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The Diversity of Animals: An Evolutionary Study (1962), by Edward Stuart Russell

In 1962 the journal Acta Biotheoretica published the final work of the biologist Edward Stuart Russell, a full eight years after his death. Entitled The Diversity of Animals: an Evolutionary Study, this short, unfinished manuscript on evolution received little recognition in the scientific presses despite both its technical discussion of adaptations in decapods (crabs, shrimp, etc.) and its different approach to evolutionary theory. The precise reason for this neglect is unclear.

Format: Articles

Subject: Publications

The Germ-Plasm: a Theory of Heredity (1893), by August Weismann

Friedrich Leopold August Weismann published Das
Keimplasma: eine Theorie der Vererbung (The Germ-Plasm: a
Theory of Heredity, hereafter The Germ-Plasm) while
working at the University of Freiburg in Freiburg, Germany in 1892.
William N. Parker, a professor in the University College of South
Wales and Monmouthshire in Cardiff, UK, translated The
Germ-Plasm into English in 1893. In The Germ-Plasm,
Weismann proposed a theory of heredity based on the concept of the

Format: Articles

Subject: Publications, Theories

"Gene Regulation for Higher Cells: A Theory" (1969), by Roy J. Britten and Eric H. Davidson

In 1969, Roy J. Britten and Eric H. Davidson published Gene Regulation for Higher Cells: A Theory, in Science. A Theory proposes a minimal model of gene regulation, in which various types of genes interact to control the differentiation of cells through differential gene expression. Britten worked at the Carnegie Institute of Washington in Washington, D.C., while Davidson worked at the California Institute of Technology in Pasadena, California. Their paper was an early theoretical and mechanistic description of gene regulation in higher organisms.

Format: Articles

Subject: Publications

The Formation of Reticular Theory

In the nineteenth century, reticular theory aimed to describe the properties of neurons, the specialized cells which make up the nervous system, but was later disconfirmed by evidence. Reticular theory stated that the nervous system was composed of a continuous network of specialized cells without gaps (synapses), and was first proposed by researcher Joseph von Gerlach in Germany in 1871.

Format: Articles

Subject: Theories

Charles Darwin's Theory of Pangenesis

In 1868 in England, Charles Darwin proposed his pangenesis theory to describe the units of inheritance between parents and offspring and the processes by which those units control development in offspring. Darwin coined the concept of gemmules, which he said referred to hypothesized minute particles of inheritance thrown off by all cells of the body. The theory suggested that an organism's environment could modify the gemmules in any parts of the body, and that these modified gemmules would congregate in the reproductive organs of parents to be passed on to their offspring.

Format: Articles

Subject: Theories

Amphioxus, and the Mosaic Theory of Development (1893), by Edmund Beecher Wilson

Edmund Beecher Wilson experimented with Amphioxus (Branchiostoma) embryos in 1892 to identify what caused their cells to differentiate into new types of cells during the process of development. Wilson shook apart the cells at early stages of embryonic development, and he observed the development of the isolated cells. He observed that in the normal development of Amphioxus, all three main types of symmetry, or cleavage patterns observed in embryos, could be found. Wilson proposed a hypothesis that reformed the Mosaic Theory associated with Wilhelm Roux in Germany.

Format: Articles

Subject: Experiments

A Treatise on the Theory and Practice of Midwifery (1752-1764), by William Smellie

A Treatise on the Theory and Practice of Midwifery is a three volume collection of patient accounts that William Smellie published from 1752 to 1764. Smellie, a physician and instructor in obstetrics in Great Britain, published these compilations to share his expertise in reproductive medicine, while also providing his students and colleagues with a source of reference in their own medical practices. Smellie wrote these books to shift obstetrics from a discipline practiced by midwives with limited medical training to one practiced in a medical context by physicians.

Format: Articles

Subject: Publications

A Treatise on the Theory and Practice of Midwifery, (1752-1764) by William Smellie

A Treatise on the Theory and Practice of Midwifery is a three volume collection of patient accounts that William Smellie published from 1752 to 1764. Smellie, a physician and instructor in obstetrics in Great Britain, published these compilations to share his expertise in reproductive medicine, while also providing his students and colleagues with a source of reference in their own medical practices. Smellie wrote these books to shift obstetrics from a discipline practiced by midwives with limited medical training to one practiced in a medical context by physicians.

