NCERT Solutions for Class 12 Biology Chapter 6 Evolution

Short Note:

• The chemical evolution theory, supported by the Miller-Urey experiment, suggests that simple organic molecules could have formed spontaneously from inorganic gases under early Earth conditions, eventually giving rise to the first life forms.

• Evidence for evolution includes fossil records (showing gradual change over geological time), comparative anatomy (homologous organs indicating common ancestry, and analogous organs indicating convergent evolution), and biogeography (distribution patterns of species across continents).

Short Note:

• Charles Darwin proposed that natural selection acts on heritable variations within a population; individuals better adapted to their environment survive and reproduce more successfully, passing on favourable traits to the next generation.

• Classic examples include industrial melanism in peppered moths (where darker moths became more common in polluted areas due to better camouflage) and the development of antibiotic resistance in bacteria.

Short Note:

• The Hardy-Weinberg principle states that allele and genotype frequencies in a population remain constant across generations in the absence of evolutionary influences, serving as a null model to detect whether evolution is occurring.

• Factors that disturb this genetic equilibrium and drive evolution include mutation, gene migration/flow, genetic drift (random changes in allele frequency, especially significant in small populations), and natural selection.

Short Note:

• Human evolutionary studies, based on fossil evidence, suggest that early hominids originated in Africa, evolving through stages such as Australopithecus, Homo habilis, Homo erectus, and Homo neanderthalensis, eventually leading to modern Homo sapiens.

• Key evolutionary trends observed include increasing brain capacity, development of bipedalism (upright walking), and tool use, which distinguished later hominids from earlier ancestors.