Friday, February 04, 2005

Cosmic accounting

A couple of people have asked me about a new discovery by Chandra (orbiting x-ray observatory) of lots of mass in distant gas clouds (NASA release).

What has been discovered is more baryons (ordinary stuff, like protons and neutrons), not the exotic dark matter. There are strong limits from nucleosynthesis (synthesis of light nuclei early in the hot big bang) that constrain the baryon fraction of the total energy density to be about 5%. The dark matter (non-baryonic matter of unknown type clumped around galaxies or clusters of galaxies) is about 25% of the total and dark energy (weird stuff with negative pressure) is the remaining 70% or so.

About half of the expected 5% baryon fraction had been accounted for in galaxies, and these huge gas clouds may be the rest of it. We're still in the dark about dark energy and dark matter, though.

One mystery puzzling theorists is why there are roughly (within an order of magnitude or so) equal amounts of these 3 types of stuff. As the universe expands, the energy density of dark energy changes very slowly compared to baryons or dark matter. Unless we are living at a very special epoch, one would expect the densities of these things to differ by many orders of magnitude. (For example, when the universe was 10 times younger the DE fraction was tiny, and when it is ten times older the DE fraction will be nearly 100%.)


Anonymous said...

Poor little disappearing baryons :) You are giving me homework. Then, if I understand all become dark energy in time. But, even you do not know what dark energy is other than that there is negative pressure to it.


Anonymous said...

A monumental thinker, scientist, humanist has died. We should notice.


Anonymous said...

Ernst Mayr, Pioneer in Tracing Geography's Role in the Origin of Species, Dies at 100

Dr. Ernst Mayr, the leading evolutionary biologist of the 20th century, died on Thursday in Bedford, Mass. He was 100.

Dr. Mayr's death, in a retirement community where he had lived since 1997, was announced by his family and Harvard, whose faculty he joined in 1953.

He was known as an architect of the evolutionary or modern synthesis, an intellectual watershed when modern evolutionary biology was born. The synthesis, which was described by Dr. Stephen Jay Gould of Harvard as "one of the half-dozen major scientific achievements in our century," reconciled Darwin's theories of evolution with new findings in laboratory genetics and in fieldwork on animal populations and diversity.

One of Dr. Mayr's most significant contributions was his persuasive argument for the role of geography in the origin of new species, an idea that has won virtually universal acceptance among evolutionary theorists. He also established a philosophy of biology and founded the field of the history of biology.

"He was the Darwin of the 20th century, the defender of the faith," said Dr. Vassiliki Betty Smocovitis, a historian of science at the University of Florida.

In a career spanning nine decades, Dr. Mayr, a professor emeritus of zoology at Harvard, exerted a broad and powerful influence over the field of evolutionary biology. His most recent book, "What Makes Biology Unique?: Considerations on the Autonomy of a Scientific Discipline" (Cambridge University Press), was published in August, one month after his 100th birthday.

Prolific, opinionated, provocative and dynamic, Dr. Mayr had been a major figure and intellectual leader since the 1940's. Setting much of the conceptual agenda for the field, he put the focus just where Charles Darwin first placed it, on the question of how new species originate.

Though Dr. Mayr will be best remembered as a synthesizer and promoter of evolutionary ideas, he was also an accomplished ornithologist. In fact, it was with the sighting of a pair of unusual birds that Dr. Mayr's long career in biology began in 1923 at age 19.

Dr. Mayr was born in Kempten, Germany, in 1904. While still a boy, he was instructed in natural history by his father, Otto, a judge. He quickly became a skilled birdwatcher and naturalist. Intending to become a medical doctor like others in his family, Dr. Mayr was about to leave for medical school when he spotted a pair of red-crested pochards, a species of duck that had not been seen in Europe for 77 years.

Though he took detailed notes, he could not get anyone to believe his sighting. Finally, he met Dr. Erwin Stresemann, then the leading German ornithologist, who was at the Berlin Zoological Museum and who recognized his talents and invited him to work at the museum during school holidays.

After two years of medical studies at the University of Greifswald (chosen because it was in the most interesting German region for birdwatching), Dr. Mayr, like Darwin before him, opted for natural history. He completed his Ph.D. at the University of Berlin in just 16 months.

