a guest post by Howard Hershey
** This is repeated in its entirety from a post in the talk.origins newsgroup. It is in response to another poster, so parts may seem a bit strange without the defining context. However, when I read this, I knew it was perfect. It’s a way of saying what I’ve been trying to get across for months now. How can you classify selection?
The full post from Howard is after the break.
>> But you may continue to present the rest of this with appropriate
>> citation as to when, where, and who and how it fits into whatever
>> argument you have (if any) with the *modern* scientific understanding
>> of NS.
> What would this be?
The modern scientific understanding of NS? I have already described it. Let me repeat:
Rather than use examples unrelated to the biological meaning of the phrases “natural selection”, “artificial selection”, and “selective neutrality”, let’s use examples that clearly point out their meaning. I will give you an opportunity to make simple replies, but you will alsohave to justify those replies. I will justify what I say by always giving a “because” explanation of why I made the choice of terms I did.
Remember that “natural selection” involves a comparison of two alternative features in an organism on some metric of “differential reproductive success”. I will use the metric of “differential survival until reproductive maturity” in my examples, but remember that there are other possible ways of measuring ‘reproductive success’.
We will be looking at an imaginary organism (but one that has features like many real ones), the Lake Monroe Oysters. The oysters have two alternative features: some are red and taste like shit, others are blue and taste like ambrosia. Once a year, the oysters, about a thousand strong, put out their little legs and walk to a small pond owned by Gene Poole, where they dump in all their gametes (sperm and eggs) and then die without ever going back to Lake Monroe. But, 10 days later, all the little oyster babies (about 10,000 strong) walk from Gene Poole Pond back to Lake Monroe, where they either grow up over the course of the next year or die. The survivors then repeat the process to make the next generation. And so on.
Now, of course, the actual percentages will probably not be exactly 30/70 for the same reason you would not expect to get exactly 50 heads: 50 tails every time you flipped an honest coin 100 times. But there are statistical ways to estimate whether the observed result is significantly different from such a random expectation. Observing a 31% to 69% ratio would not be a surprising result if the numbers are small enough in the population or in a random sample from the population. In this case, we would observe 310 red to 690 blue in the adult breeders. A deviation from expectation this large or smaller than the expected 300 and 700 would happen by chance about half the time, so I would consider this to be merely a chance deviation and not a significant deviation. [I am using a simple chi-square test and regard any deviation that could occur by chance 95% of the time to be non-significant.]
A second minor point, but an evolutionarily important one, is that, as many a gambler has found out, “chance has no memory”. If the new % entering the Gene Poole Pond is 31%/69%, the expectation of chance is that that (rather than 30/70) would be the expected %s entering Lake Monroe and exiting it the next year. This is the reason why selective neutrality leads to neutral drift and eventual fixation of one or the other phenotypes.
A third minor point. I am ignoring the diploid genetics of this case, so I am not examining specific genotypes. If I did, I might find that this is an example of “stabilizing selection” like that seen in sickle cell anemia. That would only be observable over a number of generations (by deviation from the expectations of random drift) or by examining the ratios of homozygotes and heterozygotes in the genes.
This is an example of the absence of “significant differential selection”. Or, if you prefer, an example where neither color had any differential effect on survival. In biology, this pure chance process is NOT called “natural selection” precisely because there is no differential selection related to the features. This example is (tentatively) called “selective neutrality” and leads to “neutral drift”. Again, this is NOT considered “natural selection”. However, the random walk that occurs by “neutral drift” does lead to evolution (genetic change) over time to the extent that these features are genetic. [And this would also lead to the discovery of “stabilizing selection” if that were the reason for the apparent absence of change.]
To summarize: In the absence of evidence for selection, there is no “natural selection”; there is “selective neutrality” leading to “neutral drift”. IOW, pure chance and only chance is NOT “natural selection”. It is “selective neutrality” and only selective neutrality that represents pure chance. There is no differential selection at all in the case of selective neutrality, unless it was done by a designer who was trying and succeeding in mimicking a completely random process (which is very difficult for humans to do without using a random number generator of some kind), there is no way to call such a result a product of “design”. So “selective neutrality” is almost always a “pattern” and specifically is always a “random pattern” wrt the measured metric of “differential reproductive success between the two alternative features”. The only way such a result can ever be a “design” is when a “designer” successfully mimics a random, pure chance result.
The only way to know that is by knowledge of the existence and intent of the “designer”. It would be impossible to tell by examination of the “pattern” alone. And, initially, it is not possible (if the genetics are unknown) to distinguish between “stabilizing selection” due to heterozygote vigor and “selective neutrality”. The difference between them would only become obvious as the pattern deviates over many generations from the probability expectations of neutral drift.
Now, it is your turn. Does the above random non-selective described process that biologists call “selective neutrality” produce “pattern” or “design”. Explain why you think so, if your thinking differs from mine.
Humans had been forbidden anywhere in the Lake Monroe watershed for this entire year because of a toxic (to humans) algae bloom. The lake was also much warmer than usual.
