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中文INTRODUCTION
The view of human evolution itself is as old as when man first began to form philosophies of the process. The Greek philosophers such as Anaximander postulated the development of life from non-life and the evolutionary descent of man from animal, such as apes.
Biological evolution which concentrates on the emergence of homo sapiens as a distinct species from other hominans, great apes and placental mammals is known as human evolution. At present there is great debate on this subject and a wide range of research seeking to understand and describe how this change occurred. The study of human evolution encompasses many scientific disciplines especially the fields of physical anthropology, linguistics and genetics. In terms of human evolution “human” refers to the genus Homo, but studies of human evolution usually include other hominins, such as australopithecines.
One of the founding thieories of biological evolution is that proposed by Charles Darwin. Darwin’s “Theory of Evolution” states that all life is related and has descended from a common ancestor. The theory asserts that complex multicellular creatures evolve from more simplistic and unicellular ancestors naturally over time. This occurs as random genetic mutations within an organism’s genetic code. These beneficial mutations are preserved, because they aid survival and lead to a process known as “Natural selection”, and are then passed on to the next generation. Over time the beneficial mutations accumulate and lead to the development of an entirely different organism. This organism will not be a variation of the original ancestor, but an entirely different creature.
On the other hand intelligent design is the thoery which has emerged recently and is one of the biggest challenges to the theory of evolution. This theory claims that “certain features of the universe and of living things are best explained by an intelligent cause, not an undirected process such as natural selection.”
DARWINIAN EVOLUTION
Natural selection acts to preserve and accumulate minor advantageous genetic mutations for example a member of a species developed a functional advantage such as growing wings and learning to fly in order to escape predators or even to obtain food in a time of famine. Its offspring would inherit that advantage and pass it on to their offspring. The disadvantaged members of the same species would gradually die out, leaving only the advantaged members of the species. This can be viewed in a similar fashion to domesticated breeding by breeders eliminating undesirable traits gradually over time.Similarly, natural selection eliminates inferior species gradually over time.
Darwinian Theory has been accepted by scientist worldwide in a manner similar to a religious belief. According to Darwin’s theory, the evolutionary lineage leading to humans is marked by a dramatic increase in brain size. It was postulated that genes involved in the regulation of brain size during development may also have a tendency to be involved in brain enlargement during evolution (Gilbert et al. 2005). Trimborn et al (2004) have shown that the mutated gene responsible for primary microcephaly, Microcephalin (MCPH1) may be involved in the regulation of the response when DNA damage and mitotic DNA condensation occur. Another 3 genes, involved in primary microcephalynamely CDK5RAP2, ASPM and CENPJ have all been shown by Bond et al (2005) in spindle formation during mitosis. All four genes appear to be involved in cell cycle control, and their influence on brain size may stems from their role in regulating the proliferative potential of neuroblasts during neurogenesis. Work by Evans et al. (2006) on these four genes showed that the role of these four genes has been involved in the positive selection of brain size. This is due to the evidence that CDK5RAP2 and microcephalin and ASPM, have shown high statistical significance in being phenotypically similar by showing signatures of positive selection in the lineage leading to humans (Zhang 2003). This can be attributed to the length of the evolutionary time over which the selection appears to have occurred. Work such as this support Darwin’s Theory of Natural selection.
As a consequence of genetic variation, evolution is also a physiological process. Martinez et al. (2008) identified 2 hyoid bones from the middle Pleistocene site of the Sima de los Huesos in the Sierra de Atapuerca (Spain) and compared them to hyoid bones of chimpanzees and Australopithecus afarensis. The chimpanzee-like anatomy of the hyoid appears to represent the primitive hominin condition, and its presence in A. afarensis indicates that the derived modern human morphology emerged at some point during the course of human evolutionary history. The presence of a human-like hyoid in the Neanderthal specimens Kebara 2 and SDR-034 suggests that this derived condition was also present in the last common ancestor of the Neanderthal and modern human evolutionary lineages. This work further supports the theory of evolution according to Darwin.
