Souls do not exist, and even if they did they are not part of science.
The scientifc definition of life is not completely clear, but here is the basic one..a living thing generally has these qualities (if you dont know the meanings look them up
1. Homeostasis
2. Organization
3. Metabolism
4. Growth
5. Adaptation
6. Response to stimuli
7. Reproduction
Now obvously there are exceptions.. such as that some animals cant reproduce because they are sterile like a mule..
Using this kind of definition its pretty obvious that a cat or an amoeba is alive...but about viruses? Scientice is still uncertain about the status of virses. Then there are things like prions, which are non-standard protein molecules which can actually "reproduce" and be infectious (it is believed Mad Cow disease is caused by prions).
While a simple protein doesnt seem like it can be alive, a prion does exhibit some primitive similarities to life. Viruses are even closer to living things, having a complete RNA strand.
What about a computer virus? it too has some basic similarities to life..then there are complex systems that have some life-like qualities, like weather patterns, storm systems, etc.
One of the perils of using strict definitions for things like this is that we get locked into a binary viewpoint.. where something is either purely alive or purely non-living. We should realize that like most things, there is a gradient between the poles. A rock is not alive, and an aligator surely is, and there are many stops in between..