Dr. Mayr went on to fulfill what he called "the greatest ambition of my youth," heading off to the tropics. In the South Pacific, principally New Guinea and the Solomon Islands, Dr. Mayr collected more than 3,000 birds from 1928 to 1930. (He had to live off the land, and every bird, after being skinned for study, went into the pot. As a result, he is said to have eaten more birds of paradise than any other modern biologist.)

The South Seas experience, he once said, "had an impact on my thinking that cannot be exaggerated." For it was his detailed observations of the differences among geographically isolated populations that contributed to his conviction that geography played a crucial role in the origin of species.

Though Darwin titled his book "The Origin of Species," little in the book, in fact, addresses the question of how new species arise. Dr. Mayr determined that when populations of a single species are separated from one another, they slowly accumulate differences until they can no longer interbreed. Dr. Mayr called this allopatric speciation and detailed his arguments in his seminal book "Systematics and the Origin of Species," published in 1942. Today allopatric speciation ("allo," from the Greek for "other," and "patric," from the Greek for "fatherland") is accepted as the most common way in which new species arise.

"Organic diversity had at last received a convincing explanation," Dr. Jerry A. Coyne, an evolutionary biologist at the University of Chicago, wrote of Dr. Mayr's arguments. Dr. Coyne called the book "one of the greatest achievements of evolutionary biology."

Similarly, the most commonly held view of what constitutes a species remains the one that Dr. Mayr promoted more than 50 years ago, known as the biological species concept. First explicitly defined by Dr. Theodosius Dobzhansky, it states that populations that can successfully interbreed are the same species and those that cannot are different species. While numerous other species concepts have been proposed and debated, this one continues to reign supreme....


Anonymous said...

Do finish reading the articel, and perhaps far more of this monumental thinker whose work is fresh as can be this day.


Anonymous said...

We are passing through a time when often teachers are reluctant or afraid to think to Darwin and Mayr and ideas that ground all biology. How sad. As though you might not think to Einstein and Bohr.


Anonymous said...

Evolution Takes a Back Seat in U.S. Classes

Dr. John Frandsen, a retired zoologist, was at a dinner for teachers in Birmingham, Ala., recently when he met a young woman who had just begun work as a biology teacher in a small school district in the state. Their conversation turned to evolution.

"She confided that she simply ignored evolution because she knew she'd get in trouble with the principal if word got about that she was teaching it," he recalled. "She told me other teachers were doing the same thing."

Though the teaching of evolution makes the news when officials propose, as they did in Georgia, that evolution disclaimers be affixed to science textbooks, or that creationism be taught along with evolution in biology classes, stories like the one Dr. Frandsen tells are more common.

In districts around the country, even when evolution is in the curriculum it may not be in the classroom, according to researchers who follow the issue.

Teaching guides and textbooks may meet the approval of biologists, but superintendents or principals discourage teachers from discussing it. Or teachers themselves avoid the topic, fearing protests from fundamentalists in their communities.

"The most common remark I've heard from teachers was that the chapter on evolution was assigned as reading but that virtually no discussion in class was taken," said Dr. John R. Christy, a climatologist at the University of Alabama at Huntsville, an evangelical Christian and a member of Alabama's curriculum review board who advocates the teaching of evolution. Teachers are afraid to raise the issue, he said in an e-mail message, and they are afraid to discuss the issue in public.

Dr. Frandsen, former chairman of the committee on science and public policy of the Alabama Academy of Science, said in an interview that this fear made it impossible to say precisely how many teachers avoid the topic.

"You're not going to hear about it," he said. "And for political reasons nobody will do a survey among randomly selected public school children and parents to ask just what is being taught in science classes."

But he said he believed the practice of avoiding the topic was widespread, particularly in districts where many people adhere to fundamentalist faiths.

"You can imagine how difficult it would be to teach evolution as the standards prescribe in ever so many little towns, not only in Alabama but in the rest of the South, the Midwest - all over," Dr. Frandsen said.

Dr. Eugenie Scott, executive director of the National Center for Science Education, said she heard "all the time" from teachers who did not teach evolution "because it's just too much trouble."

"Or their principals tell them, 'We just don't have time to teach everything so let's leave out the things that will cause us problems,' " she said.

