The Ancestor’s Tale
I’ve read approximately half the book by now (320 pages). As I pointed out in the last post, “It’s pop sci and I have been disappointed a few times by some of the remarks he’s made during the first 200 pages”. A few examples of ‘irritating/disappointing remarks’:
“In practice all intermediates between pure hunter-gatherers and pure agriculturalists or pastoralists are found. But, earlier than about 10,000 years ago, all human populations were hunter-gatherers.”
Naturally the last sentence is what I take issue with, not the first part. It’s not that it’s wrong as such, but it will likely give people who don’t know any better the wrong impression – you can’t really leave it at that, without qualifying the statement a bit. As I’ve pointed out before, the development of farming and husbandry took thousands of years and what we still think of mostly as ‘hunter-gatherers’ did a lot of the work that brought about the changes necessary for human groups to switch to something close to the model of farming we know today. Dawkins speaks out against the widespread tendency to adopt an essentialist mindset in the field of taxonomy later on (‘the tyranny of the discontinuous mind’), but by mentioning a cut-off point like this without any qualifiers he’s in my view close to engaging in exactly the same kind of behaviour as are the people he’s criticizing. 10,000 years ago is an arbitrary cut-off point, and the ‘hunter-gatherers’ living before then were some places well on their way to developing farming as we know it – the distinction between ‘farmers’ and ‘hunter-gatherers’ was a lot more fluid in the far past than it is now. How far into the past the process went and how gradual the process from hunter-gathering to farming was surprised me a great deal when I read THP, but unfortunately I don’t have the book at my place at this point (I’ve borrowed it to a friend) – so wikipedia will have to do for now:
“Archaeologists have conducted an exhaustive study of Hut 1 at Ohalo II; this hut yielded over 90,000 seeds. The seeds account for more than 100 species of wild barley and fruits. Such a high concentration of seeds in the hut makes it highly unlikely that they were accidentally deposited into the hut via natural forces such as wind. In addition, statistical analysis demonstrates that the concentration of plant matter was significantly higher around the walls than the center. Had the seeds been deposited by the collapsed roof, they would have evenly scattered on the ground. Furthermore, just 13 species of fruit and cereal make up about half of the total number of seeds found in the area; these include brome grains (Bromus pseudobrachystachys), wild barley (Hordeum spontaneum) and millet grass grains (Piptatherum holciforme), just to name a few. This suggests a marked preference of certain species of edible plants. A seed of particular interest comes from the Rubus fruit, which was fragile, difficult to transport, and preferably eaten immediately after collection. The presence of Rubus seeds at the Ohalo II site could indicate that the seeds were dried in the sun or by the fire for storage: early evidence for advanced planning of plant food consumption. Most importantly, the extremely high concentration of seeds clustering around the grinding stone in the northern wall of Hut 1 led Ehud Weiss, an archeologist, to believe that humans at Ohalo II processed the grain before consumption. The exact spatial distribution of the seed around a grinding stone further indicates extensive preparation.”
This settlement burned to the ground around 19,400 BP. They may not have been ‘farmers’, but people who don’t know about people like these may get the wrong idea when reading Dawkins’ statement quoted above. Later on he mentions that, “Husbandry was not the overnight brainwave of some genius” and talks about the gradual changes required to get from where we were to where we ended up, both when it comes to husbandry and agriculture; but the unqualified 10.000 year mark is still bugging me a bit, and it’d not be hard to read the book and assume that the gradual changes mentioned later on took place only after 10.000 BP.
Here’s another annoying little quote: “It [Madagascar] is a natural botanical and zoological garden, which houses about five per cent of all the plant and animal land species in the world, more than 80 per cent of them being found nowhere else.” […] [two pages later:] “If you wiped out Madagascar, you would destroy about a thousandth of the world’s total land area, but fully four per cent of all species of animals and plants.” So which is it – four or five per cent? An editor ought to have caught that one and asked him to clarify or change one of the sentences. The repetition also really isn’t necessary. I’d expect stuff like that in a blog post, not in a published book. [see info’s comment…] Yet another:
[footnote:] “Carrots are rich in beta-carotene from which vitamin A can be made: hence the rumour – rumours can be true – that carrots improve vision.”
Yeah, well, if you’re going to include a sentence like that you’re gonna have to write a little more than that. Many people today are presumably aware of how the rumour in question came about but it’s likely that far fewer readers are aware of just how severe of a problem vitamin A deficiency still is in many developing countries (“Most common cause of blindness in developing countries […] Approximately 250,000 to 500,000 malnourished children in the developing world go blind each year from a deficiency of vitamin A, approximately half of whom die within a year of becoming blind.”).
I should point out that he talks about different speciation methods/mechanisms throughout the pages, but he doesn’t mention what they are called (see this for an overview) and his coverage is non-systematic and spread out over many pages. This is understandable given that it’s a pop sci book, but stuff like this is part of the reason why I rarely read such books.
Okay, enough with the critical remarks (I could easily include a few more but it’s not worth it) – there’s lots of really good stuff in there as well. I’ll just post a few quotes below with some ‘big picture’ stuff, but do note that most of the book is concerned with the details of how all this stuff happened – it’s a big narrative, going back hundreds of millions of years, a narrative about where we came from; and given that you need to spend some time talking about what the species which came before us were actually like. Did they have the same number of limbs as we do? How big were they? What did they eat? How did they get from A to B? Who else were around back then? And so on… Anyway, big picture stuff and some other interesting stuff from the book which I couldn’t help including below:
“Biological evolution has no priviliged line of descent and no designated end. Evolution has reached many millions of interim ends (the number of surviving species at the time of observation), and there is no reason other than vanity – human vanity, as it happens, since we are doing the talking – to designate any one as more privileged or climactic than any other. […] A living creature is always in the business of surviving in its own environment. It is never unfinished – or, in another sense, it is always unfinished. So, presumably, are we.”
