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Life Lines

Johannes Gutenberg, depicted on the right, was the inventor of printing. File photo

By Elof Axel Carlson

Elof Axel Carlson

Knowledge can be conveyed by oral tradition or by written language. 

The earliest writings were on mud tablets (cuneiform tablets in Sumerian culture) or paper (papyrus sheets in Egypt in the ages of the pharaohs). Paper replaced mud or wooden tablets during the Middle Ages and some monasteries made copying texts (mostly religious commentaries and bibles) a major activity for monks. 

Most of humanity was illiterate until the 15th century. What changed? One of the greatest inventions was movable type, which allowed words to be arranged from metal letters. They could be aligned into sentences and pages and then placed in a wooden press and smeared with an oil-based ink. 

The inventor of this technology was Johannes Gutenberg (1400-1468). He raised the money from Johann Fust. Gutenberg’s son-in-law marketed the books Gutenberg printed (the Bible being his first large-scale project). 

Printed books became affordable to the new middle class emerging in Renaissance Europe.  They also became more diverse and translations (into Latin) of Greek texts were in heavy demand. The first biology text printed in 1476 was “De Animalibus” by Aristotle (translated from the Greek to Latin because Latin was the universal language of scholars throughout Europe until the 19th century). 

The first book in a different language was a German book in 1461. The first book in English was in 1475. Euclid’s “Elements of Geometry” was printed in 1482. The first book printed in North America, “The Bay Psalm Book,” was printed in 1640.

The problem with an oral tradition is its vulnerability to change with time and a high risk of losing lots of information. Written language can survive if preserved copies are kept in libraries, monasteries or royal households. The explosion of knowledge that came during the Renaissance owed much of its success to printing. 

Books were translated into Latin (and during the later Enlightenment into vernacular German, Italian, English and other languages). They could also be written to reflect new knowledge and commentary on any topic. 

Before printing, it took a monk about a year to copy a book using pen, ink and paper. Gutenberg’s press could produce 240 sheets of pages per day. It was not until the 1820s that steam-driven presses became available to scale up the production of books and newspapers. It also required the introduction of paper mills to mass produce paper from discarded clothing or from wood pulp. 

When Martin Luther led his Reformation movement and separated his followers from the authority of the Vatican, he ordered placing the Bible as the prime authority for religious instruction. He shifted it to German so it could be read by all Lutherans. This shifted printing from limited printings of scholarly or commercial technical books to mass production of texts where education was compulsory for all children and for mass production of Bibles so every household would have a Bible. 

As in many instances of new technology, these changes could not be anticipated when Gutenberg first introduced his printing press.  Once made available, more books appeared.  More books led to more readership. More readership led to the spread of diverse views of life and society. Once more diversity entered so did a ferment of ideas on how we should live, what we should revere, and what careers would emerge as new knowledge spread. 

For the scholar it led to the university and to higher degrees certifying an exposure to knowledge in dozens of fields old and new. 

Elof Axel Carlson is a distinguished teaching professor emeritus in the Department of Biochemistry and Cell Biology at Stony Brook University.

Hermann Joseph Muller

By Elof Axel Carlson

Elof Axel Carlson

My mentor, Nobel laureate Hermann Joseph Muller, described science to his graduate students as “the winning of the facts.” Three implications exist in that interpretation. 

First, it is not easy to do science. It takes skills at using instruments to obtain facts, design experiments or infer connections among isolated facts. Second, the scientist may be in competition with alternate ways to interpret the same data. The scientist may have biases that were not controlled adequately in the experimental design, or the scientist may be a victim of wishful thinking. Third, science has implications for our lives that may be received with resistance or disbelief by those who prefer their advantages for the world as they are presently enjoying it.

A good example is the effort it took Muller to work out some findings about the gene. When he joined Thomas H. Morgan’s laboratory in 1912, the gene was just an abstract idea. Its chemistry was unknown. Morgan had just found that there were genes associated with sex and that genes were associated with chromosomes in the cell. 

In 1913 Morgan’s student Alfred H. Sturtevant showed those genes could be mapped. In 1915 Morgan’s student Calvin B. Bridges showed cell division could be imperfect and an extra or missing chromosome may be present in a fertilized egg. Go fast forward about 50 years and in humans that explained why some children have Down syndrome (with three instead of two chromosomes for number 21 of 23 pairs of chromosomes). 