But this is a case where there has been a significant differential impact on the metric of “differential survival until reproductive maturity” that is clearly strongly correlated with the color of the oysters. Red oysters have increased in frequency from 30% to 80%, with a concommitant decrease in blue oysters. All in the absence of human intervention. Completely in the absence of any known conscious “designer” or intent. This is an example of what Darwin meant by “natural selection”. And, not surprisingly, it also meets the requirement of “differential reproductive success due to alternative phenotype” seen in the modern definition of NS. A simple chi square test shows the probability of such a difference occurring by chance to be much less than 0.01%. That is, the difference in the “differential reproductive success” (as measured by differential survival to reproductive age) is statistically significant.
A biologist might hypothesize that this example of “natural selection” might be due to the red oysters being more resistant to the toxin of the algae or to a temperature effect (directly or indirectly), but identifying or even correctly identifying the cause is not necessary in declaring that this meets the requirement of being “natural selection” ala the idea described by Darwin when he used that term. All that is needed is evidence to support that this is significantly different from the expectations of chance alone (that being described in Example 1) and not known to be the intentional product of a conscious agent.
To summarize: This is an example of “natural selection”, that is, significant differential reproductive success of one phenotype rather than the alternative in the absence of human intervention in a specified environment (Lake Monroe that year). It is the absence of conscious human intervention that makes this “selection” “natural” rather than “artificial” in Darwin’s terminology. Because there was no observable “designer” involved that had the intent or consciousness of selectively changing the ratio from the expectations of a “random pattern”, one cannot call this example of “natural selection” “design”. The result due to this “natural selection” is a “pattern” and specifically a “non-random pattern” because of the differential selection and the absence of a designer.
Your turn: Do you agree that the above example is an example of “natural selection” as that term was used by Darwin?, both because it involves selection and because it does not involve humans (and thus is not “artificial” by his usage). Do you agree that it is NS as defined and ideated by modern biological scientists? Do you agree that this is an example of a “pattern” rather than “design” because of the absence of a human or other designer’s involvement and also that it represents a “non-random pattern.” Explain.
This would be an example of “design”, as would any example of conscious “artificial selection”.
Your turn. Do you agree that this is an example of “design” by your understanding of that term and “artificial selection” as it was used by Darwin? Do you agree that the defining feature of “design” requires the involvement of humans or other animate design agents (at minimum, although I would add that the design agent perform its selection via conscious action)? Explain, especially if you have some other way of consistently identifying design that does not require knowledge of a designer.
The above 3 examples are rather clear cut. And they cover the typical examples of NS, AS, and selective neutrality. Of course, as in all of science and science based on induction and statistics, all conclusions of randomness and non-randomness are tentative and one can have marginal cases where one is not sure if the result is due to randomness (aka selective neutrality), natural selection (non-random and without a designer), or artificial selection (non-random due to the conscious action of a designer agent).
We have already mentioned the possibility of a designer consciously trying to mimic a non-selective result, and pointed out that that is difficult for humans to achieve. And pointed out one possible “selective” mechanism (heterozygote advantage) that might mimic “selective neutrality” temporarily if one did not know the genetics of the system. That is part of the reason why scientific explanations are always tentative and subject to change in light of further evidence. Similarly, we might reconsider an example of “natural selection” if empirical evidence presented itself of a likely designer.
But there is at least one other example that is ambiguous. Namely selection by a designer agent who is unconscious or unaware that he is producing a non-random result. And this example has been seen in the real world wrt the size of fish at maturity.
Thus the next generation of oysters is now 50:50 red:blue instead of 30:70 and there are fewer and fewer blue oysters and more and more red ones in Lake Monroe, greatly increasing the value and cost of blue oysters. This is pretty obviously not the conscious intent of the (rather ignorant) humans harvesting the oysters, since it means that there will be fewer and fewer of the desirable blue oysters. But it superficially is “artificial selection” both because it is due to human involvement and represents differential non-random selection of the alternative types of oyster. So is this an example of “pattern” rather than “design” because the selection was not consciously done to produce the result but the result was an inadvertent consequence of selective predation done without thought or intelligent foresight as to the consequences (which are opposite those a sentient human would want)? Or is this an example of “design” because it is a non-random result produced by an active designer agent, even if that result was not the intent of the designer? Perhaps “artificial selection” should be restricted to those that humans do consciously for their own purposes, like making toy poodles because they are cute and sheep dogs because they are useful to shepherds.
Unconscious selection by differential predation without intent to selectively breed, might better be considered “natural” even though done by humans, just as it would be if done by wolves. Unlike the other examples, which are pretty clear cut, this one is more ambiguous and I could support calling this either “design” or “pattern” depending on the particular definition of those terms one is using. If you limit “design” to those patterns consciously produced with that pattern as the intent of the designer, then this is not “design”. It also means that anthills and aphid slaves are not “design” because the organisms that design those do not have consciousness, but only instinct. But feel free to make an argument for one or the other. All I ask is that you be consistent, if you can.
And tell me why Example 2 (“natural selection”) is a tautology?