Format: Articles

Syncytial Theory

The syncytial theory of neural development was proposed by Victor Hensen in 1864 to explain the growth and differentiation of the nervous system. This theory has since been discredited, although it held a significant following at the turn of the twentieth century. Neural development was well studied but poorly understood, so Hensen proposed a simple model of development. The syncytial theory predicted that the nervous system was composed of many neurons with shared cytoplasm.

Format: Articles

Subject: Theories

The Gradient Theory

The gradient theory is recognized as Charles Manning Child's most significant scientific contribution. Gradients brought together Child's interest in development and his fascination with the origins of individuality and organization. The gradient theory grew from his studies of regeneration, which were largely based on work he conducted with marine invertebrates, such as the ascidian flat worm, planaria and the hydroid, tubularia.

Format: Articles

Subject: Theories

Dinosaur Egg Parataxonomy

Dinosaur egg parataxonomy is a classification system that organizes dinosaur eggs by descriptive features such as shape, size, and shell thickness. Though egg parataxonomy originated in the nineteenth century, Zi-Kui Zhao from Beijing, China, developed a modern parataxonomic system in the late twentieth century. Zhao's system, published in 1975, enabled scientists to organize egg specimens according to observable features, and to communicate their findings.

Format: Articles

Subject: Theories

"Testing the Kin Selection Theory: Who Controls the Investments?" from The Ants (1990), by Bert Hölldobler and Edward O. Wilson

In “Testing the Kin Selection Theory: Who Controls the Investments?” Bert Hölldobler and Edward Osborne Wilson discussed the predictive power of kin selection theory, a theory about the evolution of social behaviors. As part of Hölldobler's and Wilson's 1990 book titled The Ants, Hölldobler and Wilson compared predictions about the reproductive practices of ants to data about the reproductive practices of ants. They showed that the data generally supported the expected behaviors proposed by kin selection theory.

Format: Articles

Subject: Publications, Theories

Mesoderm

Mesoderm is one of the three germ layers, groups of cells that interact early during the embryonic life of animals and from which organs and tissues form. As organs form, a process called organogenesis, mesoderm interacts with endoderm and ectoderm to give rise to the digestive tract, the heart and skeletal muscles, red blood cells, and the tubules of the kidneys, as well as a type of connective tissue called mesenchyme. All animals that have only one plane of symmetry through the body, called bilateral symmetry, form three germ layers.

Format: Articles

Subject: Processes

Etienne Geoffroy Saint-Hilaire (1772-1844)

Etienne Geoffroy Saint-Hilaire, commonly known as Geoffroy, studied animals, their anatomy and their embryos, and teratogens at the National Museum of Natural History in Paris, France in the eighteenth and nineteenth centuries. Geoffroy also helped develop several specialized fields in the life sciences, including experimental embryology. In his efforts to experimentally demonstrate the theory of recapitulation, Geoffroy developed techniques to intervene in the growth of embryos to see whether they would develop into different kinds of organisms.

Format: Articles

Subject: People

Early Infantile Autism and the Refrigerator Mother Theory (1943-1970)

In 1943, child psychiatrist Leo Kanner in the US gave the first account of Early Infantile Autism that encouraged psychiatrists to investigate what they called emotionally cold mothers, or refrigerator mothers. In 1949, Kanner published Problems of Nosology and Psychodynamics of Early Infantile Autism. In that article, Kanner described autistic children as reared in emotional refrigerators. US child psychiatrists claimed that some psychological or behavioral conditions might have origins in emotional or mental stress, meaning that they might be psychogenic.

Format: Articles

Subject: Disorders, Theories

Neural Crest

Early in the process of development, vertebrate embryos develop a fold on the neural plate where the neural and epidermal ectoderms meet, called the neural crest. The neural crest produces neural crest cells (NCCs), which become multiple different cell types and contribute to tissues and organs as an embryo develops. A few of the organs and tissues include peripheral and enteric (gastrointestinal) neurons and glia, pigment cells, cartilage and bone of the cranium and face, and smooth muscle.

Format: Articles

Subject: Theories

Ernst Haeckel's Biogenetic Law (1866)

The biogenetic law is a theory of development and evolution proposed by Ernst Haeckel in Germany in the 1860s. It is one of several recapitulation theories, which posit that the stages of development for an animal embryo are the same as other animals' adult stages or forms. Commonly stated as ontogeny recapitulates phylogeny, the biogenetic law theorizes that the stages an animal embryo undergoes during development are a chronological replay of that species' past evolutionary forms.

