The Friends of Charles Darwin blog
Posts tagged ‘evolution’
CG animator Richard Spence recently uploaded a 3-minute sequence he created of Sir David Attenborough explaining the entire history of life on earth. You’ve probably seen the sequence before, but this version is in high definition, without an annoying YouTube logo in the corner.
Just came across this rather odd ‘humorous’ 1930 British newsreel on the British Pathé website:
Bizarro!
Who says the reporting of science in the media has gone downhill?
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.
See if you can guess who wrote the following:
[A]lthough each species must have passed through numerous transitional stages, it is probable that the periods, during which each underwent modification, though many and long as measured by years, have been short in comparison with the periods during which each remained in an unchanged condition.
Gould? Eldredge? Sounds like a textbook description of punctuated equilibrium, doesn’t it?
But no, the awkward comma after the word periods is the real and potentially surprising give-away: our punctuationally challenged punctuationist is none other than Charles Darwin, writing in the fourth edition of On the Origin of Species!
What’s that? Darwin a punctationist? Some mistake, surely! Wasn’t he the one who kept banging on about how Natura non facit saltum (Nature does not make leaps)?
In January 2008, Evolving Thoughts‘ John Wilkins wrote a typically thought-provoking post explaining how Linnaeus‘s phrase Natura non facit saltum doesn’t really mean what you probably thought it meant. The phrase, Wilkins explained, was originally intended to describe how Nature exists in small gradations; not how Nature comes about (i.e. evolves) gradually, in small, continuous steps. The distinction is a subtle one, and the two interpretations of the phrase are not necessarily contradictory—but neither does the fact that living and extinct species can be grouped into a continuum necessarily imply that they must have evolved at a uniform rate.
Upon reading On the Origin of Species for the first time, Darwin’s great ally (and bulldog) Thomas Henry Huxley questioned Darwin’s apparently hard-line gradualism, writing to Darwin:
The only objections that have occurred to me are 1st that you have loaded yourself with an unnecessary difficulty in adopting ‘Natura non facit saltum’ so unreservedly. I believe she does make small jumps—
Huxley’s comment seems to have put Darwin slightly on the defensive. By the second edition of Origin, published less than a year later, he had inserted a qualifier into his description of Linnaeus’s dictum, describing it as ‘that old, but somewhat exaggerated, canon in natural history of “Natura non facit saltum”‘ (my emphasis added).
Seven months before the publication of Origin, Darwin had tried to clarify his views on this subject to Joseph Dalton Hooker:
I would advise you to be cautious about stating so broadly (I thought that you perhaps knew of distinct cases unknown to me) about species not varying for many generations & then suddenly varying. To a certain extent I quite believe it; ie that a plant will not vary until after some few generations (perhaps dozen or so) & then will begin to vary possibly suddenly, more likely gradually. But even my belief in this is grounded on very few facts.— I believe another & very distinct explanation may be given of a sort of current belief in the doctrine, viz that variations are often not attended to, & till they are attended to & accumulated, they make no show.—
In other words, although Darwin was prepared to believe that some variations could appear relatively suddenly, he also suspected that variations were happening all of the time, but not always being attended to (i.e. selected) and accumulated. Again, these viewpoints are not necessarily incompatible.
But, whereas Darwin seemed to be hedging his bets somewhat in his 1859 letter to Hooker, as we have seen from the passage quoted at the beginning of this article, he was clearly less hesitant of expressing what would now be described as punctuationist views seven years later in the fourth edition of Origin.
Had something happened between the publication of the third and fourth editions of Origin (1861 and 1866 respectively) to cause Darwin to insert the passage? I believe a clue comes earlier in the fourth edition, where Darwin is again describing the punctuated nature of evolution:
It is a more important consideration, clearly leading to the same result, as lately insisted on by Dr. Falconer, namely, that the periods during which species have been undergoing modification, though very long as measured by years, have probably been short in comparison with the periods during which these same species remained without undergoing any change. We may infer that this has been the case, from there being no inherent tendency in organic beings to become modified or to progress in structure, and from all modifications depending, firstly on long-continued variability, and secondly on changes in the physical conditions of life, or on changes in the habits and structure of competing species, or on the immigration of new forms; and such contingencies will supervene in most cases only after long intervals of time and at a slow rate. These changes, moreover, in the organic and inorganic conditions of life will affect only a limited number of the inhabitants of any one area or country.