Sometimes, Dr. Scott said, parents will ask that their children be allowed to "opt out" of any discussion of evolution and principals lean on teachers to agree.

Even where evolution is taught, teachers may be hesitant to give it full weight. Ron Bier, a biology teacher at Oberlin High School in Oberlin, Ohio, said that evolution underlies many of the central ideas of biology and that it is crucial for students to understand it. But he avoids controversy, he said, by teaching it not as "a unit," but by introducing the concept here and there throughout the year. "I put out my little bits and pieces wherever I can," he said.


Anonymous said...

Striking how we tell of the story of Galileo, but make no connection to our time.


Anonymous said...

Imagine writing such an essay at 98 :)


Anonymous said...

The Biology of Race and the Concept of Equality
Ernst Mayr, 2002

There are words in our language that seem to lead inevitably to controversy. This is surely true for the words "equality" and "race." And yet among well informed people, there is little disagreement as to what these words should mean, in part because various advances in biological science have produced a better understanding of the human condition.

Let me begin with race. There is a widespread feeling that the word "race" indicates something undesirable and that it should be left out of all discussions. This leads to such statements as "there are no human races."

Those who subscribe to this opinion are obviously ignorant of modern biology. Races are not something specifically human; races occur in a large percentage of species of animals. You can read in every textbook on evolution that geographic races of animals, when isolated from other races of their species, may in due time become new species. The terms "subspecies" and "geographic race" are used interchangeably in this taxonomic literature.

This at once raises a question: are there races in the human species? After all, the characteristics of most animal races are strictly genetic, while human races have been marked by nongenetic, cultural attributes that have very much affected their overt characteristics. Performance in human activities is influenced not only by the genotype but also by culturally acquired attitudes. What would be ideal, therefore, would be to partition the phenotype of every human individual into genetic and cultural components.

Alas, so far we have not yet found any reliable technique to do this. What we can do is acknowledge that any recorded differences between human races are probably composed of cultural as well as genetic elements. Indeed, the cause of many important group differences may turn out to be entirely cultural, without any genetic component at all. Still, if I introduce you to an Eskimo and a Kalahari Bushman I won't have much trouble convincing you that they belong to different races.

In a recent textbook of taxonomy, I defined a "geographic race" or subspecies as "an aggregate of phenotypically similar populations of a species inhabiting a geographic subdivision of the range of that species and differing taxonomically from other populations of that species." A subspecies is a geographic race that is sufficiently different taxonomically to be worthy of a separate name. What is characteristic of a geographic race is, first, that it is restricted to a geographic subdivision of the range of a species, and second, that in spite of certain diagnostic differences, it is part of a larger species.

No matter what the cause of the racial difference might be, the fact that species of organisms may have geographic races has been demonstrated so frequently that it can no longer be denied. And the geographic races of the human species - established before the voyages of European discovery and subsequent rise of a global economy - agree in most characteristics with the geographic races of animals. Recognizing races is only recognizing a biological fact.

Still, the biological fact by itself does not foreclose giving various answers to the question, What is race? In particular, adherence to different political and moral philosophies, as we shall see, permits rather different answers. But I believe it is useful at the outset to bracket the cultural factors and explore some of the implications of a strictly biological approach.

The evolutionary literature explains why there are geographic races. Every local population of a species has its own gene pool with its own mutations and errors of sampling. And every population is subject to selection by the local environment. There is now a large literature on the environmental factors that may influence the geographic variation of a species. For example, populations of warm-blooded vertebrates (mammals and birds) in the colder part of their geographical range tend to larger size (Bergmann's rule). Darwin wondered whether these climatic factors were sufficient to account for the differences between geographic races in the human species. He finally concluded that sexual selection, the preference of women for certain types of men, might be another factor leading to differences between geographic races.

This kind of biological analysis is necessary but not sufficient. By itself, biology cannot explain the vehemence of the modern controversy over race. Historically, the word "race" has had very different meanings for different people holding different political philosophies. Furthermore, in the last two hundred years there has been a change in the dominant philosophy of race.
In the eighteenth century, when America's Constitution was written, all our concepts were dominated by the thinking of the physical sciences. Classes of entities were conceived in terms of Platonic essentialism. Each class (eidos) corresponded to a definite type that was constant and invariant. Variation never entered into discussions because it was considered to be "accidental" and hence irrelevant. A different race was considered a different type. A white European was a different type from a black African. This went so far that certain authors considered the human races to be different species.

