Category Archives: Genetics and Development

November 15, 1871 (a Wednesday)

Erich Tschermak von Seysenegg

On this date, the Austrian agronomist Erich Tschermak von Seysenegg was born.  He was one of the scientists, the others being Hugo De Vries and Carl Correns, who independently rediscovered the work that Gregor Mendel did in the 1860s on the laws of heredity.  Von Seysenegg published his findings in June 1900.  The priority of Mendel was acknowledged without restriction by all three researchers.  Mendel’s discovery that inheritance is particulate, and confirmation of his discovery by Von Seysenegg, De Vries, and Correns, constitutes one of the main pillars of the theory of evolution.

November 7, 1840 (a Saturday)

Aleksandr Onufriyevich Kovalevsky

On this date, the Russian founder of comparative embryology and experimental histology Aleksandr Onufriyevich Kovalevsky was born. He was the first to establish that there was a common pattern in the embryological development of all multicellular animals.

Kovalevsky began by studying the lancelet, a fish-shaped sea animal about 2-in. (5-cm) long; he then wrote Development of Amphioxus lanceolatus (1865). In 1866, he demonstrated the similarity between Amphioxus and the larval stages of tunicates and established the chordate status of the tunicates. In 1867, Kovalevsky extended the germ layer concept of Christian Heinrich Pander and Karl Ernst von Baer to include the invertebrates, such as the ascidians, establishing an important embryologic unity in the animal kingdom. This was important evidence of the evolution of living organisms. In the Descent of Man (1871), Charles Darwin took serious note of Kovalevsky’s interpretation of the embryonic development of ascidians, writing:

M. Kovalevsky has lately observed that the larvae of the Ascidians are related to the Vertebrata in their manner of development, in the relative position of the nervous system and in possessing a structure closely like the chorda dorsalis of vertebrate animals; and in this he has since been confirmed by Prof. Kupffer. M. Kovalevsky writes to me from Naples, that he has now carried these observations further; and, should his results be well established, the whole will form a discovery of the greatest importance. Thus if we may rely on embryology, ever the safest guide in classification, it seems that we have at last gained a clew in the source whence the vertebrates were derived. I should then be justified in believing that at an extremely remote period a group of animals existed, resembling in many respects the larvae of our present ascidians, which diverged into two great branches – the one retrograding in development and producing the present class of Ascidians, the other rising to the crown and summit of the animal kingdom by giving birth to the Vertebrata.

Kovalevsky was elected to the Russian Academy of Sciences in 1890.

November 5, 1892 (a Saturday)

John Haldane

On this date, British geneticist and biometrician John Burdon Sanderson Haldane was born. He was one of the three major figures to develop the mathematical theory of population genetics. (He is usually regarded as the third of these in importance, after R. A. Fisher and Sewall Wright.) Population genetics became one of the key elements of what would be called the Modern Synthesis. It revealed how mutations arise and, if they are favored by natural selection, can spread through a population, causing evolutionary change without the help of imaginary Lamarckian forces. Haldane also worked in biochemistry, and on the effects of diving on human physiology. He was the first to suggest that membranes played a role in the origin of life in his prescient note in The Rationalist Annual (1926). He wrote that “The cell consists of numerous half-living chemical molecules suspended in water and enclosed in an oily film. When the whole sea was a vast chemical laboratory the conditions for the formation of such films must have been relatively favorable . . .” In 1954, Haldane, speaking at the Symposium on the Origin of Life, suggested that an alternative biochemistry could be conceived in which water was replaced as a solvent by liquid ammonia.

J.B.S. Haldane began studying science at the age of eight, as assistant to his father (the noted physiologist John Scott Haldane). A Marxist from the 1930s, Haldane was well known for his outspoken Marxist views. He resigned from the Communist Party around 1950 on the issue of Lysenko’s claims to have manipulated the genetic structure of plants and “Stalin’s interference with science.” He became known to a large public as a witty popularizer of science with such works as Daedalus (1924), Possible Worlds (1927), and The Causes of Evolution (1932).

Purportedly, it is Haldane who made the famous comment that all that biology tells us about the nature of God is that he has “an inordinate fondness for beetles” (reported in G. E. Hutchison, 1959, Amer. Natur. 93:145-159).

References:

  • J.B.S. Haldane, “The Origin of Life,” The Rationalist Annual 148: 3-10 (1929).

November 4, 1855 (a Sunday)

Frederick Orpen Bower

On this date, the botanist Frederick Orpen Bower was born in Ripon, England. His study of primitive land plants, especially the ferns, contributed greatly to a modern emphasis on the study of the origins and evolutionary development of these plants. A man who did not shy away from theorizing, one of his most productive “working hypotheses” was his application of the alternation of generations model to explaining the way the land was colonized by early plants. This subject was explored most completely in his book entitled The Origin of a Land Flora: A Theory Based upon the Facts of Alternation, published in 1908.

From his many years studying liverworts, mosses, and ferns, Bower concluded that they had evolved from algal ancestors. Bower’s hypothesis states, in essence, that the sporophyte generation (the conspicuous vegetative stage in familiar vascular plants) developed de novo from a haploid alga that lacked a diploid sporophyte generation but instead had merely a diploid zygote (a cell formed by the fusion of two gametes, such as sperm and egg). Before the evolution of embryos, this zygote would have immediately undergone meiosis (to relieve the diploid condition) and produced spores, the propagules of the next haploid generation. Growth of such a spore into a gametophyte is analogous to growth of an isolated human sperm or egg cell into a hypothetical haploid generation. Thus, the sporophyte generation first appeared as an added generation that came into existence as a result of delayed zygotic meiosis – sort of a delayed plant puberty. In other words, what might otherwise have become the new haploid cells of the next generation by chromosome reduction instead retained its diploid character and thus added, aà la Bower, a new generation to the life cycle. The final step of spore production still eventually occurred, but not until after the diploid cells had grown and developed into a new sporophyte generation, in essence an overgrown zygote.

Under Brower’s hypothesis, we suppose that, from the point of view of the gametophyte, the sporophyte generation is like a giant multicellular spore factory. For example, in Coleochaete pulvinata, a modern freshwater green alga, the surface of the mature zygote is covered by a layer of haploid cells, which form ingrowths that penetrate the zygote to provide nutrition. The protected diploid zygote in Coleochaete gives the aquatic alga advantages because many more spores can be produced from a single fertilization event than would be the case if the zygote hurried straight to meiosis and the formation of one of those four spore tetrads so common in the fossil record. Bower’s hypothesis remains to be tested, but if it is correct, the sporophyte generation (diploid cells) came to develop inside (and be protected by) the gametophyte generation (haploid cells) precisely because the arrangement ultimately benefited both generations.