Muller took 15 more years after joining Morgan’s laboratory before he worked out genetic stocks to do an experiment that showed X-rays induce mutations. That did not make many people in the health industries happy because most of the mutations induced by X-rays had harmful effects (loss of function). 

After Hiroshima and Nagasaki, Muller’s findings interpreted cell death from broken chromosomes by high doses of radiation created radiation sickness in tens of thousands of people who lived in Hiroshima and Nagasaki when our atomic bombs exploded. During the Cold War, many legislators felt that concern over radiation exposure was a Communist plot to delay development of nuclear weapons and the need to test them in the atmosphere, at sea or on land. Muller tried to strike a balance between political fears and the need for radiation protection. 

The debate over consequences of low doses versus high doses of radiation exposure is still ongoing. The values of military needs for new or renewed weapons dominate concerns over low dose exposure. Those in the nuclear reactor industries feel the permissible doses add expenses that are not necessary because they feel no mutations are produced at low doses. 

The overwhelming number of experiments done to test radiation exposure is that it is proportional to dose or linear for thousands of roentgens to fractions of a roentgen. The experiments are difficult to do with low doses in mice or fruit flies. Fortunately, most dentists give a lead apron to patients before doing X-rays, and newer X-ray machines give a much lower dose to get even sharper images with better X-ray machines. Fortunately, most health providers protect themselves and their staff from exposure to X-rays and do not have to be in the same room with the patient. 

Basic science provides knowledge we may not want to know. But it also provides knowledge we can use to protect ourselves. It is not usually the scientists who make these findings who prevail in how science is received or used by the public. The winning of the facts is often a struggle that may be ongoing for years or decades before consensus occurs.

Elof Axel Carlson is a distinguished teaching professor emeritus in the Department of Biochemistry and Cell Biology at Stony Brook University.

Felix Hoppe-Seyler

By Elof Axel Carlson

Elof Axel Carlson

I enjoy doing history of science because I learn so much when delving into the past. If I am reading about cell theory and the types of tissues there are, I remember the course in microscopic techniques I took as an undergraduate at NYU.

I did not know then that the microtome to cut slices of tissue for making slides was first introduced by Johannes Purkinje. I did not know that growing bacteria on agar plates or slants in test tubes to obtain pure cultures was first done by Robert Koch. I did not know that the word “mutation,” as a change in heredity, was first introduced by Hugo de Vries. Similarly, I did not know that Bernhard Tollens first showed carbohydrates were composed of sugars.

It was William Cheselden who first demonstrated that the role of saliva was to break down food for digestion. I did not know the chemical notation for representing molecules, like CO2 being carbon dioxide was invented by Jöns Berzelius. I did not know the first person to show that oxygen binds to hemoglobin was Felix Hoppe-Seyler. But I did know that Albrecht Kossel was the first to isolate and name the nitrogenous biases of nucleic acid and he called them adenine, guanine, thymine, cytosine and uracil. 

I did not know ringworm was shown to be a fungal parasite by Johann Schönlein. He also changed the name “consumption” to “tuberculosis” and made a third contribution: He was the first science professor to teach in his native tongue, German, instead of Latin to his students. It was Rudolf Leuckart who worked out the nematode parasite causing trichinosis in pork, and his work led to compulsory meat inspection in most industrial countries. The first phylogenetic tree for evolutionary history of plants or animals was constructed by Ernst Haeckel (that I did know).

Even the nouns I use as a scientist have known origins: Tissue was first introduced by Marie François Xavier Bichat at the time of the French Revolution (his 20 different tissues became the four basic tissues I learned as an undergraduate).

The cell theory was first promoted by Matthias Schleiden and Theodor Schwann in 1838. It was changed to a cell doctrine (all cells arise from preceding cells) by Robert Remak and Rudolf Virchow. Most of the names I have mentioned lived in the 1700s and 1800s. We remember the names of 20th century scientists partly because they are published in textbooks. But if one studies a field and looks at old textbooks of about 100 years ago or more, lots of terms used in those past generations have disappeared. Also, the names of then recent scientists are abundant.

It is a curious honor to be a discoverer of something important and then 100 years after your death your role in it is no longer present in texts or scientific articles. Who remembers that Karl Gegenbaur first introduced the idea of homology into comparative anatomy (your hands, a bat’s wings and a horse’s forefeet are homologous because they have an embryonic common formation from an initial limb bud)?   

