SB 4.29.60
narada uvaca
yenaivarabhate karma
tenaivamutra tat puman
bhunkte hy avyavadhanena
lingena manasa svayam
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The great sage Narada continued: The living entity acts in a gross body in this life. This body is forced to act by the subtle body, composed of mind, intelligence and ego. After the gross body is lost, the subtle body is still there to enjoy or suffer. Thus there is no change.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The living entity has two kinds of body — the subtle body and the gross body. Actually he enjoys through the subtle body, which is composed of mind, intelligence and ego. The gross body is the instrumental outer covering. When the gross body is lost, or when it dies, the root of the gross body — the subtle body of mind, intelligence and ego — continues and brings about another gross body. Although the gross body apparently changes, the real root of the gross body is always there. The subtle body’s activities, be they pious or impious, create another situation for the living entity to enjoy or suffer in the next gross body. Thus the subtle body continues, whereas the gross bodies change one after another.
Since modern scientists and philosophers are too materialistic, and since their knowledge is taken away by the illusory energy, they cannot explain how the gross body is changing. The materialistic philosopher Darwin has tried to study the changes of the gross body, but because he had no knowledge of either the subtle body or the soul, he could not clearly explain how the evolutionary process is going on. One may change the gross body, but he works in the subtle body. People cannot understand the activities of the subtle body, and consequently they are bewildered as to how the actions of one gross body affect another gross body. The activities of the subtle body are also guided by the Supersoul, as explained in Bhagavad-gita (15.15):
sarvasya caham hrdi sannivisto
mattah smrtir jñanam apohanam ca
“I am seated in everyone’s heart, and from Me come remembrance, knowledge and forgetfulness.”
Because the Supreme Personality of Godhead as Supersoul is always guiding the individual soul, the individual soul always knows how to act according to the reactions of his past karma. In other words, the Supersoul reminds him to act in such a way. Therefore although there is apparently a change in the gross body, there is a continuation between the lives of an individual soul.