions are governed by thermodynamics and kinetics at all levels including molecular, so I could not get the gist of your post. Yet you can influence the reactions by using catalysts or changing the temperature, pH etc.
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Mistakes can occur from a variety of mechanisms, including improper replication, mismatching, cross-linking, and intercalation, which is the insertion of material between base pairs
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Agreed. But has there been the equivalent of double blind experiments where it has been shown that the environment has no effect on these Mistakes ? Say three colonies of organisms were placed say one in a “good” environment, one in “bad” and one controlled and then the aforementioned mistakes had no correlation to the environment for say a few generations of the organisms.
What I meant to convey is that mutations to not occur in the frequency of distribution that would be associated with something like Monte Carlo. Even that may be wrong because I should have specified viable mutations. For all I know there is a consistent distribution of mutations, most of which do not produce viable organisms.
Outside of the mathematical context, evolution is all random, as far as we know.
Not sure I can answer that precisely, but I would say: a lot fewer than most people think. Mutations often involve repeating genes are mutations in regulating genes-- genes that affect one or more other genes. These can have dramatic effects on the phenotype with only modest effects on the genotype.
One of the things that stunned scientists when they first decoded the human genome was how few genes it actually took to make a human being.
This would be a “strict mathematical” definition I’ve never heard. Things can have quite different likelihoods and still be random. In fact, unless you had a process with only two outcomes, there will always be ways to partition the outcome events so that the partitions are not equally likely.
Much has been made in the popular press lately about this sort of thing, where it appears that acquired traits are being passed on to the next generation. All of the examples of which I am aware deal with epigenetics, which is a method of persistent genetic regulation. That is, genes can be placed into an “on” or “off” state, and that state can be passed on to offspring.
This is very different from directed mutation, for the simple reason that the actual DNA sequence is NOT changed in epigenetic events. Genetic regulation is the culprit for the observed transmission of traits, not mutation.
If any cases of the genetic code being rewritten in response to environmental pressures have been documented, I haven’t heard of them. And to be honest, I think I would have if they’d been published.
I remember reading somewhere that the strength of the chemical bonds of the base pairs (A-T, G-C) are not equivalent, that one is more likely to mutate than the other. If this is true (and it seems likely that one or the other would be at least marginally more robust than the other), then true randomness flies out the window, does it not?