An older, competing hypothesis dating back to 1874 held that the algal ancestor of embryophytes already had had alternation of two generations for a long time and was thus diplobiontic, as opposed to haplobiontic. Haplobiontic organisms, such as humans, have the gametes as the only haploid cells; diplobiontic organisms develop those haploid cells into a multicellular life stage. The diplobiontic hypothesis of 1874 is less favored now because it fails to explain how the sporophytes and gametophytes, which in modern diplobiontic green algae have no long-term physical connection, could have evolved the intimate physical connection, in both nutritional and developmental respects, shared by the haploid and diploid components of all embryophytes.

Bower’s other publications included Ferns (three volumes, published 1923-28) and Primitive Land Plants (1935). Bower was elected Fellow of the Royal Society in 1891 and was awarded the Linnean Medal in 1909, the Royal Medal in 1910, and the Darwin Medal in 1938, the latter “In recognition of his work of acknowledged distinction in the field in which Darwin himself laboured.”

November 1, 1977 (a Tuesday)

Carl Woese

On this date, the American microbiologist and physicist Carl Woese published a report in the Proceedings of the National Academy of Sciences (PNAS) in which he defined the Archaeabacteria (a new super-kingdom of life) by phylogenetic analysis of 16S ribosomal RNA.  This technique was pioneered by Woese and is now standard practice. By 1990 Woese shortened the name Archaebacteria to Archaea and adopted the term “domains” for the three new branches of life: Bacteria, Archaea, and Eukarya. Archaea are neither Bacteria nor Eukaryotes. In other words, they are Prokaryotes that are not Bacteria. More than twenty kingdoms exist under the domains in the tree of life, far more than the five original kingdoms suggested by R.H. Whittaker in 1969. In fact, Woese found that Archaea are more closely related to Eukarya (plants, animals, fungi, etc.) than to Bacteria. This accounted for the renaming of Archaebacteria, the original name given by Woese, to Archaea.

According to Woese:

The archaea are unique organisms. While prokaryotes in the cytological sense, they are actually more closely related to eukaryotes than to the bacteria. They are of particular interest for this reason alone-they are simple organisms whose study should provide insights into the nature and evolution of the eukaryotic cell. Their study is also central to an understanding of the nature of the ancestor common to all life. The archaea are, of course, interesting in their own right. The group contains both the methanogens and numerous organisms that grow at extremely high temperatures (in some cases above 100°C). As such, they provide potential insights into mechanisms of thermophilia and methanogenesis.

by Carl Woese

The acceptance of the validity of Woese’s classification was a slow and painful process. Famous figures, including Salvador Luria and Ernst Mayr, objected to his division of the prokaryotes. Not all criticism of him was restricted to the scientific level. Not without reason has Woese been dubbed “Microbiology’s Scarred Revolutionary” by the journal Science. The growing amount of supporting data led the scientific community in general to accept the Archaea by the mid-1980s. A shrinking minority of scientists still adhere to concepts of evolutionary radiation, but Woese appears to have been vindicated in his convictions.

References:

October 11, 1993 (a Monday)

Richard J. Roberts

On this date, the Nobel Assembly at the Karolinska Institute awarded the Nobel Prize in Physiology or Medicine jointly to Richard J. Roberts and Phillip A. Sharp, who in 1977 independently discovered that individual genes could be discontinuous, that is, a given gene could exist in the genetic material not as one continuous segment of DNA but as several, well-separated segments. A gene may thus consist of several segments, usually termed exons, separated by intervening, irrelevant stretches of DNA called introns. Such “split genes” are typically found in eukaryotes but not in prokaryotes, which have very compact genomes.

Phillip A. Sharp

The discovery of split genes has radically changed our view on how the genetic material has changed during the course of evolution. Previously, it was thought that only minor alterations (mutations) occur within genes, producing gradual change in the genetic material. However, now it seems likely that higher organisms, in addition to undergoing mutations, may utilize another method that changes the genetic material: rearrangement or shuffling of exons that produces proteins with new functions. This can take place through crossing-over during gamete formation. This hypothesis was bolstered by the later finding that individual exons in several cases correspond to building modules (domains) in proteins and each domain has a specific function. An exon in the gene would thus correspond to a particular subfunction in the protein, and the shuffling of exons could result in a new combination of subfunctions in a protein. This kind of genetic recombination could accelerate evolution significantly.

September 25, 1866 (a Tuesday)

Thomas Hunt Morgan

On this date, the American embryologist and geneticist Thomas Hunt Morgan was born in Lexington, Kentucky. At Columbia University (1904-28), he began his revolutionary genetic investigations of the fruit fly Drosophila melanogaster (1908). In 1910, he discovered a white-eyed mutant in Drosophila. At that time, it was generally assumed that chromosomes could not be the carriers of the genetic information. Initially skeptical of Gregor Mendel’s research, Morgan performed rigorous experiments eventually demonstrating that genes are linked in a series on chromosomes and are responsible for identifiable, hereditary traits. When he was awarded the Nobel Prize in Physiology or Medicine in 1933, he was the first person awarded the Prize for genetics, for demonstrating hereditary transmission mechanisms in D. melanogaster.

September 20, 1952 (a Saturday)

The Hershey-Chase Experiments.

On this date, geneticists Alfred Hershey and Martha Chase published the findings of their so-called blender experiments, which concluded that DNA (DeoxyriboNucleic Acid) is where life’s hereditary data is found.

Prior to these experiments, so named because they were conducted using a regular kitchen blender, it was generally thought that proteins — not DNA — were the genetic stuff of life.

Their experiments used the T2 bacteriophage, which, like other viruses, is just a crystal of DNA and protein. It can reproduce when inside a bacterium such as Escherichia coli, or E. coli for short. When the new T2 viruses are ready to leave the host E. coli cell (and go infect others), they burst the E. coli cell open, killing it (hence the name “bacteriophage”).

Hershey and Chase were seeking an answer to the question, “Is it the viral DNA or viral protein coat (capsid) that is the viral genetic code material which gets injected into the E. coli?” Using the kitchen blender, Hershey and Chase separated the protein coating from the DNA of T2 bacteriophage. Injecting the DNA into the bacterial cell, they found that it was the nucleic acid itself, and not the protein, that caused the transmission of hereditary information.

