Extracts from the collection of essays Kutistuva turska ja muita evoluution ihmeitä (‘The shrinking cod and other evolutionary marvels’) by Hanna Kokko & Katja Bargum
Who cannot but stand in awe of the genius of various parasites’ nervous system manipulations or of how beautifully the orchid ensures its pollination? The astonishingly precise adaptations of organisms are the starting point for the idea of Intelligent Design. According to Intelligent Design, such adaptations are too perfect to be products of evolution – rather, they reveal the actions of an intelligent designer. It’s a fascinating idea, write Hanna Kokko and Katja Bargum – but is it science?
At first glance, the Intelligent Design movement, which began in America, seems quite satisfying with all of its pseudo-scientific genetic studies. However, the movement does not follow the rules of science. To wit, the Intelligent Design doctrine does not present a logical construct into which new puzzle pieces might fit, nor does it offer any predictions. Instead, the supporters of intelligent design deceive their listeners by presenting distorted rules for the contestation of ideas: the work in evolutionary biology that has not yet been done is counted as a victory for their side by saying ‘they haven’t been able to explain that either’.
In order to shed light on this argument, it helps to survey a few imprecise or poor adaptations. These adaptations do not fit well with the idea of intelligent design, and, additionally, they put in stark relief the capricious course of evolution. The short-sightedness of natural selection prevents evolution from achieving perfection. Thus, we relate in the following why, for example, wisdom teeth torment so many of us, how we can explain the disarray of men’s sexual organs and how sex can kill.
The first reason for the imperfection of all organisms is the harsh truth that you can’t have everything. In order to examine this truth, we journey to the South Pole.
Hardly any process for creating new life feels to the bystander quite as agonizing as the reproduction of Emperor Penguins (Aptenodytes forsteri). They incubate one single egg during the southern continent’s winter, when the temperature drops to sixty degrees below zero and the wind blows at 45 metres per second. The poor penguins shiver for months on end in this ice storm – and why? For one single chick. Couldn’t evolution come up with a more efficient means for producing new penguins?
In order to put a finer point on this question, English biologist Richard Law created the concept of ‘Darwin’s Demons’ to describe an imaginary organism that would reproduce immediately after its own birth, produce innumerable offspring every second and live forever. A demon like this would spread with the speed of lightning, filling every last nook and cranny of the Earth. All other organisms would be forced to give way. The diversity of nature would be replaced by one single demon species, the biomass of which would extend second by second farther into outer space. Luckily, we don’t see these sorts of monsters in nature. Why?
Darwin’s Demons illustrate clearly that no organism can be perfect in every trait. No organism has limitless energy resources at its disposal. Thus, natural selection is forced to choose between individuals that make their energy investments in slightly different ways. Investing in a certain trait must always be done at the expense of some other trait. Natural selection has shaped penguins into beings that have chosen quality over quantity. They brave cold and hunger for their singletons. As a counterbalance, the penguins do not burn themselves out trying to feed large broods.
Thanks to their slow-paced, if freezing cold, method of reproduction, penguins can live for more than ten years, repeating their reproductive slog numerous times. Similar choices about resource allocation can be seen in many organisms. By adjusting egg size and nutrient content, the female owl may ‘decide’ to have two large or three smaller chicks. Young fish, on the other hand, must consider whether it is most advantageous to reproduce right now or to increase their size for a few years and then reproduce more efficiently. This ‘consideration’ is of course not conscious, but rather the best solutions are sought in a comparison between faster and slower individuals. But whatever the solution, you can’t have it all.
The discomforts of old age
Organisms also display imperfect traits because natural selection just can’t get at them. For example, many diseases that strike at advanced ages, such as Alzheimer’s and Parkinson’s Disease, are mostly outside the circle of influence of natural selection. How can this be possible?
Natural selection works by weeding out individuals before reproduction. This should prevent the passing on of poorly functioning genes to the following generation. So why are there still diseases?
Doesn’t natural selection work? Yes, it does, but in the case of the discomforts of old age, much more weakly than at other times. That is, these diseases flare up after the individual has already reproduced at least a few times. Selection has not yet had a chance to ‘see’ the weak traits of the genes being passed on to the offspring. And since variation always increases from time to time, the nuisances of old age remain in the population much more readily than weaknesses that are apparent from youth.
The distribution of energy resources to the different stages of life, just as the diseases of old age, are cases in which evolution simply is unable to make all traits perfect. The slow pace of evolution may also be a reason for the imperfection of organisms.
Less wise teeth
The existence of wisdom teeth is a mystery to all of us who suffer from the problems they cause. For some, wisdom teeth erupt into a space too small, and for others they are upside down in the mouth. Wisdom teeth must often be removed in a painful operation. For some lucky souls they never appear at all. What explains the existence of these pesky teeth?