As in his 1859 letter to Hooker, Darwin is again saying that variations are happening all of the time, but their selection is down to life’s contingencies (a favourite word of punctuationists). The clue I referred to is the name Dr Hugh Falconer. In 1863, Darwin and Falconer had corresponded briefly on the subject of species formation. In one letter, Darwin wrote:
I should rather like to see it rendered highly probable that the process of formation of a new species was short compared to its duration; that is if the process was allowed to be slow and long: the idea is new to me.— Heer’s view that new species are suddenly formed like monsters, I feel a conviction from many reasons is false.
Here, I suspect, we come to the real reason for Darwin’s insertion of the passage quoted at the beginning of this article into the fourth edition of Origin. In a footnote to this letter, the Darwin Correspondence Project explains:
Working mostly with Tertiary plants and insects, the Swiss palaeontologist Oswald Heer maintained that species were generally constant, but that during occasional periods of creation, existing types underwent abrupt variation and gave rise to new species […]. By 1863, Heer’s view of new species formation was being presented in the international literature as a rival to CD’s theory of slow evolution by natural selection.
It seems to me that, by inserting the punctationist passage into the fourth edition of Origin, Darwin was trying to make it quite clear that his own theory of evolution by means of Natural Selection was quite adequate for explaining the apparently punctuated nature of species formation—without recourse to Oswald Heer’s monsters.
As usual, Darwin was correct. He understood that it was perfectly possible for evolution to be punctuated, without the need for Nature to make monstrous leaps.
Postscript (27-Feb-2009): The aforementioned John Wilkins has written again on this subject in a post entitled Myth 4: Darwin was a gradualist.
BBC: Bat fossil solves evolution poser
A fossil found in Wyoming has resolved a long-standing question about when bats gained their sonar-like ability to navigate and locate food.
They found that flight came first, and only then did bats develop echolocation to track and trap their prey.
A large number of experts had previously thought this happened the other way around.
To me, it seems obvious (always a dangerous word when talking about evolution) that bats must have been able to fly before they evolved echolocation. Echolocation would seem to have only limited use for ground-based mammals, otherwise more mammals would surely have evolved the capability.
I was curious to know, therefore, why so many experts thought that bats’ echolocation must have evolved before flight. I thought it might be because, according to the above BBC article, all bats echolocate, so, unless echolocation evolved independently several times over (which is perfectly possible), it must have evolved in a (presumably early) common ancestor. It turns out that that there was simpler explanation as to why so many experts believed echolocation evolved before flight: until this new fossil, Onychonycteris finneyi, was discovered, another species, Icaronycteris index, had, for over 40 years, been regarded as the oldest known bat—and Icaronycteris index could echolocate.
I was also surprised to learn that all bats echolocate. I had assumed that fruit bats don’t. It turns out they do have the capability, but it is greatly reduced—as is also the case with vampire bats. Echolocation in these bats, it seems, could be seen as vestigial, and might be on the way out.
Interesting stuff.
I like bats.
National Geographic: Modern Birds Existed Before Dinosaur Die-Off
Modern birds originated a hundred million years ago—long before the demise of dinosaurs, according to new research…
Fossil records suggest that modern birds originated 60 million years ago, after the end of the Cretaceous period about 65 million years ago when dinosaurs died off. But molecular studies suggest that the genetic divergences between many lineages of birds occurred during the Cretaceous period.
I’ve always had my doubts about the use of the so-called genetic clock to give absolute, rather than relative, dates for evolutionary events. My personal hunch is that this result says far more about molecular dating than it does about dinosaur/bird history.
But I could be wrong.
I just wrote a new item for this weblog, comparing Darwin’s theory of evolution with Newton’s theory of gravitation, but it turned out longer than I expected. So, by way of a minor Darwin Day Eve celebration, I’ve made it into a full-blown article, entitled A Far More Satisfactory Theory.
In science, even self-evident truths need to be put to the test. There was an interesting story in the Telegraph last week, which described how scientists have tried to show that the long necks of giraffes are adaptations to give them an advantage over shorter animals when grazing trees. Bleeding obvious, you might think, but it has also been suggested that giraffes’ long necks might be a result of sexual selection. Although the scientists concede that their experiment is not definitive, they conclude that giraffes browse at high levels in the leaf canopy out of preference (to avoid competition with shorter browsers), rather than simply because their necks happen to be long.
A small victory for common sense, then.
My first lesson in giraffe evolution occurred when I was about six years old. My primary school teacher explained to the class how giraffes tried to stretch their necks to reach the higher leaves and, over time, all giraffes ended up with longer necks. Little did I realise at the time that I was being taught a Lamarckian version of evolution. I’m sure this was not a deliberate mistake on my teacher’s behalf: she probably thought she was introducing us to Darwinian thinking.
Come to think of it, that was the only lesson I ever received in evolution at either primary or secondary school. English school biology in my day was all about the organs of species, not their origins. I wonder if it has changed much.
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