Tuesday, March 2, 2021

Getting Peed on...by a Tree

Leaves evaporate billions of tons of water vapor every day all around the world during the late spring and summer. The evaporation of water (transpiration) allows the leaves to get rid of the heat burden from sunlight and send the heat up higher into the air. Some of this water vapor ends up in the clouds. What the trees are “trying to do” is to keep its leaves cool. But this also means that when we or our houses are down in the shade, it is cool shade, cooler than the shade of a carport or building. I explain this in my book Green Planet: How Plants Keep the Earth Alive.

One would think that trees have to do a lot of work to pump all this water up from the ground, through the roots, through the trunk, and up to the leaves. But, actually, the trees allow the laws of physics to do the work for them. The water molecules cohere to one another. As water molecules transpire from the leaves, they pull the water molecules behind them. The little columns of water in the pipe cells of the trunk are stretched like tiny rubber bands. In some cases, botanists have been able to measure the tree trunk getting narrower when transpiration begins. During the daytime in the growing season, the leaves simply open their pores and let the laws of physics pull the water up. The water is under tension, which is the opposite of pressure.

But before the leaves emerge from the buds, there is no transpiration. The water cannot be pulled up to the top of the tree. Yet, we all know that the sap rises. In this case, the tree generates water pressure (by accumulating sugar and minerals) in the roots, and this pushes the water up to eventually make the buds burst open.

If the tree generates water pressure but the buds are not yet open, the water can occasionally leak out of damaged wood. The damage can be intentional, for instance when the rising sap of maple or birch trees is made to drip into little buckets. Or it can be accidental. If you are standing underneath a birch tree when the sap is rising but before the buds have opened, some of this water might drip down on you. You may think a squirrel has peed on you, but it was actually the tree. This little drop of water, coming out of what seems like a clear blue sky, hitting your head can have some of the same effect that the apple had on Newton: opening your mind to discovering something new about the world of nature—in this case, trees.

I have posted a video about this: Darwin gets peed on by a tree.

Water cannot be pushed (pressure) and pulled (tension) at the same time. The tree pushes the water into the expanding leaves and other structures. Once transpiration starts, the pressure stops and tension takes over.

All this invisible activity is going on right before your eyes!

Wednesday, February 3, 2021

Energy Storage: A Big Step in Evolution

Life on Earth has a nearly unlimited source of energy: sunlight. The light reactions of photosynthesis transduce sunlight energy (absorbed by beautiful green chlorophyll) into electricity. This would be plenty of energy for any life form. But here is the problem: as soon as the sun sets, or even becomes dim, the organism would have to go into suspended animation. The solution to this problem: store the light and electrical energy in a chemical form. Photosynthesis in chloroplasts puts sunlight energy into sugar, which can be stored and used whenever needed.

Cellular respiration in mitochondria releases chemical energy from sugar in lots of little steps, and makes it available for the cell’s chemical reactions. It does so quietly and invisibly, with an almost 50 percent efficiency. This is much better than even the most fuel-efficient vehicles.

It is easy to overlook just how much energy there is in a teaspoon of sugar. In order to appreciate it, you can release the energy all at once. It produces a very dramatic fizzle. It is not a bomb, but still impressive. It must be done in a fume hood or outside.

  • Grind up the sugar. Do not use powdered sugar, since it is not just sugar ground into a powder.
  • Grind up some potassium chlorate. This provides oxygen, but no energy, to the reaction.
  • Mix the two powders in a plastic weigh boat or other disposable, non-flammable container.
  • Pour in a little concentrated sulfuric acid.
  • Then get out of the way.

The resulting reaction is zero percent efficient. All of the energy comes from the sugar, none from the oxidizing agent or the acid. And it all goes into light, heat, and noise.

I made a Darwin video that shows the process. Enjoy!

It is this huge amount of efficiently-stored energy that makes life possible.

