Common details of the body arrangement are evidence of close relativeness of human and anthropoids: wrist with flat nails, shape of eyes and years, the same number of canine and molar teeth, complete change of baby teeth, and so forth. Physiological commonness is very important: the same blood groups, diseases (tuberculosis, fly, smallpox, cholera, AIDS, pneumonia) and parasites (louse). Besides numerous common features, there is a number of explicit differences evidencing that its current stage, human is considered to be different species. Only human has ability of upright walking and related to that peculiarity of structure of the S-shaped backbone with explicit neck and lumber bend, low extended pelvis, and etc. Human skull is higher and more rounded without superciliary arch; brain part of skull is in most part dominated by facial; high forehead, weak jaws with small canine. Human brain is about two and half times bigger than one of humanlike apes, and 3-4 times heavier.
Human being evolved from other pre-existing species. Even in ancient times it has been noticed that humans have a lot of in common with a other animals just like other animals human had the same internal organs (heart, lungs, liver etc.). Ancient Greeks had a scale of living organisms known by their time. Human being was placed at the end of the scale. Below were higher animals like houses, sheep and so forth, but it is hard to believe that humans were next step in the biological evolution of living organisms right after higher animals. Only by the eighteenth century ape-like being became known to Europe. This discover shed light on a huge gap between higher animal and humans (Darwinism defended, Ruse, pp. 230). After that some scientists (for example Huxley) assumed that humans descended from apes. Later, having examined all differences between apes and humans, Huxley came to conclusion that humans and apes descended from a common ancestor. One would probably ask why our common ancestor did split into two branches, apes and Australopithecus afarensis (which is considered to be an ancestor of all hominids). There is a scientific explanation, which relates to climatic changes in Africa. Our ancestor was used to live in the area of heavy precipitation. With a passage of time climate started turning into dry one and forestlands began retreating, leaving behind Savannah's. Some species stayed in dwindling forests. Others (our ancestors) started advancing toward opened spaces.
With a change of place of inhabitation, there were some changes in diet of our ancestor. Anthropologists suggested that tooth reduction took place because our ancestor started to use grass seeds and the like as a food source (Darwinism Defended).
Major Claims of Evolutionary Theory
Natural selection is the major moving factor of the evolution of the living organisms. Almost at the same time, several English naturalists arrived at the idea of existence of natural selection (P. Mathew (1831), A. Blight (1935), A. Wallace (1858), C. Darwin (1858)), but only Darwin succeeded in exposing of the meaning of this phenomenon as the major factor of evolution and created the theory of natural selection. On the contrary, to artificial selection held by humans, natural selection is conditioned by influence of surrounding environment upon the organisms. According to Darwin natural selection is survival of the most accommodated organisms, in consequence of which, on the basis of undefined inherited changeableness in the series of generations evolution occurs.
In process of natural selection species more accommodated to surrounding environment survive, those who do are not, go extinct. Explicit example of that is our ancestors that had advantage of standing upright to look out and look for possible object of prey. Natural selection does not specifically have to lead to perfection. It leads only to surviving of species that can survive. If entire kind of particular animals can not survive in changed environment, entire kind will dye out.
"Organisms in nature topically produce more offspring that can survive and reproduce given the constraints of food, space, and other resources in the environment. These offspring often differ from one another in ways that are heritable—that is, they can pass on the differences genetically to their own offspring. If competing offspring have traits that are advantageous in a given environment, they will survive and pass on those traits. As differences continue to accumulate over generations, populations of organisms diverge from their ancestors."
Process of natural selection consists of two steps: the first one is reproduction of genetically different species; the second step is surviving of the most adopted individuals in surrounding environment. An example can be nest of birds in which some nestlings have a little bit different coloring than others. If this coloring better matches the tree these birds in habit, this will give them advantage of better hiding from predators, which leads to increase in changes of reproduction. Below are example that Wallace, Alfred Russle uses in his book "Contributions to the theory of Natural Selection" to demonstrate natural selection.
"The Duke of Argyll, in his "Reigh of Law," has pointed out the admirable adaptation of the colors of the woodcock to its protection. The various browns and yellows and pale ash-color that occur in fallen leaves are all reproduced in its plumage, so that when according to its habit it rests upon the ground under trees, it is almost impossible to detect it. In snipes the colors are modified so as to be equally in harmony with the prevalent forms and colors of marshy vegetation. Mr. J.M.Lester, in a paper read before the Rugby School Natural History Society, observes: --"The wood-dove, when perched amongst the branches of its favorite fir, is scarcely discernible; whereas, were it among some lighter foliage, the blue and purple tints in its plumage would far sooner betray it. The robin redbreast too, although it might be thought that on its breast made it much easier to be seen, is in reality not at all endangered by it, since it generally contributes to get among some russet or yellow fading leaves, where the red matches very well with the autumn tints, and the brown of the rest of the body with the bare branches."
Core of natural selection is variation within the kind. If variation does not exist either entire kind will survive and stay unchanged or it will go extinct. But what it a source of variation? The ultimate source of variation is mutations in genes. If new traits gained through mutation leads to successful survival and reproduction than new traits will be inherited and spread within the population. Mutation is random, but natural selection is not.
All living organisms that currently inhabit the earth share common ancestry. Through the history by means of natural selection and variation first, simple forms of life were evolving into different, more complex forms. How to prove it?
"The discovery of the structure of DNA by Francis Crick and James Watson in 1953 extended the study of evolution to most fundamental level the sequence of the chemical basis in DNA both specifies the order of amino acids in proteins and determines which proteins are source of both change and continuity in evolution. The modification of DNA through occasional changes or rearrangements in the base sequences underlies the emergence of new traits, and thus of new species, in evolution. At the same time, all organisms use the same molecular codes to translate DNA base sequences into Protein amino acid sequences. This uniformity in genetic code is power evidence for the interrelatedness of living things." (Teaching About Evolution and the Nature of Science, ch. 2, pp. 4)
Another powerful argument that supports common ancestry is a fact that man is developed from an ovule, about the 125th of an inch in diameter, which does not differ from the ovules of other animals. At a very early period, the embryo can hardly be distinguished from another member of vertebrate kind.
In order to convince one that evolution happened the way evolutionary theory describes it evidences must be presented. Major evidence and argument of evolutionary theory is that all of the mechanisms of evolutionary theory change are currently observable. Let us take for example main mechanism of evolutionary change—natural selection. Nowadays our society is facing serious public health problem. Bacteria that medicine used to successfully fight with antibiotics is becoming more resistant to one. This means that week bacteria go extinct and only strong (more resistant to antibiotics) bacteria survived. (Teaching about evolution, ch. 2, pp. 5) "continued use and overuse of antibiotics has had the effect of selecting for resistant population because the antibiotics give these strains and advantage over non-resistant strains"
"Long Argument," Ernest Mayr, Harvard University Press, 1991.
"Darwinism defended," Michael Ruse, Addison-Wesley Publishing Company, 1982.
"The Descent of Man and Selection in Relation to Sex," Charles Darwin, 1974.
"Wonderful Life," Stephen Jay Gould, W.W. Norton & Company, 1989.
"Contributions to the theory of natural selection," Wallace, Alfred Russel, AMS Press, 1973.
1 Teaching about Evolution