Is Evolution tenable? Before one can even answer this, it would be prudent to define what Evolution is in the biological realm. Oxford’s Press Concise Science Dictionary does a good job defining Evolution simply without colloquialism, it states:
“The gradual process by which the present diversity of plant and animal life arose from the earliest and most primitive organism” -- Concise Science Dictionary (1987) First ed. Oxford. Oxford University Press.
Evolution deals with how diversity occurred on this planet from primitive life. Two more terms I think it is essential to have a definition of due to the nature of these debates4 is macroevolution and microevolution,
Macroevolution:
“evolution on a large scale extending over geologic era and resulting in the formation of new taxonomic groups” -- Princeton University, WordNet Search - 3.0, viewed 13 June 2007, < http://wordnet.princeton.edu/perl/webwn?s=macroevolution>.
Microevolution:
“evolution resulting from small specific genetic changes that can lead to a new subspecies” -- Princeton University, WordNet Search - 3.0, viewed 13 June 2007, < http://wordnet.princeton.edu/perl/webwn?s=microevolution>.
Now we have a basic definition of Evolution, is it tenable?
Charles Darwin provided a testable and logical theory of evolutionary change, this initial building block that is the starting point (excluding Lamarck, but kudos goes to him for noting the concept of adaption) for “The Theory of Evolution” is On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life. The main points in the book are:
(1) That animal species reproduce more rapidly than is needed to maintain their numbers, although populations do fluctuate they tend to remain stable
(2) There is competition within species and between species in this “struggle for existence” for food, living space and for animals within the same species a mate for reproduction.
(3That within a species all animals vary and this variation is inherited.
(4) In this “struggle for existence” that individuals that are best fitted to survive in a particular environment are the ones that live and produce. Other animals are removed due to the vast competition. The individuals that are best fitted to survive reproduce and pass on characteristics that made survival for the parent favourable, the favourable characteristics are accumulated in future generations, and it is this accumulation that leads to the separation of the species that are well adapted survive in an environment, this is what Charles Darwin coined “natural selection”
There is one problem with this that, and George Jackson Mivart pointed out, I shall summarize: Charles Darwin hadn’t shown how these favourable characteristics were accumulated, only how those less fitted to survive failed to survive. It is with the product of an Austrian monk Gregor Mendel and the later work of Thomas Hunt Morgan that gave the understanding of heredity that backed up Charles Darwin.
Sparing the introduction to biology/genetics lesson, and me giggling at names such as endoplasmic reticulum (had to make A-Level biology fun somehow), but variation in animals comes from the recombination and crossing over during reproduction, and new variation comes from mutation. For bacteria it is slightly different due to they reproduce by binary fission, the variation comes solely from mutation and since bacteria are haploid the mutation is noticeable immediately.
When a mutation occurs it creates a new allele, this allele is heritable and can produce changes in the organism, it is the nature of these changes that can affect the existence of the organism, the change in alleles tend to be small scale, and are of limited affect, and if they are large they are very often lethal and the organism will die before it can pass on the variation so it will not enter the populations gene pool. But most mutations are neutral, some are disadvantageous, in this case the organism will fall prey of natural selection, but others may lead to a new characteristic with a selective advantage.
And this advantageous mutation will be only spread if:
(1) It occurs within the population, so that new members are continually added to the mutant stock.
(2) If it carries some form of selective advantage so the Hardy Weinberg principle is shifted in its favour.
(3) The population is small enough for it to be spread and carried efficiently.
Now considering the amount of time life has been on Earth some circa 3000 million years, these advantageous mutations within small populations spread and up to the point of a new species.
Genetic Drift occurs if a population is very small and localized, and due to the small <myspace>
size</myspace> of the population it only contains a limited selection of the genetic variation, it is a change in the gene frequencies through randomization. These localized populations become distinct as the small population contains a distinct set of alleles.
Now for the evidence:
Genetic Drift, this is (and was one of the top links of Google) similar to research work I was doing in Svalbard on glaciers observing bacteria in small isolated populations on glaciers called cryoconite holes but the paper on this has not yet been published yet, but it is focused on hydrothermal vents, the conclusion of the study was:
“The presence of IS elements in only one population of Pyrococcus, together with MLST, revealed genetic divergence between populations occupying different geographic locations. Physical barriers to their dispersal might be the result of severe constraints on their growth conditions together with the discontinuous nature of their environment. The observed high frequency of IS elements and evidence of their deleterious effects strongly suggest that genetic drift occurred in the Vulcano Island population and that it is an important mechanism of genetic divergence in Pyrococcus. Thus, these observations and the island-like nature of their environment make hyperthermophiles good candidates to be the microbial counterpart of the giant tortoise of the Galapagos (Fenchel 2003)”
-- Patricia Escobar-Páramo, Sulagna Ghosh and Jocelyne DiRuggiero. (2005) 'Evidence for Genetic Drift in the Diversification of a Geographically Isolated Population of the Hyperthermophilic Archaeon Pyrococcus', The Oxford Journal of Molecular Biology and Evolution, Volume 22, Number 11 Pp. 2297-2303.
Macroevolution, due to the large time spans involved in the formation of new taxa comes from the fossil record, in the case of Horses we can see the a clear distinct evolutionary lineage seen in Fig 1.
Fig 1. (Source http://upload.wikimedia.org/wikipedia/en/d/dd/Horseevolution.png accessed 13 June 2007)
Also in the fossil record we can see many transitional forms such as Tiktaalik roseae, Proterogyrinus, Protoclepsydrops, Ichthyornis, Archeopteryx et al.
Microevolution, the constant information on our TV about new strains of avian flu should be enough but if not:
“Our results indicate that the outbreak was initiated by a strain related to East-African isolates, from which viral variants have evolved following a traceable microevolution history. Unique molecular features of the outbreak isolates were identified. Notably, in the region coding for the non-structural proteins, ten amino acid changes were found, four of which were located in alphavirus-conserved positions of nsP2 (which contains helicase, protease, and RNA triphosphatase activities) and of the polymerase nsP4. The sole isolate obtained from the cerebrospinal fluid showed unique changes in nsP1 (T301I), nsP2 (Y642N), and nsP3 (E460 deletion), not obtained from isolates from sera. In the structural proteins region, two noteworthy changes (A226V and D284E) were observed in the membrane fusion glycoprotein E1. Homology 3D modelling allowed mapping of these two changes to regions that are important for membrane fusion and virion assembly. Change E1-A226V was absent in the initial strains but was observed in >90% of subsequent viral sequences from Réunion”
-- Schuffenecker I, Iteman I, Michault A, Murri S, Frangeul L, Vaney MC, Lavenir R, Pardigon N, Reynes JM, Pettinelli F, Biscornet L, Diancourt L, Michel S, Duquerroy S, Guigon G, Frenkiel MP, Bréhin AC, Cubito N, Desprès P, Kunst F, Rey FA, Zeller H, Brisse S, (2006) ‘Genome microevolution of chikungunya viruses causing the Indian Ocean outbreak’, PLoS Med. 2006 Jul;3(7):e263, Epub 2006 May 23.
I have tried to keep this opening as brief as possible, this is why I haven’t included the mountains of evidence backing up evolution and only select examples, so please don’t think all that I have published is it. I will be happy to discuss issue pertaining to these if needed, and I am interested in Shane's objection to The Theory of Evolution.
