Tag: theory of natural selection

Ernest Haeckel is the scientist who had contributed much to genetic evolutionary studies. He is the one who described: "Ontogeny recapitulates phylogeny".

Organic compounds essential for life can be produced by simple inorganic constituents that were the conclusion first derived by Miller and Urey on the basis of their experiment. They took the gases thought to be present in the primitive atmosphere in a sealed flask and exposed them to electric spark. Later on analysis of flask, many organic compounds could be recovered.

The first organisms that appeared on earth resembled single-celled life forms called archaea that can live in extreme environments such as hot springs and deep-sea vents. They were prokaryotic heterotrophs and used inorganic chemicals from the environment for carbon fixation and this process is called chemoautotrophy. They were anaerobic in nature because free oxygen was absent during primitive environment on earth.

The earliest living organisms were prokaryotes which later on evolved to give rise to eukaryotes and photosynthesizing organisms.

• The giant nucleoprotein molecules were formed by the union of nucleic acid and protein molecules. These nucleoprotein particles were described as free-living genes. Nucleoproteins gave most probably the first sign of life.
• Hence Nucleoprotein gave most probably the first sign of life.
• So, the correct answer is 'Life'.

Evolution brings about several modifications to acclimatize with the changing environment. August Weismann (1834-1914) was a neo-Darwinian biologist who proposed the germplasm theory in his book Das Keimplasma. He said that variations are of two types. Some are congenital i.e., organisms are born with them. Others are acquired during the lifetime of a particular plant or animal. It was with this latter type of variations, the acquired characters, that Weismann was very much concerned. He gradually developed his 'Theory of Germplasm' to explain that acquired characters could not be inherited.