But this assumption is especially inadmissible, when we consider the peculiar circumstances of the case before us. The first generation, according to Dr. Colenso, was composed of the fifty-one grandsons of Jacob. They were already grown up, and some of them even had children when they came into Egypt. Therefore the whole of the first generation was already in existence, and the second had begun to be born some years, let us say three, before the descent. If we add the 215 years of sojourn in Egypt, we shall have 218 years from the beginning of the second generation to the Exodus. Now, according to Dr. Colenso, all those who were twenty years of age at the Exodus, belonged to the fourth generation. Therefore the fourth generation was not complete until twenty years before that time, or 198 years after the second had begun. Consequently, only three generations, the second, third, and fourth, came into existence during a period of 198 years. In other words, the length of each generation, according to Dr. Colenso's calculation, was sixty-six years. Hence it follows, that we cannot accept his argument, unless we are prepared to _take for granted_ that _all the males_ in _all the Hebrew families_ were without issue until they had reached the age of sixty-six. Let us now look into the examples of Dr. Colenso in detail. It is important to ascertain what generation is to be reckoned as the _first_. In his argument he allows but fifty-one males to the _first generation_; "supposing now _the fifty-one males of the first generation_" (p. 105). Since Jacob had fifty-one grandsons living at the time of the descent into Egypt, it follows that the _first generation_, according to the argument, was composed of the grandsons of Jacob, _and of them alone_. That this is the position assumed by Dr. Colenso, is also evident from another passage, where, replying to his opponents, he asserts: "The Scripture states that there were 600,000 warriors in the fourth generation from Jacob's _sons_" (p. 119). It is true that, when _proving_ his theory of "the Exodus in the fourth generation", Dr. Colenso counts indifferently from "the _sons_ or _adult grandsons_ of Jacob, who went down with him into Egypt" (p. 96), just as it suits his purpose. But, when he employs this conclusion to demonstrate that the number of the population at the time of the Exodus was impossible, he assumes that there were only four generations from the _sons_ of Jacob.