Scientists do science because they enjoy the opportunity to make discoveries. Very few will be remembered for centuries like Galileo, Newton or Darwin. All who have published will be dug up centuries from now by historians curious about the origins of ideas and processes of our own generation.

Elof Axel Carlson is a distinguished teaching professor emeritus in the Department of Biochemistry and Cell Biology at Stony Brook University.

By Elof Axel Carlson

Elof Axel Carlson

Science is a way of knowing based on reason. That aspect of science would also apply to logic or the creation of mathematical fields. But when science is applied to the material world, reason is not sufficient. Modern science includes the use of data from observations and from the use of tools to produce data. A third aspect of science is characteristic of modern science. It is the design of experiments that predict what type of data will be found. 

Science differs from revelation, tradition, authority or religious belief because these nonscientific ways that culture forms often require faith or do not attempt to apply science to their beliefs. This difference in interpreting the world around us allowed scientists to be skeptical, to require evidence and to apply more testing and tools to expand the applications of science to the universe and to life.  

This resulted in many new fields of science. Astronomers purged themselves of astrology. Chemists purged themselves of alchemy. Medicine purged itself of quackery. All sciences rejected magic (except as entertainment) and wishful thinking. 

Modern science arose in Italy in the 1500s.  We attribute to Galileo the origins of modern physics and astronomy. He worked out physical laws for falling bodies or bodies rolling down inclined planes. He introduced the mathematical equations to describe and to predict the time required and the distances involved in projectiles dropped, thrown or shot from cannons. He used the telescope he constructed to detect moons around Jupiter, phases of Venus, Saturn’s rings (they looked like ears to him) and mountains and craters on the moon. 

Modern science arose in Italy because the first universities arose in Italy (the University of Bologna was the first in 1088). The Renaissance began in Italy with increased members of the middle class, formation of large cities, importing of knowledge from trade with Asia and Africa and an accumulation of wealth that was spent on architecture, the arts, hobbies, scholarship and curiosity for those with leisure time. 

Artists like Albrecht Dürer went from Bavaria to Italy to study anatomy. William Harvey went from England to study medicine in Italy (Galileo was on the faculty when Harvey was a student) and brought back experimentation to the human body and the circulation of blood.  

German universities benefited from sending students to Italy. In turn the Italian-trained German professors brought their skills to France. During the Enlightenment, French science flourished with Lavoisier in chemistry and Cuvier in biology. From France, science moved to the United States and the founding president of Johns Hopkins University, Daniel Coit Gilman, went to Europe and designed the American University model for its doctorate. 

For the life sciences he recruited a student of Thomas Huxley’s, H. Newell Martin, and W. K. Brooks, one of the first American students of Louis Agassiz (famed for demonstrating and naming the Ice Age that covered large parts of Europe and North America). Martin and Brooks mentored T. H. Morgan. Morgan, at Columbia University, mentored H. J. Muller; and Muller, at Indiana University, mentored me. 

While where a student goes for a doctorate may vary with time, over the past 500 years, the three features of science – reason, data collection and experimentation have not changed. Instead, they have provided enormous applications to our lives from computers to public health, to air flight, to transcontinental roads and railways. They have extended our life expectancy by more than 50 years since the Renaissance began. They allowed humans to walk on the moon and determine how many children to have and when to have them; and they allow us to eat fresh fruits and vegetables all year round. 

Science has its limitations. It cannot design ideal governments, what values to live by, what purpose we choose for motivating us or supply the yearnings of wishful thinking (we will never be rid of all accidents, all diseases, or live forever). It co-exists with the humanities and the arts in filling out each generation’s expectations.   

Elof Axel Carlson is a distinguished teaching professor emeritus in the Department of Biochemistry and Cell Biology at Stony Brook University.

Penguins are among the few animals that live in the South Pole. Stock photo

By Elof Axel Carlson

Elof Axel Carlson

Life abounds from pole to pole and from the bottom of oceans to the peaks of Asian mountain tops. It does this by using the air, water and land to sustain life.

For most of the time on Earth life was confined to single-celled organisms, mostly bacteria. They take in water across a cell membrane. Most do not use oxygen from the air. Those that do came later, when some bacteria developed tools to use sunlight to combine carbon dioxide in the air with water to produce food (carbohydrates) and more abundant energy for the cell. They released oxygen and the atmosphere began to accumulate oxygen. 