It was the great, and far too little appreciated, achievement of Charles Darwin to have replaced this typological approach by what we now call population thinking. In this new thinking, the biological uniqueness of every individual is recognized, and the inhabitants of a certain geographic region are considered a biopopulation. In such a biopopulation, no two individuals are the same, and this is true even for the six billion humans now on Earth. And, most important, each biopopulation is highly variable, and its individuals greatly differ from each other, thanks to the unique genetic combinations that result from this variability.

Let me illustrate the implications of individual differences by analyzing the outcome of the 2001 Boston marathon. Kenyans are a population famous for producing long-distance runners. Three Kenyans had entered the race, and it was predicted that they would end the race as numbers one, two, and three. However, to everybody's great surprise, the winner was a Korean, and, even more surprisingly, number two was an Ecuadorian from a population that had never been credited with long-distance running abilities. It was a clear refutation of a typological - or essentialist - approach to thinking about race.

In a Darwinian population, there is great variation around a mean value. This variation has reality, while the mean value is simply an abstraction. One must treat each individual on the basis of his or her own unique abilities, and not on the basis of the group's mean value....


Anonymous said...

Imagine living in a time when we may fear to teach of an Ernst Mayr.


Anonymous said...


EDGE: To what extent has the study of evolutionary biology been the study of ideas about evolutionary biology? Is evolution the evolution of ideas, or is it a fact?

ERNST MAYR: That's a very good question. Because of the historically entrenched resistance to the thought of evolution, documented by modern-day creationism, evolutionists have been forced into defending evolution and trying to prove that it is a fact and not a theory. Certainly the explanation of evolution and the search for its underlying ideas has been somewhat neglected, and my new book, the title of which is What Evolution Is, is precisely attempting to rectify that situation. It attempts to explain evolution. As I say in the first section of the book, I don't need to prove it again, evolution is so clearly a fact that you need to be committed to something like a belief in the supernatural if you are at all in disagreement with evolution. It is a fact and we don't need to prove it anymore. Nonetheless we must explain why it happened and how it happens.

One of the surprising things that I discovered in my work on the philosophy of biology is that when it comes to the physical sciences, any new theory is based on a law, on a natural law. Yet as several leading philosophers have stated, and I agree with them, there are no laws in biology like those of physics. Biologists often use the word law, but for something to be a law, it has to have no exceptions. A law must be beyond space and time, and therefore it cannot be specific. Every general truth in biology though is specific. Biological "laws" are restricted to certain parts of the living world, or certain localized situations, and they are restricted in time. So we can say that their are no laws in biology, except in functional biology which, as I claim, is much closer to the physical sciences, than the historical science of evolution.

EDGE: Let's call this Mayr's Law.

MAYR: Well in that case, I've produced a number of them. Anyhow the question is, if scientific theories are based on laws and there aren't any laws in biology, well then how can you say you have theories, and how do you know that your theories are any good? That's a perfectly legitimate question. Of course our theories are based on something solid, which are concepts. If you go through the theories of evolutionary biology you find that they are all based on concepts such as natural selection, competition, the struggle for existence, female choice, male dominance, etc. There are hundreds of such concepts. In fact, ecology consists almost entirely of such basic concepts. Once again you can ask, how do you know they're true? The answer is that you can know this only provisionally by continuous testing and you have to go back to historical narratives and other non-physicalist methods to determine whether your concept and the consequences that arise from it can be confirmed.

EDGE: Is biology a narrative based of our times and how we look at the world?

MAYR: It depends entirely on when in the given age of the intellectual world you ask these questions. For instance when Darwin published The Origin of Species, the leading Cambridge University geologist was Sedgwick, and Sedgwick wrote a critique of Darwin's Origin that asked how Darwin could be so unscientific as to use chance in some of his arguments, when everyone knew that God controlled the world? Now who was more scientific, Darwin or Sedgwick? This was in 1860 and now, 140 years later, we recognize how much this critique was colored by the beliefs of that time. The choice of historical narratives is also very time-bound. Once you recognize this, you cease to question their usefulness. There are a number of such narratives that are as ordinary as proverbs and yet still work.


Anonymous said...

