GAIA: The hypothesis proposed by James Lovelock that the earth is a living organism. It is an organic world picture as opposed to the mechanized world picture of the scientific revolution. (see machine) The name Gaia means Earth Goddess and was suggested to Lovelock by William Golding, author of Lord of the Flies. Leaving aside the anthropological element, the central element of Gaia theory is that the earth is a self-regulating system in which biological life does not simply adapt to conditions which happen to sustain life but in fact ensures the stablity (homeostasis) of those conditions. It is a form of coevolution between organism and environment.
Read Morebiological
covid virus + antibodies
antibodies
in biology
An Antibody is a large protein molecule which latches on to and neutralizes foreign invaders such as bacteria and viruses. Each antibody acts only on a very specific target molecule, known as an antigen. (It can also coat microbes in a way to make them palatable to scavenger cells such as microphages.)
Read Morebiological time
Some biological patterns are cyclical and function as clocks, subject to resetting and breakdown. The Circadian rhythms ( the term means approximately daily and was coined by Franz Halberg in 1951) are an examply of biological cycles which are non-linear oscillators, which mesh with day/night cycles. They are subject to entrainment or synchronization because of their time-dependent sensitivity. Exposed to some standard disturbance beginning at different times in the cycle, there will be different phase shifts inflicted. (see Winfree, 1987. p. 12) There is a particular point of vulnerability, where circadian rhythms can break down or become unpredictable when subject to a particular stimulus known as the "critical annihilating stimulus". This arrhythmic center in the pattern of timing is called its "phase singularity"
Read Morecharacter
in biology
While genes are usually thought to entail some direct causal consequence in the expression of a character, a central tenet of genetics is that a mutant locus or the normal allele does not "control a character," but is only a differential. The production of a character involves many genes.
Read Morecoevolution
in biology
In coevolutionary processes, the fitness of one organism or species depends on the characteristics of the other organisms or species with which it interacts, while all simultaneously adapt and change." At every moment natural selection is operating to change the genetic composition of populations in response to the momentary environment, but as that composition changes it forces a concommittent change in the environment itself.
Read MoreEpigenesis/Preformation
in biology
One of the most important issues in the premodern biology of the 18th century was the struggle between preformationist and epigenetic theories of development. The preformationist view was that the adult organism was contained, already formed in miniature, in the sperm, and that development was the growth and solidification of this miniature being. Preformationists assumed that the germs of all living beings were preformed and had been since the Creation. Preformationism sought to maintain and secure--against the irritation posed by the complexity of organic phenomena--the claim for a thorough and rational determination of the material world.
Read Moreform
in philosophy, theory
Is there an independent problem of form, for which biology must develop its own concepts and methods of thought? The Pre-Darwinian project of rational morphology was to discover the "laws of form," some inherent necessity in the laws which governed morphological process. It sought to construct what was typical in the varieties of form into a system which should not be merely historically determined, but which should be intelligible from a higher and more rational standpoint. (Hans Driesch, 1914, p. 149)
Read Moreembryo
Development is the process that transforms an egg into a growing embryo and eventually into an adult form.
How is this process to be understood? According to Scott Gilbert, the aesthetic of embryology separates it from other areas of biology. It is an aesthetic informed by the ordered, directional change manifest during the life of individual organisms, as they develop from a single, fertilized egg into complex patterns of diifferent, yet interacting cell, tisssues, and organs.
A few questions have dominated the study of embryology:
First of all, how is the extraordinary process of development regulated? How does a single-celled organism turn into a highly differentiated one with millions or even billions of cells? Do Genes control development? see genotype / phenotype
Is the final form of the organism set from the start? Or are there different paths of development available to the embryo? (For a discussion of preformism and epigenesis, see epigenesis}
What is the relation between the sequence of development and the process of evolution? Why do embryos of different species look so similar, and how do they end up so different?