Most forms of multicellular life use oxygen from the air to provide the energy to sustain their cellular life. Multicellularity permitted specialization of cells to form tissues, and the tissues then permitted organs to specialize in exchanging carbon dioxide (a waste product for animals) for oxygen.

The branching of limbs on trees is efficient to increase surfaced area for gaseous exchanges. So too are the branching of filaments in the gills of fish or the trachea of insects or the branching of the bronchi in our lungs.

When I see a tree, I see those organ systems reaching skyward with terminal leaves and an equally branched underground of roots, which are bringing in water and minerals from the land into which they are penetrated. The artist sees the beauty of the landscape. The mystic feels the awe of the complexity that seems beyond human comprehension. The scientist explores the structures and assigns functions as they emerge through the tools of science and experimentation.

It is as thrilling to me to see the cellular network of living tissues or organs under a microscope as it is to watch the changing scenery of life when driving from Indiana to New York, or taking walks in Amsterdam, Capetown, Samara, the Seychelles, the nature preserves in Kenya or the beaches of Baja Mexico.

I think of life through time as a fractal drawing with many repetitions creating new patterns. All of life requires a few basic activities. Life requires molecules to form membranes. It requires carbon-based compounds to produce the organelles that compose a cell.  All life (except viruses) is cellular. Life requires molecules that can store information to provide the molecules of life — proteins, nucleic acids, carbohydrates and lipids.

I think of the tools of the artist — a palette, brushes, tubes of oil paint, a canvas stretched on a frame, an easel to hold it. The artist can meticulously render a face, a still life or a landscape with the skills of many hundreds of hours of practice. 

Life also uses cellular tools to construct more complex membranes, organelles, chromosomes and vesicles to a symphony of functioning parts. Science enriches our understanding, opens new worlds of the very small and the very large that we do not normally see.  At most, a galaxy other than our own Milky Way is a mere dot in the sky, but close up it has 100 billion stars in it, most of them like our own sun. Our universe has billions of galaxies. 

As I type a page for an article or book, I am aware that I am coordinating the 37 trillion cells composing me. Human life mimics the universe in its immensity as our Earth now contains some 7 billion people. But this is humbled by the immensity of the astronomer’s universe or the biologist’s inventory of our own cells.    

Elof Axel Carlson is a distinguished teaching professor emeritus in the Department of Biochemistry and Cell Biology at Stony Brook University.

By Elof Axel Carlson

Elof Axel Carlson

The first time I heard DNA enter popular culture was hearing a record played by my son Anders. I heard the refrain, “Hey hey, hey hey! It’s DNA that made me that way.” Anders told me it was from a song called “Sheer Heart Attack” by the rock band Queen (1977).  

Since then that idea has spread from teenage rock fans to the public sphere, and in its modified form, I hear “It’s in my DNA” when a person feels passionately about an idea. Metaphors are part of how we speak but they are not always scientifically accurate. Before the era of DNA (that began with the publishing of the double helix model of DNA in 1953 by James Watson and Francis Crick), a different set of metaphors were in use going back to antiquity. 

Intense belief or fixed behaviors have been attributed to the intestines (I feel it in my gut), to the heart (I offer my heart-felt thanks), to the skeletal system (I feel it to the marrow of my bones), to the blood (royalty are blue bloods and a psychopath’s behavior reflects bad blood) and to the nervous system (argumentative personalities are called “hot headed”). 

Sumerians studied the shape of animal guts and livers to predict the future (haruspicy). Until the Renaissance the brain was thought to be the place where blood is cooled (hence the hot-headed belief). Thoreau was described by one contemporary as sucking the marrow out of life; and blood was considered the vital fluid of life. In the Renaissance the first human blood transfusions were given to provide youthful vigor by old men who believed in rejuvenation.  

When people say, “It’s in my DNA” for a behavior, they are conveying a deeply held belief that it is part of their personality as far back as they can remember or that it is innate. But the evidence for innate human social behaviors is often lacking. There are single gene effects of the nervous system that are well documented such as Huntington’s disease, which leads to dementia and paralysis with an onset usually in middle age. 

There are also family histories of psychosis and learning difficulties. The fragile X syndrome is one such well-documented condition that leads to low intelligence. But human social traits have lots of inputs from parents, siblings, playmates, neighborhoods, regional culture, ethnicity and national identity.  

