perfectly for the next generation, sometimes make a mistake in copying-something like the printing press that sometimes makes mistakes. In some circumstances these mistakes, or mutations, have stood, and different species of living entities have been formed because of the difference in the genes.
Śrīla Prabhupāda.  But that "mistake" has been continuing since time immemorial, for you will find that all varieties of living entities have always existed. Therefore the "mistake" is eternal. But when a "mistake" is permanent, it is not a mistake; it is intelligence!
Dr. Singh.  But scientists say that if there were no mutations, then there would be only one kind of living entity in the whole universe.
Śrīla Prabhupāda.  No. Every living entity has a different mind, and therefore there are so many different species of life to accommodate the different mentalities. For example, we are walking here, but most people are not coming to join us, because they have different mentalities than we do. Why does this difference exist?
Dr. Singh  , Maybe it is a mistake.
Śrīla Prabhupāda.  It is not a mistake. It is their desire, and at the time of death everyone will get a body exactly according to his desire. Kṛṣṇa says in  Bhagavad-gītā  (8.6):
yam yam vāpi smaran bhāvam tyajaty ante kalevaram taṁ tam evaiti kaunteya sadā tad-bhāva-bhāvitah
"Whatever state of being one remembers when he quits his body, that state he will attain without fail." What you are thinking of at the time of death exactly determines your next body. Nature will give you the body; the decision is not in your hands, but in nature's, and she is working under the direction of God.
Dr. Singh.  But science seems to have evidence that different species of life do arise by mistakes.
Śrīla Prabhupāda.  That is  their  mistake! In the laws of nature there are no mistakes. In railway cars there are first-class, second-class and third-class sections. If you purchase a third-class ticket but by mistake go to the first-class section, you will not be allowed to stay there. It is not a mistake that there are sections; that is the arrangement. But it is your mistake that you have gone to the wrong section. So, God is so thorough that He knows all the mistakes that will be made. Therefore, according to the mistakes you commit, you enter a particular body: "Here, come here. The body is ready." There are 8,400,000 species of life, and nature works, assigning different bodies, with mathematical precision. When the government builds a city, it builds a prison even before the city is completed, because the government knows that there will be many criminals who will have to go to prison. This is not the government's mistake; it is the mistake of the criminals. Because they become criminals, they have to go there. It is  their  mistake.
In nature there are no mistakes. Krşna sayı:
mayādhyakṣeṇa prakṛtiḥ sūyate sacarācaram