Some organisms show little change over a (very) long period of time. Often, species that have undergone little morphological change are known as living fossils (for more about the possible definitions, and a list of examples, check the Wikipedia page).
Perhaps the best known example is the coelacanth, a fish long thought to be extinct until living ones were found near South Africa in 1938, closely resembling fossils. In fact, a recent study proposes that similar looking species of coelacanth have been around for even longer than previously thought.
Sadly, examples of morphological stasis (little external change) such as these are often used by those opposing evolution. “Where’s your evolution now, huh?,” so the reasoning goes. Should we let this slide, or should we react? A column (also discussed by Prof. Jerry Coyne on Why Evolution Is True) in the latest issue of Nature, entitled Reach out to defend evolution, suggests the latter option.
In it, a palaeontologist, Russell Garwood, recounts how surprising and interesting findings concerning evolution are frequently co-opted for the creationist cause. One of the examples that is given does indeed revolve around living fossils (in this case, fossil harvestmen).
He suggests in the column:
If research is to appear that will attract an obvious creationist interpretation, an accompanying blog post could explain the work and highlight flaws in any anti-evolution attacks.
Back to the living fossils then. Why do these NOT present any threat whatsoever for evolutionary theory? Well, there are a few points to note:
- No obligation: Evolutionary theory does not state that species have to evolve. Only that they will tend to do so when their environment (broadly construed, including interactions with other species) changes.
- Stability: The main suggestion as reason for morphological stasis. Basically, if the environment doesn’t change, then there’s not really a strong selection pressure that results in change. There’s no real ‘incentive’ to change (careful, incentive here does not imply any foresight or conscious decision!)
- Constraints: Potential evolutionary change is constrained in several ways. this means that an organism follows a certain developmental pathway, has a certain evolutionary history and a particular genetic and functional composition, all of which limit the amount and type of evolutionary change that can occur. ‘Anything goes’ doesn’t work in evolution.
- Beyond the cover: Not all evolutionary change is visible on the outside. A lot might have changed on the inside. The internal mechanisms and molecules could have changed significantly without necessarily producing an external cue.
These are of course only brief and general points, but I hope the idea is clear: living fossils are easily accommodated by evolution and in no way provide evidence against it.
But surely, we don’t know everything? Of course not. There are still mysteries and unknowns waiting to be uncovered and explained. And that’s wonderful. They are one of the reasons science is so exciting. And, as the column says:
We should not let creationist pressure alter the way we do science — the day that researchers become reticent about highlighting inconsistencies and uncertainty would be a dark one.
Garwood, R., Dunlop, J., Giribet, G., & Sutton, M. (2011). Anatomically modern Carboniferous harvestmen demonstrate early cladogenesis and stasis in Opiliones Nature Communications, 2 DOI: 10.1038/ncomms1458
Garwood, R. (2012). Reach out to defend evolution Nature, 485 (7398), 281-281 DOI: 10.1038/485281a
Zhu, M., Yu, X., Lu, J., Qiao, T., Zhao, W., & Jia, L. (2012). Earliest known coelacanth skull extends the range of anatomically modern coelacanths to the Early Devonian Nature Communications, 3 DOI: 10.1038/ncomms1764