Format: Articles

Subject: Theories

Rosalind Elsie Franklin (1920-1958)

Rosalind Elsie Franklin worked with X-ray crystallography at King's College London, UK, and she helped determine the helical structure of DNA in the early 1950s. Franklin's research helped establish molecular genetics, a field that investigates how heredity works on the molecular level. The discovery of the structure of DNA also made future research possible into the molecular basis of embryonic development, genetic disorders, and gene manipulation.

Format: Articles

Subject: People

Calvin Bridges’ Experiments on Nondisjunction as Evidence for the Chromosome Theory of Heredity (1913-1916)

From 1913 to 1916, Calvin Bridges performed experiments that indicated genes are found on chromosomes. His experiments were a part of his doctoral thesis advised by Thomas Hunt Morgan in New York, New York. In his experiments, Bridges studied Drosophila, the common fruit fly, and by doing so showed that a process called nondisjunction caused chromosomes, under some circumstances, to fail to separate when forming sperm and egg cells. Nondisjunction, as described by Bridges, caused sperm or egg cells to contain abnormal amounts of chromosomes.

Format: Articles

Subject: Experiments, Publications

Edmund Beecher Wilson (1856-1939)

Edmund Beecher Wilson contributed to cell biology, the study of cells, in the US during the end of the nineteenth and the beginning of the twentieth centuries. His three editions of The Cell in Development and Inheritance (or Heredity) in 1896, 1900, and 1925 introduced generations of students to cell biology. In The Cell, Wilson described the evidence and theories of his time about cells and identified topics for future study. He helped show how each part of the cell works during cell division and in every step of early development of an organism.

Format: Articles

Subject: People

The Origin of Species: "Chapter Thirteen: Mutual Affinities of Organic Beings: Morphology: Embryology: Rudimentary Organs" (1859), by Charles R. Darwin

Mutual Affinities of Organic Beings: Morphology: Embryology: Rudimentary Organs is the thirteenth chapter of Charles Darwin's book The Origin of Species, first published in England in 1859. The book details part of Darwin's argument for the common ancestry of life and natural selection as the cause of speciation. In this chapter, Darwin summarizes the evidence for evolution by connecting observations of development in organisms to the processes of natural selection.

Format: Articles

Subject: Publications

"Evolution and Tinkering" (1977), by Francois Jacob

In his essay Evolution and Tinkering, published in
Science in 1977, Francois Jacob argued that a common analogy
between the process of evolution by natural selection and the
methods of engineering is problematic. Instead, he proposed to
describe the process of evolution with the concept of
bricolage (tinkering). In this essay, Jacob did not deny the
importance of the mechanism of natural selection in shaping complex
adaptations. Instead, he maintained that the cumulative effects of

Format: Articles

Subject: Publications, Theories

Essay: The Cuvier-Geoffroy Debate

In 1830, a dispute erupted in the halls of lÕAcad mie des Sciences in Paris between the two most prominent anatomists of the nineteenth century. Georges Cuvier and tienne Geoffroy Saint-Hilaire, once friends and colleagues at the Paris Museum, became arch rivals after this historical episode. Like many important disputes in the history of science, this debate echoes several points of contrasts between the two thinkers.

Format: Essays

Subject: Theories

Human Evolution Inferred from Tooth Growth and Development

To study human evolution, researchers sometimes use microstructures found in human teeth and their knowledge of the processes by which those structures grow. Human fetusus begin to develop teeth in utero. As teeth grow, they form a hard outer substance, called enamel, through a process called amelogenesis. During amelogenesis, incremental layers of enamel form in a Circadian rhythm. This rhythmic deposition leaves the enamel with microstructures, called cross-striations and striae of Retzius, which have a regular periodicity.

Format: Articles

Subject: Theories

St. George Jackson Mivart (1827-1900)

St. George Jackson Mivart studied animals and worked in England during the nineteenth century. He also proposed a theory of organismal development that he called individuation, and he critiqued Charles Darwin's argument for evolution by natural selection. His work on prosimians, a group of primates excluding apes and monkeys, helped scientists better investigate the Primate group.

Format: Articles

Subject: People

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