Friday, April 5, 2013

Design, evolution and many worlds

The following image graphs the outcome of a simulation of a random process where a particle starts in the middle of the big square and moves by small steps in random directions until it reaches an edge.



It sure looks from the picture like there was a bias in the particle in favor of movement to the right, and that the particle was avoiding the black lines (you can see at a few points where it seems to be approaching the black lines and then jumps back) and searching for the red edge on the right.  If you saw the particle behaving in this way, you might even think that the particle has some rudimentary intelligence or is being guided.  To increase the impression of this, one could imagine this particle doing something like this through a complex labyrinth.

But in fact the picture shows a run that doesn't involve any such bias or intelligence or guidance.  However, it took 23774 runs until I got the one in the picture!  What I did is I had the computer repeatedly simulate random runs of a particle, throwing out any where where the particle hit the black boundary lines before it hit the red edge.  In other words, there is a bias at work  However, it is not a bias in the step-by-step movements of the particle, but a selection bias--to get the picture above, I had to discard 23773 pictures like this:



Sampling multiple cases with a selection bias can produce the illusion of design.  Most cases look like the second diagram, but if I only get to observe cases that meet the criteria of hitting the red edge before hitting any black edge, I get something that looks designed to meet the criteria (it looks like the process is run by biased chances, whereas the bias comes from conditioning on the criteria).

Now, suppose that evolutionary processes occur at a large number of sites--maybe a very large number of planets in a single large universe or maybe in a large number of universes.  Suppose, further, that intelligence is unlikely to evolve at any particle evolutionary site.  Maybe most sites only produce have unicellular critters or vast blankets of vegetation.  But a few produce intelligence.  We then will have a sampling bias in favor of the processes happening at sites where intelligence results.  And at such sites, the evolutionary processes will look like they have a forward-looking bias in favor of the production of intelligence, just as in my first diagram it looks like there is a bias in favor of getting to the red line and avoiding the black lines (think of the diagram as phase space, with the black lines marking where total extinction occurs and the red line marking where there is intelligent life).  

This means that we will have the appearance of design aimed at intelligence.  This forces a caution for both intelligent design theorists and evolutionary theorists if there is reason to think there is a large number of sites with life.  

The intelligent design theorists need to be very cautious about taking apparent end-directedness in the phylogenetic history that led to human beings to be evidence for design.  For given a large number of life sites and the anthropic principle, we expect to see apparent directedness at the production of intelligence in the process, just as in my first picture there is apparent red-directedness and black-avoidance.  This means that intelligent design theorists would do well to focus on apparent design in lineages that do not lead to us, since such design is not going to suffer from the same anthropic selection bias.  The cool stuff that spiders do is better fodder for intelligent design arguments than the mammalian eye, because the mammalian eye "benefited" from anthropic selection.  However, this also weakens the design arguments.  For design (pace some prominent intelligent design theorists) involves offering an explanation of a phenomenon in terms of the reasons a plausible candidate for a designer would likely be responsive to.  If the phenomenon is one that promotes the development of intelligent life, the design explanation could be quite good, for there are excellent reasons for a designer to produce intelligent life--intelligent life is objectively valuable.  But if the phenomenon is a spider's catching of flies, the reasons imputed to the designer become less compelling, and hence the design explanation becomes weakened.  

On the other hand, evolutionary theorists need to be careful in making precise generalizations about things like rates of beneficial mutations that apply equally to our ancestors and to the ancestors that other organisms have not in common with us.  For given a large number of sites where life develops, we would expect differences in such things due to the anthropic sampling bias.

This also suggests that we actually could in principle have evidence that decides between the hypotheses: (a) intelligent design, (b) naturalistic evolution at a small number of sites and (c) naturalistic evolution at a large number of sites.  

Suppose we find that the rate of favorable mutations among our ancestors was significantly higher than  the rate of favorable mutations not among our ancestors.  This offers support for (c), and maybe to a lesser degree for (a), but certainly against (b).  But suppose we find equality in the rates of favorable mutations among our ancestors and among our non-ancestors.  Then that offers evidence against (c) and depending on whether the rates are as we would expect on evolutionary grounds, it is evidence for (b) or for (a).  

I am assuming here that the number of sites is finite or there is some way of handling the issues with probabilities in infinite cases.

7 comments:

Paul Symington said...
This comment has been removed by the author.
Paul Symington said...

"...evolutionary theorists need to be careful in making precise generalizations about things like rates of beneficial mutations that apply equally to our ancestors and to the ancestors that other organisms have not in common with us."

