History of Biological Sciences
Some key figures in the history of biological sciences
Left to right:: Aristotle (383-322 B.C.), Leonardo da Vinci (1452-1519), Nicolaus Steno (1638-1686), Jean Baptiste de Lamarck (1744-1829), Charles Darwin (1809-1882)
Copyright J. Lavas
1. Timeline: Biological Research & Publication
2. Biological Classification
3. Glossary of Terms
1. Timeline: Biological Research & Publication
The timeline below is not intended to be comprehensive for such a wide field, but it does include selective developments in biological research and publication (including New Zealand examples), as well as related fields such as geology/palaeontology (US = paleontology) which have impacted greatly on evolutionary biology. There is a large number of timelines available on the internet, although few are formally structured in this manner and their accuracy is variable. For hints on using biological literature and some of the databases mentioned in this timeline, please consult Research and Writing Hints.
- Classical Greek scholars, in particular Aristotle (a student of Plato who had laid the foundations of western philosophy), made perceptive observations on natural history subjects using empirical reasoning. Aristotle classified 540 animals, 50 of which he dissected.
- The decline of the Roman Empire resulted in a serious depletion of scientific knowledge.
Science in the Middle Ages was located in three main centres: Latin West, Latin East, and the Islamic countries.
- Latin West used classical Greek science as passed on by scholastics in monasteries, but very little was added by them.
- Islam disseminated Greek science faster than it was disseminated in the West, and Islamic teachers promoted the study of medicine, astronomy and mathematics.
- Medieval muslim philosophers and physicians contributed towards biological knowledge from the 8th to the16th centuries during the Islamic Golden Age.
- The Afro-Arabian scholar al Jahiz described early evolutionary concepts including the struggle for existence (precursor to natural selection) food chains and environmental determinism.
- In Persia, the physician Avicenna described clinical pharmacology and clinical trials in his book The Canon of Medicine (1025).
- In Arabia, Ibn al-Baitar wrote a pharmaceutical encyclopaedia detailing 1400 drugs, plants, and foods, including many of his own discoveries, while Ibn al-Nafis carried out dissections on pulmonary and coronary circulation, suggesting the concept of metabolism.
- Pliny’s encyclopaedic Naturalis Historia contained all that was known of the natural sciences in the west.
- Byzantium was able to preserve more scientific information than was preserved in western countries, but the outcome was very similar.
Preservation only, rather than discovery, was a typical practice of the Dark Ages.
- William Harvey was the first westerner to describe systemic blood circulation of the human heart.
- Inventor/artist Leonardo da Vinci was the first person to study fossils in a systematic and scientific manner during the Renaissance.
- Galen’s physician's writings (the most important since Hippocrates) were considered as standard works until the 16th Century.
- The invention of metal printing type in the 15th Century made science publications available to a wider audience than previously.
- Scientists of importance to 17th Century biology were William Harvey, Rene Descartes, Francis Bacon, Marcello Malpighi, Nicolaus Steno and Anton van Leeuwenhoek.
- William Harvey advocated experimentation in biology, in contrast to Descartes who reduced everything to mechanical explanations, whilst Bacon was linked to the scientific revolution and the Royal Society of London, encouraging experimentation and publication of results.
- Danish anatomist Nicolaus Steno (born Niels Stenson) studied fossil shark teeth and formulated important principles in palaeontology and geological stratigraphy. However his concept for an organic origin for all fossils was not widely accepted until the late 18th Century.
- The 17th Century saw the spread of the printed word, and organization of learned societies.
- The world’s second oldest science journal Philosophical Transactions of the Royal Society of London (Phil Trans Roy Soc) began in 1665 (and is still in publication).
- Learned societies in England, France and Italy were noted transmitters of scientific communication.
- The microscope was invented in the 17th Century and the Dutch scientist Antonie van Leeuwenhoek (known as 'the father of microbiology') used it to make pioneering biological observations. The microscope would revolutionise the study of biology.
