Evolution - 2 (Class - X)

The process by which organisms with different evolutionary histories evolve similar phenotypic adaptations in response to a common environmental challenge, is called convergent evolution.

Atavism is the tendency to revert to ancestral type. In biology, an atavism is an evolutionary throwback, such as traits reappearing which had disappeared generations before. Atavisms have been observed in humans as well. Babies have been born with a vestigial tail called "coccygeal process", "coccygeal projection" or "caudal appendage".

 The dinosaurs and the mammals appeared during the Triassic period, roughly 225 million years ago. The dinosaurs went extinct 65 million years ago. The Mesozoic Era lasted about 180 million years, and is divided into three periods, the Triassic, the Jurassic and the Cretaceous.

Homo sapiens fossilis is the scientific name for Cro-magnon man.

We can determine human evolution by studying the fossils and also by studying the relationships of structure, anatomy, etc. with other species. The similarity and relationships can also be established by studying the DNA sequences of humans and comparing with other species. But skin colour cannot be used for determining human evolution because it has a huge variation in the same species.

Genetic drift or allelic drift is the change in the frequency of a gene variant (allele) in a population. It is closely related to mutation. 

Homologous organs are those which have similar internal structure and origin, but they are differently modified in various organisms to perform the functions that they require, e.g. forelimbs of a man to write; forelimbs of a horse to walk; forelimbs of a bird to fly; and forelimbs of a whale to swim. Thus, only (2) is correct. Option (3) is opposite of homologous organs because organs which are similar in function, but different in structure and origin are called analogous organs, e.g. wings of birds and bats.

This is the correct sequence of events in origin of species according to Charles Darwin's theory.

Natural selection is the gradual process by which heritable biological traits become either more or less common in a population as a function of the effect of inherited traits on the differential reproductive success of organisms interacting with their environment. It is a key mechanism of evolution. The term "natural selection" was popularised by Charles Darwin, who intended it to be compared with artificial selection, now more commonly referred to as selective breeding.

According to Darwinism, competition between two different species is the key factor for organic evolution since it results in divergent evolution.

Statement (a) is incorrect. Darwin did not differentiate between somatic and germinal variations.

According to Lamarckism, new needs produce modifications of the existing organs and formation of new organs. It is known as inheritance of acquired characters.

It is the nail present on the toe.

The book 'The Origin of Species' was written by Darwin. Lamarck gave the theory of inheritance of acquired characters, which was initially opposed. Later, this theory was supported by both Darwin and Alfred Wallace. At that time, the book 'The Origin of Species' gave a strong evidence to support Lamarck’s theory.
Mendel, on the other hand, worked only on genetics and traits. But the theories of Mendel and Darwin unfortunately were never mixed; else the evolution and its genetic basis may have been understood much before.

Natural selection refers to the phenomenon where nature selects those organisms which are well adapted. This means that they adjust with the changing environment and survive. Those which are least adapted are unable to survive.