Sunday, 4 December 2011

Discussing evolution

I recently came across something said in one of the websites I frequent,  about why the "Theory of Evolution" is "wrong." 
The person making the statement said that evolution, as it is accepted in the scientific community as the explanation for life on earth, cannot possibly be correct because "they don't have transitional fossils." He also stated that there have been no changes in lifeforms since "the creation" and "surely if evolution were true, we should have been able to see changes over the 5,000 years since the Bible story was written." 
In discussing this topic with another theist on a skeptics forum, he claimed that evolution may be true but only in the sense that after “the Flood” which saved the lives of only 16,000 animals, those animals were responsible for the millions of the different species we find on the earth today, including all the species that have become extinct in the recent past. 
Leaving the argument about the Bible creation story having not been written 5,000 years ago (and the Flood) for now, I shall, in this post, after having had the process explained to me by actual scientists, hopefully, clear up some misconceptions that people who don't understand the "Theory of Evolution" have about the process.
Evolution and the speed with which a species makes specific changes depends on, among other things, the length of its lifespan. For instance, fruit flies. The lifespan of one species of fruit fly can be completed in as little as 16 days, from the laying of one generation of eggs, to the laying of a subsequent generation, whereby in an average year, there will be 22 generations of fruit flies, A family of humans, on the other hand, with modern longevity and later reproduction, would take eleven centuries, i.e. over a thousand years to produce 22 generations. Thus evolutionary changes in fruit flies, could be noticeable in two human generations, or 100 years. Whereas the long lifespan of humans, and more than 22 generations having passed since the Bible was written, the only change in humans has been that we live longer lives than we did then, and even that is not due to evolution, but because of a variety of other reasons.
There are other factors of course that eventually cause a species to evolve into several different species and sub-species as explained in the following quote by "Calilasseia" posting in What if Atheists are wrong?
How long it takes for this to happen, however, is not yet quantitatively predictable. Depending upon many factors, such as the fecundity of the individuals in the population, the generational turnaround, the mutation rates of the genes in question, and how quickly those mutations become fixed in the population, speciation could take place in as little as five years (as happened with Dobzhansky's laboratory population of Drosophila pseudoobscura, as documented in his 1971 paper), or could take as long as ten million years. Species with fast generational turnarounds and rapid mutation rates in the relevant genes will exhibit speciation events more quickly under relevant circumstances, than species with slow generational turnarounds and slow mutation rates. Unfortunately, we are not yet in a position to use this information in a quantitatively predictive manner, but we can use this in a qualitative manner, to predict that a genetically isolated lineage will eventually exhibit reproductive incompatibility. We will only find out that this has happened, however, when appropriate tests upon the populations in question demonstrate interfertility failure between relevant populations, and of course, with large populations, it will be impractical to test every possible combination of individuals. If you have two populations, each comprising a million individuals, then exhaustive testing would require 1012 trial matings. Sadly, we're not yet in a position to try this out. In this sense, there is no well-defined point at which speciation occurs, because we lack the ability to perform massive numbers of trial matings to find that point. But that point does exist, as I've just explained.
Studying genes does reveal the history of an organism but since DNA material cannot be extracted from fossils, because fossils are not actual bones but minerals that have replaced the bones or are casts of the bones (see fossilization methods in Wikipedia: Fossils), scientists use additional methods to discover the ancestry. These methods include comparative anatomy which paleontologists use to predict the “transitions” that should have occurred in an animal’s evolutionary history. 
For an example of this we need look no further than the anatomy of our own limbs and to compare them with those of the ordinary domestic chicken. The ball-and-socket arm and leg joints, the heavy upper bone, two lower bones and phalanges in the hands and feet demonstrate the common ancestry of humans (apes) and chickens (birds) fairly obviously. Therefore they had to have evolved from a single ancestor but through the evolutionary process, and necessity, changed to suit the individual environmental needs of each shift along the chain of evolution, leading to the sort of diversification we see today. How did they arrive at this conclusion? The original animal, i.e. the common ancestor of all animals who demonstrate the limb physiology I mentioned above, was a fish with “pre-limb-like” fin bones. They named these animals “Rhipidistia;” searching for the link from Rhipidistians to human, they found “Tiktaalik”:
Tiktaalik provides insights on the features of the extinct closest relatives of the tetrapods. Unlike many previous, more fishlike transitional fossils, Tiktaalik's "fins" have basic wrist bones and simple rays reminiscent of fingers. The homology of these is uncertain; there have been suggestions that they are homologous to digits, although this is incompatible with the digital arch developmental model because digits are supposed to be postaxial structures, and only three of the (reconstructed) eight rays of Tiktaalik are post-axial. They may have been weight bearing. Close examination of the joints show that although they probably were not used to walk, they were more than likely used to prop up the creature’s body, push up fashion. The bones of the fore fins show large muscle facets, suggesting that the fin was both muscular and had the ability to flex like a wrist joint. These wrist-like features would have helped anchor the creature to the bottom in fast moving current.
This type of “comparative anatomy” predates Darwin by some 62 years and was formulated by a man named Carl Linneaus. 
Does this mean that a man can mate with a chicken and produce a chicken-man? Of course not. These changes do not happen overnight, as explained above. Also, the study of evolution involves many branches of “science.” It is not simply a matter of drawing conclusions from a single fossil example.
A really good and easy to read and understand source for people who don’t understand how evolution works is this book Why Evolution is True, by Jerry Coyne.
Thus it is easy to understand that a deity did not suddenly drop "creatures" onto the planet making them similar in many ways and different in others, nor did it happen as a result of really fast evolution after the fictional “Flood.” If two animals (and humans are included in this) share a similar physical attribute, they also share a common ancestor. This doesn’t happen because a deity was too busy to think up a new idea, it is the result of millions of years, and thousands of generations of adaptation and change. A process which is still ongoing, even in the so-called “higher” order of animals.