Darwinian Selection Logic

Darwinian selection logic is a double reverse trick. It's not that, oh, such and such feature would be beneficial to survival and reproduction and therefore presto, it appears. No.

It's that

And THEN we can look at it and see that the feature makes Sense: whatever it did, it played a key role in the survival and reproduction of the species -- just at the point of the killing and not at the point of the mutation, the survivability, the spread, or the relatively pleasant phase of low killing pressure on the population.

So having a new feature is a random event, it had to randomly happen, successfully survive and spread, and then happen to make a difference when the species is being killed left and right, and only at that point does its functional utility or lack thereof become a selection target.

However, all species grow exponentially; even the amoeba doubles its population with every generation; and resources are always finite, so there is almost always harsh population pressure on all species. The brief moments of expansion follow dramatic changes in the environment or new ecosystem opportunities for the species; the rest of the time things are a grind, and members may or may not survive simply because there are too many to be carried by the environment. (Indeed it would be kind to develop population self-regulating features: if they happened to happen, that would be nice.)

This is the logic of evolution, Darwinian Selection Logic.

You can't really intend to say such and such survival-impacting functional feature came about by Design or Intention, because it comes about by a long chain of merely possible-but-random events, it merely happens to come about and might not have. You might wait a long time for that functionality to appear, or forever. On the other hand when that HAS happened and it DOES now characterize a population, then (unless it was a free rider) there WAS some functional role of the feature (or in the case of free riders, some functional role of the feature that it is riding WITH) to better enable the survival and reproduction of the members of the species, for some Reason, so that when the others died, these lived. That reason involves the particular things it does, and what it does different or better, and how that interacts with the environment. That is, there is a functional logic: what it does, does better, and how that helps; otherwise, there couldn't have been a systematic selection of just those members, without another highly-improbable event that eventually culled all the old-type members without there being a reason to select them.

Since individual organisms encounter individual circumstances not just generic ones, some might have individually happened to be culled, one here, one there. It can be random. Bad things happen to good organisms.

In statistics we call this a Bernoulli random process with some probability P of culling. Consider a (blind) filtering that happens to select only the old type. The random event of culling all and only those, at the scale of a species population, is not impossible, but vanishingly, vanishingly improbable. It's like picking only chocolate chip cookies when they look just like raisin cookies: if you really can't tell the difference, you're going to leave some of both in the cookie jar, and approximately the same proportion as the original proportions -- if your choice really is random.

Suppose the culling uses a (Bernoulli) probability of P=0.5, and the population has 10 members, 5 old-type and 5 new-type. Let's suppose that at some point the random strokes of the scythe have killed exactly half of our imaginary species. Now, the probability that all and only the old-type ones would have been killed and all and only the new-type ones would have been saved, according to a Bernoulli model of this event, would be exactly one scenario (because there is one, it's just that it is a very particular joint event, scenario, or choice -- only one) out of 10-choose-5 total possible choices. Remember 10-choose-5 = $$\binom{10}{5} = (10*9*8*7*6)/(5*4*3*2*1) = 30240/120 = 252$$, So

$$ 1/\binom{10}{5} = 1/252 = 0.004 $$ roughly.

(If this counting method for probabilities is new to you, here: There are 10*9*8*7*6 ways to pick five out of ten, if you wanted to cull just five of them, because you could pick from 10 for the first choice, then from the remaining 9, then one out of the remaining 8, then 7, then six, and that's the way you can choose five in some particular order out of ten: 10*9*8*7*6 different ways. But since we don't care about their ordering, then we divide by the number of all the different orders for any given group of selected 5, which is 5*4*3*2*1, because for that group you could put them in order by first choosing one of 5, then one of 4, one of 3, one of 2, then the last one there's no choice so one of 1. All the ordered groups of five out of ten, divided by all the orderings for any group of five, gives you all the different groups of five out of ten, which are all distinguishable by group membership not by ordering the same ones in a different order. This is called the number of different subgroups you can choose of 5 out of 10, a.k.a. "10 choose 5".)

In this case, one out of that many is one out of 252 or less than half of one percent, and that's just an imaginary species of only ten members. With an imaginary species of 100 members we have 1/100-choose-50 which is about 0.00000000000000000000000000001. The number n-choose-m gets really big really fast.

