Wednesday, May 25, 2011

Why Special Creation Failed - An Introduction to Genetics and the Origin of Species

Special creation, defined as the direct creation of fixed (unchanging) species by God, was the predominant view of the origin of species among scientists during Darwin’s time.  Writes David Reznick in The Origin Then and Now, ‘Today we think of the advocates of special creation as representing non-scientific, religious opponents to evolution.  In Darwin’s day, they were the scientific establishment.  Virtually everyone, ranging from his professors at Cambridge to all those who had the greatest influence on Darwin’s intellectual development, advocated some form of special creation.’

It has often been said (by Reznick, for one, and Darwin, for another) that Darwin’s theory of evolution disproved special creation.  But this is not entirely accurate.  Not because special creation is true, but because only certain aspects of special creation are actually testable.

Imagine that you believed that the evidence of design in the world was overwhelming, and that a divine Designer had specially created every form of life on the planet.  What would such a belief cause you to expect about the patterns of the distribution and similarites of life?

It is difficult to see how the special creation theory could give us any hypotheses about any patterns involving living things.  Perhaps we could expect organisms in, say, cold regions to be similarly adapted to the cold (larger bodies, denser hairs, perhaps white colouration to blend in with the snow), while in the deserts we could expect adaptations for heat (smaller bodies, fewer hairs, large appendages for radiating heat, perhaps brown colouration to blend in with the sand).  Indeed, this is what we see!  But this is not really an expectation of special creation per se, it only follows if we add intelligence and beneficence to our knowledge of the designer.  Special creation by itself does not lend to such expectations.

What about similarity in design?  Maybe we would expect the designer to reuse parts, such that organisms would be grouped into categories based on similarity of appearance.  And indeed, this is what we see!  The bat wing, whale flipper, and human hand are all extensions of the same principle of form, being comprised of the same bones modified into different shapes.  But, alas, such an expectation only holds if we assume that the Creator likes to limit His imagination when constructing organisms.  The hypothesis of an unlimited Creator should cause us to expect every form of life to be wonderfully and uniquely different in every imaginable way; by assuming nothing about the designer, we can make no hypotheses.

What about the degree of similarity between organisms in one type of habitat compared to those in another?  Should we expect all desert animals from all of the world’s deserts to be more alike than they are to jungle animals?  This is slightly different than our question about similar adaptations.  The question here is whether large-eared desert mice in the Sahara should be more similar to large-eared desert mice in the US than to small-eared field mice in the region around the Sahara.  What about island plants and animals?  Should island species, which are found nowhere else in the world, be more like species on the nearest mainland than to species on far-away continents?  Or should their degree of similarity to continental organisms not be affected by the distance between them?  Or if the nearest mainland is a desert but the island is a jungle, should the island creatures be more like other jungle creatures? 

The special creation hypothesis can only answer yes to all of these questions.  If the Creator so chose, he could have made it so that each species was equally related to every other species, with ‘related’ being a measure of similarity in body form or genetic similarity.  Or he could have made it so that island creatures are different from everything else on the planet.  Or more similar to the mainland.  Or more similar to those further away.  Or more similar to creatures in similar habitats.  There is no way of knowing the will of the Creator when He created; any pattern could be possible.  The only thing to do is to discover the patterns that the Creator decided on, if He even decided on any.

This is why Darwin did not disprove special creation; to disprove something implies that some expectation essential to the theory had been falsified.  That simply cannot happen with special creation.

There are two things that Darwin did do.  First, he proposed a theory of evolution which demanded very specific patterns.  It demanded, for example, that island denizens be more like those on the closest mainland than those further away, even if the island and continental habitats differed strongly.  His theory demanded that creatures that share a more recent common ancestor would also share greater genetic similarity and similarity in body plan.  His theory demanded that there be a modification of similar parts among closely related species.

And indeed, this is what was found.  Every pattern expected for Darwin’s theory of natural selection was confirmed in nature.  By itself, this does not rule out special creation, since the Creator could have created any pattern at all.  But it did present evolution by natural selection as a stronger candidate, because out of all of the possible patterns in nature, only those predicted by evolutionary theory were true.

The second thing that Darwin did was establish that the fixity of species implicit in the definition of special creation was wrong.  Species are not static entities that were created to remain the same forever; Darwin showed that they were quite dynamic, changing entities.  The fixity of species demanded that species’ boundaries be sharp and definable, with no interbreeding between species.  Darwin’s theory demanded that species be blurry and difficult to define, since species in the process of speciating (‘incipient species’) should not yet have the full properties of a true species.  Hybridism between two species, which was seen in many plants and fish and insects, was evidence for Darwin against the fixity of species.  So was the difficulty that naturalists were having in simply counting the number of plant species found in England - plant experts in Darwin’s time were coming up with vastly different numbers, with some arguing for twice as many recognized species as others.  This was inexplicable with the belief in a God who created static, bounded entities; this was easily reconciled by a process of continuous change in populations of the same species that occupied different environments.

If a species is divided into populations, and those populations encounter different environments and interact with different species in those environments, each population should become adapted to its unique environment.  Thus varieties of a species are born.  And as these differences accumulate, species are born.  And as species split into new populations and themselves speciate, higher-level categories like the genus or family are born.  And in the in-between stages, as populations are turning into different species, there should be difficulties in identifying and even defining a species.  This was Darwin’s great contribution to the problem of special creation.

But disproving the fixity of species is not the same thing as disproving special creation.  If we removed ‘fixity’ from special creation and presumed that the Creator directly created forms that could in turn evolve, albeit within limits, then the theory of special creation could still survive.