- Botanist Robert Hooke described cells within cork, and Marcello Malpighi used the microscope in embryological observations of epigenesis and ovism.
- Botanist John Ray first described the concept of species but classification problems remained with both extant (living) and extinct forms.
- The 18th Century was an age of exploration, collection and organization in biology, with the science in a very transitional stage.
- In the year 1700, only 6000 species of living organisms were recognized - by the year 1800 there were 50 000 identified.
- Englishman William Sherard was the world’s first dedicated taxonomist.
- Carolinus Linnaeus was the most dominant figure of 18th Century science, as supreme classifier and inventor of the binomial system of classification (genus/species) for botany and zoology in his landmark work Systema Naturae (1735) (See chart 2. below). Linnaeus considered species to be immutable and fixed.
- Georges-Louis Leclerc, Comte de Buffon proposed that species may change over time, suggesting the theory of common descent with ideas that would greatly influence the work of Lamarck and Darwin in the 19th Century.
- In the New World, much biological work was carried out by naturalists or physicians who had been trained as botanists.
- Many scientific results were published in Phil Trans Roy Soc.
- Learned societies began to publish their scientific papers. By 1900 there were 10 000 scientific journals, a stimulus for indexing and abstracting services to begin.
- The word Biology was first used in the early 19th Century by French naturalist Jean Baptiste Lamarck
- The 19th Century saw a consolidation of concepts in cellular organization, the germ theory of disease, and evolution which was the major biological concept at this time.
- Chemistry and chemical processes were used to describe physiological processes.
- By 1880 there were 100 science journals being published worldwide.
- The work of Buffon, Darwin, and Lamarck laid the groundwork for evolutionary theory.
- On the second voyage of H.M.S. Beagle (1831-1836), Charles Darwin studied the biology, geology, and anthropology of southern lands and islands (including New Zealand which he visited in 1835), gaining material for two landmark books, The Voyage of the Beagle (1839) and On the Origin of Species by Means of Natural Selection (On the Origin of Species, 1859), in which he collated his theories on evolution by natural selection.
- Alfred Russel Wallace and Henry Walter Bates’ field work in South America provided further evidence for evolutionary theory, with Wallace's work (both there and later in the Malay Archipelago) having resulted in similar conclusions to those reached by Darwin.
- Botanical and zoological collections made in South America by German naturalist and explorer Alexander von Humboldt (arguably the world's greatest scientific explorer) added much information on species diversity and distribution. Along with the work of Wallace, von Humboldt's monumental work Kosmos (1845) laid important foundations for the study of biogeography.
- The Bohemian monk Gregor Mendel studied the inheritance of traits in garden peas and published his paper Experiments on Plant Hybridization (1866) which was largely ignored by the scientific community until 1900.
- Following the American Revolution, US contacts with Britain and the Royal Society were broken – there were few American natural historians at this time.
- Science was still based on field work (empirical) rather than theoretical, and there was conflict between science and religion in the US.
- After the American Civil War (1861-65), American education was re-organised, with Harvard and Johns Hopkins universities being founded upon German laboratory and university models.
- At the end of the 19th Century, the US had many scientific institutes, journals, and societies with ‘social approval’.
- One of the world's leading biological journals Nature (London) began publication in 1869.
- Great advances were made in vertebrate palaeontology in the US by the end of 19th Century, with museums gaining extensive collections of extinct animals, especially dinosaurs and mammals from the American west, stimulating scientific debate on evolution and extinction.
- The discipline of geology brought natural history and natural philosophy closer together, whilst geological stratigraphy linked the spatial and temporal distribution of organisms, a precursor to later theories of evolution.
- The great French anatomist Baron Georges Cuvier made detailed comparisons between fossil and living mammals. He also claimed (erroneously) that all large vertebrates had already been identified (see 3rd entry under 20th Century).
