Suppose that you were an alien visiting Earth for the first time and someone asked you to put the following two organisms into a Darwinian cladogram. How would you do it?
Now obviously because most of us have a rudimentary understanding of Earth biology, we already know the answer on the above. Not only are these two organisms the same species, they’re actually the same individual (see http://lifecycle.onenessbecomesus.com/indepth.html for the full picture cycle (note that I don’t endorse anything on that site; just happened to find these graphics there).
Assume that you are an alien who has never before seen the Earth, however. Further assume that all you have are these snapshots. You do not have the ability to see these creatures in motion. You can’t watch the caterpillar turn into a butterfly. You only have the two pictures: one organism looks worm-like, the other looks moth-like. There is nothing morphologically-speaking that would link these two organisms.
The relevance to this topic comes when we study the fossil record. Just as the aliens in the example would not have access to a video of the caterpillar turning into a butterfly, so we do not have the ability to see fossils as they grow and change through life. We are left with “snapshots” and not only that, we only have snapshots of organisms as they died (not as they lived).
And the difference between an adolescent organism and an adult organism are not the only things to consider. For instance, take this picture (from http://www.bluechameleon.org/Madagascar%20Photo%20Gallery%20(long%20Thumbnail%20Page).htm:
Is this a picture of Darwinian change, of an adult and an adolescent, or is it simply a picture of two of the same species after one has been mangled by a predator? The answer is none of the above. Instead, what this picture shows is the sexual dimorphism between male and female of the same species of (the rather interestingly named) satanic leaftails.
This example is particularly relevant since, unlike the first, these two organisms look similar to each other, and yet different enough to bring one to question whether they are the same animal. If we have only fossils of these organisms, there is no way to tell what their behavior would be. It would be easy to assume that we have proof of two similar organisms that obviously evolved from a common ancestor, when it’s really just the same species that naturally exists in two forms depended on the sex of the organism.
Again, we have the ability to view these organisms in their living habitat so we know that this is sexual dimorphism. But what if we can’t view the living habitat? What if we had to classify the following, for example:
Here we have three trilobites. These trilobites look similar, yet there are differences between them. The question is, therefore: are these differences proof of Darwinian evolution, sexual dimorphism, or the differences between an adolescent and an adult trilobite? Or is there another answer?
After all, we haven’t even dealt with environment yet (although mentioned obliquely in the question of the satanic leaftails when we questioned whether one had been mangled by a predator). In fact, when it comes to morphology, it is not simply DNA at work, but the environment plays a huge role too. For example, if you take identical Caucasian twins and raise one inside a cave and the other at the equator in the sun, the twins will have completely different shades of skin color. The one in the cave will be pale; the one at the equator will be tanned. This is a morphological difference caused solely by environmental changes that has nothing to do with Darwinian selection pressures or DNA mutations.
Another example is the fact that many Inuit’s have a different jaw structure from other Inuits for the sole reason that some Inuits use their teeth to pull at whale blubber and the skins of animals. Over time, this actually pulls their jaw out of alignment, but it’s gradual enough that the muscular structure can adapt somewhat to the new bone structures. If one compared two skulls, one of an Inuit who did this “teeth pulling” and the other who did not, the jaw structure would be morphologically different. Yet these would not be two difference species: they could be identical twins, after all!
So what about those trilobites? Scientists have a problem. We can’t view the original environment that these creatures lived in, and all we have is a snapshot of individual organisms in fossils. We don’t even have the context of those individual organisms in many cases. We only have isolated organisms sprinkled in the fossil record.
Given the magnitude of variations within the species we can see today, there is no reason to expect that all organisms of the same species must have looked nearly identical in the fossil record. And since we have many instances where only one or two organisms make up the totality of our fossil record of that species, it is fallacious to try to plug those into a cladogram with any sense of certainty. Polymorphism exists within the same species today, and therefore polymorphism cannot be proof of Darwinian evolution.