The Hershey–Chase experiment, its predecessors, such as the Avery-MacLeod-McCarty experiment, and successors served to unequivocally establish that hereditary information was carried by DNA.

Alfred Hershey was awarded the Nobel Prize in Physiology or Medicine in 1969. He shared the prize with two American scientists, Max Delbrück and Salvador Luria, for “discoveries concerning the replication mechanism and the genetic structure of viruses” but Chase, who served as Hershey’s lab assistant during his experiments and whose name appears on the paper, was snubbed.

References:

  • Hershey, A and Chase, M (1952). “Independent functions of viral protein and nucleic acid in growth of bacteriophage,” J Gen Physiol 36 (1): 39–56.

September 19, 1864 (a Monday)

Carl Erich Correns

On this date, the German botanist and geneticist Carl Erich Correns was born. He is famous for rediscovering, independently of but simultaneously with the biologists Erich Tschermak von Seysenegg and Hugo De Vries, Gregor Mendel’s historic paper outlining the principles of heredity.

In 1892, while at the University of Tübingen, Correns began to experiment with trait inheritance in plants. On January 25, 1900, he published his first paper, “G. Mendel’s Law Concerning the Behavior of the Progeny of Racial Hybrids”, in which he restated Mendel’s results and his law of segregation and law of independent assortment. Although the paper cited both Charles Darwin and Mendel, Correns did not fully recognise the relevance of genetics to Darwin’s ideas.

In attempting to determine the extent to which Mendel’s laws are valid, Correns undertook a classic study on heredity in the four-o’clock plant (Mirabilis jalapa). The blotchy leaves of these variegated plants show patches of green and white tissue, but some branches carry only green leaves and others carry only white leaves. Whether a tissue is green or white depends on whether there are green or white chloroplasts in the cytoplasm of its cells. Flowers appear on all types of branches, and Correns performed a variety of crosses.

Two features of his results were surprising. First, unlike what Mendel had observed, Correns found that there was a difference between reciprocal crosses, that is, leaf color depended greatly on which parent (i.e., flower’s branch) had which trait. Such results are normally encountered only for sex-linked genes, but Correns’ results cannot be explained by sex linkage. Secondly, the phenotype of the maternal parent was solely responsible for determining the phenotype of all progeny, that is, the phenotype of the male parent appeared to be irrelevant, making no contribution to the progeny at all! Although the white progeny plants did not live long because they lacked chlorophyll, the other types of progeny did survive and could be used in further generations of crosses. The same patterns of maternal inheritance always appeared in these subsequent generations.

Maternal inheritance can be explained if the chloroplasts are somehow genetically autonomous and furthermore, are never transmitted via the sperm. This is reasonable since the chloroplasts come exclusively from the mother in most angiosperms. In his 1909 paper, Correns established variegated leaf color as the first conclusive example of cytoplasmic inheritance (cases in which certain characteristics of the progeny are determined by factors in the cytoplasm of the female sex cell), also known as extrachromosomal or non-Mendelian inheritance.

Unfortunately, most of Correns’ work went unpublished and was destroyed in the Berlin bombings of 1945.

July 28, 1840 (a Tuesday)

Edward Drinker Cope

On this date, the American paleontologist, herpetologist, and mammalogist Edward Drinker Cope was born. Cope was a scientist by self-study and personal nature — he held no degrees except honorary ones from Haverford College and, late in life, from the University of Munich. He made many important dinosaur discoveries in western North America but spent 20 years in a protracted battle with his archrival, O.C. Marsh, for professional prestige in what came to be known as the Great Bone Wars. Financially ruined in his later years, Cope had to sell his house and move in with his museum collections. He spent his final days on a cot surrounded by piles of bones.

Cope accepted the fact of evolution but thought that change in developmental (embryonic) timing, not natural selection, was the explanation for how evolution occurs. That is, a new developmental stage would be tacked onto the end of the developmental process, pushing the old end stage further back in development. Such was the view of the American school of self-proclaimed, so-called neo-Lamarckians, who invoked an internal drive for “accelerated growth” as well as Lamarckian inheritance of acquired characteristics to account for the seemingly linear pattern of biological evolution that they detected in specimens from the rich fossil beds of the American West. That is, new developmental stages would cause some body parts to become very well developed if those body parts were in heavy use. Thus, the neo-Lamarckians thought that variation and speciation were due to changes in timing of development in different organ systems due to use. In Europe, important contemporaneous neo-Lamarckians included the German biologist Ernst Haeckel and the British botanist George Henslow.

July 22, 1910 (a Friday)

On this date, the American embryologist and geneticist T(homas) H(unt) Morgan reported in the journal Science:

In a pedigree culture of Drosophila which had been running for nearly a year through a considerable number of generations, a male appeared with white eyes.

White-eyed and wild type Drosophila.

For the science of genetics, the portent of the white mutation was enormous. Quickly, additional sex-linked mutants were discovered by Morgan and his students. By 1913 Sturtevant, with unsurpassed intuition, constructed the first linear genetic map of the X chromosome, followed by Bridges’ cytogenetic proof in 1916 of the chromosomal theory of inheritance. In 1915, Morgan, Sturtevant, Calvin Bridges and H. J. Muller wrote the seminal book The Mechanism of Mendelian Heredity. By 1925 the vast amount of information accumulated by Morgan and his students in less than 15 years was summarized in the monograph The Genetics of Drosophila. Documented therein are those fundamental principles of genetics derived from the study of Drosophila, principles that have withstood the test of time and that are included in all contemporary textbooks of genetics.

Interestingly, the period from approximately 1875 to 1925 has been called “the eclipse of Darwinism.” The phrase refers to the circumstances prior to the modern evolutionary synthesis when evolution was widely accepted in scientific circles but relatively few biologists thought that natural selection was its primary mechanism. In fact, many biologists considered natural selection to have been a wrong guess on Darwin’s part, and during his early career, Morgan had been one of them. In Evolution and Adaptation (1903), he had argued the anti-Darwinist position that selection never could produce wholly new species by acting on slight individual differences.