- Gideon Mantell, Mary Anning, William Buckland and anatomist Richard Owen either discovered or described Mesozoic fossil reptiles showing that an Age of Reptiles (Mesozoic) had preceded the present Age of Mammals (Cenozoic).
- Many geologists of the era followed catastrophist principles, but Charles Lyell's landmark book Principles of Geology (1830-33) described geological processes as constant and ongoing.
- The oldest continuous zoological database, Zoological Record, was launched in 1864.
- The Royal Society of New Zealand (RSNZ) was founded in 1851 as the country's leading learned society. The RSNZ awards the Rutherford and Pickering Medals for outstanding achievements in science and technology, and Rutherford PhD scholarships to outstanding students, whilst its publications include NZ Journal of Zoology, NZ Journal of Botany, and NZ Journal of Marine and Freshwater Research.
- Much New Zealand scientific research was published in Transactions and Proceedings of the New Zealand Institute (began 1868) which later became Transactions and Proceedings of the Royal Society of New Zealand.
- The discovery of radioactive isotope decay in 1898 by Marie Curie would later enable the dating of geological strata and refinement of the time scale.
- Darwin’s work became accepted in principle after Mendel’s work was rediscovered by Hugo de Vries and Carl Correns in 1900. The mechanism of inheritance was unknown, and the debate on how evolution occurred continued.
- Mendelian inheritance had a large impact on naturalists, statisticians and researchers. By 1911, the US led the research with Thomas Hunt Morgan having begun genetic studies on the fruit fly Drosophila melanogaster.
- By early 20th Century, Cuvier's claim that all large species had been identified was refuted with many new discoveries, including the Kamchatka brown bear, mountain gorilla, okapi, Ituri Forest wild boar, mountain nyala, pygmy hippo, and Komodo Dragon.
- In 1912 German meteorologist Alfred Wegener proposed the concept of continental drift (erroneously assuming that continents moved due to centrifugal force). The theory was only validated in the 1960s and explained plate tectonic movements from two great landmasses, Gondwana in the south and Laurasia in the north. It also accounted for the biogeography of species. In New Zealand, Harold Wellman later used plate tectonics to explain the South Island Alpine Fault.
- Painter/sculptor Charles Knight was the American pioneer of palaeo-reconstruction at the American Museum of Natural History (AMNH) and other US museums.
- AMNH palaeontologist Henry Fairfield Osborn suggested Central Asia as the origin of placental mammals and the earliest humans. The museum's pioneering expeditions to the Gobi Desert (1922-1930) found important Mesozoic fossils including dinosaur eggs (by Walter Granger).
- Early human fossils increasingly suggested Africa rather than Asia as the cradle of human evolution.
- Biochemist Aleksandr Oparin postulated the origin of life from basic elements in a ‘primordial soup’ in his book The Origin of Life (1924).
- Biological Abstracts, for decades one of the primary indexes to life science literature (especially taxonomy) was launched in 1926.
- In New Zealand, the Department of Scientific and Industrial Research (DSIR) was founded in 1926 by Ernest Marsden. It conducted research on entomology and agriculture/horticulture (primarily crop protection and development) and was eventually superceded in 1992 by Crown Research Institutes (CRIs). The DSIR's Australian equivalent, also founded in 1926, is the Commonwealth Scientific and Industrial Research Organisation (CSIRO).
- By the 1930s, palaeontology, geology, genetics, and natural history were all contributing to theories on evolution.
- Theodosius Dobzhansky was pivotal in establishing the modern evolutionary synthesis as expounded in his book Genetics and the Origin of Species (1937) which fused evolutionary biology with genetics. Another major contributor was Ernst Mayr who defined the concept of species and methods of speciation in his book Systematics and the Origin of Species (1942).
- Barbara McClintock studied the cytogenetics of maize to identify fundamental genetic concepts including recombination and transposition, and the function of telomeres and centromeres.
