 दाविन also observed की कुईसी भी पोपूलेशन में बिलोंगस to the same specie, उसके in two individuals, they can't be same. तो have similarities, but they can't be exactly like each other, because for every trait, there is a variation among the individuals of same specie. ये वोही a variation सैंजिसको असने गलाप गय स्थोर्टरिस or finches के केस में observe किया. तो 14 different species of finches, तो each of the individuals belong to a same specie, थो चव ने साईज ने तो असा वीगार जाय तो भी थे। this is due to the height and the fitting of the individual. तो वीगार दीखार ये वीगार जाय दीखार तो आपने जगे्ये सेंच्य तो आपने लै जगें to place some variations and these variations are related to the ability of the individual to survive and reproduce, which means every individual in one population of same species would be different from the other individual of same species in case of same trait or evo variation hai which these individual has acquired to survive in a better way as compared to other individuals or ye variation of traits which is appearing in the same population of the same species it is coming because of competition for same resources in that environment to be better survive kane kale hai, bethe tari kase reproduce kane kale hai, her individual bugth ka saa saat usme ye next generation tak usme ase variations aayangi jo ke usko better survive kane kale hai, ek opportunity provide karte hai and these variations not necessarily ke hameisa jo hai, productive ho ya uske li beneficial ho so these variations could be harmful as well and ye possibility hai ke they are neither helpful and they are not the harmful and these variations which are acquired through their phenotype and the genotype they are passed on to their offspring for example in case of this survival differential survival we go back again to those gallup against benches here in 1976 the population size of deafney birds is 751 so if we look at this graph we can see ke yaha par jo beak ke width hai was 6 millimetre se lekar ase be kuch individuals hai which have 14 millimetre wide beak but in 1978 iska number 751 se reduce ho kar 90 pe chala jaata hai and at same time we will see ke isme ase traits hai which are lost for example 6 millimetre beak wale birds they have disappeared they have eliminated similarly 14 millimetre ki jo beak width hi wo wala group jo hai individuals ka that population is also eliminated so there are certain which are growing very well for example 10 millimetre ki width ke jo beak ke length hai ya uske depth hai wo proportion of population is increasing in its number so there is a continuous elimination and then there is a continuous process of improvement and this improvement and elimination is because of the variation of traits in another case ke kese ye variations jo hai wo continuously aate rite hai we will study this example here is example of the beak depth in offspring's and here is the beak depth of the parents so we can see in 1976 these blue dots mostly those individuals in that population in ke beak ke depth 8 millimetre se lekar 9 millimetre ke darmyan mein but in 1978 we will see that most of individuals they have the beak depth between 9 millimetre and 10 millimetre which means ke 1976 mein jo environmental conditions us habitat mein hai they are more supportive for the beak depth of 8 se lekar 9 millimetre lakin ek saal ke arse mein jaa bhi environment change hot hai yaha pe wo individuals zada survive kare hain aur reproduce kare hain jinn ki beak depth 9 se lekar 10 millimetre ke darmyan mein so there is a continuous variation in environment environmental conditions and resultantly wo individuals wo species jo kese habitat mein survive kare hain they have to change themselves or wo individuals which have the good variations which those variations good variations ka matlab yei ke assi variations assi traits jo unko maximum potential tak reproduce karne mein help out kare aur unki survival ki jo strategies hain they are better than the others so they have these these are animals which have the good variations and these variations are coming with the passage of the time as environment is changing so the variations are also appearing wo svag when davan he proposed his theory and he proposed that concept of variations he was not familiar with the factor behind these variations so usko yei malum tha ke assi ek phenotypic variations hai for example beak depth hai for example length of neck hai so these are the phenotypic or morphological variations which he observed but later when in the modern age jab mandal ne apne genetics ke principles or theories jo ki usko proposed kya then he proposed that genes are actually responsible for these variations and then he proposed the concept of inheritance that the genes from the parents are transferred to the offspring's so the parents they are transferring their traits both phenotypically and genotypically to their offspring's and then we know that the mandal's law of independent assortment also proposed that these genes they assort from each other independently and he also proposed the concept of then later on there was a concept of crossing over and we know that these alleles can cross the dna and this exchange of dna it would bring the variations and then meosis itself is also bringing variations that's why offsprings are not exactly like their parents so they have variations in the traits and they are dissimilar in certain traits from their parents so this confirmed the second postulate of davin in the modern age as well therefore davin theory is still acceptable because it is in agreement with the modern research