Sunday, January 31, 2021

Guillotines and Other Instruments of Mercy

Several methods of execution, which we consider to be cruel, were actually invented in order to make the process of execution more humane, in several ways. For example, some were invented to hide the identity of the executioner, who was only obeying orders and did not want to receive animosity from the family and friends of the victim who were watching. Others were invented to make the execution itself less painful.

Consider the first purpose.

  • In ancient and medieval times, executioners who used an axe to cut off the condemned person’s head, wore black masks to hide their identity.
  • Later, when guns were used, there was no single executioner, but a firing squad, only one or two of whom had live ammo in their guns. No one, including the other executioners, could be sure who, or who else, fired the fatal bullet or bullets.

Consider the second purpose.

  • The black-masked executioners would hide the axe blade itself until the victim had a blindfold put on, to reduce the tension of both the victim and the executioner.
  • When we think of the French Revolution, we think of crazy people running around and cutting everyone’s heads off with the guillotine. But the guillotine was an invention to make the execution less painful. The heavy blade slid down grooves, attaining gravitational acceleration, and made a precise and decisive cut. Previously—and even today, in some cultures, where beheading by axe or sword is still practiced—the executioner might miss his aim just slightly, or not chop hard enough, thereby prolonging the torture of the victim. We cannot know (no one has lived to report it) what the brain experiences at the moment of beheading. It might be prolonged agony, or shock might instantly set in, causing immediate unconsciousness.
  • If the authorities simply hung a criminal, the person would slowly and painfully suffocate. But the trap door allows the criminal to fall, and the knot, if tied correctly, instantly breaks the victim’s neck.
  • Execution by electrocution? I don’t know much about that one.
  • But lethal injection is a mixture of drugs, at least one of which induces lethargy. Certainly better than cyanide, which makes you suffocate and you know you are suffocating.

Through recent history, executions have become more humane and also less common. Unfortunately, torture remains very common, even when it is called “enhanced interrogation techniques” by supposedly humane nations. Further, assassins give no attention to reducing pain. When the Russians use nerve poison to assassinate victims, the pain of the victim is their last thought. And terrorists, whether Muslim jihadists or Christian white supremacists, probably consider their reputation enhanced by not only the suffering of the victim but the shock of entire nations.

Social evolution has diverged: more humane executions, and more dreadful tortures and technologically advanced terrorism.

Monday, January 25, 2021

Population Thinking and Why It Matters

According to the foremost philosopher of biology, the late Ernst Mayr, one of the most important advances in biological science has been population thinking. That is, we now understand that all the members of a population (or any other set of individuals) have individual variability. They are not all the same. Without this understanding, nobody could grasp the concept of natural selection. How could some individuals in a population (of bacteria, trees, or humans) have more offspring than others (aside from sheer luck) if they were all the same?

Here is one simple example. In this photo, I hold in my hand acorns from two post oak trees. The acorns from one tree are larger than those from another tree. I show that this difference in size is greater between trees than it is among the acorns from a single tree. The two on the left are from one tree, the two on the right from another, of the same species.


Darwin based his theory of natural selection on the work of Thomas Robert Malthus, the economist who said that there were always more people than resources, at least most of the time. Suffering and privation were, therefore, inevitable. Darwin did not simply apply this idea to plants and animals, as some people think. Darwin had to make the transition to population thinking. Even Malthus did not have population thinking; to him, all members of a human population were the same: they all worked, ate, had babies, and died, pretty much the same way.

The lack of population thinking is also why early experiments did not have replication. Bacon used only two chickens in his freezing experiment, and Redi had only two flasks for his spontaneous generation experiment. If all chickens, and all flasks with meat in them, were the same, then replication is not necessary.

Common sense, they say, is neither common nor sense. Many people, when they see an example of something, assume that it represents the entire picture. If some Republicans commit an act of domestic terrorism, as happened this last January 6, then all of them will, if given the opportunity. This is not true (I think). Because of individual differences, you need a sample. When I studied how much garbage was left along Oklahoma roadsides, I counted the garbage from many different stretches of roadside, and not just the ones that looked trashy. If I simply looked at the trashiest roadside, and assumed it was typical, I would have reached the incorrect conclusion that Oklahoma highways have over 300 pieces of garbage per mile. (Actually, it is “only” 100.)