Read MoreImmune System
in biology
The immune system is engaged in a process of somatic selection. It is constantly distinguishing foreign molecules or bacteria, viruses, and even another person's skin from the molecules of an individual body, or soma. The well-spring of immunologic defense is scattered through the body in the tissues and organs of the lymphatic system and is carried out by a set of proteins called antibodies. The ultimate target of all immune responses is an antigen, which is usually a foreign molecule from a bacterium or other invader.
Read Moreinduction
How can a cell "know" to respond to the presence or absence of an enzyme? What is it that induces genes to work only when needed?
Using a fine baby's hair, taken from his own daughter, Hans Spemann tied off and separated the two halves of a two-celled newt embryo. The cells on either side of the knot gave rise to normal newt tadpoles. When Spemann divided the egg differently, by tying it perpendicular to the furrow between the two cells of the embryo, he obtained a dramatically different result. Only one side made a normal tadpole, while the other made a disorganized mass of belly tissue. This eventually lead to the recognition that a region of the embryo, called the dorsal lip of the blastopore, was critical for the organization of the embryo. If this region of the embryo was removed, the embryo formed a blob of tissue lacking structures that normally form on the top (dorsal) side of the animal. In 1924, Spemann proved that a graft could induce host tissues adjacent to it to completely change their fate and to form a second embryo in relation to the graft. If the dorsal lip was transplanted to the presumptive belly region of another developing embryo, it organized a second embryonic axis, and two embryos formed that were joined together. Spemann dubbed this region the "organizer" because he deduced that it organized the dorsal parts of the embryo into neural structures and could induce development of another embryonic axis. All organizers share the property of influencing the formation of pattern, or morphogenesis, in tissues or cells. The basic interpretation of their special activity is that the cells of organizers produce substances that can influence the development of other cells. Such substances have been dubbed morphogens. It has long been thought that morphogens produced in one site diffuse outward and form concentration gradients from their source. The idea then is that cells surrounding the source respond to the amount of morphogen they experience. The affected area is also called the zone of polarizing activity (ZPA). Recent advances in embryology have correlated these zones with the expression of specific genes (toolkit genes)
Read Moremitosis/meiosis
in biology
At cell division, or mitosis, the nucleus of the cell divides. Each chromosome within the nucleus is first duplicated, and one copy passes to each daughter nucleus, and hence to each daughter cell.
Read Moremorphic fields
in biology, form, self-organization, theory
A field is a region of physical influence. Fields are not a form of matter, rather, matter is energy bound within fields. In current physics, several kinds of fundamental fields are recognized: the gravitational and electro-magnetic fields and the matter fields of quantum physics.
The field concept in biology has its origin in the work of Hans Driesch, although the concept itself was elaborated by A. Gurwitsch and P. Weiss. (see account in Gerry Webster and Brian Goodwin, Form and Transformation, pp 94-100) For Joseph Needham, fields are "wholes actively organizing themselves."
In the last decade of the nineteenth century, the embryologist Wilhelm Roux proposed a "developmental mechanics" (Entwicklungsmechanik ) to account for origin and maintenance of organisms through a causal morphology that would reduce them to a "movement of parts," and would prove that biology and physics were completely one with each other. Roux sought to transform biology from a purely historical into a causal discipline through analytic thought and experiment. His "mosaic theory" described development as the self-differentiation of hereditary potentialities with the irreversible functional differentiation among cells. This hypothesis was supported in part by Roux's own experiments at the marine biological station in Naples. When he killed one of the first two cleavage cells in a frog's egg, the surviving cell, as he expected, gave rise to only half of a normal embryo.
in 1891, while working at the Naples station with a different organism, Hans Driesch obtained radically different results. Driesch demonstrated that, contrary to the Roux-Weismann hypothesis, each cell of a sea urchin embryo, when isolated at the two-cell stage, does not produce a half-embryo but a complete, miniature pluteus larva of normal form. (see mechanism / vitalism for philosophical interpretations of these experiments.)
