Thus in such situations the characters used to recognise the species becomes merely diagnostic, not distinctive. Biologically speaking, these are a connected series of the species in neighbouring areas which interbreed with two end populations which are too phenotypically and geographically separated that they cannot interbreed. These two genetically and phenotypically diverse populations which represent the end populations may exist in the same geographic region, yet due to genetic and phenotypic diversity would not interbreed. As an example, the case of Larus gulls can be taken, the different species of which form a ring around the North Pole. The Lesser Black-beaked Gulls in Siberia form a part of this ring, and although they descend from the same species, adjacent Herring gulls are so different from them that they do not interbreed.
Earnst Mayr's Biological species concept tends to recognise species based on defined phenotypic characters. Mayr defined species as groups of interbreeding populations, which do not reproduce across other species. This builds in a concept of reproductive isolation from other such groups. Particular species specific phenotypic characters or attributes prevent interbreeding with other species. Although the biological species concept places the taxonomy of natural species within the concept of population genetics, it fails to explain the ring species. Although there are apparent differences between naturally occurring ring species, the phenotypic distinction within the same or adjacent geographic areas blur, so in actuality, they interbreed. Secondly, the existence of connecting population distinguishes the ring species from two separate species. These features raise questions about the species concept (Liebers et al., 2004).
Q2. Neo-Darwinism and Lamarckism
The Neo-Darwinism of evolution contends that all life on earth arose from a common ancestor. This was postulated to occur due to random mutations of genes, which survived following the process of natural selection. Where these mutations were beneficial and had survived natural selection, it led to a replicative process leading to more offspring. On the contrary, those with deleterious mutations have fewer or no offspring. Some of these mutations which were beneficial could help new adaptations to altered environments changed or new. These adaptations were incorporated in the genetic traits leading to generation of newer species. It has been postulated that the genetic makeup of the complex organisms is a result of duplication and useful mutation of existing genes of simple organisms. Lamarck's theory of evolution on the other hand posits that when environmental conditions change, an organism goes through the need for changes. With these changes, organs or organ systems may also go through the drives of these changes, which ultimately would need use or disuse of some organs. If used, these organs will develop, and if disused, these organs will demonstrate diminution. In this way a new characteristic or genetic trait is acquired. When acquired traits run in generations, these become hereditary, and the organism demonstrates an evolution. These two theories differ in the concept of causation of mutation. While the neo-Darwinian