Last Friday I gave you these tiny bones to identify:
Several suggestions were put forward with soph coming close with the suggestion of a broken furcula and Lena and henstridgesj correctly suggesting the clavicles (or collarbones) of a Cat Felis catus Linnaeus, 1758.
Cat clavicles, like the clavicles of a variety of other animals, are much reduced and are no longer connected to the scapulae (shoulder blades). This allows the scapulae to move much more freely during running, which can increase stride length and in the case of Cats it allows the animal to fit through holes big enough to get their heads through (assuming the Cat isn’t a bit too portly).
These sorts of vestigial structures are interesting from an evolutionary perspective, since they serve little or no direct function, but they still develop as a result of inheritance from ancestral forms that did use them.
Since that divergence of the Chiroptera and the lineage giving rise to the Pangolins, Carnivora and Ungulata the clavicle has been pretty much completely lost, so it’s interesting that even a vestigial form occurs in Cats.
It’s funny to think how such small bones can raise questions that lead us through millions of years of evolution in search of answers, but that’s the nature of studying nature!
If you’re not familiar with the AAH it basically suggests that human ancestors passed through a semiaquatic stage which provided the selective pressure that has led to the differences seen between humans and other primates. Some people call it the Aquatic Ape Theory, but it lacks the necessary scientific support to be considered a theory so it remains a hypothesis [see comments for discussion of the terminology].
The idea was first suggested by pathologist Max Westenhöfer in 1942 and the first line of evidence in support of the hypothesis was proposed by marine biologist Alister Hardy in 1960. Hardy noted that subcutaneous fat is unusual in terrestrial mammals and is normally associated with marine mammals – raising the very good question ‘why do humans have subcutaneous fat?’ (the answer being because we eat too much and exercise too little – just like some lab monkeys).
The baton was then picked up by writer Elaine Morgan who has championed the AAH since 1972. Here’s Elaine in action on a TED video from 2009:
Elaine Morgan is a great communicator and she’s done a remarkable job of delivering the AAH to a wide audience, but I have concerns that the packaging is more impressive than the contents, from a scientific perspective.
In the video Elaine does a cracking job of setting up the AAH in opposition to the more established Savanna Hypothesis (SavH), which suggests that humans diverged from other primates as a result of exploiting more arid environments. She then suggests that the SavH has been discounted on the basis of palaeoenvironmental data, leaving a paradigm gap that should (she suggests) be filled by the AAH.
But of course, a paradigm gap should only be filled by a robust theory and when it comes to plotting evolutionary trajectories there is not solid theoretical foundation on how to do it, beyond relying on the physical evidence provided by the fossil record.
In this case that would require fossils of human ancestors to be found in primarily aquatic deposits, something which we do not see, which is surprising, since aquatic environments are usually far better for fossil preservation than terrestrial environments. In fact, taphonomy suggests that early hominid fossils would be more common if the individuals were living and dying in water with any frequency.
Without having physical data in the form of fossils linking hominids to water, it becomes difficult to make a connection without falling back on evolutionary ‘just-so stories‘, that try to explain an observation by relying on a plausible narrative.
The trouble with this is that the public and media love a good narrative, but it simply isn’t scientific unless it can be falsified. I think this is the part of the process that Elaine Morgan doesn’t quite grasp – she is convinced by her own narrative and believes in the hypothesis, but for a scientist it is more appropriate to subscribe to none of the available hypotheses if they cannot provide factual evidence in support. This is where I currently stand.
I am certainly not convinced by statements like:
“Docosahexaenoic acid (DHA) is an omega-3 fatty acid that is found in large amounts in seafood,… It boosts brain growth in mammals. That is why a dolphin has a much bigger brain than a zebra, though they have roughly the same body sizes. The dolphin has a diet rich in DHA. The crucial point is that without a high DHA diet from seafood we could not have developed our big brains. We got smart from eating fish and living in water.” [Quote attributed to Dr Michael Crawford]
This statement starts by comparing two utterly different species, with a very different evolutionary history and current mode of life, then offers a single dietary explanation for the difference in brain size. This is patently nonsense.
If a seafood diet is the main driver of large brain size then the relatively very large brains of Chimpanzees and other Apes become a remarkable oddity and the relatively small brains of Blue Whales become bizarre variants. Moreover, what about people that don’t have access to seafood? Are they unable to grow large brains? No. Clearly there is more going on.
Brain size is not directly linked to a single dietary chemical, it is linked to managing interactions in and with a complex environment – keeping track of seasonal and spatial variation in fruiting or schooling of fish, coordinating group efforts and understanding prey behaviour to hunt more effectively, or problem solving to access food sources that are hard to acquire. Where a big brain provides a selective advantage, it will evolve.