- James Watson and Francis Crick published research on DNA in 1953 based partly on the work of NZ-born Maurice Wilkins (all three received the 1962 Nobel Prize, see also Maurice Wilkins Centre) and Rosalind Franklin, whose data was used to create the double helix model. Molecular biology thus had foundations in physical, biochemical and structural research.
- Stanley Miller created amino acids from basic elements and electricity in 1953 using the Oparin-Haldane Theory.
- Lynn Margulis formulated the endosymbiotic theory to explain how certain organelles form, and how prokaryotic cells could form eukaryotic cells by symbiosis.
- Post-WWII Russian and Polish palaeontological expeditions to the Gobi (particularly Nemegt Valley) led by Ivan Efremov and Zofia Kielan-Jaworowska, respectively, shed light on Laurasian evolution, especially Mesozoic theropods, birds and mammals. Further Gobi expeditions followed from the US, Canada, Japan, China, and France.
- Collaborating with palaeontologists Josef Augusta and later Zdenek Spinar, palaeo-artist Zdenek Burian's reconstructions of prehistoric life (1930s -1980s) became standard works for many palaeontologists and anthropologists.
- Russian scientific indexing and abstracting services were developed. Sputnik initiated the Space Age (1957).
- Concerned with Russian advances in space, the US govt. initiated indexing/abstracting services for chemistry and engineering, aimed mainly at space projects including the Apollo lunar landings. Generous funding became available to scientists at this time.
- US indexing and abstracting services included BIOSIS (Biological Abstracts), US National Library of Medicine (MedLine/PubMed), and ISI's Science Citation Index (now Web of Science), a major science citation database.
- In New Zealand, scientific research from the various Crown Research Institutes and the Royal Society of New Zealand was indexed for the database New Zealand Science.
- In western countries, academic science libraries were decentralized, while many institutional libraries struggled to subscribe to all required resources.
- During the 1960s and '70s, three landmark biological field studies of the chimpanzee, the mountain gorilla, and the orangutan, were initiated by primatologists/ethologists Jane Goodall, Dian Fossey, and Birute Galdikas, respectively, all three of whom had been chosen by anthropologist Louis Leakey to study anthropoid apes in the wild. Each researcher subsequently became an advocate of conservation and anti-poaching campaigns in their respective study areas of Tanzania, Rwanda, and Borneo.
- By the 1970s, many biotechnologies were developed using controlled biological processes (eg. fermentation) to produce penicillins, steroids, proteins, and high-yield crops. The use of recombinant DNA techniques led to attempts to synthesise human hormones such as insulin, human growth hormone and clotting factors. With many gene patents requested, there was much interaction between biology, industry and law.
- In the 1980s protein sequencing and cladistics changed the study of taxonomy by uniting molecular evolution with evolutionary biology (which had previously relied on traditional taxonomic methods such as morphology).
- Modern polymerase chain reaction (PCR) techniques of the 1980s increased the speed of genetic analysis and discovery of greater numbers of genes, making it easier to sequence complete genomes.
- By the late 1990s, many previously print journals were available electronically. 'Open access' online publication of journals also became more common, using a system whereby institutes pay for articles published by their staff, rather than a fixed subscription..
Parts of this timeline were modified from material in Davis, E.B. and Schmidt, D. (1995). Using the Biological Literature: a practical guide. New York: Marcel Dekker, inc.
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2. Biological Classification
The internationally recognised method of classification used in biological sciences is the Linnaeus binomial taxonomic system whereby animals and plants are identified as belonging to a particular species within a given genus (there may be from one to several species within each genus). Species may sometimes be further divided into sub-species. Carolus Linnaeus published his basic taxonomy for the natural world in 1735 and introduced scientific names for all species in the 1750s. Linnaeus considered species to be immutable and fixed. The first specimen of a species to be described is considered to be the 'type' or holotype which resides at a particular collection and to which others are later compared (note that a holotype may be a trace fossil, photograph or drawing in the absence of actual biological material). Such taxonomic information has traditionally been indexed by databases such as Biological Abstracts (began 1926) and Zoological Record (began 1864). An example of the Linnaeus classification system is given below.