You issue warnings against both the ID and evolutionary theorists alike, but it seems to cut particularly hard against the ID theorist.

However, could it be that there is an anthropic selection bias against design strong enough on the evolutionary theorist side that it undercuts justification in a Darwinian (or specifically a kind of mechanistic account of) evolution? That is, one could argue that "not seeing" design in nature might itself be the result of a selection bias, let's say for a view of things on the model of a machine (think of a watch) that had its parts brought together randomly? Perhaps it is no coincidence that the western mind was captivated by the complex clocks devised by those in the Islamic Empire in the Middle Ages before the scientific revolution. So, thinking of the world in a mechanistic way followed from an anthropic predilection to modeling our understanding of things on machines. Support for this theory may lie in the fact that people often think that science explains things mechanistically (bouncing billiard balls), when in fact this is not a correct model for understanding the breadth of scientific theory today (even if only considering physics). I'm specifically thinking of Einstein's denial of mechanism as he defines it in his "The Evolution of Physics" as well as Burtt's account.

Alexander R Pruss said...

Here is an example of a piece where the anthropic bias is relevant.

Alexander R Pruss said...

Paul,

That is a very interesting suggestion about a bias, but is it a selection bias?

Paul Symington said...

Yes, I think it is relevant to the question of selection bias. One characterization of a selection bias is perhaps as follows: given a de facto scenario in which one makes a judgment one on the basis of that scenario infers that some intelligibly discernible and recognizable pattern accounts for some feature of that scenario. So, from our specific situation and looking back on our history one might infer that there must have been a designer to account for the existence of human beings. In this case the recognizable pattern would be that of an artist fashioning an object. However, justification for such an inference is undermined by the selection bias problem. It would be similar to shooting an arrow into the air (where it lands I know not where), finding its exact resting place then thinking, "Wow! How improbable that it would land in this spot given all of the possible places that it could have landed! I see here an intelligible pattern by which I must infer that something guided it to this spot!"

With that in mind, perhaps my earlier suggestion (some inference against design) could be thought of also as involving a selection bias of this sort. The best way to do this is to apply the characterization of selection bias to an inference against design. The de facto scenario is the existence of human beings given evolutionary descent. From this fact one infers that the process was not a product of design by identifying a recognizable pattern to serve as an explanation; namely, that of a machine that exists in virtue of the accidental joining of preexisting independent parts resulting in a functioning whole in virtue of the intrinsic properties of its parts. (Let's say that the person who sees things this way came across in a forest one day something that could function as a figure-four deadfall animal trap that came out without human agency as the result of a thunderstorm and subsequent flooding). From this recognition, she infers that human beings must not have come about from design. I see this particular case as parallel to the charge of selection bias for the ID theorist.

However, I'm inclined to think that neither scenario actually suffers from bone fide selection bias. One can only commit a selection bias if one knows (or has reason to think) that some particular pattern is at work. On the one hand, it seems to me that the reason why one wouldn't be justified in inferring from Pruss's computer simulation that there was a forward-looking bias in the movement toward the red line is only in the case that one knows that this was one of 23773 unsuccessful attempts. On the other hand, regarding the inference to non-design, let's say that God was running a computer simulation like Pruss's but basing his simulation on the actual factors that fully account for the evolutionary development. And in this case, 23773 simulations had less circuitous paths to the coming to be of human beings! Thus, I don't think that one could charge the person with a selection bias unless she had some idea of what the results of God's computer simulation were.

My suspicion at this point is that we should think that the design explanation (design) is a bad explanation and the non-design (mechanism) inference is a good one. But why should this be so? Its not like design is a bad explanation for something and it does allow the existence of things that mechanism has a hard (or impossible) time accounting for. For example, design might be a good explanation for why biologists find answers when they ask the question, "why does this function work the way that it does?"

Paul Symington said...

However, anti-ID folks could respond by saying that the best explanation is one that relies only on the intrinsic properties of tiny things that can come together in various causal ways because these are free from anthropic bias. However, I remember Chisholm mentioning at the end of the "Problem of the Criterion" that the best pattern for thinking about efficient causation is that based on our innate and insider sense of agency in the world--all efficient cause is something like my ability to push my coffee cup across the table. A similar thing can be said for how we envision the properties of physical elements. So it might not be as simple as that.

Paul Symington said...

Example of a figure-four deadfall:

http://ironwoodandstone.blogspot.com/2010/06/trap-figure-four-deadfall.html

Ouch!