However, after discovering many small stable heritable mutations in Drosophila, Morgan had gradually changed his mind.  Since Morgan (1915) had ‘solved the problem of heredity’, he was in a unique position to examine critically Darwin’s theory of natural selection.  On February 24, 1916, Morgan began a series of lectures that would later be the basis of a book he published entitled A Critique of the Theory of Evolution (1916). The subsequent lectures occurred on March 1, 8, and 15.  He discussed questions such as:

  • Does selection play any role in evolution?
  • How can selection produce anything new?
  • Is selection no more than the elimination of the unfit?
  • Is selection a creative force?

After eliminating some misunderstandings and explaining in detail the new science of Mendelian heredity and its chromosomal basis, Morgan concluded that “the evidence shows clearly that the characters of wild animals and plants, as well as those of domesticated races, are inherited both in the wild and in domesticated forms according to the Mendel’s Law.”  “Evolution has taken place by the incorporation into the race of those mutations that are beneficial to the life and reproduction of the organism.”  “Injurious mutations have practically no chance of becoming established.”  Far from rejecting evolution as the title of his 1916 book may suggest, Morgan not only laid the foundation of the science of genetics, but by doing so, he also laid the theoretical foundation for the mechanism of evolution: natural selection.  Heredity was an essential  requirement of Darwin’s theory of natural selection, but Darwin had a wrong theory of heredity. Therefore, Darwinism could not progress without a correct theory of genetics. Morgan furnished that foundation, which is why his  work was so important for the neo-Darwinian synthesis, despite his criticism at the beginning of his career.

References:

  • Bridges, C . B., “Nondisjunction as proof of the chromosome
    theory of heredity” Genetics 1: 1-52, 107-163 (1916).
  • Green, M.M., “The ‘Genesis of the white-eyed mutant’ in Drosophila melanogaster: A reappraisalGenetics 142: 329-331 (Feb. 1996).
  • Morgan, T.H., “Sex-limited inheritance in Drosophila” Science 32: 120-122 (1910).
  • Morgan, T.H., A Critique of the Theory of Evolution (Princeton, NJ: Princeton University Press, 1916).
  • Morgan, T.H., Sturtevant, A.H., Muller, H.J. and C. B. Bridges, The Mechanism of Mendelian Heredity (New York, NY: Henry Holt, 1915).
  • Morgan, T. H., Bridges, C.B. and A.H. Sturtevant, “The
    genetics of Drosophila” Bibliogr. Genet. 2: 1-262 (1925).
  • Sturtevant., H., “The linear arrangement of six sex-linked
    factors in Drosophila as shown by their mode of association” J.
    Exp. Zool.
    14: 43-59 (1913).

July 20, 1822 (a Saturday)

The earliest known photograph of Gregor Mendel.

On this date, Gregor Johann Mendel was born (the day he was baptized, July 22nd, is often given erroneously as his birthday). He performed a series of beautifully designed experiments on pea plants over a period of seven years, from 1856 to 1863, to discover the principles of heredity. His studies were the first to focus on the numerical relationships among traits appearing in the progeny of hybrids; and his interpretation, clear and concise, was based on material hereditary elements that undergo segregation and independent assortment.

Mendel delivered two lectures on the results of his experiments at the meetings of the Society of Natural Sciences in Brünn, Austria on February 8th and March 8th in 1865. He turned these lectures into a (long) paper, published in the 1866 issue of the Proceedings of the Society, but it received little notice. Mendel apparently even sent one of his scientific papers to Darwin, but Darwin never bothered to read it. Mendel abandoned his experiments in the 1860s after he was appointed abbot of his monastery and his time was taken up in administrative duties.

The importance of Mendel’s work was not recognized until about thirty years after the publication of his seminal paper, when Hugo de Vries in 1900 in Holland, William Bateson in 1902 in Great Britain, Franz Correns in 1900 in Germany, and Erich Tschermak in 1901 in Austria were all to acknowledge Mendel’s legacy, and hail him as the true “father” of classical genetics.

Curiously, proponents of Intelligent Design (ID) theory have attempted to appropriate Mendel. Steve Fuller openly declares that ID theorists “would do well to reclaim the likes of Newton, Linnaeus, and Mendel as their own” (2007, p 7). Fuller claims that Mendel was no evolutionist, but a “special creationist with a grasp of probability theory”. For Fuller, the Mendelian rules of heredity are laws designed by God, that define “the range of traits that God deemed permissible in a given species”.

The only occasion that Mendel expressed himself directly on the subject of evolution was in an examination paper he sat in 1850. Discussing the origin of plant and animal forms, in the context of the formation of the earth, he wrote:

As soon as the earth in the course of time had achieved the necessary capability for the formation and maintenance of organic life, plants and animals of the lowest sorts first appeared.

[In time, organic life] developed more and more abundantly; the oldest forms disappeared in part, to make space for new, more perfect ones.

[This is] at the present time the generally accepted view of the emergence and development of the earth (Orel 1984, pp 237-8).

This is far from any “creationism” (even “special creationism”).

When he wrote this, he had been a monk for seven years. He finished his studies at the University of Vienna three years later, in 1853; began his Pisum experiments in earnest in 1856; and did not deliver his talk on those experiments until 1865. Of course, his ideas may have changed in time—and in any case, the views expressed in an examination may not always reflect the writer’s real opinion; but in the absence of any other statement by Mendel on the origin of species, this would appear to undermine any notion that he was a “special creationist.”

References:

  • Fisher, R.A. “Has Mendel’s work been rediscovered?Annals of Science, v. 1: 115-137 (1936)
  • Fuller, Steve (2007). Science vs. Religion? (Cambridge: Polity Press).
  • Orel, Vitěslav (ed.) (1984). ‘Mendels Hausarbeit in Naturgeschichte von 1850’. In: Folia Mendeliana 18 (Special edition).

July 5, 1904 (a Tuesday)

Evolutionary biologist Ernst Mayr.

On this date, the American biologist Ernst Mayr was born in Germany. He began bird watching as a young boy, and by the age of ten, he could recognize all of the local bird species by call as well as sight. Mayr was known for his work in avian taxonomy, population genetics, and evolution. He led development of what has become known as the “modern synthesis,” the establishment of Darwin’s theory of evolution on a firm foundation of experimental genetics and population statistics. In 1940, Mayr proposed the concept of a species as a group of populations that are reproductively isolated from other such groups, the definition most widely used by biologists today.

Mayr was productive throughout his life and lived to a ripe old age but could never fully explain his longevity. “There is no history of it among my ancestors and both my parents died of cancer,” he said. “Probably it results from exercising every day, living a healthy life and having an active mind. My mind is still in very good shape; I have never let it rest. I’ve always had a tremendous breadth of interest; I’ve always wanted to know everything and read everything.” He died on February 3, 2005.