Linnaeus classification for the extinct New Zealand giant moa Dinornis maximus
In addition to the categories above, there are also greater and lesser categories that may be employed as required (eg. Superfamily, suborder, etc).
Palaeontologists and evolutionary biologists often constructed family trees of assumed phylogenetic relationships, such as the example below (left) for the vertebrates. These were the results of anatomical and molecular studies, and comparisons between extinct and extant types. Today, cladograms are often used to depict such relationships.
The 20th Century saw the development of Palaeo-reconstruction (fusion of art and science) whereby artists collaborate closely with palaeontologists to recreate the probable appearance and behaviour of extinct species. Notable artists in this field were Charles Knight and later Zdenek Burian, who reconstructed the flora and fauna of all geological ages (below right).
Above: Images copyright J. Lavas (left), and Z. Burian (right)
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3. Glossary of Terms
This selection of biological and palaeontological terms (including historical ones that may otherwise not be readily identifiable) is partly based on course guide glossaries for BIOSCI 103 by K. Clements and BIOSCI 107 by C. Quilter. It is not comprehensive and some terms may have more than one meaning depending on the context. A suitable print reference for biology undergraduate students is Henderson's Dictionary of Biology, copies of which are available on short loan.
Acoelomate: Lacking a coelom (acoelomates include all diploblasts and some triploblasts).
Actinopterygii: Ray-finned fishes (eg. teleosts).
Afrotheria: Group of eutherian African mammals (golden moles, tenrecs, elephant shrews, aardvarks, hyraxes, dugongs, manatees, and
Agnatha: Group of jawless fishes that are basal vertebrates, including living hagfish and lampreys.
Allantois: Membranous outgrowth of the hindgut (vestigial in the human embryo).
Amnion: Innermost membrane surrounding the embryo, and which contains amniotic fluid.
Analogy: Feature found in a group of species with shared functionality, but not found in the common ancestor of the group.
Angiosperms: Flowering plants, believed to have evolved in the early Cretaceous or late Jurassic.
Apomorphy: A derived trait.
Archaeopteryx: The earliest known bird, dating from the Jurassic period.
Archenteron: Endoderm-lined cavity formed during gastrulation, and develops into the digestive tract.
Arthropoda: The phylum that includes crustaceans, insects, spiders, and trilobites (extinct), with segmented bodes and jointed appendages.
Artiodactyl: Even-toed ungulates including pigs, hippos, cows, deer, antelopes, giraffes and camels.
Autapomorphy: Unique derived trait found in only one taxon.
Basilosaur: Ancestral whale from the Eocene Period that retained tiny hind limbs.
Bilaterian: Eumetazoan animal with bilateral symmetry.
Biotechnology: The use of living cells or microorganisms (eg. Bacteria) in industry and technology to manufacture drugs, and chemicals to break down waste. More recently, refers to the use of genetically modified cells and organisms.
Bipedal: Moving on two-legs.
Blastocyst: Embryonic stage at implantation (Greek: blastos = germinal or budding, kystis = small hollow bladder).
Blastomere: One cell of an early embryo.
Blastopore: Opening of the archenteron in the gastrula that develops into the mouth in protostomes.
Buccopharyngeal: Of the mouth and the throat.
Burgess Shale: Canadian Rockies Cambrian sedimentary rock formation with well preserved specimens of numerous soft-bodied animals.
Cambrian: Geological period from 543-490 million years ago.
Carboniferous: Geological period from 363-290 million years ago.
Caudal: Towards the tail.
Cenozoic: Geological era from 66 million years ago to the present.
Cerebellum: Dorsal outgrowth of hindbrain.
Cerebral hemispheres: Paired outgrowths of the forebrain.
Cervical: Structures connected with the neck (ie. nerves, bones, blood vessels).
