Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): Evolution for Darwin was gradual while deVries believed mutation caused speciation and hence called it saltation (single step large mutation).
Reason (R): Even though Mendel had talked of inheritable ‘factors’ influencing phenotype, Darwin either ignored these observations or kept silence.
In the light of the above statements, choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Both (A) and (R) are true but (R) is not the correct explanation of (A).
Assertion (A): Evolution for Darwin was gradual while deVries believed mutation caused speciation and hence called it saltation (single step large mutation). — True. A compares how fast new species arise in the two views: slowly by small steps for Darwin, in one large step for de Vries.
Reason (R): Even though Mendel had talked of inheritable ‘factors’ influencing phenotype, Darwin either ignored these observations or kept silence. — True. R is about Darwin’s silence on Mendel’s factors of heredity.
Why R does not explain A? R tells us what Darwin did not take up, namely Mendel’s idea of inheritable factors. It says nothing about why Darwin saw evolution as gradual, which came from the small heritable variations he described, or why de Vries called it saltation, which came from his work on mutations in evening primrose. Both statements are true, but R is not the correct explanation of A.
NCERT Extract:
Mechanism of Evolution – “What is the origin of this variation and how does speciation occur? Even though Mendel had talked of inheritable ‘factors’ influencing phenotype, Darwin either ignored these observations or kept silence. In the first decade of twentieth century, Hugo deVries based on his work on evening primrose brought forth the idea of mutations – large difference arising suddenly in a population. … Mutations are random and directionless while Darwinian variations are small and directional. Evolution for Darwin was gradual while deVries believed mutation caused speciation and hence called it saltation (single step large mutation).”