June 29, 1935 (a Saturday)

On this date, Wendell Meredith Stanley announced the isolation of tobacco mosaic virus (TMV) as a crystalline molecule in the journal Science. For this feat, he later was a co-recipient of the Nobel Prize in Chemistry for 1946.

Stanley’s work had great significance for the ongoing debate about the scientific distinction between life and non-life. In 1937 Barclay Moon Newman noted that, “It has astonished the scientific world that a single molecule can be the causative organism of a disease. How can a crystal be made up of living molecules?” Stanley said in his Nobel Prize Lecture on 12 December 1946:

Reproduction, mutation and metabolic activity have long been regarded as unique and special properties of living organisms. When viruses were found to possess the ability to reproduce and to mutate, there was a definite tendency to regard them as very small living organisms, despite the fact that the question of metabolic activity remained unanswered. Because of their small size they could not be seen by means of the ordinary light microscope. Although. this fact puzzled some investigators, it was pushed aside and for over thirty years interest in virus research was centered about the discovery of new viruses and on studies of the pathological manifestations of viruses.

Then, around 1930, Elford… demonstrated that different viruses possessed different and characteristic sizes, and that some viruses
were as large as about 300 mμ, whereas others were as small as 10 mμ… The fact that, with respect to size, the viruses overlapped with the organisms of the biologist at one extreme and with the molecules of the chemist at the other extreme only served to heighten the mystery regarding the nature of viruses. Then too, it became obvious that a sharp line dividing living from non-living things could not be drawn and this fact served to add fuel for discussion of the age-old question of “What is life?”.

(…)

Needless to say, for a time there was great skepticism that the crystalline material could be tobacco mosaic, due chiefly to the old idea that viruses were living organisms… As a whole, the results indicated that the crystalline material was, in fact, tobacco mosaic virus.

Untitled

Stanley did not realize the importance of the nucleic acid component of TMV. Viruses today are recognized to be literally “parasitic” chemicals, segments of DNA or RNA wrapped in a protein coat. They can reproduce within cells, often with disastrous results to the host organism, but they cannot reproduce on their own, which is why they are not considered alive by biologists. Earlier ideas that viruses represent a kind of halfway point between life and non-life have largely been abandoned. Instead, viruses are now viewed as detached fragments of the genomes of organisms due to the high degree of similarity found among some viral and eukaryotic genes.

Stanley co-authored the book Viruses and the Nature of Life (1961).

References:

  • Angela N. H. Creager. The Life of a Virus: Tobacco Mosaic Virus as an Experimental Model, 1930-1965 (Chicago, IL: University of Chicago Press, 2002) p. 47.
  • Wendell Stanley, “Isolation of a crystalline protein possessing the properties of tobacco-mosaic virus” Science, vol. 81, issue 2113: 644-645 (1935).
  • Wendell Stanley and Evans G. Valens. Viruses and the Nature of Life (New York: Dutton, 1961).

May 27, 1961 (a Saturday)

Marshall Nirenberg and Heinrich Matthaei.

On this date, in a laboratory on the seventh floor of Building 10 on the NIH campus in Bethesda, Maryland at three o’clock in the morning, J. Heinrich Matthaei combined the synthetic RNA made only of uracil (called poly-U) with cell sap derived from E. coli bacteria and added it to each of 20 test tubes. This time the “hot” test tube was phenylalanine. The results were spectacular and simple at the same time: after an hour, the control tubes showed a background level of 70 counts, whereas the hot tube showed 38,000 counts per milligram of protein. The experiment showed that a chain of the repeating bases uracil forced a protein chain made of one repeating amino acid, phenylalanine. The genetic code could be broken! UUU=Phenylalaline was a breakthrough experimental result for Marshall Nirenberg and Heinrich Matthaei.  In August 1961, they published their now-classic report, “The Dependence of Cell-Free Protein Synthesis in E. Coli upon Naturally Occurring or Synthetic Polyribonucleotides,” in the Proceedings of the National Academy of Sciences.

May 23, 1905 (a Tuesday)

Nettie Stevens (1904)

Nettie Stevens (1904)

On this date, Nettie Maria Stevens submitted her manuscript “Studies in Spermatogenesis with Especial Reference to the ‘Accessory Chromosome'” to the Carnegie Institution for publication in the Carnegie monograph series. It was sent on May 29 to E.B. Wilson, a member of the institution’s advisory committee, for his opinion. He returned it on June 13 with the brief statement: “It is in every way a most admirable piece of work which is worthy of publication by any learned society, and I do not hesitate to recommend it to you for publication by the Institution.” Wilson’s comments were an understatement; her research paper was one of the 20th century’s major scientific breakthroughs.

Stevens’ monograph was published in September 1905, the first documentation that observable differences in chromosomes could be linked to an observable difference in physical attributes, i.e. if an individual is a male or a female. This caused many at the time to re-evaluate earlier conclusions of sex determination, and to begin looking more generally at a chromosomal basis for animal sex determination.

Nettie Stevens, educated at Stanford University and Bryn Mawr College (Ph.D., 1903), taught throughout her relatively short life, inspiring many students to careers in science. She published more than 38 papers from 1901 to her death (1912), in cytology and experimental physiology.

The ‘biblical view’ that’s younger than the Happy Meal

The ‘biblical view’ that’s younger than the Happy Meal.

April 25, 1953 (a Saturday)

James Watson (left) and Francis Crick in 1959.

On this date, James Watson and Francis Crick published an article in the journal Nature describing the structure of DNA in terms of the now-familiar double helix. Watson was working at the Cavendish Laboratory, University of Cambridge, in early October 1952. He met Francis Crick there and they agreed that, working together, they should be able to discover the structure of DNA that had eluded others. Crick brought to the project his knowledge of x-ray diffraction, while Watson brought knowledge of phage and bacterial genetics. In April 1953 they jointly published their theory, complete with a diagram of “two helical chains coiled round the same axis.” Watson (age 25 at the time), was born in Chicago; Crick (age 36 at the time), was born in Northampton, England. Their discovery won them both, with Maurice Wilkins, the Nobel Prize in Physiology or Medicine in 1962.