Cervix: The neck or narrow mouth of an organ, such as the uterine cervix
Character: Any recognizable trait, feature or property of an organism.
Character analysis: Method of sorting taxa into the hierarchy of phylogenetic trees.
Chondrichthyes: Clade of cartilaginous fishes including sharks, rays and chimeras.
Chordata: the vertebrate animals, as well as cephalochordates and urochordates, and characterized by possession of a notochord.
Chorion: Outermost fetal membrane which in humans forms the placental wall.
Circadian rhythm: Metabolic or behavioral rhythm usually with a cycle of 24 hrs.
Clade (in cladistics): Branch of a phylogenetic tree containing the set of all organisms descended from a particular common ancestor which is not an ancestor to any non-member of that group. A monophyletic group. See Cladistics/Cladogram.
Cladistics: The study of the relationship between species or other taxa due to recent origin from a shared ancestor. Groups organisms in terms of relative recency of divergence). See Clade/Cladogram.
Cladogram: Diagram showing evolutionary relationships between taxa, with branching points or nodes representing ancestral species.
Cloaca: Caudal end of the hindgut.
Cnidaria: The phylum of eumetazoans that includes corals, anemones, and true jellyfish.
Coelom: body cavity lined with mesoderm.
Conodonts: Extinct eel-shaped predators with toothlike plates but lacking true jaws.
Convergent evolution: Process whereby a similar trait evolves independently in different taxa.
Cranial: Towards the head.
Cretaceous: Geological period from 145-66 million years ago.
Crown group (in cladistics): Clade that includes all descendants of the shared ancestor of living members of that clade. See also Stem group.
Ctenophora: Phylum of eumetazoans that includes comb jellies.
Cuticular appendage: Appendage sheathed in a cuticle (exoskeleton) as seen in crustaceans and insects.
Decidua basalis: Maternal portion of the placenta which is shed at birth.
Dermatome: Portion of a somite which contributes to the dermis of skin.
Deuterostomia: Major group of bilateral animals including chordates and echinoderms.
Devonian: Geological period from 409-363 million years ago.
Diencephalon: Portion of the forebrain including the thalamus and hypothalamus.
Differentiation: Process by which embryonic cells become specialized for a certain adult form and function.
Diploblastic: Two-layered construction consisting of the ectoderm and endoderm.
Dorsal aorta: Fetal artery receiving blood from the aortic arches and then distributing it to the body.
Dorso-ventrally: Top to bottom. Organisms are sometimes described as dorso-ventrally flattened, eg. flounder/sting ray, as opposed to laterally flattened (eg. snapper).
Ecdysis: Moulting of the exoskeleton, triggered by the hormone ecdysone.
Ecdysozoa: One of the three major groups of bilaterian animals characterized by moulting of the exoskeleton. Includes arthropods, nematodes, onycophorans, and priapulids.
Echinodermata: Group of deuterostome animals including starfish, sea cucumbers, and sea urchins.
Ectoderm: Outer layers of cells in the three-layered embryo.
Ectopic pregnancy: Implantation outside of the uterus.
Ediacaran fauna: Precambrian group of fossil soft-bodied animals possibly related to cnidarians.
Endoderm: Inner layers of cells in the three-layered embryo.
Endometrium: Mucous membrane lining of the uterus.
Eocene: Geological period from 57-35 million years ago.
Epiblast: Upper layer of two-layered embryo.
Eukaryote: Organism whose cells are organised into complex structures and enclosed by membranes. see Prokaryote.
Eumetazoan: Member of the clade of multi-cellular animals that excludes the Porifera (sponges).
Extinct: No longer living.
Extraembryonic: Outside of the embryo’s body.
Functional genomics: Study of the functions of the sequenced genes from a genome.
Gamete: Germ cell (ie. either a sperm or egg).
Ganglion: Cluster of nerve cell bodies, usually in the peripheral nervous system.
Ganoid: Historically used to refer to armour-like fish scales.
Gastrulation: Folding and migration of cells which transforms a two-layered embryo into three layers.