However although modern biotechnological techniques have allowed scientist to delve into the molecular structure of organisms, there still remains some doubt into the theory of evolution as proposed by Darwin. Krings et al (1997) undertook some work on DNA analysis. This group extracted DNA from a Neanderthal-type specimen found in western Germany (1856), and sequenced clones from short overlapping PCR products. They identified mitochondrial (mt) DNA sequence and using multiple controls, found that this sequence is endogenous to the fossil. Sequence comparisons with human mtDNA sequences was conducted and a phylogenetic analyses undertaken. The results show that the Neanderthal sequence falls outside the variation of modern humans and the age of the common ancestor of the Neanderthal and modern human mtDNAs is estimated to be four times greater than that of the common ancestor of human mtDNAs. These finding suggests that Neanderthals went extinct without contributing mtDNA to modern humans and as such the modern humans did not evolve form ape like ancestors as proposed by Darwin.
Darwin himself confessed, “To suppose that the eye with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection seems, I freely confess, absurd in the highest degree.” [Darwin p155]. This shows that at some level Darwin himself did not fully identify with his theory of natural selection.
INTELLIGENT DESIGN
The intelligent design theory proposes that development of a species through genetic mutation does not take place randomly or from random environmental pressures. According to Darwin, all life on earth evolved form unicellular organisms from the primordial slime. If this is the case, then there is limited explanation for the existence of bacteria, which are also unicellular in many cases and also have a haploid genetic code. The events of natural selection also fail to explain why the evolutionary pressures differentiated living organisms into plants and animal, and why sentient animals have evolved into different species. Genetic variation, or the occasional spontaneous generation of a sequence alteration (mutation) in the genome of an organism, is a prerequisite for biological evolution to occur. Genetic variation thus drives biological evolution. If natural selection caused mutations and genetic variants, then natural selection would drive the survival of the fittest. Ultimately one species would have evolved which was the fittest of all. However this is not observed in the current network of life on the planet as there are still biological cycles of predation and competition. These all point to an intelligent design of living organisms which fit within their niches. Thus as the intelligent design theory states, there is a reason for the existence of each organism and each has developed due to a specific reason.
Arbur (2003) states that geneticists working with micro organisms or higher organisms common observe spontaneous DNA sequence alterations that lead only turn out to be useful or beneficial for the organism. Additionally attempts in molecular genetics have failed to identify evolutionary adaptation as a phenomenon by which changes in the environment would specifically induce useful mutations in appropriate genes. This kind of purpose-oriented mutagenesis could not be a general natural mechanism.
It has been shown that no obvious differences between the cranial morphology of Neanderthals and modern humans have been left by natural selection has. Detailed functional analyses also fail to support several candidate adaptive explanations for Neanderthal cranial form (Weaver et al. 2007). Work by Ackerman and Cheverud (2004) also failed to find evidence that natural selection shaped facial differences between australopithecine and early Homo. Many critics of intelligent design have dubbed it as a non-science. However it can be shown that it does qualify as scientific due to the fact that for a theory, hypothesis or conjecture to be considered scientific, it must meet most of the criteria listed below.
- Consistent
- Parsimonious
- Useful Empirically testable and falsifiable
- Based on multiple observations
- Correctable
- Progressive
- Provisional
Although it can be proven that Intelligent design fulfils many of these criteria, typical objections include the lacks consistency violation of the principle of parsimony, not scientifically useful, is not falsifiable, is not empirically testable, and is not correctable, dynamic, tentative or progressive. Another criticism of this theory is that there has been a failure to follow the procedures of scientific discourse and the failure to submit work to the scientific community that withstands scrutiny. To date, the intelligent design movement has yet to have an article published in a peer-reviewed scientific journals.
CONCLUSION:
Darwin’s theory of evolution has been widely accepted across the globe as the main theory of evolution, until recently with the emergence of the intelligent design theory of evolution. Although both theories provide a viable option for the development of living creatures across the millennia, there are several drawbacks in both theories. Additionally it can be said that the genetic code of all living organisms contains a number of redundancies. If Darwin’s theory of evolution is maintained, that what is the purpose of these redundancies, and should they not be eliminated if they are not useful? Scientific research has shown that some of the genetic codes which do not directly code for a phenotypical feature have been involved in control mechanisms and regulation of molecular processes. This also points to the view that intelligent design is at work even at the most complex level.
