bookmark_borderThe Evidential Argument from Biological Evolution, Part 2: Is Evolution Evidence for Theism?

Let’s begin reviewing the logical form of the argument, as described in Part 1 of this series.

(1) Evolution is antecedently much more probable on the assumption that naturalism is true than on the assumption that theism is true.
(2) The statement that pain and pleasure systematically connected to reproductive success is antecedently much more probable on the assumption that evolutionary naturalism is true than on the assumption that evolutionary theism is true.
(3) Therefore, evolution conjoined with this statement about pain and pleasure is antecedently very much more probable on the assumption that naturalism is true than on the assumption that theism is true. [From (1) and (2)]
(4) Naturalism is at least as plausible as theism.
(5) Therefore, other evidence held equal, naturalism is very much more probable than theism. [From (3) and (4)]
(6) Naturalism entails that theism is false.
(7) Therefore, other evidence held equal, it is highly probable that theism is false. [From (5) and (6)]

One objection to the evidential argument from biological evolution (ABE) is that premise (1) is false; evolution is evidence for theism. William Lane Craig, among others, has used precisely this objection in his debates with Frank Zindler, Massimo Pigliucci, and Paul Draper, among others. In his words:

In fact, that leads me to his other argument, concerning biological evolution. And I’m going to suggest that the idea that evolution could have occurred without an intelligent Designer is so improbable as to be fantastic. This has been demonstrated by Barrowand Tipler in their book The Anthropic Cosmological Principle. In this book, they list ten steps in the course of human evolution, each of which is so improbable that before it would have occurred the sun would have ceased to be a main sequence star and would have burned up the earth. They estimate the odds of the evolution of the human genome by chance to be on the order of 4-360 (110,000), a number which is so huge that to call it astronomical would be a wild understatement. In other words, if evolution did occur, it would have been a miracle, so that evolution is actually evidence for the existence of God![1]

Craig takes this to be an effective refutation of ABE.
Craig’s Objection Isn’t Even a Prima Facie Objection to ABE
But how? Look again at Draper’s formulation of the argument. If Craig’s objection is to be even relevant to ABE, it needs to be an objection to premise (1). For convenience, here is that premise again:

(1) Evolution is antecedently much more probable on the assumption that naturalism is true than on the assumption that theism is true.

But, taken at face value, Craig’s argument is not even a prima facie good undercutting defeater for (1), much less the rebutting defeater he makes it out to be. Remember that we have stipulatively defined “evolution” as the hypothesis that (a) complex life evolved from simple life; and (b) all evolutionary change in populations of complex organisms is or is the result of trans-generational genetic change. In the passage just quoted, however, Craig, doesn’t even present an argument against evolution so defined. Rather, he objects that unguided evolution (in his words, “evolution … without an intelligent Designer”) is false. Thus, he is presenting an argument against Darwinism, a hypothesis which entails but is not entailed by evolution. But Draper, in his written work, explicitly states that ABE is an evidential argument from evolution, not an evidential argument from evolution conjoined with Darwinism. So Craig’s objection isn’t even a rebutting defeater for ABE.
Draper (or any other proponent of ABE) could, for the sake of argument, consistently agree with both ABE and Craig’s argument. In other words, one could consistently believe both “The fact of evolution is more probable on naturalism than on theism” and “Given that evolution is true, the fact that intelligent life evolved on Earth is more probable on theism than on naturalism.” So, again, Craig’s objection is, at best, an independent argument for theism, not a refutation of ABE.
Is There a Good Theistic Evidential Argument from Evolution?
Furthermore, a careful reading of Craig’s comments reveals that he isn’t arguing that “evolution” so defined is evidence for God’s existence. Rather, he argues the fact that humans evolved is evidence favoring theism over naturalism. I’m going to quote his comments again, this time emphasizing the references to human evolution.

In fact, that leads me to his other argument, concerning biological evolution. And I’m going to suggest that the idea that evolution could have occurred without an intelligent Designer is so improbable as to be fantastic. This has been demonstrated by Barrowand Tipler in their book The Anthropic Cosmological Principle. In this book, they list ten steps in the course of human evolution, each of which is so improbable that before it would have occurred the sun would have ceased to be a main sequence star and would have burned up the earth. They estimate the odds of the evolution of the human genome by chance to be on the order of 4-360 (110,000), a number which is so huge that to call it astronomical would be a wild understatement. In other words, if evolution did occur, it would have been a miracle, so that evolution is actually evidence for the existence of God![1]