How do we know that we have looked at enough samples of people, things, or places to draw a legitimate conclusion about them? That, my friend, is what the science of statistics is all about. And that is another story, though not one you will probably read in this blog.

Monday, January 18, 2021

The Scientific Method--In a Comic Book

As part of the process of learning French, I read a French comic book called La Page Blanche (the blank page). In this unlikely place, I found lots and lots of examples of hypothesis-testing. This comic, though not openly related to science in any way, was a celebration of the adventure of scientific discovery.


A young woman (Éloïse) has just experienced an emotional shock so great that she has lost her memory. Sitting on a bench, she realizes that she does not remember how she got there, where she lives, where she works, or even her own name. She partly reconstructs this information from documents in her purse and on her cell phone. She finds her address, then figures out train routes to take her back home. When she finally gets to her apartment, she has no idea what to expect when she enters.

At this point, her scientific reconstruction of her identity goes into full swing. She does not know how long she has been missing. A neighbor, whom she does not know, welcomes her back tells her that her cat has been mewing, unfed, for about a day. She imagines different possibilities for what she might find inside her apartment. A slob partner who drunkenly awaited her return from work so she could cook supper? A murder scene? A surprise birthday party? Her partner (if she had one) in flagrante delicto with another woman? Gangsters? A law enforcement team happy at the reappearance of the lost amnesiac? In each of these scenes, a cat mews. She opens the door to another mystery: an empty apartment with a cat.

Éloïse then uses the apartment to partly reconstruct her life. She does not remember whether or not she has a partner. She tests the hypothesis “I live alone” (J’habite tout seule) in two ways. First, if she had a partner, the cat would have been fed. Second, she finds just one toothbrush in the bathroom. She finds pictures of people she does not know and of trips she does not remember having taken on the wall. The photo of New York City showed the Twin Towers, so she concluded the trip was before September 11, 2001. (The book was published in 2013.) None of the pictures, receipts, etc., help her very much. She even wondered if the swollen red spot on her neck might be a clue, but after imagining dramatic scenarios, she concludes it must just be a mosquito bite (piqûre de moustique). In this cartoon book, as in science, many hypotheses lead nowhere.

Éloïse finds her computer but does not know the password. She has to come up with a creative way to find out. She finds out where she works (a bookstore) when she gets an angry phone call from her manager. She has a vague recollection that the password was an American male first name. It turns out an information technologist at work had reset her password recently and was astonished that she had already forgotten it. The information now available to her on her computer still left a lot of things unexplained. Her only hope was to confide in a co-worker who was a Facebook friend. The empathetic co-worker encouraged her to see a doctor and then a psychiatrist. It is not clear to me whether she did or whether she imagined that she did, because the panels depicting her medical visits had extreme cliches of doctors, medical visits, and psychiatrists. They all told her there was nothing wrong with her body or brain…

And so on. The scientific method can be the basis of an entire plot, and I don’t mean just science fiction or mysteries, into neither of which categories this book fits. Science is an adventure of discovery, and it can show up in places where you least expect it.

Sunday, January 3, 2021

Face to Face with War: The Four Horsemen of the Apocalypse, part 3

This is the third essay I have written about the novel The Four Horsemen of the Apocalypse by Spanish novelist Vicente Blasco Ibañez. The world in 2021 is no less vulnerable to war than in any previous year, decade, century, or millennium.

I suppose it is about time to describe the novel itself. It is focused on Marcelo Desnoyers, a Frenchman who fled France to avoid being drafted into the Franco-Prussian War of 1870. He earned a fortune in Argentina and returned to France for what he considered to be the pinnacle of cultured life. He bought a big house, and then bought a castle in the country near the Marne River. He filled both places with incredible treasures. His two children were Argentinian citizens. One of them, his son Julio, became well-known in Paris for his dancing and his wasteful lifestyle. In particular, a married woman was his lover.

