The Red Notebook

Maiacetus inuus, c. 47.5 million years ago

As so-called missing links go, here’s yet another: the delightfully named Maiacetus inuus, a proto-whale from the middle Eocene.

The species has just been described in Gingerich PD, ul-Haq M, von Koenigswald W, Sanders WJ, Smith BH, et al. (2009) New Protocetid Whale from the Middle Eocene of Pakistan: Birth on Land, Precocial Development, and Sexual Dimorphism. PLoS ONE 4(2): e4366. doi:10.1371/journal.pone.0004366.

M. inuus is the latest in a series of discoveries which record the transition of whales from land to sea. Like other recent proto-whale finds, it still had a full complement of legs, but was amphibious. M. inuus is a particularly interesting find, however, because a foetus found within one of the two specimens shows clear signs that the species still gave birth on land.

The problem with missing links is that for each one discovered, two more are created: if species C fills a gap between species A and B, there now exist missing links between A and C and between C and B. Don’t let anyone try to tell you that evolution must be wrong because there are too many missing links. Such people will never be satisfied. Instead, remind them of all the wonderful missing links which have already been discovered. They tend to forget about those.

People who harp on about missing links also tend to claim that the theory of evolution by means of Natural Selection is not scientific because it makes no testable predictions. Once again, not true. The fact that the theory is mostly used to explain things which happened in the past (there’s a reason they call it natural history) makes predictions difficult, but not impossible. Before any proto-whales were discovered, it was confidently predicted that the recent ancestors of whales would have had legs—as evidenced by future finds in the fossil record. Furthermore, it was predicted that the earliest amphibian proto-whales would have given birth on land. Clearly, these could not be not sure-fire testable predictions, because there could be no guarantee that any proto-whale fossils would ever be found—but found they eventually were, and the predictions turned out to be spot on.

Chalk up another one for evolution.

[T]he great tragedy of Science—the slaying of a beautiful hypothesis by an ugly fact…

Thomas Henry Huxley
Biogenesis and Abiogenesis (1870)

Back in 2002, I wrote an essay entitled (in tribute to Huxley) …So Let’s All Be Scientists! It was my contribution to Darwin Day Collection One: The Single Best Idea Ever [ISBN: 0972384405, Amazon.com], a collection of articles, reviews and cartoons in celebration of Darwin and science. In the essay, I observed:

…for all the thousands of slugs I have found, I have never come across a single snail in my garden. Why is that? Is it too cold (I live in the Pennines)? Do the slugs eat them […], or out-compete them? Am I just not looking hard enough? Or is there simply not enough calcium in the area to allow snails to make shells (possibly because the soil is too acidic)?

Well, it would appear that the not looking hard enough hypothesis had some merit. The other weekend, I was moving a rockery in my garden (don’t ask), when I came across this:

A very small snail!

OK, as snails go, it wasn’t exactly the biggest (or, indeed, the alivest), but a snail is a snail, and an ugly fact (no matter how small) is an ugly fact: my no snails in my garden hypothesis is well and truly falsified. So now I have had to modify it slightly:

There are no big snails in my garden.

Actually, I have been keeping an active look-out for snails ever since I wrote my essay, and I can confidently say that I believe my modified hypothesis is correct. Which is odd, because I have observed large snails a couple of hundred yards away from my garden, albeit at a significantly lower altitude (I live on a very steep hill).

But, despite this stark evidence to the contrary, I still like my acidic soil explanation for the (near) absence of snails in my garden. In fact, until last week, I was growing increasingly confident that it was the correct explanation, having first confirmed that the soil in my garden is indeed acidic, and having recently come across the following in the New Scientist subscribers’ archive:

Acid attack

Acid rain has progressively thinned the shells of eggs laid by British thrushes over the past 150 years, a new study suggests. Ornithologists fear that the trend could make thrush eggs less likely to hatch…

[Rhys Green of the Royal Society for the Protection of Birds] thinks that acid rain, caused by sulphur emissions from the burning of fossil fuels, is the most likely cause. This would reduce both the calcium content of leaf litter consumed by worms and the abundance of snails, which together make up a large part of the birds’ diets.

So maybe there is still enough calcium in my garden for some very small snails, but not enough for any snails bigger than a couple of millimetres across.

I will get to the bottom of this one! Eventually.

Postscript [18-Jun-2007]: Hypothesis well and truly falsified!