 So, is fossil record, geological record or those observations which Darwin recorded on the Galapagos Islands, based on that he proposed his theory and he published his book of region of species in 1859. In this theory there are major four different postulates and each postulate describes the driving force behind the evolution. So these four driving forces or these postulates we will discuss one by one. First one is competition. So Darwin was also familiar with the pressure of population on natural resources. Darwin has proposed his theory of population pressure and this is a theory which we have discussed in the previous lectures when we were discussing about the population size. So we know when the population size is increasing, it exerts pressure on the resources. The increasing population size, these individuals they are consuming resources but the resources are limited. They would support the increase in population to certain limit but after that the population size increase will stop. And then there is a termination or a decrease in the size of population. So what's up organisms which are present most of them in one habitat they have greater reproductive potential as compared to the bigger animals. So mostly all these smaller animals until the level of the birds they have a greater reproductive potential. For example a female sea star it could releases about 1 million eggs each season. So if we assume that 1 million eggs all of them are fertilized, all of them develop and then they get opportunity to develop into adults. They become mature and all these 1 million are capable of reproducing and producing 1 million eggs again or the 1 million animals again in the next generation. So there would be a drastic increase in the population size in all these species which are reproducing with the greater potential. As a population size is so drastic increase there would be an unimaginable resource problems there would be an unimaginable pressure on the resources present in that environment. So these limited resources and increasing population sizes they create competition between the species or among the individuals of same species. So we have two different types of competitions. One is intraspecific, the other one is intraspecific competition which is happening between two or more than two different species present in that habitat. So they all are competing for food, for the shelter, for all these climatic resources which are available in that habitat and they need a place and a shelter for the reproduction and for their offspring. So there is a very tough competition when the population size has increased. So to understand this process of competition we can study here it's again the Galapagos finches. The only example like number of finches is higher and then it is increasing with the passage of the time. But once those resources climatic resources are not favourable because there was a drought conditions in Galapagos island during 1977 or this dry conditions ki wajah se waha par food resources they or water resources they were dropped or there was a direct there is a direct linkage association between climatic factors and size of population. Toh jab climatic factors ya temperature conditions or food ki availability is not sporting increase in population so there was a decrease in size of population. That is because this decrease or the drop is because of lesser availability of resources available in that habitat. But in 1978 jabi drought conditions improved mi uske saath hi population size dubhara se improve hona shuro gaya but it couldn't reach up to that limit. Because there is a big proportion of individuals or the populations joke in 1977 mi reduce ho gaya. So now the resources are gradually increasing and the population is gradually increasing. So that one driving force which is called the competition and this competition is responsible for bringing the evolution in.