Quiz 8: Social Relations

Charles Darwin was a naturalist who spent his life studying plants and animals. He sought to understand their variations, similarities, reasons for being and the basic forces that cause them to change. Darwin observed the variations as caused due to phenotypical changes. Gregor Johann Mendel was a scientist who was later known as the father of genetics. This was based on his extensive experimental observations and conclusions which are based on genetics. Mendel proved the variations as the result of the genetic changes. Both Darwin and Mendel are known for their contributions to science which. However, their approach towards their discoveries was entirely different. Darwin's Approach • Darwin's studies were completely based on his long-term observations of geographical areas. • He added onto the extensive studies of other scientists. However, his conclusions were unique and based on his own ideas. • He did not use mathematical methodology in his works. Mendel's Approach • Mendel preferred experimentation and observation in all of his works. • His approach involved physical sciences, like mathematics, which enabled him to convert the data gathered by him into a more approachable form. • He worked with plants, such as garden peas, which were easy to cultivate and maintain under normal conditions. • He had more segregated and recorded work, which made it easier for him to present his results. Darwin's Main Discoveries 1) The theory of natural selection is considered a milestone in to the study of evolution. It states that evolution is a natural process by which a population acquires biological traits on the base of differential reproduction to survive and adapt. 2) The theory of compelling evolution explains natural selection as the basic mechanism for evolution. 3) The majority of his work and discoveries were based on his work on plants and animals of different geographical areas. Some of his major works are published in the following books; • Origin of Species • Descendants of Man • Selection in Relation to Sex • The Expression of Evolution in Man and Animals Darwin spent a long tenure of his life observing populations, and he understood the differences between successive generations on the basis of characters. With his observations and guidance from the works of Thomas Malthus, he was able to develop the theories mentioned above. Mendel's Main Discoveries 1) The principle of segregation states that alleles account for variations in inherited characters. 2) The principle of independent assortment states that a random assortment of homologous chromosomes leads to a variety of allele recombinations in gamete cells. These chromosomes are independent from the distribution of alleles of other chromosomes during gamete formation. Mendel explained the reasoning behing genetic inheritance using terms such as alleles, homozygotes, dominant trait, recessive trait, and variation. Once he developed a complete set of data collected via experiments and observation, he mathematically converted the patterns to a more reliable and reproducible form. The studies of Darwin helped ecologists and scientists to understand the trends of nature. It led to further research on population studies. Mendel's work helped to generate a foundation of genetics. Mendel and Darwin complement each other's work, and the correlation of their postulates has led to major scientific findings. A few of these discoveries are are as follows: • Genetic variation and its impact on population and evolution • The Hardy Weinberg equilibrium law • Variation-based population changes in large and small populations. • Reasons for and consequences of genetic drifts • Production of captive breeding techniques on the basis of genetic variation

The regression analysis of the degree of heritability of body length in three hypothetical populations of water lily leaf beetles has been represented in the book. In the regression analysis, the average body length of two parents was considered to be the independent variable and the body length of the offspring as the dependant variable. The three hypothetical populations indicate different relations between the two variables. The regression coefficient indicates the degree of heritability of body length in three populations. • In population (a), the regression coefficient of 0.00 indicates that the body length of offspring is not dependant on the body length of the parents. The variation in body length among offspring is entirely determined by the environment. • In population (b), the regression coefficient is 0.52, indicating that half of the variation in body length of the offspring is genetically determined and half is determined by the environment. • In population (c), the regression coefficient is 0.8, indicating that about 80% of the variation in body length of offspring is determined genetically and the remaining variation by the environment. The evolutionary implications of the three patterns exhibited by populations (a), (b) and (c) are as follows: • Population (a) indicates that the body length is not a heritable feature. It is under the influence of the environment. Body length does not have much potential to evolve by natural selection. The variation in body length will depend on the changes in the environment. Hence, a parent of small body length can give rise to an offspring of large body length and vice versa, depending on the environment. • In population (b), the body length shows intermediate heritability. The body length is governed equally by genetic effects and the environment. The body length shows scope for evolution by natural selection. Body size has been observed to control mating success in males. Hence, the large-sized males may get selected for mating and give rise to a large-sized offspring if the environmental influences remain the same on the parents and the offspring. • In population (c), the body length shows higher heritability and hence, maximum potential to evolve by natural selection. The body length of the parent will largely decide the body length of the offspring with few environmental influences. The natural selection will favor one of the body lengths, which will contribute to a large number of offspring with similar body length.

The studies of Clausen, Keck and Hiesey demonstrated that different populations of the same species may not only differ genetically but also be clearly adapted to the local environments in which they grow naturally. The studies of Hansen, Elven, and Brochmann demonstrate how combining morphological and genetic information can be used to distinguish variation within species versus variation between species.