I don’t want this post to turn into a refutation of the AAH, since there’s a lot to say and much has been done elsewhere. What I do want this post to do is highlight that a scientific theory needs to be testable, it needs to consider contradictory information and it needs to be aware of confirmation bias.
The AAH relies strongly on observed similarities in condition between humans and aquatic mammals, but it dismisses other similarities out of hand. For instance, Naked Mole-rats are simply dismissed by Morgan as an example of a non-aquatic mammal that has lost body hair, but they provide evidence that hair loss can occur for reasons beyond aquatic adaptations – which is worthy of note.
It is also worth considering the supporting examples in the context of phylogeny and physiology, which doesn’t seem to happen often. For instance, the Cetacea, walruses and Sirenia are examples of naked aquatic mammals cited in the AAH, but both the Sirenia and walruses retain a short coat of hairs, quite different in structure to the fine body hair of humans. Whales and Sirenia have also been adapting to an aquatic habitat for 50 million years and the ‘nakedness’ of modern examples may be more related to the evolution of large body size and the benefits to thermoregulation provided by mass – which is supported by the fact that the largest species in the Pinnipedia (like the Elephant Seal and Walrus) are much less reliant on fur than the smaller species of seal.
Unless our ancestors were massive, it seems unlikely that they would have been losing their hair in order to survive better in the water.
Of course, that’s not to say that our ancestors avoided water – far from it. Marginal environments are rich sources of food and most terrestrial animals that live near water will exploit it in some way or another. I’m sure our ancestors would have done the same, I’m just unsure about how immersive and influential that exploitation was on our evolutionary trajectory.
So far I am unconvinced by the AAH and the more bad science and overstated arguments I see in support of it, the less convinced I become. Let’s see if any good supporting science with hard facts emerge from the conference in May.
Well, it seems that my earlier post on Darwin has ruffled some feathers in the Intelligent Design (ID) camp, so they’ve been trolling the comments section on my personal blog. This post started out as a response, but I decided to expand it to include some of the context surrounding Darwin’s work.
…One wonders why no one noticed “natural selection” before. And there were ingenous minds in the history! One answer might be this – it was never observed because it doesn’t exist. Darwin implanted this speculation there. And “On the origin of species” reads sometimes like comedy. One should try to count how many times Darwin used words like “which seems to me extremely perplexing” etc….
One reason why some scientific theories may have been slow to come to light
It’s interesting how ‘simple’ natural mechanisms and systems can take longer to be acknowledged than one might have thought. Heliocentrism is another example of something that now seems very obvious, but was historically slow to be recognised (and is still not recognised or not known about by some). It’s easy to blame organised religion for the suppression of such observational truths about the universe, since challenges to traditional belief were seen as heresy and dealt with accordingly, but there’s far more to it than that.
Let’s set the scene – Darwin’s formative years were tumultuous with regard to sociopolitical events. The Napoleonic wars drew to an end with the Battle of Waterloo when Darwin was six years old, the Peterloo Massacre occurred and the Six Acts were drawn up by the Tories to suppress radical reformers when he was ten – reflecting the ongoing social division between the establishment and the public. When Darwin was in his twenties the power of the strongly traditional British establishment finally began to wane, when the Whigs came to government allowing the 1832 Reform Act and the 1833 Slavery Abolition Act to be passed. There was also the devastating Great Famine in Ireland when Darwin was in his thirties and all of this was set against a background of the Industrial Revolution, which was providing the impetus for science to play an increasingly important role in society.
Peterloo Massacre
This meant that Darwin’s work was by no means formulated in intellectual isolation. Theories of evolution had been proposed 2,400 years previously, but they were poorly developed. Natural philosophers like Darwin’s own grandfather Erasmus and Jean-Baptiste Lamarck raised the issue of evolution at around the time of Darwin’s birth, but the mechanisms for evolution were either ignored or flawed. Evolution was an established topic of discussion and publication by the time Charles Darwin came onto the scene, with people like Robert Grant being more radical on the subject than Darwin found palatable in his early manhood. Despite this interest, the mechanism of evolution remained elusive – perhaps unsurprisingly, since the academic community addressing natural sciences was largely composed of members of the clergy and the natural theology of the time was seen as being mechanism enough.
But a literature base that was to inspire non-traditional hypotheses was also developing at the time – Vestiges of the Natural History of Creationin particular offered an alternative view that was seen as too radical by many – clearing a path for subsequent works that challenged orthodox views. Given this context, it is perhaps unsurprising that Darwin and Alfred Russell Wallace converged on the same premise at the same time. In short, the ideas evolved to fit the intellectual and social environment. The same has been true of other discoveries and inventions where there was a requirement for the right intellectual groundwork to be laid in advance. This groundwork is required before a robust theory can take root – and Natural Selection is a component of the robust theory of Descent with modification.
