Biology · Evolution · NEET
NCERT asks this exact question: "What is the origin of this variation?" Variation in a population comes from three main sources: (1) mutation — an alteration in the DNA sequence that changes genotype and phenotype, (2) genetic recombination — new combinations of alleles formed during meiosis, and (3) sexual reproduction, which shuffles parental genes into new mixtures in offspring. Mutation is the ultimate source because it creates brand-new alleles; recombination and sexual reproduction rearrange existing ones.
Mutation creates the variation. Natural selection does NOT create anything new — it only acts on variation that already exists, keeping the better-fit variants and removing the less-fit ones. This is a very common NEET confusion. Order to remember: variation appears first (mutation/recombination), then selection sorts it. Selection is a filter, not a source.
NCERT states meiosis "increases the genetic variability in the population of organisms from one generation to the next." It does this through crossing over (exchange of segments between homologous chromosomes) and independent assortment (random arrangement of chromosome pairs). Together these produce recombinant gametes with new allele combinations, so offspring differ from parents and from each other.
Variation is the raw material of evolution, not the direct cause. NCERT says "variations are very important for the process of evolution" and "variations in a population result in variable fitness." Without variation, every individual would be equally fit and there would be nothing for natural selection or genetic drift to act on. So variation is necessary but the actual change in allele frequency is driven by selection and drift.
De Vries, based on his work on evening primrose, said evolution is driven by mutations — large differences arising suddenly in a population. NCERT gives the key contrast: "Mutations are random and directionless while Darwinian variations are small and directional." So mutational variation = large, sudden, random, directionless; Darwinian variation = small, gradual, directional. This exact line is a repeated NEET question.
Variations caused by mutation, as proposed by Hugo de Vries are
According to Hugo de Vries, the mechanism of evolution is
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Mutation (new DNA changes), genetic recombination during meiosis (crossing over and independent assortment), and sexual reproduction (mixing of parental genes). Mutation is the ultimate source of new alleles.
Because evolution acts by changing allele frequencies. Variation gives different individuals different fitness, so natural selection and genetic drift have something to act on. No variation means no evolution.
Mutation is random and directionless — it does not aim toward any useful trait. Whether a mutation helps or harms depends on the environment, which is decided later by natural selection.
Mutation creates a completely new allele by altering the DNA sequence. Recombination does not make new alleles; it produces new combinations of already existing alleles during meiosis.
Hugo de Vries, based on his work on the evening primrose (Oenothera). He proposed mutation theory and the idea of saltation — evolution by sudden large mutations rather than Darwin's small gradual variations.
