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organism's evolutionary history. Not all possible tests have been performed, but many
hundreds have been done, and not one has given evidence contrary to evolution. There is
probably no other notion in any field of science that has been as extensively tested and as
thoroughly corroborated as the evolutionary origin of living organisms.
"The Theory of Evolution: The evidence for evolution: MOLECULAR BIOLOGY" Britannica
Online.
Homology, in biology, similarity of the structure, physiology, or development of different
species of organisms based upon their descent from a common evolutionary ancestor.
Homology is contrasted with analogy, which is a functional similarity of structure based not
upon common evolutionary origins but upon mere similarity of use. Thus the forelimbs of such
widely differing mammals as humans, bats, and deer are homologous; the form of
construction and the number of bones in these varying limbs are practically identical, and
represent adaptive modifications of the forelimb structure of their common early mammalian
ancestors. Analogous structures, on the other hand, can be represented by the wings of birds
and of insects; the structures are used for flight in both types of organisms, but they have no
common ancestral origin at the beginning of their evolutionary development. A 19th-century
British biologist, Sir Richard Owen, was the first to define both homology and analogy in
precise terms.
"homology" Britannica Online.
Figure 3: The labellum of
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Evolution
the mirror ophrys (Ophrys
speculum). The colouring
so closely resembles that of
the female wasp Colpa
aurea that males of the
species are attracted to the
flower and pick up pollen
during their attempts at
copulation.
E.S. Ross
DOBZHANSKY: Between 1920 and 1935, mathematicians and experimentalists began laying
the groundwork for a theory combining Darwinian evolution and Mendelian genetics. Starting
his career about this time, Dobzhansky was involved in the project almost from its inception.
His book Genetics and the Origin of Species (1937) was the first substantial synthesis of the
subjects and established evolutionary genetics as an independent discipline. Until the 1930s,
the commonly held view was that natural selection produced something close to the best of all
possible worlds and that changes would be rare and slow and not apparent over one life span,
in agreement with the observed constancy of species over historical time.
Dobzhansky's most important contribution was to change this view. In observing wild
populations of the vinegar fly Drosophila pseudoobscura, he found extensive genetic
variability. Furthermore, about 1940 evidence accumulated that in a given local population
some genes would regularly change in frequency with the seasons of the year. For example, a
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Evolution
certain gene might appear in 40 percent of all individuals in the population in the spring,
increase to 60 percent by late summer at the expense of other genes at the same locus, and
return to 40 percent in overwintering flies. Compared to a generation time of about one
month, these changes were rapid and effected very large differences in reproductive fitness of
the various types under different climatic conditions. Other experiments showed that, in fact,
flies of mixed genetic makeup (heterozygotes) were superior in survival and fertility to pure
types.
"Dobzhansky, Theodosius" Britannica Online.
INDUSTRIAL MELANISM: Melanism refers to the deposition of melanin in the tissues of living
animals. The chemistry of the process depends on the metabolism of the amino acid tyrosine,
the absence of which results in albinism, or lack of pigmentation. Melanism can also occur
pathologically, as in a malignant melanoma, a cancerous tumour composed of melanin-
pigmented cells.
Melanic pigmentation is advantageous in many ways: (1) It is a barrier against the effects of
the ultraviolet rays of sunlight. On exposure to sunlight, for example, the human epidermis
undergoes gradual tanning as a result of an increase in melanin pigment. (2) It is a
mechanism for the absorption of heat from sunlight, a function that is especially important for
cold-blooded animals. (3) It affords concealment to certain animals that become active in
twilight. (4) It limits the incidence of beams of light entering the eye and absorbs scattered
light within the eyeball, allowing greater visual acuity. (5) It provides resistance to abrasion
because of the molecular structure of the pigment. Many desert-dwelling birds, for example,
have black plumage as an adaptation to their abrasive habitat.
"Industrial" melanism has occurred in certain moth populations, in which the predominant
coloration has changed pale gray to dark-coloured individuals. This is a striking example of
rapid evolutionary change; it has taken place in less than 100 years. It occurs in moth species
that depend for their survival by day on blending into specialized backgrounds, such as
lichened tree trunks and boughs. Industrial pollution, in the form of soot, kills lichens and
blackens the trees and ground, thus destroying the protective backgrounds of light-coloured
moths, which are rapidly picked off and eaten by birds. Melanic moths, by their camouflage,
then become selectively favoured. "Industrial" melanic moths have arisen from recurrent
mutations and have spread via natural selection.
"melanin" Britannica Online.
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Creationism
The Creationist Debate
Last modified on Sunday, October 11, 1998, by Malcolm R. Forster
Background: Creationists are happy with either of two claims: 1) Creationism is not a
science, and neither is evolutionary theory (which should not be taught in schools), or 2)
evolutionary theory is a science but so is creationism (which should be taught in schools along
side evolutionary theory). They would be happier with 1) but will settle for 2). In recent years,
anti-creationists have concentrated on blocking arguments to the second conclusion.
Ruse's criteria for science
1. Science looks for patterns in nature, order, and natural regularities (laws).
2. Science is explanatory, and the use of natural regularities is necessary for this purpose. [ Pobierz całość w formacie PDF ]