So, despite his claims to the contrary, Craig’s theistic argument here is not an argument from evolution to theism. Rather, it’s an argument from human evolution to theism.
This raises an interesting possibility. Regular readers of this blog are familiar with the fallacy of understated evidence; Craig could argue that the naturalistic evidential argument from evolution commits the fallacy of understated evidence. It successfully identifies some fact (evolution) which is evidence favoring naturalism over theism, but ignores other, more specific evidence (human evolution) which favors theism over naturalism. Of course, that reply would require him to admit that evolution is evidence favoring naturalism. I will leave it as an exercise for the reader to determine if “human evolution” constitutes “understated evidence” which favors theism.
Is There a Good Theistic Evidential Argument from Human Evolution?
But does Craig’s theistic argument from human evolution even work? I believe the most charitable formulation of Craig’s argument begins with an inductive argument from authority.
(8) The vast majority of statements made by Barrow and Tipler concerning the probability of the Darwinist evolution of Homo sapiens on Earth are true.
(9) “Darwinist evolution of Homo sapiens on Earth is fantastically improbable” is a statement made by Barrow and Tipler.
(10) [probable] Therefore, “Darwinist evolution of Homo sapiens on Earth is fantastically improbable” is true. [by Statistical Syllogism]
An inductive argument from authority, however, is evidentially worthless if (a) equally qualified  authorities disagree; or (b) the authorities mentioned in the argument do not actually make the statement attributed to them. As I shall argue below, Craig’s argument from authority violates condition (b), viz., Barrow and Tipler (B&T) do not claim that the Darwinist evolution of Homo sapiens on Earth is fantastically improbable.
Barrow and Tipler’s “Ten Steps”
B&T’s discussion discussion is very sophisticated; it would probably take a 25- to 50-page essay to fully summarize and assess the intricacies of their sensitivity analysis and corresponding mathematical model. But, for our purposes, that isn’t necessary. Let’s begin by investigating Craig’s reference to B&T’s “ten steps in the course of human evolution.” Turning to their book, they describe those ten steps as “crucial steps,” which they summarize as follows.

Crucial Step #1: The development of the DNA-based genetic code.
Crucial Step #2: The invention of aerobic respiration.
Crucial Step #3: The invention of glucose fermentation to pyruvic acid is unique seme which evolved in bacteria and remained unmodified in all eukaryotes.
Crucial Step #4: The origin of autotropic photosynthesis (oxygenic photosynthesis).
Crucial Step #5: The origin of mitochondria: these are the bodies in the cytoplasm of eukaryotes wherein the energy molecule ATP is synthesized.
Crucial Step #6: The formation of the centriole/kinetosome/undulipodia complex; such an event was essential to the evolution of the reproductive system of eukaryotes and of nerve cells.
Crucial Step #7: The evolution of an eye precursor.
Crucial Step #8: The development of an endoskeleton.
Crucial Step #9: The development of chordates.
Crucial Step #10: The evolution of Homo Sapiens in the chordate lineage.[2]

B&T’s discussion is very nuanced; they are very careful to state that the “arguments for the above 10 steps as being crucial … are not conclusive by any means; they are offered as suggestions only…” [3] But I don’t propose holding that against them. For the record, as a non-biologist, I’m fine with granting the assumption that these ten steps are crucial in the sense they have in mind. Now what?
As I was reading B&T’s discussion, I expected them to estimate the probability of each step conditional upon the prior step. Assuming these ten steps are statistically independent (which seems right to a non-biologist such as myself), I then expected them to apply the chain rule in an equation like this:
Pr(evolution of Homo Sapiens) = Pr(Step #1) x Pr(Step #2 | Step #1) x Pr (Step #3 | Step #1 & Step #2) + ….
Instead,they take the discussion in a totally different direction and use the minimum number of “crucial steps” to estimate “an upper bound for the length of time the biosphere can continue in the future.”
So where does the probability estimate quoted by Craig come from? B&T attempt to estimate the probability of human evolution by focusing on the evolution of the unique set of proteins coded by the human genome. They do that by using (a) an estimate of the number of unique genes; and (b) an estimate for the “odds for assembling a single gene.” Regarding (a), Dobzhansky et al estimate that the human genome has approximately 110,000 different genes. As for (b), they cite DeLey, who estimated the probability to be between 4^(-180) and 4^(-360). B&T use (a) and (b) to arrive at the following result.