Children growing up in poverty have different expectations than children whose parents are well off and send them to elite schools. Each generation uses, as best as it can, what it knows. Our knowledge of many important aspects of life and behavior is incomplete. Hence, we keep modifying our interpretations of how life works.  

Much of what is called evolutionary psychology or genetic determinism will be modified or abandoned in years to come as we learn how our genes use memories and other acquired knowledge to shape our personalities. For many cellular processes we know the flow of information from DNA (genes) to cell organelles to cellular function to tissue formation and to organ formation.  

That detailed interpretation of human behavior is not possible now for social traits. I would love to say, “It’s in my DNA” to write these Life Line columns, but my conscience would remind me that it is based on Freudian “wish fulfillment” and not careful experimentation down to the molecular level.

Elof Axel Carlson is a distinguished teaching professor emeritus in the Department of Biochemistry and Cell Biology at Stony Brook University.

By Elof Axel Carlson

Elof Axel Carlson

Occasionally, I read an item on Facebook that engages my attention. One item asked several celebrities (like successful billionaires) to list the five books they most enjoyed reading and briefly tell why they were important. Here are my five favorite books: 

‘Civilization and Its Discontents’ by  Sigmund Freud

Freud introduces the source of the tensions between creativity and destructiveness. He assigns it to the id/superego conflict. I would use instead our capacity for love, empathy and sympathy versus our capacity for hate, bigotry and violence. Freud calls the process sublimation. He began writing this book in 1929 and published it two years later. He predicted that the rise of Nazism was imminent and would lead to massive death because humanity does not know how to sublimate its discontents into the path of the joys of civilization — its arts, humanity, play and immense scholarship.  

‘Jean Barois’ by  Roger Martin du Gard

This is my favorite novel. It is the story of a young French boy raised by a devout Catholic family who thinks he will become a priest. He discovers instead that the more he learns the more doubts arise not only about his calling but his faith. He teaches biology and is fired for teaching evolution. His wife and daughter separate from him. He throws himself into the Freethinkers movement in France and gets involved in the Dreyfus case. He discovers that reason alone cannot sustain his life but returning to his faith is equally inadequate.  

‘The Essays of Michel de Montaigne’

Montaigne’s essays describe his life and the times in which he lived in the context of a rich appreciation of classical literature. He tries to make sense of a world that is pretentious, at war with itself and filled with irony, contradictions and lessons we can extract from the past. Read a 20th-century translation of these essays rather than the 16th-century English translation. Start with his essay on friendship and his essay: “How by various means we all end at the same place.”   

‘The Diary of Samuel Pepys’

I loved reading Pepys’s diaries and was thrilled that he was an eyewitness to the bubonic plague that swept through England in 1665 and the London fire that destroyed most of the city in 1666. Pepys is an imperfect person — not immune to accepting sacks of gold for awarding contracts for the British Navy, flirting with other women but loving his wife and learning to avoid threats to his career from others drawn to the politics of the time.

‘The Origin of Species’ by Charles Darwin 

Darwin is an excellent observer and narrator. He wrote this book as an abstract of a huge multivolume plan for presenting his theory of evolution of species by natural selection. He is careful to distinguish evidence from theory and uses the facts to derive his interpretations of how evolution works. Darwin did not start with a theory and then seek facts to support it. He went with no idea about evolution and instead allowed the hundreds of observations and findings guide him to the only interpretation that made sense of the relations he found whether it was the work of hobbyists and breeders creating new varieties of plants and animals, the geographic distribution of plants and animals he encountered in his trip around the world, or the fossils he encountered.  

——————————————————————————————————————————

I have learned to sublimate my discontents and have had 14 books published for which I thank Freud. I find Jean Barois to be the finest writing on the conflict between science and belief, science and politics and the difficulty of finding a life that sustains us. Montaigne taught me that in difficult times, we can find many things to avoid and how diverse the world is for each new generation that emerges. I have kept a diary (now 112 volumes) more years than not since I first read Pepys’s diary in 1949. Darwin’s book taught me how to use a Baconian approach to science, letting the data amass and allowing an unbiased mind to connect the dots that make new findings and interpretations possible. 

Elof Axel Carlson is a distinguished teaching professor emeritus in the Department of Biochemistry and Cell Biology at Stony Brook University.