Human Genome Project director Francis Collins says, even 50 years later, it’s impossible to overstate the importance of knowing the structure of DNA:

It is so intertwined in every bit of what we do experimentally, in terms of perceiving our own position in the scheme of life on this planet. It has become one of those givens that is so central to your thinking that you stop thinking about it, but if somebody took it away from you, your whole intellectual foundation would collapse, and it would be unimaginable what we would be doing now if we didn’t know about the double helix.

Furthermore, DNA is not just an instruction book for the present and something to pass on to future generations – it is also record of our genetic past. No longer do researchers look for clues to human history merely in fossil bones and stone tools, they also seek “genetic fossils” in the DNA of living peoples.

April 18, 1865 (a Tuesday)

Karl Wilhelm von Naegeli, the man who discouraged Gregor Mendel from further work on genetics.

Karl Wilhelm von Naegeli, the man who discouraged Gregor Mendel from further work on genetics.

On this date, Austrian monk Gregor Mendel, 42, sent the results of his seven-year study of peas to the eminent biologist Karl Wilhelm von Nägeli in Munich. Within these results were the basic laws of genetics, which the humble Mendel discovered single-handedly in a small garden at the Brünn monastery (now in Brno, Czech Republic). Nägeli failed to see the importance of the work; he suggested that Mendel try new experiments with different plants. Nägeli’s cool reception, coupled with the failure of the new experiments, were instrumental in Mendel’s abandoning serious research.

April 1, 1578

William Harvey

On this date, the English physician and scientist William Harvey was born. He is credited with being the first in the Western world to describe correctly and in exact detail the systemic circulation and properties of blood being pumped around the body by the heart. Harvey published his discovery in a treatise entitled Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus (On the Motion of the Heart and Blood in Animals) in 1628. Brief, well argued, and clearly written, De Motu Cordis is very probably the one and only great classic of Western science written before 1800 that is still widely read today. His discovery was dramatically confirmed later in the seventeenth century by microscopist Marcello Malpighi’s discovery of capillaries.

Functional knowledge of the heart and the circulation had remained almost at a standstill ever since the time of the Greco-Roman physician Galen – 1,400 years earlier. With Harvey, life began to receive mechanistic explanation. The essential idea of mechanistic explanation is that “natural” events have “natural” causes and can be explained by cause-and-effect relationships that do not involve special action of supernatural agency. This is fundamental to modern science.

Title page of *De Motu Cordis*

Just as important was Harvey’s methodology. De Motu Cordis quickly became understood as a rejection of traditional methods. It was viewed as challenging the traditional system of deductive reasoning via syllogisms, instead advocating experimentation and sensory experience. The empirical methodology observable in Harvey’s work is now the acknowledged scientific method and has been universally adopted across all science and medicine.

Harvey clearly understood the implications of his work, for he wrote at the opening of Chapter VIII (“Of the abundance of blood passing through the heart out of the veins into the arteries, and of the circular motion of the blood”), in which he demolishes the core of the Galenic model:

Thus far I have spoken of the passage of the blood from the veins into the arteries….But what remains to be said upon the quantity and source of the blood which thus passes, is of a character so novel and unheard-of that I not only fear injury to myself from the envy of a few, but I tremble lest I have mankind at large for my enemies, so much has wont and custom become second nature. Doctrine once sown strikes deep its root, and respect for antiquity influences all men. Still, the die is cast, and my trust is in my love of truth and the candor of cultivated minds.

He also left a message in De Motu Cordis that is as true today as it was 500 years ago:

True philosophers, who are only eager for truth and knowledge, never regard themselves as already so thoroughly informed, [so that they do not] welcome information from whomsoever and from wheresoever it may come; nor are they so narrow-minded as to imagine any of the arts or sciences transmitted to us by the ancients, in such a state of forwardness or completeness that nothing is left for the ingenuity or industry of others. On the contrary, very many maintain that all we know is still infinitely less than all that remains unknown. [Nor] do philosophers pin their faith to others’ precepts in such [ways] as they lose their liberty, and cease to give credence to the conclusions of their proper senses. Neither do they swear such fealty to their mistress Antiquity, that they openly, and in sight of all, deny and desert their friend, Truth. [emphasis added]

In Exercitationes de Generatione Animalium (On the Generation of Animals) in 1651, Harvey was extremely skeptical of spontaneous generation and proposed that every living animal originally comes from an egg, introducing the oft-quoted phrase “ex ova omnia” (all [life] from eggs). [However, Harvey did not completely reject spontaneous generation.] His experiments with chick embryos supported the theory of epigenesis, which states that organisms develop from substances in the egg that differentiate during embryonic development.  This was in conflict with the now-descredited preformationist view that perfect miniature versions of offspring exist in the gametes and grow during development.  [Please note that the term ‘epigenesis’ carries different meanings. Here, it used used in the older sense, as a theory of animal and plant development. In more modern times, it refers to mechanisms by which gene regulation over generations is controlled by elements other than DNA.]

References:

  • Schultz, S.G., “William Harvey and the circulation of the blood: The birth of a scientific revolution and modern physiology,” News in Physiological Sciences 17: 175-180 (Oct 2002).

February 28, 1953 (a Saturday)

James Watson (left) and Francis Crick in 1959.

On this date, Cambridge University scientists James D. Watson and Frances H.C. Crick announced that they had determined the structure of DNA, the molecule containing human genes. On the morning of February 28, they determined that the structure of DNA was a double-helix polymer, or a spiral of two DNA strands, each containing a long chain of monomer nucleotides, wound around each other.

In his best-selling book, The Double Helix (1968), Watson later claimed that Crick announced the discovery by walking into the nearby Eagle Pub and blurting out that “we had found the secret of life.”

Watson and Crick’s solution was formally announced on 25 April 1953, following its publication in that month’s issue of the journal Nature. The article revolutionized the study of biology and medicine.

Along with Maurice Wilkins, a colleague, Watson and Crick won the Nobel Prize in 1962 for their discovery.

February 17, 1890 (a Monday)

Ronald Fisher

On this date, the English geneticist Ronald Aylmer Fisher was born. His book The Genetical Theory of Natural Selection (1930), with its ground-breaking treatment of the concepts of fitness and dominance, was a milestone work in that field.

February 16, 1848 (a Wednesday)

Hugo de Vries

On this date, the Dutch botanist and early geneticist Hugo Marie de Vries was born. He is known chiefly for suggesting the concept of genes, rediscovering the laws of heredity in the 1890s while unaware of Gregor Mendel’s work, for introducing the term “mutation”, and for developing a mutation theory of evolution.

