A fugue is a musical piece in which several overlapping variations on a theme are played simultaneously by different sections of an orchestra. Each section is called a "voice." The overall effect suggests rapid flight, hence the term. The word "fugue" comes from the same root as our word "fugitive."
At the risk of offending serious music lovers, the general idea of a fugue is similar to the familiar round singing of "Row, Row, Row Your Boat", except that in a round, each voice simply repeats the same theme over and over ... and over ... and over... In a fugue, the theme is continuously varying and the overall organization is far more complex.
Sagan likens the possible variations of life in the Universe to a fugue in which each voice (planet) is playing its own variations on the main theme. So where's the fugue in this episode? Although there is some Baroque-sounding music, ironically, there is no fugue anywhere in the music in this episode!
Here's Sagan at his in-your-face best. A lot of people, of course, are opposed to evolution on religious or ideological grounds, and try to maintain some intellectual "wiggle room" that allows them to deny evolution. Sagan takes one of the most widespread of these scams head-on.
As used by many people, "theory" means "hypothesis", therefore a guess that can be disregarded. But "theory" in science actually refers to any coherent, organized body of ideas. The structural integrity of the Sears Tower was calculated using "stress theory" but nobody believes the Sears Tower was built using guesswork or unproven hypotheses. The portion of music training that describes notation, chords, and harmony is called "theory" although its basic ideas have been highly refined and workable since before Bach.
If evolution really happened, then its opponents are wrong, and they will have to deal with the religious and ideological problems that raises. But that's not science's problem. Opponents of evolution created their own problems and they will have to solve them. This is one of the meanings of the dictum "Science is Value-Neutral"; if scientific findings conflict with your value system, your value system must be wrong. This is anything but a "value-neutral" stance; it's a strident assertion that we are more likely to find the truth by following the evidence honestly than by tailoring findings to fit a preconceived belief system.
Evolution by natural selection was discovered by Charles Darwin and Alfred Russell Wallace. Darwin had been naturalist on the famous Beagle expedition in the 1830's. He mulled over his observations for a quarter-century and was just about to publish when he got a letter from Wallace outlining the theory. What could have been a seriously nasty priority squabble became a model for scientific cooperation. Darwin, as senior scientist, got most of the credit at the time (and took most of the heat) but Darwin worked to ensure that Wallace got a fair hearing for his ideas. Wallace, for his part, actively defended Darwin and his writings. Historians now give both scientists equal credit for the discovery.
The interactions of science and society following the discovery of evolution are fascinating, complex, and far-reaching. They are discussed in more depth at these two sites:
The geologic record contains the history of life on earth. The overall conclusions we can draw from it are:
Sagan uses the Heike crabs of Japan as an example of unconscious artificial selection by humans. We can see that there are several different kinds of natural and artificial selection:
We have not been observing long enough to witness the appearance of entirely new species but we have certainly observed enough important pieces of the evolutionary mechanism to be reasonably sure how it works:
Most popular discussions of evolution suggest that mutations, or genetic changes, occur and then an organism evolves to a new form. But if you randomly tinker with the engine of your car or some electronic component in a computer, you will virtually certainly make things worse, not better. Similarly, most organisms are well-adapted to their environment; any genetic change is almost certain to make them less well-adapted, not more.
If the chances of a beneficial mutation happening are very tiny, nature has a huge number of organisms to work with. If the chance of a beneficial mutation occurring are one in billions, but there are trillions of organisms during the lifetime of a species, some will win the lottery.
More likely, though, is that mutations serve as genetic contingency plans. Fins that can double as crude legs may make you less agile in the open water, but are just the ticket if you find yourself trapped in a shrinking pond. When the environment changes, some mutations that had been harmful might become advantageous. Likewise, when organisms move into new environments (say colonize remote islands), their mutations may become useful or at least harmless. Island organisms, free of competition, tend to radiate rapidly into all kinds of specialized forms. They also tend to be easy prey for the more generalized organisms from the continents. That's one reason why humans have deliberately and unwittingly driven so many island organisms to extinction.
The hereditary code for humans is contained in the molecule DNA, Deoxyribonucleic acid. The DNA in humans contains a few billion pairs of molecules arranged in a spiral ladder form. An atom is about 10-8 centimeters in diameter, and each rung on the ladder is a few atoms high, so the total length of human DNA in a single cell is about a meter. Most cells are microscopic; the DNA fits in such a tiny space because it is tightly coiled. The act of uncoiling DNA, splitting it, replicating it and separating the strands without tangling in such a tiny space is mind-boggling. Ever put your clothes on in a sleeping bag? Imagine taking raw wool or cotton, spinning it into thread, weaving the cloth, sewing it into clothes, and putting them on in the sleeping bag. That's what replicating DNA amounts to.
A human body contains about 20 trillion cells. The total length of DNA in a human body is thus 20 trillion meters, or twenty billion kilometers, the circumference of the orbit of Pluto. The DNA in a human body would wrap around the Solar System.
Few things about evolution cause as much misunderstanding as the use of terms like "random". To most people, "random" means without order or purpose, but it has quite a different meaning in science. Consider a couple of examples:
Are the following letter sequences random: crvn, smrt, vrlo, gdje, trg?
The look random enough; most don't even have vowels. That's a problem in English, not in Serbo-Croatian. The words mean, respectively, red, death, very, where and town square. Moral: the fact that something looks random doesn't mean it is. It may convey meaning in a way you don't understand.
Is the following number sequence random: 592653589793238462643383279?