Giovanni Alfonso Borelli

By Elof Axel Carlson

Elof Axel Carlson

Scientists have a tradition of citing those whose work helped shape their own ideas and experiments. Almost every scientific paper has a list of such journal articles or books cited by the authors of a published article in a peer-reviewed journal. Usually these references are to recent work that the author or authors have read. 

But one could chase back the references of each cited article and keep doing this to work that was published in the 1600s. Before that things get more complicated because science as we know it dates to the Renaissance. Most of those cited names are forgotten to us and we are taught the names of only a few of these many scientists. 

Thus, we single out the major contributors like Galileo and his work supporting the Copernican theory that Earth and other planets move around the sun. We cite Vesalius’s work on human anatomy, the first accurate depiction of the organs of the human body. We also cite Harvey’s work on the circulation of the blood. What these all have in common is the belief that living organisms are like machines and the laws of physics apply to interpreting their structure and function. 

One of the forgotten contributors to this view of life was Giovanni Alfonso Borelli (1608–1679). Born in Naples, he was the son of a Spanish father, Miguel Alonso, and an Italian mother, Laura Porrello. His father had been exiled from Spain for association with a heretic. This led young Giovanni at the age of 20 to change his baptismal name from Giovanni Francesco Antonio Alonso to the fully Italian sounding Giovanni Alfonso Borelli, which was a version of his mother’s surname Porrello. 

At that time Naples was a Spanish colony and Borelli grew up with his sympathies for Italian culture and political rule. He became a mathematician and astronomer first. He worked out the orbits of Galileo’s discovery of the four large moons of Jupiter and showed they were ellipses. He showed that a comet of 1664 had a parabolic path and was farther than the moon, contradicting church belief then that the comets were not as far as the moon. Isaac Newton cited his work.  

Borelli shifted to medicine and showed that the motions of animals was caused by muscle contractions and the mathematics of levers, pulleys and other machines applied to the components of the body that he studied. He rejected the prevailing view that motion was caused by a vital fluid in the muscles coming from nerves by cutting muscles and showing no such fluids were released. Instead he worked out the center of gravity for different activities of animals and founded the field of biomechanics.  

He kept moving whenever his Spanish ancestry was revealed or when he contradicted fellow scientists who clung to Aristotelian theories that Borelli rejected as nonscientific. In his later life while writing his works, he was supported by Queen Christina of Sweden who went into exile in Rome after converting to Catholicism. He taught mathematics in the convent school that she established and she paid for the publication of his book on animal motion that he dedicated to her.  

Elof Axel Carlson is a distinguished teaching professor emeritus in the Department of Biochemistry and Cell Biology at Stony Brook University.

placozoa

By Elof Axel Carlson

Elof Axel Carlson

Biologists classify living things using a system that Carl Linnaeus (1707–1778) introduced in the 18th century and that has grown in detail over the decades as new forms of life are found and studied. Humans are familiar with being vertebrates (a class of the phylum Chordata). Chordates are animals with a spinal cord, spine or an embryonic structure called a notochord. There are 55,000 chordate species. So far there are 109 phyla covering plants, animals, protozoa, fungi, bacteria and archaea, which are less precisely organized into kingdoms and domains.  

One phylum, first discovered in 1883, consisted of just one species until recently. These are the Placozoa (placo = flat and zoa = animal). They are small (about an eighth of an inch or 1 mm) and are roughly disc shaped with three layers. The top layer has cells with a hairlike thread called a cilium. The bottom layer is also ciliated but has additional cells that take in food from the ocean muck on which the placozoa live. The middle layer has amebalike cells and fiber-bearing cells that contract, making the placozoa lumpy in appearance.  

They reproduce by forming a bud that enlarges and eventually pinches off to produce identical twins. In laboratories, some of the placozoa produce sex cells (sperm and eggs), but these rarely survive the embryonic stage with about 150 cells at the time they die. No such embryos are found in samples of ocean sediments where placozoa dwell. Their DNA has been analyzed and it shows they have a past history of doubling their gene number and rearranging the sequences of their genes as they have moved about the oceans for more than 500 million years.  

Today three species are recognized from samplings around the world. They have about 12,000 genes and portions of these they share with sponges (the phylum Porifera) and comb jellies (the phylum Ctenophora).