The knowledge that wisdom teeth were once useful is probably not of any comfort to the patient languishing in the dentist’s chair. In apes, the wisdom teeth line up nicely in a row with the other molars, and they are used in the same way for mastication. That is, in our animal cousins all of the teeth fit in the mouth, but in humans, the expansion of the skull as the brain grew resulted in a smaller jaw size. Nowadays it’s a tight squeeze for wisdom teeth to grow in properly. In addition, the change in our diet from raw ingredients to cooked, soft meals has reduced the work load of the molars, and wisdom teeth aren’t much needed for food processing. It may be that wisdom teeth are slowly evolving out of use.
Wisdom teeth may be selected against for two reasons. Because they are not used, at the moment their development consumes energy needlessly. However, the total expenditure of energy for forming a small piece of bone does not perhaps seem terribly large. The more important factor may be the fact that wisdom teeth can cause considerable harm. We all remember how dangerous infectious diseases were just a few decades ago before the invention of antibiotics. Just a hundred years ago teeth were one of the greatest health problems in what are now the western nations.
Hey, let’s make bones…or not…
Wisdom teeth are only one example of the remnants of evolutionary history. In fact, the human body is full to overflowing with similar vestiges, which give us clues about our progenitors’ way of life. Many of these vestigial remnants have withered away, becoming smaller as they became unnecessary. The caecum and appendix are vestiges of this kind. In many animals the caecum is an important organ in the digestion of plant-derived nutrients. In rabbits, the caecum makes up as much as half of the whole intestine. However, in humans, the caecum has shrunk subsequent to our move to a more meat-rich diet.
Bones can also lose their purpose and atrophy. Many of us only notice our tail bone once it gets broken in a fall.
Evolution never starts from a blank slate, rather fumbling around with existing DNA instructions. So what do you do if you have to create a legless animal based on a currently legged being? This is achieved much more easily by giving a sort of halt command (‘…not!’) the development of the individual than by purging all of the original instructions for creating legs from the genotype.
Whales are not fish but mammals. That is, both whales and humans have a family tree that stretches far back through the reptiles all the way to fish. These sorts of familial relationships demonstrate that a certain line of four-legged land mammals returned to even more watery digs and finally set out to sea entirely. In fact, whale embryos are four-legged just like human embryos, and only later in the development of the individual do the rear legs receive the instruction to atrophy. If something goes wrong with this instruction, the old four-legged traits can sometimes pop up again. Accordingly, a dolphin was recently discovered in Japan that in addition to pectoral fins had ‘hind leg fins’, the specimen also being astonishingly reminiscent of 40-million year old dolphin fossils. In 1919, a humpback whale was caught near Vancouver that had metre-long hind legs with bones and all.
Stories of baby chicks with teeth have circulated in scientific circles for years, but it was not until 2006 that the mutation was photographed, a change that really does give the beak of the chick developing in the egg very crocodile-like teeth – clear greetings from bygone days, that is. In addition to genetic-level information that demonstrates the ‘recycling’ of the same genes from one animal group to another, vestigial remains like this tell amazingly interesting stories about the evolutionary descent of organisms.
Prisoners of their own history
The evolutionary history of organisms can also create roadblocks to future development. A characteristic trait of insects and other arthropods is a hard shell that acts as an external skeleton. The shell helps arthropods withstand the aridness of deserts and protects against predators and parasites, but it also creates limitations. Like a growing baby that to her parents’ despair only fits in a given outfit for a month, arthropods are forced to shed their shells as they grow. This growth can be even more costly than buying children’s clothing, because the arthropod produces the new shell using its own energy reserves. The size of arthropods is also limited by the weight of the shell, which in a sizeable creature becomes disproportionately large. Because of the limitations created by their shells, one rarely finds arthropods of any kind weighing more than ten kilos.
The shell also creates metabolic challenges. The oxygen necessary for the respiration of insects living on land passes into the insect through small holes in the shell. This is not a terribly efficient way to breathe, and it makes insect movement quite difficult. This is particularly true of flying, which is difficult work and requires a lot of oxygen. Keeping large insects in the air is extremely difficult, and with the current oxygen content of the atmosphere, flying insects will never turn into the monsters of horror films. (In order to comfort the children, let it be said that about 360 million years ago there were dragon flies on parade with wing spans of nearly a metre. This was possible because the oxygen content of the air was much higher than it is now.)
As strange as it might sound, it is true that in finding a new structure (like the arthropod exoskeleton), natural selection also limits future evolution – not everything is possible any more. Although evolution can both build and disassemble different mechanisms, it very often goes in one direction: when a certain path has been trod for long enough, it is difficult to turn far enough back that another direction entirely can be chosen.