For an initially non-endangered species, a species of any reasonable level of robustness, we have to be talking thousands, millions, or billions of species members, not ten, or even a hundred. With a bigger group, it is even more impossible to remove just the old-type ones on the random-culling plan. So please just give up the point: it's Impossible to do it randomly.

Whereas: if there is an actual functional reason, then the selection pattern, or the systematic culling result, WOULD make sense, and by the faith of a yet-uncomprehending intellectual, it WILL make sense if we will just understand the process to the point we can see the differentiating reason. The cookies are chocolate, duh, that's why we pick them from the cookie jar. For example. Someone, some irrationalist, say, could deny the efficacy of reasons in general, which is tantamount to saying things do happen systematically for no systematic reason. I'm saying, No. Things happen for no reason on the Individual level, not on the level of all members of a species doing the same thing the same way over and over such that all of them are now surviving with this particular way and only this way and none of the others.

Free rider selection is an exception to this rule, due to an implementation detail. Genes are not copied as separate functional units during reproduction. The cut points of the genetic mix-and-match process for sexual reproduction do not necessarily coincide with the gene endpoints.

It is possible that some random variant of a random varying gene (a.k.a. an "allele") might happen to occur adjacent or close to a functionally selected gene. When the egg or sperm splits to send half of its parental gene inventory to one descendant and half to another, it is called "meiosis". Meiosis does a mixing and matching process. First it chunks up the DNA chromosome into segments, and then randomly gives to the two children, sperm-or-egg cells, opposing halves of the different segments, so that each ends up with a half chromosome but containing a mix-and-match random selection from its parental genes.

The implementation detail is, these cut points are random, and they don't respect gene boundaries. Whatever genes happen to be adjacent to a selected-for gene, will often, probabilistically, travel along with the selected-for gene just because the mix-and-match cut points are random and therefore usually not exactly at the edge of the selected-for gene. Based on the distance along the chromosome, some free riders will land in the living descendants not because they got selected functionally but because they got selected by chromosome-adjacency to a selected gene. Let's call this the free rider exception, which could give spots to the descendants who got selected for speed, as an imaginary example, if the spots gene variant was close to the speed gene, and the speed gene got selected for. Still, even then, there was a functional selection that applied to the driving choice on which the free rider was a free rider. Thus I say, "modulo free riders".

To review, Darwinian Selection Logic is a kind of double reverse logic. The new thing didn't happen by logical functional design, but when it happened randomly (and was survivable individually and spread to be survivable as a species), it could only be selected for, and come to characterize the species, because of what I will call a Logical design characteristic that functionally impacted survival and reproduction in a species under population pressure. So as a whole the system went Away from logic, function, and design -- in the creation and stabilization of the new feature -- but then it came Back to logic and function, which are some of the characteristics of design, in the selection phase. "Designed"-looking, logically (systematically), functional features come to characterize species through this first anti-logical and then anti-anti-logical path. Double reverse.

So when I go on talking about system design, this is what I mean. I'm not saying some feature evolved outside this double reverse process through the tender fingers of some embodied-individual God's design, a designer independent of a ("His") design. No. But humans (like you) are great with ideas and logic and designs and my audience gets my point when I talk about a system design. There doesn't have to be a designer for there to be a design: a consistent pattern or mechanism or way that things work, and which works for an understandable logical reasons. Yet through random operation of mutation and selection, designs arise -- and then systematically, logically persist by means of some particular, differentially adaptive, functionality.

(On the centrality of logic you may be interested in: Tautologus Rex; and Aristotle's 12 missed syllogisms; and finally Contra Borges: the Crease of Logic, which separates the idea of a design from the mind of a designer).

I talk a lot about the functional logic of evolution, so this note might need to be referenced often. So I will annotate my text with this tag, DSL, to reference this Darwinian (Double-reverse) Selection Logic I'm expressing in a given case. Then if you, dear reader, are actually one of my biology professor friends who feels the need to discredit fascist misuse of evolutionary theory or to police theocratic science-denial, you might be satisfied that I'm not the problem you are patrolling for.

Okay? DSL. Okay.

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Copyright © 2023 Thomas C. Veatch. All rights reserved.
Created: February 10, 2023, Modified: July 28, 2023