Note that the placozoa do not have organized tissues (we have epithelial, muscular, connective and nervous tissues), a basic symmetry (we have a bilateral or left and right sides that are roughly mirror images) or body organs (we have kidneys, lungs, internal bones and eyes, ears, a nose and mouth). They have no nerve cells, muscle cells, bony structure, intestines or sense organs.  

What makes the placozoa interesting to biologists in this molecular era is the opportunity to compare the genomes of related phyla and see what genes they have to work out a molecular tree similar to the trees of life that have been worked out by comparative anatomists since Darwin’s theory of evolution provided a model of how to organize life. They represent the launching state of life before the familiar phyla of sponges, worms and more complex phyla appear in the fossil records.  

Most of the familiar phyla appear in the Cambrian era about 500 million years ago, and the placozoa are first seen in rocks designated as Ediacaran, which existed 100 million years earlier. Rocks can be dated by isotopes present in atoms that have decayed over the millennia. 

Of future interest will be identifying genes in later phyla and genes in placozoa and how they function in these different organizations of life. Also, it will be interesting to follow the genes in placozoa and in their ancestors back to protozoa in the animal kingdom. As interesting as placozoa are, they are too small to be adopted as pets in saltwater aquariums and hard to differentiate without a lens from the muck that accumulates in a fish tank.     

Elof Axel Carlson is a distinguished teaching professor emeritus in the Department of Biochemistry and Cell Biology at Stony Brook University.

By Elof Axel Carlson

Elof Axel Carlson

In 1974 I was a Hill Foundation visiting professor at the University of Minnesota, invited by the History of Science Department to interact with its faculty and students. One faculty member who showed up to my seminar class was Robert Desnick who was interested in medical genetics and he had completed both an M.D. and Ph.D.  

Four years later I arranged with Desnick, who was on the faculty of the medical school, to go on rounds with his pediatric fellows so I could learn what human genetics disorders were like (30 percent of the pediatric patients had some medical genetic condition). I also used my time there to study the genetics of retinoblastoma, a cancer of the eye in children that can affect one or both eyes, and I published two papers with Desnick on that study. I also met Robert Gorlin who had a dental degree and became a world expert on syndromes of the head and neck and whose book on those conditions was a classic (now in its fifth edition).     

I thought about those experiences recently as I read articles in the Public Library of Science (PLoS) on the web about the genetics of the face. All vertebrates have heads with eyes, nose, mouth and ears. I knew from my embryology class as a graduate student that the vertebrate embryo forms a neural tube and one end balloons into a brain. A group of cells along the seamline of the tube migrates and portions of it form the face as do slabs of embryonic tissue that come together to form the skull or cranium. Genes controlling these movements and managing the tissues involved were known from a variety of genetic disorders that Gorlin and Desnick had been following.  

In reading the PLoS articles I felt like Rip van Winkle becoming acquainted with a new world that I had slept through. There are now almost a thousand syndromes of human disorders of the head, neck and face. Hundreds of genes involved have been isolated and sequenced. A smaller portion have had their functions worked out. There is one major gene for cleft lip and palate and dozens of other genes that can modify its severity. Some are tied to a vitamin (folic acid) deficiency and may also lead to spina bifida.  

The story unfolding at a molecular level is still in its infancy but enough is known to make some reasonable predictions. In a few decades it may be possible to examine the DNA of persons (even mummies or the bones of ancient humans) and reconstruct on a computer screen the portraits of their faces as adults. I toyed with this possibility in 1968 in a public lecture I gave at UCLA (50 years go by like a flash when you turn 87). Back then it was all based on speculation.

In 50 years, as the PLoS articles demonstrate, the changes in knowledge are accelerating thanks to the zebrafish (Danio rerio) as a model organism for vertebrate embryology. The zebrafish embryo has transparent cells, so one can look at embryos forming and identify each of the cells involved. 

Biologists have known since Darwin’s writing in the 1860s that facial expressions exist among animals, but humans are remarkable in the nuances facial expressions convey — a Mona Lisa smile, a raised eyebrow of skepticism, a pout, a crying child and the contracted muscles of a bigot shouting slurs are only a few of the many ways we read other people’s faces. At present we can only guess how many genes are involved in these facial gestures. A genetic component is involved because identical twins raised apart for many years show remarkable similarity in their facial expressions and mannerisms.    

Elof Axel Carlson is a distinguished teaching professor emeritus in the Department of Biochemistry and Cell Biology at Stony Brook University.

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