Ernst Mayr's interview "What Evolution Is" was given October 2001, at 97, in time for the publication of the book :)


Anonymous said...

Who should we guess might write the introduction to "What Evolution Is" by Ernst Mayr? After all, Mayr was an evolutionary biologist and a geographer.

October 2001

What Evolution Is: An Introduction
By Jared Diamond:

When the first bird survey of the Cyclops Mountains was carried out. I found it hard to imagine how anyone could have survived the difficulties of that first survey of 1928, considering the already-severe difficulties of my second survey in 1990.

That 1928 survey was carried out by the then-23-year-old Ernst Mayr, who had just pulled off the remarkable achievement of completing his Ph.D. thesis in zoology while simultaneously completing his pre-clinical studies at medical school. Like Darwin, Ernst had been passionately devoted to outdoor natural history as a boy, and he had thereby come to the attention of Erwin Stresemann, a famous ornithologist at Berlin's Zoological Museum. In 1928 Stresemann, together with ornithologists at the American Museum of Natural History in New York and at Lord Rothschild's Museum near London, came up with a bold scheme to "clean up" the outstanding remaining ornithological mysteries of New Guinea, by tracking down all of the perplexing birds of paradise known only from specimens collected by natives and not yet traced to their home grounds by European collectors. Ernst, who had never been outside Europe, was the person selected for this daunting research program.

Ernst's "clean-up" consisted of thorough bird surveys of New Guinea's five most important north coastal mountains, a task whose difficulties are impossible to conceive today in these days when bird explorers and their field assistants are at least not at acute risk of being ambushed by the natives. Ernst managed to befriend the local tribes, was officially but incorrectly reported to have been killed by them, survived severe attacks of malaria and dengue and dysentery and other tropical diseases plus a forced descent down a waterfall and a near-drowning in an overturned canoe, succeeded in reaching the summits of all five mountains, and amassed large collections of birds with many new species and subspecies. Despite the thoroughness of his collections, they proved to contain not a single one of the mysterious "missing" birds of paradise. That astonishing negative discovery provided Stresemann with the decisive clue to the mystery's solution: all of those missing birds were hybrids between known species of birds of paradise, hence their rarity.

From New Guinea, Ernst went on to the Solomon Islands in the Southwest Pacific, where as a member of the Whitney South Sea Expedition he participated in bird surveys of several islands, including the notorious Malaita (even more dangerous in those days than was New Guinea). A telegram then invited him to come in 1930 to the American Museum of Natural History in New York to identify the tens of thousands of bird specimens collected by the Whitney Expedition on dozens of Pacific Islands. Just as Darwin's "explorations," sitting at home, of collections of barnacles were as important to Darwin in forming his insights as was his visit to the Galapagos Islands, so too Ernst Mayr's "explorations" of bird specimens in museums were as important as his fieldwork in New Guinea and the Solomons in forming his own insights into geographic variation and evolution. In 1953 Ernst moved from New York to Harvard University's Museum of Comparative Zoology, where even today he continues to work at the age of 97, still writing a new book every year or two. For scholars studying evolution and the history and philosophy of biology, Ernst's hundreds of technical articles and dozens of technical books have been for a long time the standard reference works.

But in addition to gaining insights from his own fieldwork in the Pacific and from his own studies of museum bird specimens, Ernst has collaborated with many other scientists to extract insights from other species, ranging from flies and flowering plants to snails and people. One of those collaborations transformed my own life, just as the meeting with Erwin Stresemann transformed Ernst's life. While I was a teenaged schoolboy, my father, a physician studying human blood groups, collaborated with Ernst in the first study proving that human blood groups evolve subject to natural selection. I thereby met Ernst at dinner at my parents' house, was later instructed by him in the identification of Pacific island birds, began in 1964 the first of 19 ornithological expeditions of my own to New Guinea and the Solomons, and in 1971 began to collaborate with Ernst on a massive book about Solomon and Bismarck birds that we completed only this year, after 30 years of work. My career, like that of so many other scientists today, thus exemplifies how Ernst Mayr has shaped the lives of 20th-century scientists: through his ideas, his writings, his collaborations, his example, his lifelong warm friendships, and his encouragement.


Anonymous said...

Oh Steve, I loved the guy. So would have you.


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