Question

Write short notes based upon the information known to you.
a. Lamarckism
b. Darwin’s theory of natural selection
c. Embryology
d. Evolution
e. Connecting link

Answer 1

a. Lamarckism: Lamarck gave the principle of 'use or disuse of organs’. He proposed that the reason behind evolution was the changes in the morphological activities of the organism. For example: giraffe has a long neck because it used to browse on leaves of tall plants by extending their neck for several generations, shoulders of iron smith are strong due to repetitive hammering movements, wings of ostrich and emu are weak because they are not used for flying, legs of birds and swan are used for swimming because they live in water. These characters are termed as acquired characters which are transferred from one generation to another.

b. Darwin’s theory of natural selection: Darwin is famous for the theory which he published in the book titled ‘Origin of Species’. In this book he explained the theory of natural selection which talks about the survival of the fittest. He stated that there is a continuous competition between organisms for survival and the strongest of all survives. The chances of survival are higher for organisms which show modifications which will help them to survive. He also said that, nature also plays an important role in the selection of the fittest. Nature selects only those organisms which are capable of adapting to the changing situations while the rest which are incapable to do so perish away. The organisms which are selected by the nature then reproduce and give rise to new species which have their own characteristics

c. Embryology: Embryology is the study of the formation and development of embryo and foetus. Embryology is used as one of the evidences of evolution. Comparative study of embryos in vertebrates shows that there is lot of similarity in them at the initial stages whereas this similarity decreases gradually. This similarity in the development of embryos represents common origin of organisms.

d. Evolution: Evolution refers to the gradual change which occurs in an organism over a long duration of time. It is a slow going process which results in the development of the organism. Life originated on earth about 3.5 billion years ago. It is believed that there might have been presence of simple elements on earth which may have given rise to simple organic and inorganic molecules. From these simple molecules, complex molecules like proteins, DNA etc. may have been formed. Other evolutionary changes may have resulted in the formation of simple cells and the result of the continuous evolution on earth is the several species of plants and animals which exist on earth. Today, the diversity on earth varies from unicellular Amoeba to a human being and from a unicellular algae like Chlorella to huge Banyan tree.

e. Connecting link: Connecting link refers to plant and organisms which show characteristics related to two different groups. For example, Peripatus is considered a connecting link between annelida and arthropoda. It has characteristics like segmented body, thin cuticle and parapodia-like organs which are similar to annelids. It also shows tracheal respiration and open circulatory system which is similar to arthropods. Another example is duck billed platypus which is a connecting link between reptiles and mammals as it lays eggs like reptiles and has mammary glands like mammals.