The Talk.Origins Archive Post of the Month: August 2010

The modern scientific understanding of NS? I have already described it. Let me repeat:

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.

Example 1: The adults that go to Gene Poole Pond are 30% red/shit and 70% blue/ambrosia. They empty their gametes into the Gene Poole Pond and, because fusion to produce zygotes is a random process according to Mendelian genetics and according to the rules of Hardy-Weinberg, we get just about 30% red and 70% blue progeny in the pond that will travel back to Lake Monroe. Quite a number of these progeny (about 90%) will die over the course of the year (see Malthus for an explanation). But, when we look at the progeny that survive their year in Lake Monroe and go back to the Gene Poole Pond for the next oyster orgy, we observe that 30% are red and 70% are blue. What this means is that there has been no "differential survival until reproductive maturity" with respect to the two alternative features (phenotypes) we are following: red or blue. That is, all the death that has occurred was due either to chance alone or to features unlinked to the color/taste of the oysters. The key feature to look at is the % of red versus blue in the parent generation at birth (actually, at zygote fusion) and in the adult breeders.

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.

Example 2: The adults that go to Gene Poole Pond are 30% red/shit and 70% blue/ambrosia and produce just about 30% red and 70% blue progeny in the pond that will travel back to Lake Monroe. Quite a number of these progeny will die over the course of the year (see Malthus for an explanation). But, when we look at the progeny that survive their year in Lake Monroe and go back to the Gene Poole Pond for the next oyster orgy, we observe that now 80% are red and 20% are blue.

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.

Example 3: Start out with the same 30/70 red/blue ratio. But now we introduce humans who love the blue oysters and, in fact, are part of a Blue Oyster Cult. The Blue Oyster Cult has observed the life cycle of oysters, and consciously recognize that if they go to the Gene Poole Pond and prevent the shit-tasting red oysters from reaching the pond, that they will have more of the delicious blue kind. So they frantically remove red oysters (and compost them). Only 1/6th of the starting 30% red oysters still manage to reach the pool. That is, the ratio of new oysters in the pool is now 5 to 70 (7% to 93%) red to blue. The next generation to reach the pool is now also 7%/93% (indicating that, in the absence of the human intervention, the traits were indistinguishable from being selectively neutral wrt each other; in this case we can rule out "stabilizing selection" by heterozygote advantage). This is an example of what Darwin meant by "artificial selection" and represents a significant conscious change in frequency due to the conscious actions of humans to selectively favor the blue feature over the red.

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.

Example 4: As in the other examples, the starting population is 30% red and 70% blue oysters and that is also the %s of the offspring that enter Lake Monroe to mature. But now humans, who dearly love the blue oyster taste have, instead of doing selection to increase the frequency of blue oysters as in Example 3, harvested mature blue oysters in Lake Monroe just before the time of year in which the oysters walk to the Gene Poole Pond to mate. They put the blue oysters in their pots, stewily, and toss the red oysters back because they love to eat the blue ones and are disgusted by the red ones. The humans ignore the oysters after they leave Lake Monroe and walk to Gene Poole Pond. Not surprisingly, the % that reach the pond now are changed, to a significantly different 50% red and 50% blue, because of the selective harvesting of blue oysters by humans.

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.

Example 5: Invent an invisible undetectable superintelligent and omnipotent agent that can produce whatever it wants and whatever can be observed without itself being observed. Explain all or any random subset of the other examples as being due to the actions of this invisible and undetectable agent; thus everything is due to the actions of this unobservable agent. Is everything then "design"? Or are there still some results that are only "pattern"? Which are they?

Classifying Selection as Natural, Artificial, Neutral or by Design

Post of the Month: August 2010