Genome: The entire genetic sequence of an organism.
Gnathostomes: Jawed vertebrates.
Gracile: Graceful/light – often used in palaeontology to describe skull/skeletal morphology.
Grade (in cladistics): Group of organisms sharing the same level of organization (see clade).
Gradualism: Concept that evolution occurs through gradual change of populations rather than sudden production of new types.
Haemocoel: Body cavity filled with blood especially characteristic of arthropods.
Heritable: Trait passed from parent to offspring.
Homeosis: Alteration in spatial patterning of body parts.
Homeotic genes: Genes controlling animal body plans by determining the developmental fate of cell groups.
Homologous character: Trait shared by a set of species and present in their shared ancestor.
Homology: Similarity due to common ancestry.
Homoplasty: False homology, usually due to convergent or parallel evolution.
Hox genes: Class of genes that have a role in animal development especially in controlling spatial patterning. Found in all eumetazoans.
Hypoblast: Lower layer of two-layered embryo.
Insectivora: Historical group of insect-eating mammals including shrews, hedgehogs and moles, now known to be polyphyletic.
Intermediate mesoderm: Two columns of mesoderm running parallel to the notochord, intermediate in position between somites and lateral mesoderm.
Jurassic: Geological period from 208-145 million years ago.
Lacunae: A small space.
Laurasiatheria: Group of eutherian mammals including hedgehogs, moles, shrews, bats, whales, artiodactyls, horses, carnivores and pangolins.
Macroevolution: Evolution above species level. used to refer to fundamental changes in body plan. See also microevolution.
Medulla oblongata: Caudal portion of the brain stem, between the pons and the spinal chord.
Mesoderm: Middle layer of cells in the three-layered embryo.
Mesoglea: Gelatinous layer separating endoderm from ectoderm in cnidarians and ctenophores.
Mesozoic: Geological period from 248-66 million years ago.
Metazoan: Multicellular animal with nervous systems, muscles and an alimentary canal.
Microevolution: Small evolutionary change due to gene frequency within populations over many generations. See also macroevolution.
Monophyletic: Group that consists of an ancestor and all of its descendants.
Morula: Early embryonic stage resembling a blackberry (the stage preceding the gastrula).
Myotomes: Zig-zag muscular blocks characteristic of fish and cephalochordates.
Myriapods: Group of arthropods that includes millipedes and centipedes.
Neuropore: Opening in the embryonic neural tube leading to the exterior.
Node (in cladistics): Branching point on a cladogram, representing the common ancestor of all taxa branching above it.
Notochord: Longitudinal rod of mesoderm on the midline between the neural tube of chordate embryos.
Oncogenes: Gene carried by a tumour virus or cancer cell responsible for tumorigenesis.
Ontogeny: The history of development and growth of an individual including the fetal/embryonic stages. See also Phylogeny.
Onychophora: Group of basal arthropods with soft, flexible bodies and walking appendages called lobopods.
Oocyte: Immature ovum.
Ordovician: Geological period from 510-439 million years ago.
Osteichthyes: Group of bony fishes.
Osteolepiforms: Devonian lobe-finned fish that gave rise to the tetrapods (four-limbed land dwellers).
Ostracoderms: Group of fossil agnathans that had bony exoskeletons.
Outgroup (in cladistics): Taxon closely related to a taxa being studied, but not as closely related as are any of the studied taxa to each other.
Pakicetids: Fossil vertebrate group that shared features with whales and artiodactyls.
Paleozoic: Geological period from 543-248 million years ago.
Paraphyletic: Group that excludes some descendants of a common ancestor.
Parasagittal: Walking with the limbs held directly under the body (as in mammals or theropod dinosaurs).
Parietal: Relating to the outer wall of the body rather than to the visceral (outer) portion.
Parsimony (in cladistics): Concept whereby the simplest explanation involving the fewest steps, is the most likely.
