As we’ve discussed here in the past, molecular clocks are notoriously unreliable indicators of a lineage’s evolutionary age. Typically the problem is that the molecular clock is ticking “too fast” and suggests a lineage is older than the fossil record shows. Viewed through a non-Darwinian lens, genes in different organisms seem to be more dissimilar than one would expect under an evolutionary perspective. In other words, there are more informational differences between the organisms than, according to Darwinism, should be the case. Intelligent design has no problem with this finding.
Now, a recent article at Science Daily, “Turn back the molecular clock, say Argentina’s plant fossils,” reveals that not only do molecular clocks sometimes tick too fast, but alternatively they may also tick “too slowly.” More precisely put, sometimes molecular clocks show fewer molecular differences than an evolutionary interpretation of the fossil record would predict. The article explains why this indicates that molecular clocks are untrustworthy:
The finding suggests serious biases in molecular clocks, which are heavily used to date many kinds of living things. … “Paleontology and molecular clocks have a long, uneasy relationship,” said Peter Wilf, a paleobotanist and professor of geoscience, Penn State. “Paleontologists want molecular clocks to work. However, for years we have seen molecular dates, mostly for very deep evolutionary events, that are much older than the corresponding fossils. This situation has been a frustrating Catch-22 because if the clocks are wrong, no fossils exist that could demonstrate they are wrong. Here, we looked at many new plant fossils from the extremely productive region of Patagonia, and we found the opposite, that the fossils are much older than the clock dates. In this case, we can definitely say that the clocks are wrong. The fossils prove it.”
The paper that Science Daily reports on is in the journal New Phytologist, “Green Web or megabiased clock? Plant fossils from Gondwanan Patagonia speak on evolutionary radiations.” It too discusses difficulties in testing molecular clocks:
As paleontologists who frequently collaborate with geochronologists, we expect that molecular ‘timetrees’ will help fill gaps in the fossil record. However, we find molecular divergence-age estimates (‘dates’) difficult to evaluate, and not only because many results differ strikingly from the fossil data. Molecular dates are extremely sensitive to placements of calibrating fossils at stem vs crown nodes and to choices of methods and calibration scenarios. Perhaps most significantly, molecular dates usually cannot be tested adequately with fossils. If molecular estimates are truly too old, they cannot be falsified because the required fossils never existed. If they are younger than comparable fossils, they are still ‘not wrong’ because they represent minimum ages. We dispute this logic because dated fossils also represent minimum ages of their lineages (clades). Arguments in support of molecular dating tend to emphasize the perceived similarities of results from different genes and models, thus lacking any geological validation, or they present small sets of clock-rock comparisons without any supporting stratigraphic discussion. (internal citations omitted)
When fossils show a lineage is very old, but molecular clocks suggest it’s very young, which date are you going to trust? The answer, according to these authors, is the fossil date. Why? Because fossil ages are rigorously determined, and not dependent upon ambiguous biological evolutionary assumptions. As the paper observes, “Significant geochronologic errors are extremely rare … [b]y contrast, the relatively new field of molecular dating does not yet have standards that define comparisons with the geologic timescale.”
Severe disconnects between molecular dates and fossil dates suggest that some of the assumptions of molecular clocks must be wrong. The question is: Which assumptions? It could be that the phylogeny that was used to calibrate the molecular clock is flawed. Or it could be that it’s wrong for molecular clocks to assume that mutations accumulate at a constant rate across deep time. But one of the most important — and least acknowledged — assumptions of molecular clocks is that common ancestry is correct. Perhaps that assumption is wrong. Maybe,a process of descent with modification did not produce these species. Or maybe it’s some combination of these assumptions that are wrong.
Worse, this molecular clock failures could also suggest a biogeographical problem for neo-Darwinism. As the paper explains, similar plant fossils are found in South America, Antarctica, and Australia — continents that were once part of the supercontinent Gondwanaland in the Southern Hemisphere. Neo-Darwinism assumes that similarities between these plants indicate they shared a common ancestor. Normally, neo-Darwinian thinking would look at such similarities and assume that the lineages must have diverged before the continent broke apart. The problem is that the molecular clock dates indicate that the divergence dates are so recent that the linages must have diverged after Gondwanaland broke up. This suggests a severe biogeographical discontinuity between geology and evolutionary history. If the geological history is right, perhaps the evolutionary history — i.e., the assumption that these plants group shared a common ancestor — is wrong.
Needless to say, most evolutionary biologists who accept these molecular clock dates refuse to consider that possibility. But if you accept common ancestry, and you don’t challenge the molecular clock dates, then you’re forced to conclude that these plants diverged after Gondwanaland broke apart and yet still ended up on continents that already were separated across the globe. Some evolutionary biologists in fact go this route.
This view raises the question: how did supposedly related species end up on separate continents? No problem: the researchers invent a “Green Web hypothesis,” where plants somehow crossed over oceans to seed new continents after their lineages diverged. On rafts (or some other hypothetical trans-oceanic transport mechanism), perhaps? I’m not entirely kidding. This is very reminiscent of the problem that evolutionary biologists sought to fix by invoking “rafting monkeys” to explain how monkeys arrived in South America millions of years after the continent separated from Africa.
Bottom line? The discrepancy reported in this paper dictates one of two problems for Darwinian evolution: either (a) we’ve got another case where molecular clocks are severely wrong, or (b) some plant distributions in the Southern Hemisphere pose a major biogeographical problems for neo-Darwinism. The paper opts for the former conundrum, offering the following caution:
We urge significantly greater caution when using molecular dates in the explicit context of geologic time and Earth history. The fossil record is always incomplete, but its exciting potential is only beginning to develop in many parts of the world. Future improvements in molecular dating seem very likely, but for now, fossils and geochronology provide the only rigorous, enduring temporal framework for evolutionary radiations.
Evolutionary biologists must pick their poison. There need be no conflict, however, for those of us willing to entertain fresh ideas about evolutionary history, even questioning sacred beliefs about common ancestry.