The odds against assembling the human genome spontaneously is even more enormous: the probability of assembling it is between 4^(-180)^110,000 … and (4^360)^110,000. These numbers give some feel for the unlikelihood of the species Homo sapiens.[4]

If you compare this quotation to the Craig quotation at the beginning of this post, however, you’ll notice that Craig mentions only the lower bound of this range without mentioning the upper bound or the fact that they estimated a range rather than a single number. But let that pass.
The important point is this. The word “spontaneously” is key; it reveals that B&T are not estimating the probability of the Darwinist evolution of human beings. Rather, they are estimating the probability of the “spontaneous” assembly of the human genome. As Craig himself admits, they are estimating the probability of the human genome arising by chance.  But evolution and especially Darwinist evolution denies–i.e., is logically incompatible with–the spontaneous emergence of the human genome. That entails, however, that premise (9) is false.
Furthermore, on the next page Barrow and Tipler seem to caution against precisely the sort of intelligent design inference which Craig makes.

We should emphasize again that the enormous improbability of the evolution of intelligent life in general and Homo sapiens in particular at any randomly chosen point in space-time does not mean we should be amazed we in particular exist here. This would make as much sense as the Elizabeth II being amazed she is Queen of England. Even though the probability of a given Briton being monarch is about 10^-8, someone must be. Only for the person who is monarch is it possible to ask, ‘how improbable is it that I should be monarch?’ Similarly, only if an intelligent species of a particular kind does evolve in a given space-time location is it possible for its members to ask how probable it was intelligent life of some form to evolve there. And, provided that the Universe is of a sort in which intelligent life is likely to arise somewhere, then both cases are examples of WAP self-selection in action.[5]

If Craig has an objection to this paragraph and specifically B&T’s use of the WAP (Weak Anthropic Principle), he doesn’t tell us what it is. But rather than pursue that line of thought, instead I want to close with this observation. It seems rather one-sided for Craig to appeal to part of B&T’s probability estimate, which supports his point, without also mentioning that B&T apparently endorse WAP, which undermines his point. The upshot is that Craig’s argument from authority fails and therefore his evidential argument from human evolution likewise fails. It’s possible that there may be a logically correct inductive argument from human evolution to theism, but this one clearly isn’t it.
Notes
[1] See, e.g., William Lane Craig, “First Rebutal,” Does God Exist? William Lane Craig vs. Massimo Pigliucci (1998), http://www.reasonablefaith.org/does-god-exist-the-craig-pigliucci-debate#section_3. Craig’s reference to Barrow and Tipler is John Barrow and Frank Tipler, The Anthropic Cosmological Principle (Oxford: Clarendon Press, 1986), 561-565.
[2] Barrow and Tipler 1986, 561-562.
[3] Barrow and Tipler 1986, 564.
[4] Barrow and Tipler 1986, 565.
[5] Barrow and Tipler 1986, 566, my emphasis.

bookmark_borderMassimo Pigliucci on Metaethics, Part 1

William Lane Craig and Massimo Pigliucci debated the existence of God in 1998. (Click here to read the transcript.) In his opening statement, Craig presented his standard moral argument for God’s existence.

(1) If God does not exist, objective moral values do not exist.
(2) Objective values do exist.
(3) Therefore, God exists.

In his opening statement, Pigliucci denied (2).

Finally, the problem of morality, which I’m sure we’ll have more to say about–oh yeah, I agree with Dr. Craig when he cited Dr. Ruse, a philosopher of science. There is no such a thing as objective morality. We got that straightened out.

Although this was much too quick to constitute anything much like an effective debate rebuttal, this quotation is useful for another reason. It reveals that Pigliucci agrees with Michael Ruse’s argument against (2). Regular readers of this blog will remember that Ruse’s argument for error theory has been the subject of much criticism by philosophers (see here and the references provided; cf. the links here), but Pigliucci says nothing in the debate which would answer or pre-empt those objections. In fairness to Pigliucci, some or all of those criticisms were published after the debate. The point here is not that Pigliucci should be faulted for failing to refute objections before they are published. Rather, the point is that he (apparently) relied upon a fallacious argument to justify his denial of (2).
He continues:

Morality in human cultures has evolved and is still evolving, and what is moral for you might not be moral for the guy next door and certainly is not moral for the guy across the ocean, the Atlantic or the Pacific Ocean, and so on. And what makes you think that your personal morality is the one and everybody else is wrong? Now a better way of putting this is that it is not the same as to say that anything goes; it is not at all the same. What goes is anything that works; there are things that work. Morality has to work. For example, one of the very good reasons we don’t go around killing each other is because otherwise the entire society as we know it would collapse and we’d become a bunch of simple isolated animals. There are animals like those.

