Ch 6Evolution — Class 12 Zoology, concept-first.

Evolution refers to the heritable changes that accumulate in one or more characteristics of a population of a species from one generation to the next.

Several competing explanations have been offered for how life on Earth began. Special creation holds that a supernatural power, respectfully called God, brought life into existence — Hinduism credits…

The 4.5-billion-year history of the Earth is organised into a geological time scale made of three broad eras — Paleozoic, Mesozoic and Cenozoic — themselves divided into periods, and the most recent p…

Biological evolution begins with the transition from simple organic chemistry to structures that behave like living matter.

Evolution is supported not by any single line of proof but by several independent kinds of evidence that all point the same direction.

Paleontology is the scientific study of prehistoric life through fossils, which are often described as the true witnesses or documents of evolutionary history.

Comparative anatomy studies structural similarities between groups of organisms as indicators of evolutionary relationship.

Embryology, the study of development from egg to adult, shows that very different adult animals pass through strikingly similar early stages.

Explaining evolution required more than documenting that it happens — biologists needed a mechanism for how heritable change accumulates across generations.

Jean-Baptiste de Lamarck, in his 1809 book 'Philosophie Zoologique', was the first to formally propose a theory of evolution, resting on two principles.

Charles Darwin set out his theory of evolution by natural selection in 'On the Origin of Species' (1859), drawing on extensive observations of plants and animals made during his round-the-world voyage…

Hugo de Vries put forward the mutation theory after studying the Evening Primrose plant, Oenothera lamarckiana, in which he observed sudden, striking variations appearing without any obvious environme…

The Modern Synthetic Theory, developed by Sewall Wright, R.A. Fisher, Ernst Mayr, Julian Huxley, Theodosius Dobzhansky, George Gaylord Simpson and Ernst Haeckel, reinterprets natural selection using p…

Industrial melanism in the peppered moth, Biston betularia, is the classic real-world demonstration of natural selection in action.

Adaptive radiation is the evolutionary process by which new species, all diverging from a single ancestral form, become adapted to a range of newly available habitats or resources, typically over a co…

Microevolution refers to evolutionary change on a small scale — specifically, change in allele frequencies within a single population — and is driven by four fundamental forces: natural selection, gen…

Natural selection occurs whenever a particular allele, or combination of alleles, makes its bearer more or less likely to survive and reproduce in a given environment; alleles that reduce fitness tend…

Gene flow is the movement of alleles between populations, occurring either through the movement of gametes (e.g.

Genetic drift, also called the Sewall Wright effect, is a mechanism of evolution in which a population's allele frequencies change from one generation to the next purely by chance — that is, by random…

Mutation is the ultimate, original source of all genetic variation — without it, none of the other evolutionary forces would have any raw material to act on.

The Hardy–Weinberg principle describes the theoretical condition under which a population's allele and genotype frequencies remain exactly constant from one generation to the next — in other words, a…

The lineage leading to modern humans can be traced through a sequence of hominid fossils spanning several million years, each stage showing incremental change in brain size, posture, dentition and beh…

Isolation is the separation of members of a single population into sub-populations, which preserves the genetic integrity of each resulting group.

Speciation is the process by which one species evolves into one or more distinct new species, and is regarded as a fundamental process within evolution as a whole. A.E.

Sympatric speciation is a mode of speciation in which a new species forms from within a single ancestral species while both the ancestral and the newly forming species continue to occupy the very same…

Allopatric speciation (geographical speciation) occurs when populations of a single species become physically separated by a geographic barrier — such as land separation, migration to a new area, or t…

Extinction — the permanent disappearance of a species — has been a common, arguably inevitable, feature of the history of life, because species cannot always adapt successfully to large or rapid envir…

This chapter-end Evaluation set brings together everything covered across the chapter — the origin of life and its supporting chemistry, the geological time scale, the several strands of evidence for…

Sample papers and previous-year board questions for this subject.