Biology is replete with instances of convergence — repeated designs in distant species. Marsupials and placentals, for instance, are mammals with different reproductive designs (placentals have significant growth in the embryonic stage attached to the nutrient-rich placenta whereas marsupials have no placenta and experience significant development after birth) but otherwise with many similar species.

The marsupial flying phalanger and placental flying squirrel, for example, have distinctive similarities, including their coats that extend from the wrist to the ankle giving them the ability to glide long distances. But evolutionists must believe that these distinctive similarities evolved separately and independently because one is a marsupial and the other is a placental, and those two groups must have divided much earlier in evolutionary history. Simply put, evolution’s random mutations must have duplicated dozens of designs in these two groups.

It is kind of like lightning striking twice, but for evolutionists — who already have accepted the idea that squirrels, and all other species for that matter, arose by chance mutations — it’s not difficult to believe. It simply happened twice rather than once (or several times, in the cases of a great many convergences).

What is often not understood, however, by evolutionists or their critics, is that convergence poses a completely different theoretical problem. Simply put, a fundamental evidence and motivation for evolution is the pattern of similarities and differences between the different species. According to this theory, the species fall into an evolutionary pattern with great precision. Species on the same branch in the evolutionary tree of life share a close relationship via common descent. Therefore, they share similarities with each other much more consistently than with species on other branches.

This is a very specific pattern, and it can be used to predict differences and similarities between species given a knowledge of where they are in the evolutionary tree.

Convergence violates this pattern. Convergence reveals striking similarities across different branches. This leaves evolutionists struggling to figure out how the proverbial lightning could strike twice, as illustrated in a recent symposium:

Does convergence primarily indicate adaptation or constraint? How often should convergence be expected? Are there general principles that would allow us to predict where and when and by what mechanisms convergent evolution should occur? What role does natural history play in advancing our understanding of general evolutionary principles?

It is not a good sign that in the 21st century evolutionists are still befuddled by convergence, which is rampant in biology, and how it could occur. This certainly is a problem for the theory.

But a more fundamental problem, which evolutionists have not reckoned with, is that convergence violates the evolutionary pattern. Regardless of adaptation versus constraint explanations, and any other mechanisms evolutionists can or will imagine, the basic fact remains: a fundamental evidence and prediction of evolution is falsified.

The species do not fall into the expected evolutionary pattern.

The failure of fundamental predictions — and this is a hard failure — is fatal for scientific theories. It leaves evolution not as a scientific theory but as an ad hoc exercise in storytelling. The species reveal the expected evolutionary pattern — except when they don’t. In those cases, they reveal some other pattern.

So regardless of where you position yourself in this debate, please understand that attempts to explain convergence under evolutionary theory, while important in normal science, do nothing to remedy the underlying theoretical problem, which is devastating.

Photo: Baby sugar glider, example of a flying phalanger, by Mariposa Veterinary Wellness via Flickr.

Cross-posted at Darwin’s God.