In 1889, De Vries published his book Intracellular Pangenesis, in which, based on a modified version of Charles Darwin’s theory of pangenesis of 1868, he postulated that different characters have different hereditary carriers. He specifically postulated that inheritance of specific traits in organisms comes in particles.

De Vries conducted a series of experiments hybridizing varieties of multiple plant species in the 1890s. Unaware of Mendel’s work, De Vries used the laws of dominance, segregation, and independent assortment to explain the 3:1 ratio of phenotypes in the second generation. His observations also confirmed his hypothesis that inheritance of specific traits in organisms comes in particles.

In the late 1890s, De Vries became aware of Mendel’s obscure paper of thirty years earlier and he altered some of his terminology to match. When he published the results of his experiments in the French journal Comtes Rendus de l’Académie des Sciences in 1900, he neglected to mention Mendel’s work, but after criticism by Carl Correns he conceded Mendel’s priority. Thus, Correns, Erich Tschermak von Seysenegg, and De Vries now share credit for the rediscovery of Mendel’s laws.

February 16, 1834 (a Sunday)

Ernst Haeckel

On this date, the German biologist, naturalist, philosopher, physician, and artist Ernst Heinrich Philipp August Haeckel was born at Potsdam. He is probably one of the most contentious evolutionary biologists that ever lived. He abandoned his medical practice after reading Charles Darwin’s The Origin of Species in 1859 and returned to school, studying zoology and anatomy and eventually earning a position as professor in Jena.

Haeckel embraced the pre-Darwinian notion that life formed a series of successively higher forms, with embryos of higher forms “recapitulating” the lower ones. He thought that, over the course of time, evolution of new life forms occurred by the addition of new adult stages to the end of ancestral developmental sequences. Haeckel, who was very good at packaging and promoting his ideas, coined both a name for the process – “the Biogenetic Law” – as well as a catchy motto: “Ontogeny Recapitulates Phylogeny.”

Thus, according to Haeckel, embryonic development was actually a record of evolutionary history. He expressed it this way, as quoted in Russell (1916) [1]:

The organic individual… repeats during the rapid and short course of its individual development the most important of the form changes which its ancestors traversed during the long and slow course of their paleontological evolution…

The human zygote, for instance, was represented by the “adult” stage of the protists; the colonial protists represented the advancement of development to the blastula stage; the gill slit stage of human embryos was represented by adult fish. Haeckel even postulated an extinct organism, Gastraea, a two-layered sac corresponding to the gastrula, which he considered the ancestor of all metazoan species. [2][3][4]

PZ Meyers at Talk.Origins Archive [5] writes that the Biogenetic Law as conceived by Haeckel says:

…that development (ontogeny) repeats the evolutionary history (phylogeny) of the organism – that if we evolved from a fish that evolved into a reptile that evolved into us, our embryos physically echo that history, passing through a fish-like stage and then into a reptile-like stage.

Haeckel came under fire for this embryo comparison, for excluding the limb buds of the echidna embryo.

Haeckel came under fire for this embryo comparison, for excluding the limb buds of the echidna embryo.

Haeckel was so convinced of his biogenetic law that he was willing to bend evidence to support it. In 1874, he had claimed that members of all vertebrate classes pass through an identical evolutionarily conserved “phylotypic” stage, which presumably represents the form of their most recent common ancestor. Only later in development would specific differences appear, he said.

In fact, there is a highly conserved embryonic stage among the vertebrate classes; at the late tailbud stage, vertebrate embryos of most all classes possess somites, neural tube, optic anlagen, notochord, and pharyngeal pouches. However, Michael Richardson and his colleagues (1997) [6] discovered significant differences between groups at this stage. For example, in echidnas, limb buds are already present at the tailbud stage, whereas in other species, these are not seen until significantly later.

But in his illustrations of vertebrate embryos, Haeckel deceptively omitted limb buds at an early stage of the echidna, despite the fact that limb buds do exist then, in order to make his vertebrate embryos look more alike than they do in real life. Haeckel’s motive is clear from the text accompanying his drawings: “There is still no trace of the limbs or ‘extremities’ in this stage of development…”. [7]

Near the conclusion of the Brass-Haeckel Controversy [8] of 1908, after months of vociferous and emphatic denial, in the Berliner Volkszeitung published on 29 December 1908, Haeckel apparently admitted he had altered drawings of embryos, as quoted in Haeckel’s Frauds and Forgeries (1915) [9]:

To cut short this unsavory dispute, I begin at once with the contrite confession that a small fraction of my numerous drawings of embryos (perhaps 6 or 8 per cent.) are really, in Dr. Brass’s sense, falsified – all those, namely, for which the present material of observation is so incomplete or insufficient as to compel us, when we come to prepare a continuous chain of the evolutive stages, to fill up the gaps by hypotheses, and to reconstruct the missing-links by comparative syntheses… After this compromising confession of “forgery” I should be obliged to consider myself “condemned and annihilated,” if I had not the consolation of seeing side-by-side with me in the prisoner’s dock hundreds of fellow-culprits, among them many of the most trusted observers and most esteemed biologists. For the great majority of all the figures – morphological, anatomical, histological, and embryological – that are widely circulated and valued in the best text- and handbooks, in biological treatises and journals, would incur in the same degree the charge of “forgery.” All of them are inexact, and are more or less “doctored,” schematised, or “constructed.” Many unessential accessories are left out, in order to render conspicuous what is essential in form and organisation. [ellipsis in original]

The truth is that the development of embryos does not fit into the strict progression that Haeckel claimed, but it has also been shown that ontogeny (development of a fertilized ovum through to maturity) and phylogeny (development of a species over time) are closely related. That is, similar features in embryos of different species often reliably demonstrate that the species share a recent common ancestor. This is nicely summarized by Douglas Theobald online at Talk.Origins Archive [10]:

The ideas of Ernst Haeckel greatly influenced the early history of embryology in the 19th century. Haeckel hypothesized that “Ontogeny Recapitulates Phylogeny”, meaning that during its development an organism passes through stages resembling its adult ancestors. However, Haeckel’s ideas long have been superseded by those of Karl Ernst von Baer, his predecessor. Von Baer suggested that the embryonic stages of an individual should resemble the embryonic stages of other closely related organisms, rather than resembling its adult ancestors. Haeckel’s Biogenetic Law has been discredited since the late 1800’s, and it is not a part of modern (or even not-so-modern) evolutionary theory. Haeckel thought only the final stages of development could be altered appreciably by evolution, but we have known that to be false for nearly a century. All developmental stages can be modified during evolution… [emphasis in original]

'Tree of Life' by Haeckel (1866).

