Evolutionary Mechanisms

Biological evolution is a change over time in the genetic composition of members of a population of organisms that are mating with one another. Thus, evolution is a population process, not a 

Eon/Era Period Began Major physical and biological events 

Archean 3.8 Gyr Origin of life prokaryotes flourish. Photosynthetic cells liberate oxygen, O2 first appears in the atmosphere 

Proterozoic 2.5 Gyr O2 levels increase to 1% of current level. Eukaryotes evolve several animal phyla appear 

Paleozoic Cambrian 600 Myr Climate warms, O2 levels approach current level most animal phyla present, including some that failed to survive algae and cyanobacteria diversify 

---

Inevitably, the study of evolution will take a modeling approach, and discussions such as those above, on strange bedfellows , parasitism and tissues, will point to and illuminate the types of relationships and evolutionary mechanisms that should (and must) contribute to the broader study of evolution. Of course, I am not alone among biologists in advocating such an approach, but my most important allies in the struggle to study the complexity of evolution are philosophers, particularly the biophilosophers and the philosophers of becoming who sometimes wear the same hat . 

It has recently been suggested that the comets also went through a number of subtle, but important, evolutionary processes in the Oort cloud and the Kuiper belt. Thus, their present nature is probably not the original one, as was previously thought (Stern, 2003). The assumption that the material which comets contain is in the same state as it was when the solar system was formed must be revised or modified. The evolutionary mechanisms to which they were subjected are likely to have changed their chemical composition. 

Baker, H. G. (1963). Evolutionary mechanisms in pollination biology. Science 139,877-883. 

Based on major and trace element variations, it has been argued that fractional crystallisation was the dominant evolutionary mechanism for Ustica magmas (Cinque et al. 1988). The lack of correlation between silica and Sr isotopic ratios has been interpreted as evidence that assimilation of crustal rocks played a minor role during magma evolution. The variable contents of K20, P2Os incompatible elements and radiogenic Sr in the mafic rocks most likely reflect the occurrence of various types of primary melts at Ustica. 

Fig. 1. Schematics of evolutionary mechanisms of domain swapping in nature. Multifunctional proteins arise from the fusion of the genes coding for individual enzymes. Often the individual domains of multifunctional proteins catalyze successive steps in metabolic pathways. In tandem duplication, a gene is duplicated and the 3 end of one copy is fused in-frame to the 5 end of the second copy. In domain recruitment, a functional unit (whole gene or gene fragment) from one gene is either inserted within or fused to an end of a second gene. Circular permuted genes are believed to arise via tandem duplication followed by introduction of new start and stop codons (Ponting el at, 1995).

Dover underlined that there is no rigid one-to-one relationship between evolutionary mechanisms and environmental processes, but noticed nonetheless that a certain correspondence does exist. He concluded therefore that adaptation is the normal result of natural selection just as exaptation is characteristic of neutral drift, and adoptation is typical of molecular drive. To our purposes, what matters is that we can indeed speak of three mechanisms of evolution the first two are natural selection and neutral drift, while the third mechanism can be called either genomic flux or molecular drive. 

As always happens, a new conclusion inevitably raises new questions, and in this case the first problem that calls for our attention is the origin of cell memory, a problem which takes us back to evolution and to the evolutionary mechanisms. Now, however, we have something new to discover in the past, and we can look at the history of life from a point of view which has not been considered before. 

The pattern which is observed before the phylotypic stage simply cannot be explained by the same evolutionary mechanism that produce the opposite pattern of the other stages, and this is a problem which has never been given a satisfactory answer. Haeckel, for example,... 

Hybridization techniques are also the methods of choice to look at the RNA expression of repeated DNA family members. Such studies46-48 are not discussed here, but they can be an important part of understanding the function and evolutionary mechanisms associated with a repeated DNA family. 

Evolution strategies (ESs) were developed in the 1960s, at around the same time as early work on GAs. In its first form, ES was not really an EA, more a slightly disguised, moderately sophisticated hill-climber however, it has since metamorphosed into a true EA through the use of a population of potential solutions and a more sophisticated evolutionary mechanism. 

Cellular and viral IL-lOs and IFN-7 form intercalated dimers (Fig. 2). The intercalated dimer is formed from the first four secondary structural elements from one chain (A-D) and the final two (E and F) from the other. The intertwined dimer fold observed for IFN-7, IL-10, and many other protein structures, is proposed to be an evolutionary mechanism of protein oligomerization referred to as 3D domain swapping (Bennett et at., 1995). This theory suggests IFN-7 and lL-10 evolved from a monomeric protein by exchanging structural domains (a-helices E and E) with another monomer to create the dimer. This hypothesis is strengthened by the discovery of the monomeric IL-lOFMs, lL-19, IL-20, and IL-22. In fact, the close relationship between the intertwined dimeric IFN-7 and monomeric type 1 IFNs was clearly identified when the first structure of IEN-7 was completed in 1991 (Ealick et at, 1991). 

Detection of Dopa 4,5-dioxygenase in higher plants and clarification of the level of glucosylation, at betanidin and/or ci/do-Dopa, are the last two steps in betalain biosynthesis to be confirmed. Molecular studies are still needed to elucidate the evolutionary mechanisms of the mutual exclusion of the two pathways (Stafford, 1994), one leading to the ubiquitously occurring anthocyanins and the other to the rare betalains. 

Directed evolution has been successfully used to alter existing enzyme properties and even to create novel enzyme functions. In addition to creating enzymes for specific industrial applications, directed evolution has also been increasingly used to address fundamental questions in biology, such as the evolutionary mechanisms of novel protein functions, protein structure-function relationship, and protein folding mecha-... 

See also Catastrophism Cosmology Evolution, evidence of Evolutionary mechanisms Meteors and meteorites. 

The new catalytic function may eventually improve the accuracy of replication. Then gene duplication represents a powerful evolutionary mechanism to increase the catalytic capacity of a replicating system, which makes replication more precise whenever this is necessary and possible. 

---