I, for one, find that statement to be so  vague as to be of little philosophical value. What, precisely, does Pigliucci mean when he says, “Morality in human cultures has evolved?” And what does that have to do with the branch of metaethics known as moral ontology, the actual focus of Craig’s moral argument? One possible answer is that Pigliucci is simply making the point that human beliefs–about moral goodness and badness; moral obligation, permittedness, and prohibition; and the like–have changed over time. If that is what Pigliucci meant, then perhaps his point was that changes in human moral beliefs over time is further evidence against (2).
But if that is the sort of argument Pigliucci had in mind, it’s hard to see how it could be successful. Consider the following argument.
(4) Human beliefs about the laws of physics have changed over time.
(5) The best explanation for these changes in human beliefs is that there are no objective truths about the laws of physics.
(6) Therefore, there are no objective truths about the laws of physics.
I think probably everyone would agree that this argument fails because (5) is false. Now consider the parallel argument from changes in moral beliefs over time.
(7) Human beliefs about morality have changed over time.
(8) The best explanation for these changes in human beliefs is that there are no objective truths about morality.
(9) Therefore, there are no objective truths about morality.
It’s far from obvious why the moral beliefs argument is any better than the physics belief argument.
In Pigliucci’s First Rebuttal, he said this:

Let’s go back to this thing of objective morality. I think that there’s a little bit of twisting and turning around here with terms. Again, it’s not a matter of “Is there out there an objective morality?” We know that there isn’t. There are some components of your own morality that are not shared by other human beings. So either you are pretentious enough to think that your morality for whatever reason is the only correct one, or everybody else in the world is wrong.
I think that that is pretentious. ….
 

In this passage, Pigliucci seems to be stating a version of the argument from moral disagreement. But, as it stands, this argument is multiply flawed. First, Pigliucci conflates “the existence of ontologically objective moral values” with “my [the speaker’s] moral beliefs are the only correct moral beliefs.” The former neither entails nor makes probable the latter; this argument is a non sequitur. Second, Pigliucci fails to consider rival explanations to error theory, such as “the fact that much moral disagreement is due to disagreement about non-ethical facts” and “moral disagreement is much more surprising on the conjunction of theism and moral objectivism than on moral objectivism and metaphysical naturalism.”
Moving on, Pigliucci next makes a comparison between the behavior of human beings and other animals.

Of course there are some universals that all human beings share. Just today, for example, I told my students in a biology class that there are some things that human beings and society would never approve because of the way human societies are built. One, of course, is homicide; another one, of course, is rape. However, what we call homicide or rape or, in fact, even infanticide is very, very common among different types of animals. Lions, for example, commit infanticide on a regular basis because they want to make sure that the little offspring that is being raised by the lioness is their own and not someone else’s. Now, are these kinds of acts to be condoned? I don’t even know what that means because the lion doesn’t understand what morality is, that’s for sure.

It’s not entirely clear to me what point Pigliucci is trying to make in this passage. Perhaps his idea is that human “universals,” such as the beliefs that homicide and rape are morally wrong, aren’t evidence for an “objective morality” because those same behaviors are common in other animals. Again, it’s far from clear how such an argument would work. Here are two objections. First, humans are moral agents whereas lions are not. (Note: the previous sentence should not be interpreted as implying that humans possess libertarian free will.) Second, even if there were such a thing as ‘lion morality,’ it’s far from obvious why facts about ‘lion morality’ have any relevance to or bearing upon human morality. If Pigliucci has an argument, he hasn’t yet told us what it is.

Morality is an invention of human beings. It’s a very good invention. I’m not suggesting we should abandon morality. I’m not suggesting, more to the point, that we should abandon ethics. Ethics is a perfectly valid way of thinking about things. We can all agree as a society that there are things that are wrong and things that are good. We can act on them, and we can enforce those things, but there is no higher power or no higher reason to tell us that this is right or this is wrong. Unfortunately, we are on our own; that’s my humble opinion. I would really like for somebody to come down from the sky and tell me what is right and what is wrong. My life would be much, much easier. Unfortunately, that doesn’t happen.

The key claim in this paragraph is its first sentence: “Morality is an invention of human beings.” There’s no argument presented for that claim, however.
Finally, it’s worth noticing the reasons Pigliucci gives to deny the existence of objective moral values and obligations. He doesn’t claim, “Objective moral values and duties can exist only if God exists, but God doesn’t exist; therefore, objective moral values and duties don’t exist.” Rather, Pigliucci gives independent reasons for rejecting moral objectivism, i.e., reasons that are independent of his atheism. The upshot is this: although Pigliucci denies the existence of objective moral values and obligations, atheism does not entail the non-existence of objective moral values and obligations.