Read Morephyllotaxis
in biology, mathematical, form
Phyllotaxis (gr: phyllous means leaf, taxis means order) refers to the arrangement of leaves on a stem or florets in a composite flower such as a sunflower or pinecone along logarithmic spirals, or summation series, in which each term is the sum of the two preceding ones: 1,2,3,5,8,13,21,34,55,89,144 etc.. The scales form in double spirals which radiate from the center, one clockwise, the other counterclockwise. The surprising feature is that the number of spirals in one direction is related to the number in the other direction as two adjacent numbers in the Fibonacci series.
Read Morepositional info
in biology
One way of explaining regulation is to think of cells being able to obtain positional information as to where they are and to use that information in development. This way, cells can be moved about and interchanged (in experiments or accidents) without disturbing the developmental process. Gradient fields could be one source of positional information. (see also morphic fields) For Lewis Wolpert, "positional information is about graded properties" measured with reference to a "coordinate system." Wolpert's simple "French flag" model appealed to the "non-mathematical but theoretically minded." A gradient described as a straight inclined line, could have threshold points translating into patterns (eg red, white, and blue). But "just what moves this answer beyond the realm of tautology remains obscure." Evelyn Fox Keller
Read Moresex / gender
in feminism, psyche, theory, anthropological
On ne nait pas femme; on le devient -- Simone de Beavoir
At its simplest, the distinction between sex and gender is between a physical difference and a cultural difference. Gender is the mapping of socially and ideologically important distinctions onto biological differences between the sexes. (see also sexuality.)
The distinction between sex and gender becomes important in arguments that lean towards social constructionism, in which gender is given more attention, and is presumably more open to change, than sex. Feminism asserts that gender is a fundamental category within which meaning and value are assigned to everything in the world, a way of organizing human social relations. In a further twist on the relation between culture and nature, Brian Massumi calls gendering the process by which a body is socially determined to be determined by biology.
Read Moresymbiosis
in biology, metaphorical
The term symbiosis was defined by the German mycologist Anton De Bary (1879) as meaning the "living together" of "dissimilar" or "differently named" organisms.
Today, in most current biological literature, it is taken to mean "mutualistic biotrophic associations" (biotrophy: one partner requires a nutrient that is a metabolic product of the other partner.) For example, lichens consist of algal and fungal components in nearly equal mass in symbiosis.
T-cells, B-cells
in biology
B-cells are formed in the bone marrow, and provide humoral immunity mediated by antibodies. They can recognise parts of antigens free in solution, by fitting them to the antibodies they carry on their surface. When a particular B-cell come into contact with an antigen which it fits, the B-cell swells and divides (through mitosis, or clonal selection)and the new activated B-cells (Plasma cells) secrete antibodies proteins that attack the invader. Once activated, a B-cell can pump out more than 10 million antibody molecules per hour. The antibodies neutralize or precipitate the destruction of the antigens by complement enzymes or scavenger cells. The B-cell can also produce different isotypes of the antibodies, who fit the same antigen but who defend the body in different ways.
Read Moreunity
in philosophy, theory
For Kant, the categorial principle of unity is a requirement for the very concept of nature. As he puts it in the Prolegomena to the Critique of Pure Reason, "nature is the existence of things, considered as existence determined according to universal laws." For Kant, the idea of God serves to symbolize or "schematize" the highest form of systematic unity to which empirical knowledge can be brought, the purposive unity of things. (B714)
According the Kant, the idea of space, a priori, is that of a unity. In the Critique of Pure Reason, Kant defined space as "the form of all phenomena of the external sense, that is, the subjective condition of the sensibility, under which alone external intuition is possible." (p.26) (For Ernst Cassirer, the recognition of non-Euclidean geometries seemed to mean renouncing the unity of reason, which is its intrinsic and distinguishing feature." (see scientific space )
In the Critique of Judgement, he realizes that the absolute conditions of experience are not enough, and that experience depends on our ability to arrange the particular laws of nature according to the idea of a system. The empirical unity of nature in all its diversity is not identical with the categorical one, not constitutive of our experience, but a regulative one.
It is the business of our understanding to introduce unity into nature. For a scientist to succeed at his task, he must assume that something corresponding to this unity actually exists in nature to be discovered.
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