‘Tree of Life’ by Haeckel (1866).

Interestingly, in 1866 Haeckel created the first evolutionary tree to incorporate all life known at the time.

Although a strong supporter and defender of evolution (especially against attacks from religious leaders), Haeckel did not share Darwin’s enthusiasm for natural selection as the main mechanism for generating the diversity of the biological world. Instead, he favored a type of Lamarckism.

According to Jean-Baptiste Lamarck (1744-1829), change in the environment causes change in the behavior of individuals; altered behavior leads to greater or lesser use of a given structure or organ. Use would cause the structure to increase in size over many generations, whereas disuse would cause it to shrink or even disappear, because physical characteristics acquired by parents during their lifetimes are passed along to their offspring. The mechanism of Lamarckian evolution is quite different from that proposed by Darwin, although the predicted result is the same: adaptive change in lineages, ultimately driven by environmental change, over long periods of time.

PZ Meyers explains in his essay why Haeckel was completely wrong:

He argued that evolutionary history was literally the driving force behind development, and that the experiences of our ancestors were physically written into our hereditary material. This was a logical extension of his belief in Lamarckian inheritance, or the inheritance of acquired characters. If the activity of an organism can be imprinted on its genetics, then development could just be a synopsis of the activities of the parents and grandparents and ever more remote ancestors. This was an extremely attractive idea to scientists; it’s as if development were a time machine that allowed them to look back into the distant past, just by studying early stages of development.

Unfortunately, it was also completely wrong.

The discoveries that ultimately demolished the underlying premises of the biogenetic law were the principles of genetics and empirical observations of embryos. Lamarckian inheritance simply does not occur… DNA is the agent of heredity, and it is not modified by our ordinary actions – if you should get a tattoo, it is not also written into the chromosomes of your sperm or ova, and there’s no risk that your children will be born with “Mom” etched on their arm. The discovery that Haeckel had taken unforgivable shortcuts with his illustrations was a relatively minor problem for his theory, because the general thrust of his observations (that vertebrate embryos resemble each other strongly) had been independently confirmed. What really scuttled the whole theory was that its foundation was removed.

Much later, Haeckel attempted to develop a comprehensive philosophical system informed by biological and evolutionary findings. This system was to encompass ethics, theology, psychology, and politics. Some authors claim that Haeckel’s work was later appropriated by the Nazis who used it as justification for their racism and nationalism. [11] Others dispute that claim. Complicating this issue is the fact that, depending on whether you disparage or praise Haeckel, you are often assumed to be either a fundamentalist Christian, opposed to evolution, or an atheist, opposed to morality.

Haeckel’s major works are The History of Creation (1868) and The Riddle of the Universe (1899). Some of the terms he coined are still in use today, including ecology, phylum, phylogeny, and Protista.

References:

  1. E. S. Russell. Form and Function (London: John Murray Ltd., 1916) p. 253.
  2. Ernst Haeckel. Generelle Morphologie der Organismen (Berlin: Georg Reimer, 1867).
  3. —————— Anthropogenie. Third edition. (Leipzig: W. Engelmann, 1879).
  4. S.J. Gould. Ontogeny and Phylogeny (Cambridge, MA: Harvard University Press, 1977).
  5. PZ Meyers. “Wells and Haeckel’s Embryos: A Review of Chapter 5 of Icons of Evolution.” The Talk.Origins Archive. Last modified 6 December 2006. Accessed on 14 July 2013 at http://www.talkorigins.org/faqs/wells/haeckel.html.
  6. Michael K. Richardson, James Hanken, Mayoni L. Gooneratne, Claude Pieau, Albert Raynaud, Lynne Selwood, and Glenda M. Wright. “There is no highly conserved embryonic stage in the vertebrates: implications for current theories of evolution and development.” Anat. Embryol. 196: 91-106 (1997). Accessed on 17 July 2013 at http://www.oeb.harvard.edu/faculty/hanken/documents/Richardson%20et%20al%201997%20Anat%20Embryol.pdf. [Archived here.]
  7. Michael K. Richardson and Gerhard Keuck, “A question of intent: when is a ‘schematic’ illustration a fraud?” Nature 410/6825: 144 (8 March 2001).
  8. “‘MAN-APES’ THE SUBJECT OF A WAR OF SCIENCE; Between Prof. Haeckel and Dr. Brass Rages a Controversy in Which Prehistoric Heads and Tails Are the Fruitful Themes.” The New York Times, 7 February 1909. Accessed on 16 July 2013 at http://query.nytimes.com/mem/archive-free/pdf?res=F30F11F83C5C15738DDDAE0894DA405B898CF1D3.
  9. J. Assmuth and Ernest R. Hull. Haeckel’s Frauds and Forgeries (Bombay: Examiner Press, 1915), pp. 14, 15.
  10. Douglas Theobald, Ph.D. “29+ Evidences for Macroevolution: The Scientific Case for Common Descent. Part 2: Ontogeny and Development of Organisms.” The Talk.Origins Archive. Last modified 17 May 2013. Accessed on 14 July 2013 at http://www.talkorigins.org/faqs/comdesc/.
  11. Daniel Gasman. “From Haeckel to Hitler: The Anatomy of a Controversy.” eSkeptic, 10 June 2009. Accessed on 14 July 2013 at http://www.skeptic.com/eskeptic/09-06-10/#feature. [Archived here.]

February 7, 1877 (a Wednesday)

On this date, the English mathematician Godfrey Harold Hardy was born. Although Hardy considered himself a pure mathematician, early in his career, he nevertheless worked in applied mathematics when he formulated a law that describes how proportions of dominant and recessive genetic traits will propagate in a large population (1908). Hardy considered it unimportant but it has proved of major importance in population genetics and evolutionary biology. Ironically, in his book entitled A Mathematician’s Apology (1940), he wrote:

I have never done anything ‘useful’. No discovery of mine has made, or is likely to make, directly or indirectly, for good or ill, the least difference to the amenity of the world.

As it was also independently discovered by Wilhelm Weinberg, it is known as the Hardy-Weinberg principle.

Hardy–Weinberg principle for two alleles: the horizontal axis shows the two allele frequencies p and q, the vertical axis shows the genotype frequencies and the three possible genotypes are represented by the different glyphs.