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The Case for Blunders

Another cause of catastrophic blunders is religion. A legendary example of a religious blunder is the story of Tsar Lazar, king of Serbia in the year 1389 when his kingdom was invaded by the Turks. He confronted the Turkish army on the fatal battlefield of Kosovo Polje. The story is told in the Serbian national epic The Battle of Kosovo. The Virgin Mary happened to be in Jerusalem at the time when the Turks invaded, and sent a falcon with a message for the tsar. The falcon arrived on the battlefield and told the tsar that he must make a choice between an earthly and a heavenly kingdom. If he chose the earthly kingdom, his army would defeat the Turks and he would continue his reign in Serbia. If he chose the heavenly kingdom, his army would be annihilated and his people would become slaves of the Ottoman Empire. Being a very pious monarch with his mind concentrated on spiritual virtue, the tsar naturally chose the heavenly kingdom, and his people paid for his choice by losing their freedom.

Seven years after Darwin published The Origin of Species, without any satisfactory explanation of hereditary variations, the Austrian monk Gregor Mendel published his paper “Experiments in Plant Hybridization” in the journal of the Brünn Natural History Society. Mendel had solved Darwin’s problem. He proposed that inheritance is carried by discrete units, later known as genes, that do not blend but are carried unchanged from generation to generation. The Mendelian theory of inheritance fits perfectly with Darwin’s theory of natural selection. Mendel had read Darwin’s book, but Darwin never read Mendel’s paper.

The essential insight of Mendel was to see that sexual reproduction is a system for introducing randomness into inheritance. In sweet peas as in humans, each plant is either male or female, and each offspring has one male and one female parent. Inherited characteristics may be specified by one gene or by several genes. Single-gene characteristics are the simplest to calculate, and Mendel chose them to study. For example, he studied the inheritance of pod color, determined by a single gene that has a version specifying green and a version specifying yellow. Each plant has two copies of the gene, one from each parent. There are three kinds of plants, pure green with two green versions of the gene, pure yellow with two yellow versions, and mixed with one green and one yellow. It happens that only one green gene is required to make a pod green, so that the mixed plants look the same as the pure green plants. Mendel describes this state of affairs by saying that green is dominant and yellow is recessive.

Mendel did his classic experiment by observing three generations of plants. The first generation was pure green and pure yellow. He crossed them, pure green with pure yellow, so that the second generation was all mixed. He then crossed the second generation with itself, so that the third generation had all mixed parents. Each third-generation plant had one gene from each parent, with an equal chance that each gene would be green or yellow. On the average, the third generation would be one-quarter pure green, one-quarter pure yellow, and one-half mixed. In outward appearance the third generation would be three-quarters green and one-quarter yellow.

This ratio of 3 between green and yellow in the third generation was the new prediction of Mendel’s theory. Most of his experiments were designed to test this prediction. But Mendel understood very well that the ratio 3 would only hold on the average. Since the offspring chose one gene from each parent and every choice was random, the numbers of green and yellow in the third generation were subject to large statistical fluctuations. To test the theory in a meaningful way, it was essential to understand the statistical fluctuations. Fortunately, Mendel understood statistics.

Mendel understood that to test the ratio 3 with high accuracy he would need huge numbers of plants. It would take about eight thousand plants in the third generation to be reasonably sure that the observed ratio would be between 2.9 and 3.1. He actually used 8,023 plants in the third generation and obtained the ratio 3.01. He also tested other characteristics besides color, and used altogether 17,290 third-generation plants. His experiments required immense patience, continuing for eight years with meticulous attention to detail. Every plant was carefully isolated to prevent any intruding bee from causing an unintended fertilization. A monastery garden was an ideal location for such experiments.

In 1866, the year Mendel’s paper was published, but without any knowledge of Mendel, Darwin did exactly the same experiment. Darwin used snapdragons instead of sweet peas, and tested the inheritance of flower shape instead of pod color. Like Mendel, he bred three generations of plants and observed the ratio of normal-shaped to star-shaped flowers in the third generation. Unlike Mendel, he had no understanding of statistical fluctuations. He used a total of only 125 third-generation plants and obtained a value of 2.4 for the crucial ratio. This value is within the expected statistical uncertainty, either for a true value of 2 or for a true value of 3, with such a small sample of plants. Darwin did not understand that he would need a much larger sample to obtain a meaningful result.

Mendel’s sample was sixty-four times larger than Darwin’s, so that Mendel’s statistical uncertainty was eight times smaller. Darwin failed to repeat his experiment with a larger number of plants, and missed his chance to incorporate Mendel’s laws of heredity into his theory of evolution. He had no inkling that a fundamental discovery was within his grasp if he continued the experiment with larger populations. The basic idea of Mendel was that the laws of inheritance would become simple when inheritance was considered as a random process. This idea never occurred to Darwin. That was why Darwin learned nothing from his snapdragon experiment. It remained a brilliant blunder.