“for particular genes, you are more closely related to some chimpanzees than to some humans. And I am closer related to some chimpanzees than to you (or to ‘your’ chimpanzees). Humans as a species, as well as humans as individuals, are temporary vessels containing a mix of genes from different sources. Individuals are temporary meeting points on the crisscrossing routes that genes take through history. […]
We normally assume that we can draw a single evolutionary tree for a set of species. But […] different parts of DNA (and thus different parts of an organism) can have different trees. I think this poses an inherent problem with the very idea of species trees. Species are composites of DNA from many different sources. […] each gene, in fact each DNA letter, takes its own path through history. Each piece of DNA, and each aspect of an organism, can have a different evolutionary tree. […] Species trees can be drawn, but they must be considered a simplified summary of a multitude of gene trees.”
“Rodents are one of the great success stories of mammaldom. More than 40 per cent of all mammal species are rodents, and there are said to be more individual rodents in the world than all other mammals combined.”
“Selection drives evolution only to the extent that the alternative types owe their differences to genes: if the differences are not inherited, differential survival has no impact on future generations.”
“Carnivora is an irritating name because, after all, it simply means meat-eater, and meat-eating has been invented literally hundreds of times independently in the animal kingdom. Not all carnivores are Carnivora […] and not all Carnivora are carnivores (think of the gentle giant panda, eating almost nothing but bamboo).”
“Geological time is large not only in comparison to the familiar timescales of human life and human history. It is large on the timescale of evolution itself. This would surprise those, from Darwin’s critics on, who have complained of insufficient time for natural selection to wreak the changes the theory requires of it. We now realise that the problem is, if anything, opposite. There has been too much time! If we measure evolutionary rates over a short time, and then extrapolate, say, to a million years, the potential amount of evolutionary change turns out to be hugely greater than the actual amount. […] Darwinian selection, if we impose it artificially as hard as we’re able, can drive evolutionary change at a rate far faster than we ever see in nature. […]
One million years, which is too short to notice in most parts of the fossil record, is 20,000 times as long as it takes to triple the oil content of maize seeds. […] these experiments serve to warn against looking at apparent trends spread over millions of fossil years, and naively interpreting them as responses to steadily sustained selection pressures.
Darwinian selection pressures are out there, for sure. And they are immensely important […] But selection pressures are not sustained and uniform over the sort of timescales that can normally be resolved by fossils, especially in older parts of the fossil record. The lesson of the maize and the fruit flies is that Darwinian selection could meander hither and yon, back and forth, ten thousand times, all within the shortest time we can measure in the record of the rocks. My bet is that this happens.
Yet there are major trends over long timescales, and we have to be aware of them too. To repeat an analogy I have used before, think of a cork, bobbing about off the Atlantic coast of America. The Gulf Stream imposes an overall eastward drift in the average position of the cork, which will eventually be washed up on some European shore. But if you measure its direction of movement during any one minute, buffeted by waves and eddies and whirlpools, it will seem to move west as often as east. You won’t notice any eastward bias unless you sample its position over much longer periods. Yet the eastward bias is real, it is there, and it too deserves an explanation.”
“Why bother to lose the wings? They took a long time to evolve, why not hang on to them in case one day they might come in useful again? Alas (for the dodo) that is not the way evolution thinks. Evolution doesn’t think at all, and certainly not ahead. […] Evolution, or its driving engine natural selection, has no foresight. In every generation within every species, the individuals best equipped to survive and reproduce contribute more than their fair share of genes to the next generation. The consequence, blind as it is, is the nearest approach to foresight that nature permits. Wings might be useful a million years hence when sailors arrive with clubs. But wings will not help a bird contribute offspring and genes to the next generation […in the specific setting in which the ancestors of the dodos found themselves, US. It seems obvious that in the general case wings do help birds get more offspring or they wouldn’t bother with them…], in the immediate here and now. On the contrary wings, and especially the massive breast muscles needed to power them, are an expensive luxury. Shrink them, and the ressources saved can now be spent on something more immediately useful such as eggs: immediately useful for surviving and reproducing the very genes that programmed the shrinkage.
That’s the kind of thing natural selection does all the time. It is always tinkering: here shrinking a bit, there expanding a bit, constantly adjusting, putting on and taking off, optimising immediate reproductive success. Survival in future centuries doesn’t enter into the calculation, for the good reason that it isn’t really a calculation at all. It all happens automatically, as some genes survive in the gene pool and others don’t. […]
Moas are extreme among flightless birds in that they have no trace of wings at all, not even buried vestiges of wing bones. They thrived in both the North and South Islands of New Zealand until the recent invasion by the Maori people, about 1250 AD. They were easy prey […] and the Maoris slaughtered them all, eating the choicer parts and discarding the rest, belying, not for the first time, the wishful myth of the noble savage living in respectful harmony with its environment. […] Perhaps as many as 200 species [of flightless rail] have gone extinct on tropical Pacific islands since human contact.” […other estimates are even higher]