Title: ANTHROPOLOGY Paper: PAPER No. 2 Course name: PHYSICAL ANTHROPOLOGY Module: NEO-LAMARCKISM AND NEO-DARWINISM (12/15) The concepts and theories regarding the origin and evolution of organisms so far discussed are not totally satisfied. Perhaps, Albert Einstein s view that there is no absolute reality but only relative truth is true. Theories which are accepted today may be wrong tomorrow. And, many of the concepts and theories are modified and changed after deeper researches have been carried out in course of time. Similarly, the theories of Lamarckism and Darwinism have been discussed by many scientists and the shortcomings are shown and improved. We shall now discuss the new developed theories of Lamarckism and Darwinism. Neo-Lamarckism Lamarckism also known as the theory of inheritance of acquired characters can be defined as the changes in structure or function of any organ acquired during the life-time of an individual in response to changes in the surrounding environment which is inherited by its offspring and keep on adding up over a period of time. The changes are because of use and disuse as demanded by the environmental pressure.
Lamarckism has many drawbacks and this is evident from the experiments carried out by various scientists. Experiments such as the one carried out by Weismann in which he mutilated the tails of white rats and mated them but found no loss of tail in succeeding generations, McDougall s (1938) experiment on rats to observe that acquired behavioural traits are inherited or not etc. Limitations of Lamarckism as were shown by many researchers led to the formation of a new school of thought that support evidences in support of Lamarckism. Harrison s experiment on a pale variety of moth, Selonia bilunaria showed interesting findings. By feeding manganese coated food, these moths in areas where food plants were infected with manganese salts from industrial smoke produce a different, a melanic variety breed moth showing that the influencee of manganese can influence on the germ cells and acquired to the offspring. Tower exposed young ones of potato beetle to abnormal conditions of temperaturee and humidity. The strong heat did not produce any somatic changes in the beetles themselves, but their offspring showed marked colour changes in the next generation. Interestingly, these changes were found to pass on to the succeeding generations. Muller also experimented the role of X-rays in producing heritable variations in Droshophilia that revealed the change in the chromosome structure. Likewise, C. Auerback in collaboration with Robinson and Carr produced heritable changes in Drosophilia by using a chemical mutagen, mustard gas. Thus, Neo-Lamarckians proved that: 1. Germ cells are influenced by the environmental changes. 2. Germ cells may carry acquired or somatic variations to the offspring (Harrison s expt.) 3. Germ cells may be affected directly by the environmental factors (Tower s experiment)
4. Somatic traits are the product of nature and nurture i.e. genes and environment interaction. This infers that environment affect the gene expression of organisms. Thus, we have seen that the difference in view point of Lamarckism and Neo-Lamarckism was that Lamarck believed in the direct action of environment, which he thought was responsible for achieving final perfection of the individual. Neo-Lamarckians modified the concept. They are of the view that a considerable time period is required to act up to the level of germ cells that produce visible and invisible traits. Neo-Darwinism The theory of natural selection or Darwinism is a breakthrough in the history of evolution. It is a simple concept easy to grasp. In a species, there are individuals that differ genetically from one another as a result of which their ability to adapt and survive to different environment differs. Nature is the causative force that sorts out bad adapted ones replaced by best and the their progeny is spread. In this course of nature s scrutiny, the trait that changed and adapted is selected by nature and the bad ones screened out. However, Darwinism also has certain drawbacks. He did not know the mechanism of inheritance. He laid emphasis on individual variation and lack clarity in accounting the sources of variation and ignored the role of recombination. This leads to the formation of a new school of thought in the middle of the 20 th century by combining all sources of knowledge from genetics, palaeontology, ecology and others. Edward O Dodson and David J. Merrill called this new theory of evolution as Neo-Darwinism. George Gaylord Simpson and his followers, however, strongly refuted the labelling of Neo-Darwinism as synthetic theory of evolution. Simpson argued that the synthetic theory had no Darwin. However, we shall consider the two labels as synonymous. The new concept of evolution is the product of two rival camps of thought. One supporting the traditional Darwinian view centering around natural selection as the key role
player of evolution and the camp centering around the central role of mutation and a whole new branches of science, undreamt of by Darwin such as molecular biology. The synthesis of these two camps leads to the formation of Modern Synthetic Theory of Evolution. Therefore, the theory has two stages of process: Natural Selection whereby genetic differences in some individuals lead to their higher reproductive success, and production and redistribution of variation which are genetically influenced differences between individuals which are inherited. In order to understand the modern concept of evolution, one has to study and understand the short term events of evolution called microevolution, the slow accumulations of changes seen and unfold in every generation. Using such a modern population genetics perspective, we define evolution as a change in allele frequency from one generation to the next. Alleles are the alternative forms of genes that occur at the same locus. The synthetic theory considers evolution to be the result of changes in the gene frequencies of populations that produces variations. Following are the important factors of modern synthetic theory of evolution: 1. Natural Selection. This is a process of nature in which continuation of one line of organisms which are selected and the elimination of another from the evolutionary record thereby making changes in the gene frequency of the population. Through this process of natural selection, some genotypes in a population develop advantage over others in fertility and viability that leads to change in gene frequency of the population. The proportion of an offspring genotype contributes to the next generation is the Darwinian Fitness measured by reproductive capacity. 2. Mutation. The change in the genetic material of an organism result to the formation of new traits thereby producing variation in the population of the organism. Such a change in the DNA sequence is called mutation. The majority of mutations are thought to occur because of occasional mismatching of the sequences of the chemical bases that make the DNA. This is just
like a typist making error in copying manuscript, so will DNA in duplicating itself. Though most of changes through mutation are harmful, some of the changes are selected by nature, some are eliminated and yet some are neutral in selection. The degree of severity of the effect of mutation is based on place where the DNA regulates the production of proteins. All these lead to change in the gene frequency of a population. One interesting case is of industrial melanism in which grey moths which were adapted more than the black moths before pre-industrialization, become adaptive after industrialization after which the tree trunks become darker and the black moth are less seen to their predators from attack. 3. Genetic Drift. It refers to various random processes that affect gene frequencies in small, relatively isolated populations. The isolation may be because of social factors as in the case of a religious sect of Dunkers who emigrated from Germany to the USA in the early 1700s. As a result, blood group and other genetic traits of the Dunkers are genetically drifted away from the parental population Dunkers in Germany. According to Hardy-Weinberg Law, in large populations (assuming evolutionary forces are not operated), the gene frequency of a population tends to remain in balance. But in smaller populations the probability and chance play a great role in increasing or decreasing of alleles. 4. Gene Flow. Gene flow is a process by which genes from one gene pool or populations of a species may be brought into another population. Since these flowed genes differ from their initial frequency, they produce change in the gene pool which receives them. Such changes occur through migration and hybridization. Difference between Darwinism and Neo-Darwinism After knowing the above discussed important factors of Neo-Darwinism, lastly, let us try to see few important
differences between Darwinism and Neo-Darwinism. Neo-Darwinism is the advance and updated theory of evolution. 1. Unit of evolution is a population not species as is mentioned in Darwinism, because species are subdivided into local populations. 2. It is the gene pool of the population that evolves and not the individual level. 3. Differences among individuals in a population are the consequence from accumulation of mutations and recombination of genes due to independent assortment, crossing over and fertilization. These reasons of variations are not known to Darwin. Conclusion: Lastly, understanding of modern theory of evolution needs knowledge of molecular genetics. Students shall attempt to know the basic knowledge of it, without which they will face handicapped in understanding the theory.