(a) Define the term organic evolution
(b) Outline the contribution of
(i) Larmack
(ii) Darwin to organic evolution
(c) List three evidences of organic evolution
(d) Explain the role of
(i) Mutation
(ii) Isolation in the form of new species
Explanation
(a)Organic evolution is a sum total of adaptive changes from pre-existing or old forms which have taken place over a long time and which result in diversity of form, structure, and functions among organisms.
(b) (i) Larmack contributed greatly to organic evolution as he brought great changes in environment resulting 'in a corresponding changes in the species. These changes cause the organism to form new structures or habits to adjust to the new or prevailing environment. The organism then develop specialised characters by use and dis-use of organs which when frequently used become well developed while the ones not used degenerate and become atrophied/useless/vestigial. The well developed or dominant acquired characters are inheritable.
(ii) Darwin in his contribution to organic evolution postulated that species have abilities to produce large number of offspring into the environment with limited resources, thus leading to competition by these offspring. The survivors which must have inherited the useful traits then reproduce and pass on these good traits to their offspring. Those that could not survive the struggle die off or are eliminated. This phenomenon is often referred to as the survival of the fittest/natural selection. There is great variability with population as this process continues through many generations while the population gradually becomes better adapted to the environment. This gives rise to the origin of new species.
(c) Evidences of organic evolution are:
(i) Geological /fossil records/palaeontology/archeological/ historical records,
(ii) Geographical distribution
(iii) Comparative anatomy/ structure
(iv) Embryology
(v) Vestigial organs
(vi) mesticated organism.
(d) (I) Mutation brings about sudden appearance of distinct trait or character in large population of organism due to minor change or alteration in the gene or chromosome. Mutation can only be inherited when it occurs in the gene or gametes leading to production and perpetuation of new species. Mutation elsewhere in the body can not be passed on or inherited.
(ii) The role of isolation in the formation of new species is that if members of a specie are separated into two or more populations by natural barriers like desert, mountains, oceans, rivers, continental drift, etc for a long period, their genes may change to the extent that they cannot interbreed again to produce viable offspring; and the population thereby may have produced new species.