Tag: zoology

Darwin, in the fourth edition of his 'On the Origin of Species', wrote that the first author who in modern times has treated in a scientific spirit was Buffon a significant reference from the man known as the father of evolutionary theory. Buffon was known to have changed his views often during the course of his life and this is possibly why he is rarely referred to in the history of evolutionary thought. However, he is lauded by modern evolutionists as having posed significant questions about the development of life on Earth. Therefore, the correct answer is option B.

Late in the 1930s, Dobzhansky discovered "isolation mechanisms", i.e., finely-tuned sex traits, other genetic factors and to him physical barriers in the environment which impede gene flow between populations.  Without these mechanisms incorporated into evolutionary theory, it would under-explain the level of species-diversity found in nature. The theory of origin of isolation which stresses that nature is not in favour of hybridization was given by Dobzhansky. Thus, option C is correct. 

The modern synthetic theory of evolution is the result of the work of a number of scientists namely T. Dobzhansky, R.A. Fisher, J.B.S. Haldane, Swall Wright, Ernst Mayr, and G.L. Stebbins. Stebbins in his book, Process of Organic Evolution, discussed the synthetic theory. It includes the following factors - Gene mutations, Variation (Recombination), Heredity, Natural selection and Isolation. In addition, three accessory factors affect the working of these five basic factors. Migration of individuals from one population to another as well as hybridization between races or closely related species both increase the amount of genetic variability available to a population. The effects of chance acting on small populations may alter the way in which natural selection guides the course of evolution. Thus, option D is correct.

• The Modern Synthetic theory of Evolution explains the evolution of life in terms of genetic changes occurring in the populations that leads to the formation of new species. 
• It also explains the genetic population or Mendelian population, gene pool and the gene frequency
  
• Hence, According to the modern synthetic theory, the unit of evolution is a/an Population.
• So, the correct answer is 'Population'.

• The theory of evolution by natural selection, first formulated in Darwin's book "On the Origin of Species" in 1859, is the process by which organisms change over time as a result of changes in heritable physical or behavioural traits.
• Different characteristics tend to exist within any given population as a result of mutation, genetic recombination and other sources of genetic variation.
• Evolution occurs when evolutionary processes such as natural selection and genetic drift act on this variation, resulting in certain characteristics becoming more common or rare within a population. 
• Hence, Modern evolution theory involves Natural selection, Genetic variations and Isolation. 
• So, the correct answer is 'All of the above'.
  

Postmating isolating mechanism is any structure, physiological function, or developmental abnormality that prevents organisms of two different populations, once mating has occurred, from producing vigorous, fertile offspring. Postmating isolating mechanisms includes, gametic. Gametic incompatibility  (Sperm transfer takes place, but egg is not fertilized), Zygotic mortality (Egg is fertilized, but zygote does not develop), Hybrid inviability (Hybrid embryo forms, but of reduced viability), Hybrid sterility (Hybrid is viable, but resulting adult is sterile) and Hybrid breakdown (First generation (F$ _{1}$) hybrids are viable and fertile, but further hybrid generations (F$ _{2}$ and backcrosses) may be inviable or sterile). Thus, option D is correct and other options are wrong.

Geographic isolation: In the fruit fly example, some fruit fly larvae were washed up on an island and speciation started because populations were prevented from interbreeding by geographic isolation. Scientists think that geographic isolation is a common way for the process of speciation to begin. Rivers change course, mountains rise, continents drift, organisms migrate and what was once a continuous population is divided into two or more smaller populations. So, a new species is formed from existing population when it is geographically isolated and not by different size of genitalia, different mating time and seasonal variations.