It not only looks random: it is random. This particular number sequence has passed every test for randomness mathematicians have ever used on it. But lacking in meaning? No. These are the digits of pi beginning with the fourth decimal place. Not only is this a very meaningful number sequence, it is absolutely determined: the trillionth digit of pi is absolutely fixed, even if we haven't yet computed it.
The trillionth digit of the fraction 1/3 in decimal form is 3. The only known way to predict the trillionth digit of pi is to calculate it. You can guess the next decimal digit of 1/3 with 100 per cent accuracy. If you try to predict the next digit of pi your overall accuracy is ten per cent. So one very important meaning of "random" is that something cannot be predicted with better accuracy than that predicted by statistics. This unpredictability can occur even in something as precisely defined as pi.
One important reason why things may be unpredictable is lack of information. If you pick a date in the past or future and guess the positions of the Moon and planets, you will do no better than random guessing, even though the positions of the planets can be foretold with high accuracy. Since you don't carry formulas for the motions of the planets in your head, your guesses will have no accuracy. I omit the Sun from this discussion because you can guess the Sun's position from the date.
One approximation to pi is 22/7 = 3.142. A much better one is 355/113 = 3.1415929. But note that in each case the fractions have as many digits as the accuracy they achieve. It is just as much work to write or remember the fractions as it is simply to remember pi to the same accuracy. If you had absolutely precise information about the forces on a coin and the surface it lands on, you could, in principle, predict how a coin toss will turn out. It would take far more effort than simply flipping the coin. One other definition of randomness is that it takes as much information or effort to describe an event fully as it does simply to produce the event itself. In other words, the actual event is its own simplest description.
In addition, some things are inherently unpredictable. We can predict climate (the overall physical conditions on Earth) with ever-improving accuracy, but weather forecasts become increasingly unreliable after only a few days. We can predict general trends during an El Nino season, but whether it will snow Christmas Eve in Green Bay is still unpredictable. And mounting evidence suggests it may never be possible; that tiny uncertainties in measurement now may result in increasingly great differences as time goes by. Systems of that sort are called chaotic. They are completely governed by the laws of physics, but incomplete information prevents us from achieving completely accurate long-term predictions.
We can see easily how these concepts apply to evolution: biological systems are far too complex to describe mathematically, we have incomplete information, and significant events like climate change or asteroid impact are unpredictable.
The Second Law of Thermodynamics is often paraphrased as "things always go from bad to worse." Most popular descriptions describe it as "disorder in the Universe is always increasing." The law is often illustrated by dumping a jigsaw puzzle on the floor and imagining the likelihood of it spontaneously self-assembiling. But the actual concept at the core of the Second Law is something called entropy. In discussing order and evolution, the only concept that is relevant at all is entropy. Intuitive notions of whether one outcome is more disorderly than another are of no relevance whatsoever. Entropy often corresponds to our intuitive notions of disorder, but not always.
For example, when you assemble the jigsaw puzzle, you are reducing the disorder in that system. But, at the same time, you are expending energy to move the pieces around and perform the mental tasks needed to solve the puzzle. Complex organic molecules you ate a few hours ago are broken down into simpler molecules, some of which are exhaled as carbon dioxide and water vapor. Liquid water in your body is vaporized as perspiration. The puzzle as a whole has gone to a state of lower entropy, but the entire system - you, the puzzle, your food, the surrounding atmosphere, has gone to a state of higher entropy.
It is possible for water to run uphill, over rocks in a stram perhaps, if it's first picked up speed by falling. Similarly, entropy can decrease locally, if entropy in a larger sense increases to make up for it. Spontaneous order arises all the time in nature, but always as the result of a larger increase in entropy somewhere else.
Although we speak of random motions of molecules in the origin of life, we mean random in the sense of statistically complex. Chemical reactions are not random. For example, if we had a bucket of dimes and pennies and dumped them on the floor, the chance of their arranging like this would be negligible:
PDPDPDPDPDPDPDPDPDPDPDPDPDPDPDPDPDPDPDPD DPDPDPDPDPDPDPDPDPDPDPDPDPDPDPDPDPDPDPDP PDPDPDPDPDPDPDPDPDPDPDPDPDPDPDPDPDPDPDPD DPDPDPDPDPDPDPDPDPDPDPDPDPDPDPDPDPDPDPDP PDPDPDPDPDPDPDPDPDPDPDPDPDPDPDPDPDPDPDPD DPDPDPDPDPDPDPDPDPDPDPDPDPDPDPDPDPDPDPDP PDPDPDPDPDPDPDPDPDPDPDPDPDPDPDPDPDPDPDPD
Yet the atoms in table salt have precisely the same arrangement:
It's easy to form salt crystals naturally: just let a container of salt water evaporate. The chances of sodium and chlorine atoms arranging by chance in a rigidly cubic alternating array is zero, but it doesn't happen by chance. The sodium atoms have a positive charge, the chlorines a negative charge. The opposing charges attract and like charges repel. The chance of their arranging this way is virtually 100 per cent.
Some people have attempted to calculate the likelihood of forming complex organic molecules as if the molecules assemble by random addition of components. Of course the probability of forming a molecule that way is vanishingly small because molecules don't form like that. The missing half of a replicating DNA molecule spontaneously assembles from simple organic molecules in the cell (see above). A simple-minded probability calculation would put the probability at near zero; actually it is virtually 100 per cent.
This video is an excellent place to observe the role of artistic conventions in portraying science. Some of the conventions used in this video include:
Refer to the links above for some of these items:
Created 13 January 1998, Last Update 27 April 1998
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