Indeed, since Darwin’s time we have seen a subset of Creationists who study baraminology, the study of ‘created kinds’, organisms with unique properties that allowed them to change and evolve into a multitude of similar species.  During Darwin’s time, it was believed that varieties within a species had not been directly formed by God, but were the product of some unknown secondary cause.  Today baraminologists have extended this above the species level, to the genus or even family.  Thus the Creator could create a carnivore-type that speciated into all of the known carnivorous mammals.  This is perhaps an extreme example, the examples usually given are of the dog-type (so a subset of carnivores), or the horse-type (donkeys, horses, zebras), etc.

Of course, such a theory again gives us no reasonable expectations.  One could argue that, if God created each form separately, then there need not be any genetic similarity between them, but this is not the case; all forms of life share some of their DNA, with an increase in similarity in DNA being linked with the time in which they last shared a common ancestor.  Thus freshwater stickleback in one lake are genetically more like nearby marine stickleback than they are to freshwater stickleback in another lake, because each freshwater population was the result of an independent invasion from the ocean.  Thus humans share more DNA with chimpanzees than with dogs or fish or plants or bacteria.  However, who is to say what the Creator would or would not do?

So Darwin was really unable to disprove special creation, which is evidenced by the number of people who still believe in special creation today.  However, he did offer a significant challenge to the fixity of species, and unlike special creation, his theory made firm, risky predictions that turned out to be true.

Perhaps his riskiest prediction of all had to do with how offspring inherit their parents’ traits.  For his theory to work, parents needed to pass on their traits to their offspring, without the traits being lost.  The problem was, during Darwin’s time no one had any idea how this could work.  In fact, the prevailing view of his day directly contradicted his theory.  The prevailing view was called the blending theory of inheritance.  This theory argued that the traits of the mom and the traits of the dad are mixed together in the offspring and cannot be separated; a child is thus an intermediate between its mom and dad.  Possible evidence for this could be when parents of distinct skin colours produce children with an apparently intermediate skin colour.  The blending theory demands that, once blended, the parental traits cannot emerge again in later generations.  For fixed species, this made sense, as such blending would tend to remove any environmentally-caused deviations from the ideal species’ form.

Darwin’s theory, however, required a particulate theory of inheritance, which argued that traits were passed on as discrete units that, even if hidden in one generation, could re-emerge in the next.

The supporters of the blending theory attacked Darwin’s theory of evolution by natural selection.  The reason for this is simple: if an individual were to suddenly be born with an improved trait, it would inevitably mate with one of the unimproved varieties; their offspring would receive a trait intermediate to the parents.  This offspring would mate with an unimproved variety, reducing the novel trait even further.  In such a way, any new varieties would be lost, and selection would have nothing to work with.

The particulate theory, on the other hand, worked for Darwin.  The problem was that no mechanism for particulate inheritance had been found.   Darwin died without ever knowing how inheritance worked.

A further problem with his theory was that there was no known mechanism for producing new varieties.  So not only was it not known how parents passed on their traits, but it was not known how new traits could be developed. 

All of this doubt was cast aside with the findings of the Augustinian monk Gregor Mendel, whose meticulous work with pea plants supported the particulate theory of inheritance.  In one of the biggest ironic twists of history, Mendel published his work in 1866, nine years after Darwin published On the Origin of Species, but it would go unnoticed until 1900.  And then it would spark a remarkably unhelpful debate between the biometricians, who supported natural selection but rejected Mendelian inheritance, and the mutationists, who talked about genes but rejected natural selection.

By the 1930s mathematical work had been done that showed how evolution by natural selection and the particulate theory of inheritance through genes as discovered by Mendel worked together.  Variation was caused by mutations; inheritance involved the movement of genes from parents to offspring, with the action of genes only sometimes causing a blended appearance in the offspring, without the structures of the genes themselves blending.

But this was mathematical work only.  Experimental work from the laboratory and from nature was still required.  This is where Theodosius Dobzhansky enters our story.  A Russian-born biologist, Dobzhansy emigrated to New York in 1927 and rocked the world of evolutionary biology.  You can read about him on Wikipedia, so there is no point in my giving a full biography, but there are four things you should know:

1.       Dobzhansky is considered one of the founding fathers of the Modern Synthesis of evolutionary biology, an intense period of research in the 1930s and 1940s in which several fields of biology were reconciled with evolution.
2.       Dobzhansky is considered a pioneer in the study of speciation and in the role that genes play in shaping species
3.       Dobzhansky’s most famous line is that ‘nothing in biology makes sense except in the light of evolution.’
4.       While doing all of this, Dobzhansky remained a devout and practicing Russian Orthodox Christian.

This has become a rather convoluted introduction, primarily because Reznick’s book has gotten me thinking about special creation, but allow me to summarize by saying that Darwin dedicated his time to disproving special creation, but was only successful in that he made some risky predictions that were verified in nature. These were risky predictions that the theory of special creation simply could not make; the verification of Darwin’s predictions served to discredit special creation, even if it could not disprove it.  The fact that special creation could not be disproved may explain why many people today still hold to it.  One of Darwin’s riskiest predictions was that newly evolved traits would somehow persist in a population without being blended and swamped by the existing traits.  Genetics was Darwin’s saving grace, remarkably explaining both how inheritance works, and how new varieties are formed.

It was up to Dobzhansky to say how.  In the weeks that follow, we will walk through his landmark book, Genetics and the Origin of Species (1937) and hopefully discover just how risky Darwin’s theory really was, and how beautifully genetics rescued Darwin from sure defeat.

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