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

Every organism alive today, and every organism that has ever lived, is connected through an unbroken chain of ancestry stretching back roughly 3.5 to 4 billion years, to a time when Earth held no life…

By the early twentieth century, biologists broadly accepted that life must have arisen from non-living matter at some point in Earth's distant past, but no one had proposed a scientifically testable m…

Palaeontology is the scientific study of fossils — the preserved physical remains, impressions or mineralised traces of organisms that lived at some point in the geological past — and it provides some…

Comparative anatomy is the branch of biology that systematically compares the structure of body parts across different species, and it provides a second, largely independent line of evidence for evolu…

Embryology, the study of the development of an organism from a fertilised egg through to birth or hatching, provides a further, independent line of evidence for evolution, one first noticed and emphas…

Charles Darwin's landmark 1859 book, 'On the Origin of Species by Means of Natural Selection', proposed a specific, testable mechanism — natural selection — to explain how populations of organisms cha…

Darwin's original 1859 theory of evolution by natural selection was, in its own time, a genuinely revolutionary and largely correct account of HOW favourable heritable variations spread through a popu…

Natural selection, as described in the preceding two sections, can only act upon a population, and can only drive evolutionary change within that population, if the population actually contains herita…

When any measurable, continuously varying character within a population — human birth weight, or the depth of a bird's beak, for instance — is carefully recorded across a large number of individuals a…

Beyond natural selection itself, population genetics recognises two further, quite different processes that can each independently change the relative frequencies of different alleles within a populat…

The Hardy-Weinberg principle, formulated independently in the very same year, 1908, by the British mathematician G. H.

Adaptive radiation is the distinctive evolutionary process by which a single ancestral species, upon reaching some new environment that happens to offer a number of different, previously unexploited e…

Human evolution is the specific evolutionary history of our own species, Homo sapiens, tracing our particular lineage backward through time through a whole succession of extinct hominin ancestors and…

This chapter traced the complete arc of evolutionary biology, beginning with the chemical origin of the very first living cells and ending with the specific evolutionary history of our own species.

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