Kissing cousins
Two recent reviews refer to what is becoming received wisdom 鈥� the genetic closeness of humans to chimpanzees. The first talks about the “minute genetic difference between us and pygmy chimpanzees” (“Chimps like us”, Review, 18 November), while the second says “We share more than 98 per cent of our genes with chimpanzees” (“The wonder of it all”, Review, 18 November). Similar statements are also used by those in animal liberation groups to justify the laudable aim of halting experiments on chimpanzees. However, such statements suffer from a number of numerical misapprehensions.
First, the scale on which these statements are based does not have its origin at zero. Could there exist a living object with, say, 1 per cent of its genetic material in common with humans? Given that all life as we know it is based on exactly the same DNA processes involving the same bases, it is more likely that there is a very large set of common features across both plants and animals without which life does not exist in any form. It would be an interesting exercise to estimate this minimum set. On this scale, I’d be just as impressed to find that I shared 10 per cent of my genetic material with a tomato.
Secondly, the unfolding and expression of a strand of DNA is explicitly a feedback process and as such is highly nonlinear. Even in the simplest nonlinear system, tiny changes in initial conditions or in system parameters can lead to widely different outcomes. A minor defect in a DNA strand can lead to nonviable offspring. Here we might be talking of an error of 0.0001 per cent (this is just a guess and, given the length of time it is reputed to need to map the whole human genome, a very conservative guess). For this case the appropriate comparison is that the difference between a human and a chimpanzee is 2500 times as large as that between a human and a nonviable human 鈥� a very different comparison.
Thirdly, humans carry many genes which are recessive, once again indicating the nonlinearity of the measurement scale.
Fourthly, genes make up only 3 per cent of DNA in humans, the remaining 97 per cent appears to have nothing to do with making protein. Is it 98 per cent of this 3 per cent that we are talking about as being in common?
Finally, the whole issue is an anthropocentric exercise. Using linear scaling, if we were to view humans as more complex chimpanzees, we might be able to estimate that chimpanzees share 99.6 per cent of their genetic material with humans, humans simply having additional material. Would we be any the wiser?
Altruistic genes
May I recommend Richard Dawkins’s book The Selfish Gene to Jeremy Burgess (Forum, 25 November). The mistake made by Burgess, and many others before him, is in thinking that “the individual is the unit of natural selection”. As Dawkins clearly and entertainingly explains, the unit of natural selection is the gene, not the chromosome, cell, organism or species.
The altrustic sacrifice therefore is performed by the genes which are lost when an Anabaena azollae bacterium changes into a heterocyst and starts converting nitrogen into ammonia. In performing this apparently altruistic sacrifice, the genes ensure the continuation of more of their own kind by helping the survival and reproduction of the Azolla fern and the Anabaena bacterium.
Melting zone
The article on the effects of global warming on Greenland raises the important question of how the polar ice sheets will react to a warmer climate (Science, 11 November). However, the issues are not as clear cut as John Gribbin suggests.
Around the margins of the Greenland ice sheet is the ablation zone where the ice melts during the summer months, contributing to a loss of mass and a rise in sea level. As temperatures rise, the area of this zone increases and more ice melts. The question is whether the increased precipitation of a warmer climate outweighs the increased melting.
Models of how the surface balance of the ice sheet will respond to global warming indicate that the net effect is a mass loss. In fact one model predicts that as much as half the ice sheet could disappear within 500 years. This would raise global mean sea level by 3 metres.
In Antarctica, however, mean annual air temperatures are typically significantly below 0 掳C, except for the northern part of the peninsula, which means there is no ablation zone and temperatures would have to increase by more than 10 掳C to produce one. Consequently in the short term, global warming would produce greater precipitation without an increase in mass loss due to melting. Therefore, the Antarctic ice sheet would reduce mean sea level, in the short term.
Philosophical hiss
The evolution of the venom-injecting mechanism in vipers cannot be compared to the chance meeting of several miners in the middle of a mountain through which they have dug tunnels (Forum, 11 November).
Venomous snakes exist with various gradations of the venom delivery system, some without any obvious anatomical differentiation from non-venomous species (all snakes have movable upper jaws that enable them to swallow large prey). The venom can be effective without the special adaptations in the fang mechanism found in vipers. But all snakes that have some of their teeth enlarged 鈥� whether in the front or the back of the upper jaw and whether additionally grooved or with an injection canal 鈥� are, to some degree, venomous for their prey.
It follows that the secretion of venom must have evolved first and that the evolution of a perfectible venom apparatus depended on venom being there. The allegorical miners meeting in the core of Mount Everest were not tunnelling independently, as E. Ram贸n Moliner assumes.
Moliner could have made his point by using the vertebrate eye as his example for supporting teleology or creationism, but then he would have found that his line of reasoning had been refuted innumerable times by evolutionists. In that case photoreceptors can be assumed to have evolved first (like the venom) and the complex camera-type eye could then have evolved in stages as can be seen among vertebrates and invertebrates living today. If no one knew the intermediate state the case for teleology and creationism would be stronger 鈥� as in “find the missing link”.