When the Great War started, Marcelo was too old to fight, and Julio was exempt because he was not a French citizen. The war changed everything for all of them. Marcelo went out to his castle, just in time, it turned out, for the Battle of the Marne. He saw it all from his castle, which the Germans attacked and plundered. The Germans not only slaughtered all of the people they could find in the village near the castle but were also full of arrogance. The German officers feasted on Marcelo’s food, and even dressed themselves in his daughter’s dresses and danced around. They shat upon the rugs. Ibañez vividly describes the scenes, using all of the senses. In the wounded villagers, brains were visible, throbbing behind faces without noses. A cannon ball tore off the head of one soldier, who for just a split second kept walking, with two jets of red blood shooting upward from his neck. Disemboweled horses trampled their own entrails. It was at the greenest time of year, when the wheat was in full grain, the most vivid contrast possible between life and death.

The German officers also pretended to be sincerely good people. They carried photos of their beloved families and proclaimed that only by destroying France would their families be able to live. This was an incredible lie but one that, Ibañez suggested, the Germans actually believed. They recognized Marcelo as the castle owner, and instead of just shooting him they tried to convince him of the righteousness of their cause.

But the Germans were beaten back. During their retreat, they transformed the ruined castle into a military hospital. Here Marcelo watched some of the very officers who had so recently boasted of their inevitable victory return, mangled almost beyond recognition, and die. When the French army returned, the Germans fled.

Northern France began to recover. But life for the Desnoyers family changed forever. Julio’s lover, feeling guilty at cuckolding her husband, found that the husband had become a military hero as he was wounded in battle. She sought him out, stayed by his side, and nursed him back to health. Julio, heartbroken, felt that he could do only one thing: join the French army as a foreign volunteer. He did so and became a hero himself. His motivation was not patriotism so much as it was forlorn love, and to just do something with his life rather than just to enjoy his wealth. His father Marcelo, who every day felt the guilt at having fled his patriotic duty in 1870, was now intensely proud of his son.

As you can certainly guess, Julio was killed in battle. The story ends, after almost 500 pages, with Marcelo and his family feeling almost infinite grief out in the middle of the burial fields, months after the battle was over. The bodies of slaughtered French soldiers had been piled up and their burial places marked only with little wooden crosses. The bodies of the German soldiers were piled in unmarked pits and covered with dirt.

The scale of the burial fields is nearly impossible to imagine apart from Ibañez’s description. I got only a tiny glimpse of what it must have been like when I hiked with my son-in-law’s family in the Vosges Mountains that divide Alsace and Lorraine in France in 2016. We went quickly past a World War One cemetery. The French family had seen it, and dozens of others, scattered throughout the mountains, but for me it was a powerful experience.




To a large extent, The Four Horsemen of the Apocalypse was a story that wove together improbable circumstances in order to give the author, who was a journalist with first-hand experience, the excuse to write about the ideas that led to the war. How likely would it be that the sister of Marcelo’s wife would just happen to marry a German who became a top official in the evil German government, and explained his point of view to the rest of the family in great detail? How likely that Julio and later Marcelo should befriend a Russian socialist living in Paris, who explained his point of view in great detail? He said that the supposed Christianity of the Germans was actually the worship of Thor rather than of Jesus. It was the atheist socialist, not the German Christians, who believed that “blessed are the peacemakers.” But the characters were not simply excuses for ideas; they were, to me, vividly real.

And was it not all ultimately futile? Ibañez wrote, through the mind of Marcelo, “I wonder if any star knows that Bismarck ever existed! I wonder if the plants are aware of the divine mission of the German nation!” But I wonder if Ibañez would have been able to guess that, a hundred years later, the European Union, led by France and Germany, would get the Nobel Peace Prize?

But hope remains defiant. At the very end, Marcelo’s daughter hugged her fiancé, a wounded hero, right out in the middle of the burial fields—love may not triumph over, but it remains defiant against, death.