Mendel made a brilliant blunder of a different kind. He published his laws of heredity, with a full acount of the experiments on which the laws were based, in 1866, seven years after Darwin had published The Origin of Species. Mendel was familiar with Darwin’s ideas and was well aware that his own discoveries would give powerful support to Darwin’s theory of natural selection as the cause of evolution. Mendelian inheritance by random variation would provide the raw material for Darwinian selection to work on.

Mendel had to make a fateful choice. If he chose to call Darwin’s attention to his work, Darwin would have understood its importance, and Mendel would inevitably have become involved in the acrimonious public disputes that were raging all over Europe about Darwin’s ideas. If Mendel chose to remain silent, he could continue to pursue his true vocation, to serve his God as a monk and later as abbot of his monastery. Like Tsar Lazar five hundred years earlier, he had to choose between worldly fame and divine service. Being the man he was, he chose divine service. Unfortunately, his God played a cruel joke on him, giving him divine gifts as a scientist and mediocre talents as an abbot. He abandoned the chance to be a world-famous scientist and became an unsuccessful religious administrator.

Darwin’s blindness and Mendel’s reticence combined to delay the progress of science by thirty years. But thirty years is a short time in the history of science. In the end, after both men were dead and their personal shortcomings forgotten, their partial visions of the truth came together to create the modern theory of evolution. Thomas Hunt Morgan at Columbia University understood that the fruit fly Drosophila was a far better tool than the sweet pea and the snapdragon for studying heredity. Fruit flies breed much faster and are more easily handled in large numbers. With fruit flies, Morgan could go far beyond Mendel in exploring the world of genetics.

In my own life as a scientist, there was one occasion when I felt that a deep secret of nature had been revealed to me. This was my personal brilliant blunder. I remember it with joy, even though my dreams of glory were shattered. It was a blissful experience. It arose out of work that I did with my colleague Andrew Lenard from Indiana University, investigating the stability of ordinary matter. We proved by a laborious mathematical calculation that ordinary matter is stable. The physical basis of stability is the exclusion principle, a law of nature saying that two electrons can never be in the same state. Matter is stable against collapse because every atom contains electrons and the electrons resist being squeezed together.

My blunder began when I tried to extend the stability argument to other kinds of particles besides electrons. We can divide particles into two types in three different ways. A particle may be electrically charged or neutral. It may be weakly or strongly interacting. And it may belong to one of two types that we call fermions and bosons in honor of the Italian physicist Enrico Fermi and the Indian physicist Satyendra Bose. Fermions obey the exclusion principle and bosons do not. So each particle has eight possible ways to make the three choices. For example, the electron is a charged weak fermion. The light quantum is a neutral weak boson. The famous particle predicted by Peter Higgs, and discovered in 2012 at the European Centre for Nuclear Research (CERN), is a neutral strong boson.

I observed in 1967 that seven of the eight possible combinations were seen in nature. The one combination that had never been seen was a charged weak boson. The missing type of particle would be like an electron without the exclusion principle. Next, I observed that our proof of the stability of matter would fail if electrons without the exclusion principle existed. So I jumped to the conclusion that a charged weak boson could not exist in a stable universe. This was a new law of nature that I had discovered. I published it quietly in a mathematical journal.

I knew that my theory flatly contradicted the prevailing wisdom. The prevailing wisdom was the unified theory of weak and electromagnetic interactions proposed by my friends Steven Weinberg and Abdus Salam. Weinberg and Salam predicted the existence of a new particle as a carrier of weak interactions. They called the new particle W. The W-particle had to be a charged weak boson, precisely the combination that I had declared impossible. Nature, speaking through an experiment at CERN in Geneva, would decide who was right.

The decision did not come quickly. It took the experimenters fifteen years to build a new machine and use it to search for the W-particle. But the decision, when it came, was final. Large numbers of W-particles were seen, with the properties predicted by Weinberg and Salam. With hindsight I could see several reasons why my stability argument would not apply to W-particles. W-particles are too massive and too short-lived to be a constituent of anything that resembles ordinary matter. I quickly forgot my disappointment and shared the joy of Weinberg and Salam in their well-deserved triumph. As my mother taught me long ago, the key to enjoyment of any sport is to be a good loser.

In Livio’s list of brilliant blunderers, Darwin and Einstein were good losers, Kelvin and Pauling were not so good, and Hoyle was the worst. The greatest scientists are the best losers. That is one of the reasons why we love the game. As Einstein said, God is sophisticated but not malicious. Nature never loses, and she plays fair.

Letters

Respectable Blunders April 3, 2014

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