Week 2 - life as we know it or don't know it

Our book gives 7 properties "associated" with life. But this is not a list that can be used to decide if an individual is alive.

Particularly evolution is an emergent property of life. A living individual does not evolve. You need time and a population for that. Ok if you want to reduce this to its smallest unit, a single individual that can reproduce asexual and whose offspring may eventually be different that it, could be said to "evolve". In this case, I would call the offspring over time a population. That is really a stretch.

Likewise, reproduction is not required to define life in an individual. Not all individuals reproduce. Some hybrids cannot reproduce, yet they are alive. Likewise, some social insect colonies depend on sterile workers. I suppose in the case of the sterile individuals, we could make the excuse that they are the product of reproduction.

The growth, energy utilization and response to environment may be difficult to determine in a dormant seed. If the seed is still alive, these properties are potential as opposed to being currently demonstrated. We need to distinguish between dormancy and death and thus need to know how to bring the individual out of dormancy.

On the other hand, viruses give us pause. Some people say they are not alive. Others say they are on the edge of living objects. They do evolve. They reproduce but only with help from the hosts they invade. They do not "grow" or respond to their environment.

And how would we recognize life in exobiology? We would probably try to use the same rules that we are developing for earth-based biology, but life elsewhere may be different molecularly from earth-based life.

Ok... these are just a few thoughts of mine on the subject.