The Intelligent Design agenda
The critiques I have seen of evolutionary theory have come from people who quite clearly don’t understand it – and such critiques tend to rely on statements of incredulity rather than a strong factual base. No well-supported alternative hypotheses have been constructed or presented and a lack of understanding hardly counts as a robust refutation of a well supported theory.
An accusation by IDers is that ‘Darwinists’ (N.B. I don’t know anyone who would call themselves a Darwinists following the New Synthesis) stick with Natural Selection because they are atheist. I think I see the real agenda emerging here, particularly when you see evolution as a theory being conflated with just one of the mechanisms involved. After all, Natural Selection is not the only mechanism involved in evolutionary adaptation and speciation – there are also other factors like hybridisation, horizontal gene transfer, genetic drift, perhaps some epigenetic influences and artefacts of EvoDevo processes. But these factors are still constrained by the simple fact that if they are selected against, they will not be perpetuated.
Natural selection is a powerful force in nature. It has but one function which is to prevent change. That is why every chickadee looks like every other chickadee and sounds like every other chickadee – chickadee-dee- dee, chickadee-dee-dee. Sooner or later natural selection has always failed leading to the extinction of nearly all early forms of life. They were replaced by other more prefected forms over the millions of years that creative evolution ws in progress…
Salamander ring species
First and foremost, the suggestion that Natural Selection prevents change is erroneous – change will occur if there is a change in the environment and/or if beneficial mutations arise in a population (tell me that mutations don’t happen – I dare you…). The obvious response to the next statement is that I can think of six different ‘chickadee’ species, with an additional three subspecies (and this is ignoring numerous other very similar members of the Paridae), all are similar, but all are different – so the statement makes no sense as it stands. Getting to the meat of what is being implied about the Creationist interpretation of species, another bird provides a good example to the contrary. The Greenish Warbler shows a distinct pattern of hybridising subspecies across their vast range, until they form reproductively isolated species at the extreme ends of their range, where they happen to overlap yet not hybridise (a classic ring species [pdf of Greenish Warbler paper]). This is a well-known example of how genetic variation can accrue and give rise to new species without any supernatural intercession.
…But no wonder that Darwin considered “natural selection” for such a complicated force. Even nowadays Dawkins speculates that NS operates on genes, whereas E.O.Wilson has brushed up “group selection”recently (citing of course Darwin as debeatur est .
So may we “uncredulous” ask on which level “natural selection” operates?
As to this question about the level on which Natural Selection operates, I thought the answer was pretty obvious – it operates at every level. Change the focus of Natural Selection from passing on genes to the only alternative outcome – the inability to pass on genes. It doesn’t really matter which level this occurs at or why – be it a reduction in reproductive success when not in a group, or a deleterious single point mutation – if it happens then Natural Selection can be said to have occurred. Being ‘fit’ simply means that an organism has not been selected against.
There’s a lot more to modern evolutionary thought than Darwin’s key early contribution, but Darwin is still respected because he was the first to provide a viable mechanism by which evolution is driven. This mechanism has helped make sense of an awful lot of observations that were previously unaccounted for and, moreover, evolution has been observed and documented on numerous occasions [here’s a pdf summary of some good examples].
I fail to see why Intelligent Design has been taken seriously by some people – it relies on huge assumptions about supernatural interference (so it fails to be a science) and I have as yet never seen a single piece of evidence that actually supports ID claims. The only research I have seen mentioned by proponents of ID are old, cherry-picked studies that report a null result from an evolutionary study – this is not the same thing as support for ID, as anyone who can spot the logical fallacies of false dichotomy and Non sequitur (in particular the fallacy of denying a conjunct) will tell you.
Intelligent design as a scientific idea
I like to keep an open mind, but as soon as I see logical fallacies being wheeled out I lose interest in getting involved in the discussion. This may be a failing on my part, because I should probably challenge misinformation, but quite frankly I don’t have the time or the patience – much as I hate to stoop to an ad hominem, my feelings on this are best summed up by the paraphrase:
when you argue with the ID lot, the best outcome you can hope for is to win an argument with the ID lot
and my time is far too precious to waste arguing with people who ignore the arguments of others and construct Straw man arguments based on cherry-picked and deliberately misrepresented information. I have no problem with other people believing in a god, but please don’t try to bring any god into science (and heaven-forbid the classroom) – since it is neither necessary nor appropriate.
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Zygoma 