Revisiting repeats
In “Hard maths? No problem” (28 October), Robert Matthews cites a claim that our results are valid only for algorithms that never sample the same point in the search space twice. This claimed limitation is, putting it generously, based on a cursory understanding of those results.
Our results simply choose to have the comparisons between any search algorithms based on the number of distinct points from the search space that they visit. The algorithms themselves can revisit points as often as they like.
If instead (to give an example) one were to compare algorithms based on the total number of points visited, distinct or otherwise, then there would be trivial, and silly, distinctions between algorithms. (For example, on average any non-repeating algorithm will have found a better solution to a particular search problem than will a repeating algorithm.) To uncover the truly important issues, any formalism should eliminate such effects, which is precisely what our way of comparing algorithms does.
We discuss this issue of allowing repeats and how it affects our results extensively in our paper. We hope readers will decide for themselves whether this issue is a problem. Our paper can be found at .
Lisbon waves
The broad expanses of the Pacific are undoubtedly the chief foci for the generation of tsunami, but tsunami of a far from derisory magnitude have made their appearance elsewhere (“On watch for the killer wave” 25 November)
The tsunamis and seiches generated by the Lisbon earthquake of 1 November 1755 made a tremendous impact upon history. That earthquake consisted of three big shocks spaced over 40 minutes. According to the Reverend Thomas Milner, in the 24 hours after the earthquake there were 17 tides at Tangier on the north African coastline 鈥� an average of one every one and a quarter hours.
At Cadiz, the tsunami reached a height of 18 metres and after crossing tbe Atlantic it was 6.5 metres in height at Suba in the Dutch West Indies. If seismographs had been available they would have had a lot to tell us, but they were not introduced until about 100 years after the Lisbon earthquake.
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Peregrine guilt
The suggestion that many pigeons are found dead in their crates is far-fetched in the report on the Dutch study on racing pigeon mortality (This Week, 18 November).
Racing pigeons are transported in specially constructed vehicles and their built-in ventilation systems are more than adequate to ensure that the birds arrive in the best possible condition for racing. They are given water at preset intervals en route (in accordance with the latest Welfare of Animals legislation); on arrival, and until they are released, they can drink freely. The number of birds in each crate is dictated by recommended area per pigeon, depending on the time the birds have to spend in the crates. Interestingly, pigeons do not drink in the dark 鈥� for anything up to 14 hours 鈥� irrespective of the temperature.
Racing pigeons are valuable; rearing and training them is time consuming and labour intensive and owners accept only the highest standards of transportation to ensure the best possible treatment for their costly and carefully reared and trained birds.
Regarding the peregrine population, the remark by Chris Harbard of the Royal Society for the Protection of Birds that “most live in northern Scotland and other places far from races” is patent nonsense. There are large numbers of peregrines in Devon and Cornwall, North and South Wales, Cumbria and many other places 鈥� a recent study has shown that where they are available a peregrine eats an average of 0.8 pigeons per day. Even if there are only 1300 pairs of peregrines, as is often claimed, this amounts to about three-quarters of a million pigeons a year. And then there are sparrowhawks, even worse predators so far as the racing pigeon is concerned, and there are over 60 000 of them.
The reference to the Barcelona International race was incorrect 鈥� this year’s race attracted 20 936 pigeons. Debora MacKenzie’s figures of 774 entries and 250 making it back to their home lofts presumably refer to a single club or to another race.
It is also important to remember that pigeon fanciers want their birds to return (that is the whole point of the sport) and it is in everyone’s interests to ensure that transport is as quick and as comfortable as possible.
Frequently reported attacks by birds of prey on pigeon lofts indicate the growing pressure on food resources within the peregrine and sparrowhawk populations. Currently, it is illegal even to scare off a peregrine that is eating one of your pigeons on your lawn.
Chris Harbard of the RSPB is quite right to say that racing pigeons form a small part of the peregrines’ diet. But peregrines kill millions of small birds and the decline in numbers of corn buntings and song thrushes, for example, is mirrored by the increase in the raptor population. And as the small birds become rarer, more and more pigeons are being eaten by peregrines.
The routes taken by racing pigeons frequently cross the territories of high peregrine population. While only one or two of each racing flock may be taken by predators, the rest of the flock may panic and not make it home.
Conservation has rightly helped re-establish the peregrine in Britain, but it would be folly to protect the peregrine at the expense of our rare and rapidly declining small bird population. I would rather hear a skylark sing than see it being ripped apart by a peregrine.
It is disturbing that the Department of the Environment should consider removing legal protection for peregrines and sparrowhawks, despite the lack of evidence showing significant predation on racing pigeons. Any weakening of the legislation could set a dangerous precedence for other raptors, such as the already illegally persecuted hen harrier.
The population levels of many British raptors are low and are still recovering from previous widespread human persecution. By the beginning of this century, several species such as the osprey and goshawk had been lost as breeding birds. Such a shameful situation must never be allowed to return by the “back door”.