Evolution: Biology | |
Basic Ideas: Natural Selection |
ContentIn the previous article mutations have been introduced as a source of evolutionary innovation: In this connection it has also been mentioned, that detrimental mutations are wiped out. The removal of disadvantageous changes is called selection. Detrimental mutations are removed by the carrier having less or no offspring at all. That is selection means varying success of reproduction. In this article, observed examples for the effect of selection are introduced and it is explained, which conclusions can be drawn from this. Condition: polyvalent gene pool The best-known example for selection: the peppered moth |
This scenario has been criticized for some time already. The most important objection is, that after detailed field studies the peppered moth nearly never settles on the stem of trees (pic. 60 is posed). Until today, the resting place of the peppered moth has remained unknown. Secondly, the number of light forms reincreased, before the lichen had repopulated the barks. Furthermore, the moths don´t tend to choose surfaces matching their color. If there should be a connection between the environmental pollution and the frequency of the dark moths, it is far more complicated than expected and up to now not understood. Selection probably took place, but the conditions in detail are quite unclear. Either way shows a typical case of microevolution. It is not documented, where the dark moths come from. What has been observed, is a shift in the frequency of the different forms of moths – but not the development of new varieties. Even if the dark form did evolve by mutation, it still would be microevolution, because the light forms as well carry the dark-brown pigment melanin, which is responsible for the coloring of the dark form (they have brown spots or bands), so that the dark form could develop without any new formation of structures. |
A worm, exposed to changing environmental factors, may become a “better” (better adapted) worm, but not an insect. Signs of a change towards an insect no longer mean adaptation as a worm; these attempts would therefore be wiped out by selection (pic. 61). This argument goes as well for hypothetical common ancestors of worms and insects. |
Selection: often only claimed |
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The examples for selection given above (Finches, Iguanas, peppered moth) are based on observations in the field. They obviously only give evidence for microevolution. It is often said, that more complex structures developed by selection, as well as the slight changes of beak size, leg length or wing coloring in the given examples. Often the hypothetical acquisition of new organs is described as “adaptation”, as well. That way it is suggested, that selection (in combination with mutation) can be made responsible for the acquisition of organs – and that the emerging of new structures is basically understood. Wings for instance would then be an adaptation to flight or a long, sticky, protrudable tongue to nutrition with small insects etc. This way of expressing oneself is common but nevertheless factually incorrect. The term adaptation can only be used in the sense of a fine tuning: An already existing wing might be adaptive to the different requirements of flight. But a wing itself is as much an adaptation to flight as a washing machine is to the washing of dirty clothes. Here the adequate use of the term is important: Wings are not an adaptation, but equipment for a certain purpose, constructions, by which certain tasks can be fulfilled. Actually, the development of new organs by selection (and other evolutionary factors) never has been observed. Selection is a factor of variation, not of creation. |
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