The monstrous myopia of natural selection
The unidirectional – or misdirected – nature of evolution’s path is also demonstrated by the laughably long vasa deferentia of warm-blooded animals. In cold-blooded animals the testicles are located within the body cavity, in the same place as the ovaries of females. The vas deferens takes a direct path from the testicles to the penis, passing by the bladder on the way. As warm-bloodedness developed, a new place had to be found for the testicles, because the production of spermatozoa works better at lower temperatures. Therefore natural selection promoted the migration of the testicles outside the body cavity, into the scrotum. This migration can still be seen in the foetal stage of humans, and the dropping of the testicles is examined throughout the live of the child, to the horror of every schoolboy.
The bladder is also located in the same area of the body as the testicles, which along with the urinary tracts, can be passed on two sides. The selection of which side is of little consequence in four-legged animals, but as the preference tended towards standing upright in the evolution of humans, the testicles ended up hanging from a sort of loop – a bit like a dog on a leash can go around a lamp post on the wrong side. For example, at this moment the vas deferens in humans is at least three times longer than it would be if it went straight from the scrotum to the penis without circling around the urinary tract ten centimetres above.
Why hasn’t evolution corrected its mistake? In the case of the dog, the dog, or more likely the owner, can step back and untangle the leash by going around the pole on the correct side. In the case of evolution, fixing the mix-up would require temporarily raising the testicles back into the noisome heat of the body cavity (or returning humans to four legs). In addition, during the gradual migration of the testicles, the ducts lengthened only a little bit from one generation to another, so it did not represent any significant cost compared to the previous state. But the final cost grew step by step, and now humans are forced to produce three times more ducts than would be necessary otherwise. Nowadays the only possibility for shortening the ducts would be a large, sudden mutation that would produce a direct connection between the testicles and the penis. Giant leaps like this are unlikely.
This loop in the vas deferens demonstrates the difference between evolution and far-sighted design. While a designer is able to sketch his desired final result and build a trait accordingly, natural selection acts much more blindly. From the current working solutions it selects a few to continue on, and this then limits the basic solutions of future generations. This being the case, in situations of selection the traits that are most immediately beneficial win, even though they might not be the best solutions in the long run once all is said and done.
The length of the vasa deferentia might seem like a trifling inconvenience. But sometimes the short-sightedness of evolution has catastrophic consequences over the long run. For example, competition over mating can lead to a true war between the sexes. The male viviparous, or ‘common’, lizard ensures the success of mating in a rather extreme manner: he holds onto the female by biting her on the neck. These bites often leave visible scars. In populations with a lot of males, the females have more scars. That is, the more males there are, the more the females get slapped around.
How serious a problem is the harassment the females experience then? In order to figure this out, researchers compared the fertility and mortality of females in captive populations that contained different numbers of females and males. In populations where there were many males relative to the number of females, the females had fewer progeny and died younger. For this reason, in male-dominant populations the number of lizards decreased with time, while female-dominant populations grew at a healthy clip. Most disturbingly, in male populations it was precisely the males that lived while the females died, and thus the proportion of males in the population continued to increase. This meant even greater abuse and shorter life spans for the females. The spiral was complete.
Male-dominant population are thus in a vicious circle where the abuse of the males causes a diminution of the population, and, for good measure, more abuse. The vicious circle can quickly lead to the destruction of the entire population. Thus, the males are driving themselves to evolutionary suicide.
So why don’t male lizards behave themselves better? The reason is, once again, the short-sightedness of natural selection. Because the most aggressive male mates the most and has the most progeny, natural selection promotes abuse, and evolution careens blindly towards extinction. Researchers calculate that a lizard population that slips into male dominance would become extinct within about 40 years. There might not even be lizards in the world if there were not temporal and locational variation in nature in the relative proportions of males and females, and, thus, there were not always a sufficient supply of progeny from female-dominant localities to make up for extinctions elsewhere. Common lizard populations observed in nature are generally female-dominant.
Painful wisdom teeth, excessively long deferent ducts and males that condemn themselves to extinction are in their imperfection robust evidence of the way natural selection shapes organisms and traits. Similarly, they give evidence against the idea of an intelligent designer, unless in addition to intelligence the designer’s character traits include a somewhat warped sense of humour – or the designer has some other reason to muddle up organisms to make them look like evolution would be the best explanatory construct for the puzzle. That is not, of course, a logical impossibility, but by no means is it a claim that follows the rules of science either.
It is more comparable to the idea from sci-fi literature that we are all a computer simulation, the rules of which will always be unknown to us, created only for someone’s amusement. The task of science is to at least try to understand and investigate how far our understanding can get us.
Translated by Owen Witesman
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