Pericardium: Sac surrounding the heart.
Peritoneal cavity: Body cavity surrounding the stomach and intestine.
Permian: Geological period from 290-245 million years ago.
Phanerozoic: Geological time period from 543 million years ago to the present day.
Pharmacodynamics: The effect a drug or other agent has on an organism.
Pharmacokinetics: How an organism reacts physiologically when absorbing a drug or other agent.
Pharyngeal: Relating to the throat.
Phenotype: Various traits of an organism, due either to inheritance or the environment.
Phylogeny: The evolutionary history and line of descent of a species (or higher taxonomic group). See also Ontogeny.
Phylum: Major taxonomic grouping in biological classification, of which 35 are recognised.
Placenta previa: Placenta formed near or across the internal os (opening) of the cervix.
Platyhelminthes: Flatworms with unsegmented, dorsoventrally-flattened bodies.
Plesiomorphy: Ancestral traits.
Polyphyletic: Group that lacks the most recent shared ancestor of its members.
Pons: Cranial and ventral portion of the hindbrain.
Precambrian: Geological period older than 543 million years ago.
Primitive streak: Transient shallow groove in the epiblast, and which is caused by cell migration.
Prokaryote: Organism that lack a cell nucleus. See Eukaryote.
Proteomics: Introduced in 1995, the word ‘proteome’ refers to all proteins coded for by a genome.
Proterozoic: Geological period from 2500-543 million years ago.
Protostomes: Group of animals comprising the ecdysozoans and lophotrochozoans.
Sarcopterygii: Group of lobe-finned fish that includes the coelocanth, lungfish and early tetrapods.
Sclerotome: Portion of a somite which contributes to the vertebrae.
Silurian: Geological period from 439-409 million years ago.
Sister taxa (in cladistics): Taxa that shared a recent common ancestor, and are considered to be each other's closest relatives.
Somatic: Relating to the body wall and limbs rather than to the viscera.
Somite: Condensed ball of mesoderm lateral to the notochord.
Somitomere: Loose ball of mesoderm which later condenses to form a somite (except in the head).
Species: An interbreeding natural population of organisms that does not interbreed with other groups.
Spina bifida: Spinal defects caused when the vertebral arches fail to fuse.
Stem group (in cladistics): Extinct basal lineage of a clade sitting outside the 'crown' group (ie.having diverged early in the clade's history). See also Crown group.
Structural genomics: The first stage of decoding the genomic sequence during which the approximate genome sequence is defined.
Symplesiomorphy: Shared ancestral (primitive) trait inherited from a distant ancestor.
Synapomorphy: Shared derived trait present in the common ancestor of two or more taxa.
Syncytium: Tissue comprising cytoplasm and multiple nuclei but not subdivided into cells.
Tertiary: Geological period from 66-1.8 million years ago.
Tetrapods: Group of vertebrates with four toe-bearing limbs that includes amphibians, reptiles, birds and mammals.
Triassic: Geological period from 245-208 million years ago.
Trilobites: Extinct group of marine arthropods characterized by a three-part division of the body and crab-like exoskeleton.
Trimester: Three-month interval during pregnancy.
Triploblastic: Three-layered construction consisting of the endoderm, mesoderm, and ectoderm.
Trocophore: Ciliated larvae characteristic of molluscs, marine annelids and some protostome phyla.
Trophoblast: Outer covering of blastocyst which erodes the uterine wall during implantation.
Urbilateria: Common ancestor of bilaterian animals.
Vestigial: Trait present only as a trace.
Villus: Small finger-or hair-like projection from a surface.
Visceral: Relating to the inner part of the body, or of an organ, rather than to its outer wall.
Vitelline: Relating to the yolk of an egg.
Xenarthra: Group of eutherian mammals, including sloths, anteaters and armadillos.
Zona pellucida: Transparent acellular layer surrounding the oocyte.
Zygote: Fertilised egg, the diploid cell resulting from the union of sperm and ovum.
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