1.3. A population of organisms evolves as follows. Each organism exists, independent of the other organisms, for an exponentially distributed length of time with parameter 0, and then splits into two new organisms, each of which exists, independent of the other organisms, for an exponentially distributed length of time with parameter 0, and then splits into two new organisms, and so on. Let X(t) denote the number of organisms existing at time t. Show that X(t) is a Yule process.