First molecular biologist: What’s the difference between a Creationist and a Crustacean?
Second molecular biologist: I don’t know – what is the difference between a Creationist and a Crustacean?
First molecular biologist: Well, it seems you’re in the wrong job, then.
This joke derives pretty closely from a sentence in a thought-provoking 2009 paper, What is the viewpoint of haemoglobin and does it matter by Jonathan Marks, a geneticist and biological anthropologist. His actual words are:
In other words, if you cannot tell a human from a gorilla, you really should not be in biology.
He was commenting on some 1963 research which had suggested that, since there are less than a handful of base differences between human and gorilla haemoglobin, humans must be essentially a sub-variety of gorilla, or vice versa. In reply the celebrated George Gaylord Simpson wrote:
From any point of view other than that properly specified, that is of course nonsense. What the comparison really seems to indicate is that … haemoglobin is a bad choice and has nothing to tell us about affinities, or indeed tells us a lie.
Jonathan Marks adds to this comment:
Does it not stand to reason that if you essentially cannot tell human haemoglobin from gorilla haemoglobin, the sensible thing to do is look at something else? In other words, if you cannot tell a human from a gorilla, you really should not be in biology.
His larger aim in the paper is to point to the more recent equally, and comparably, fallacious conclusion that because human DNA is 98.5% the same as chimp DNA, it means that humans are “really” almost the same as chimps… from which follows, amongst other things, the move to accord human rights to chimps (when, as Marks acidly observes, they haven’t yet been applied to many humans). He states what ought to be obvious:
It is not that difficult to tell a human from an ape, after all. The human is the one walking, talking, sweating, praying, building, reading, trading, crying, dancing, writing, cooking, joking, working, decorating, shaving, driving a car, or playing football. Quite literally, from the top of our head (where the hair is continually growing, unlike gorillas) to the tips of our toes (the stoutest of which is non-opposable), one can tell the human part from the ape part quite readily if one knows what to look for. Our eye-whites, small canine teeth, evaporative heat loss, short arms and long legs, breasts, knees, and of course, our cognitive communication abilities and the productive anatomies of our tongue and throat are all dead giveaways. However, they are not readily apparent in a genetic comparison.
In other words, predicating chimp and human similarity on the apparent similarity of their genomes is like finding rather similar-looking Japanese manuals with your new car and your new camera and assuming that a car must be much the same thing as a camera. It’s a sign that you are losing hold on reality.
As well as describing how it’s easy to be obsessed with genes to the point of missing the “bleedin’ obvious”, Marks writes seriously about how today’s commonest taxonomic tool – cladistics – similarly diverts our attention in its very basis by dealing entirely with similarities, when the main interest of evolutionary theory ought to be differences, and how to account for them. It seems to me that poses questions that are deeper than they first appear.
The general idea that classification systems, which are necessarily based on similarities, tend to hide the need to explain difference, is not restricted to the assumption that if chimp genes and human genes are similar, the species are similar, or that if two taxa are close on a cladogram, we can ignore their divergences. One thing (almost the only thing) I found helpful in the postmodernist Michel Foucault’s book The Order of Things) was his discussion of the Linnean classification system and its various precursors and alternatives. This too highlighted the fact that how we classify things depends entirely on what similarities we choose to make significant in our worldviews.
In a different way of seeing the world, for example, the similarities caused by convergence could be considered more noteworthy than those of descent. A dolphin would be closer to an ichthyosaur than to an artiodactyl. After all, when you’re hiring staff you compare their qualifications, not their parents’ professions or genomes.
But once we turn the coin over and ask, “How do I account for the differences between chimps and man, as opposed to their similarities?” the first step, surely, must be to decide just how different they are: what it is that needs to be explained. In order to ask, “How did chimps become humans?” (or “How did they diverge from a common ancestor?”), you have to ask first “What is a chimp, and what is a human, so that we know what differences need explaining?” The answer has to be, “Everything that isn’t included in the cladogram as a shared character.” The classification is therefore of minimal help for the task.
We need to measure difference, then, not similarity, in some way that is more direct and complete than comparing their haemoglobin or even their genome as proxies. It’s a vital scientific task because, after all, demonstrating common ancestry has little real purpose beyond refuting Special Creationism, whereas evolutionary theory is supposed to explain the origin of the different species.
As I think about this, I begin to sense that “difference” may be rather an intractable scientific problem. At the instinctive level, it’s easy, as Marks’s list of obvious human characters shows. But his list is not in the least exhaustive – and perhaps some of the differences he lists are are not essential. Should the list of differences also include playing music? If so, how is music defined, as opposed to a chimp, perhaps, taking pleasure in the noise of smashing stones together? Is preferring Country and Western to Bach a significant difference, or not?
There is simply no way one can do the job of objectively and scientifically quantifying all the differences even between two closely-related taxa. There is no way of presenting the results in a robust mathematical way that would, for example, tell you that there is 30% more similarity between man and chimp than between chimp and gorilla. There is no way to decide, apart from some entirely subjective and arbitrary list of attributes with scales of magnitude, that since the two species separated, 5X10^4 Tb, rather than 4 tonnes, of differences have resulted, and that is what needs to be accounted for – there isn’t even an SI unit for “difference”.
And yet there can be absolutely no doubt that the differences are objective, unchanging and actually very easy to detect and describe individually. How can it possibly be that one of the most fundamental categories in science – difference – cannot be reduced accurately to scientific expression? What’s wrong with the world?
Now, in the disputes about intelligent design, one of the major critiques is that whilst those like Bill Dembski have developed statistical models to distinguish design from pure chance, these are scientifically useless because necessary categories like “functional information” fight shy of scientifically robust definitions. Instinctively it may seem obvious that organisms as a whole, or the constituent systems thereof, are purposefully designed, but since that design cannot be objectively quantified, design cannot be said to be a scientific category.
But do you see that this is exactly the same situation that exists with the fundamental concept of “difference” between species? There are profound differences between species, as any fule gno. But if those differences cannot be quantified, apart from flawed and incomplete models like genetic comparisons, how can it be considered to be a real constituent of science?
If design must be excluded from science because it cannot be quantified or even exhaustively defined, then so must biological difference, for the same reason. Do we really want to go there? If that logic is valid, then maybe we have to live with giving chimps the vote, and accept madness as the price of scientific progress.