Short Answer Questions (submit online)
- Give two fields of study that require an understanding of the nature of life and why.
- What is the problem with defining life in terms of the detailed celular process that we associate with life on Earth?
- Explain the NASA "working definition" of life.
For Further Discussion
- The 'checklist' approach to life. In school textbooks, a common checklist of features that living things have consists of Movement, Respiration, Response to Stimuli, Growth, Reproduction, Excretion and Nutrition.
- Give examples of non-living things that also satisfy some of these requirements. Can you think of a non-living thing that satisfies all of them?
- Give examples of living things that do not satisfy some of these requirements. Can you think of any living thing that fails to satisfy any of them?
- What is wrong with this check-list kind of approach, when our aim is to understand what the nature of life is?
- The n=1 problem. The n=1 problem is a response to the suggestion that life should be identified with the particular biologicla and cellular processes that are shared by living organisms on Earth. The variable "n" is supposed to refer to the size of the sample size of living organisms on Earth that we are considering.
- We are currently at a moment in time in which n = trillions. At what moment in time was it the case that n=1? What is significant about such an event?
- All known life is composed of large amounts of carbon molecules. Does it seem reasonable to expect that all living things must be built in this way? Why or why not?
- Suppose that we could construct a system that has all the functional properties of life, but is mostly made of silicon rather than carbon. Could this system be considered alive?
- The first example of life on Earth is thought to have been contingent: it is not a matter of law, but a matter of accidental fact about our planet that life occurred in the way that it did, analogous to the fact that Earth has one moon. Why might this be a problem for the explanation of life in terms of cellular processes?
- The evolution of life. Life as we know it consists in populations that undergo Darwinian evolution. Some have argued that this could be used as part of a definition of life.
- What would this definition say about a population of mules?
- Suppose we build a machine that is able to reproduce itself, with small random variations in its building programmed in. Such a machine could produce a population that undergoes Darwinian evolution. Would this make it alive?
- Thermodynamic approaches to life. An isolated system slowly becomes more and more disordered. One can view a living system as a entity that fights against this process, by constantly lowering its disorder, while raising the disorder of its environment.
- Is this a necessary feature of life?
- Suppose we enountered a single entity, which did not replicate, but which kept its disorder low at the expense of its environment. Would this be a living thing?
- An interesting thing about this perspective is that it suggests an account of the origin of life. The Earth is a system in which energy is flowing in (from the sun) at a much higher rate than energy flows out. This is a lot like charging a battery, or increasing the voltage on a Tesla ball. When the energy becomes high enough, order can spontaneously emerge out of disorder, just as the little filaments of light are spontaneously emitted from the centre to the edge of the ball. Is this a possible explanation of the origin of life? Or is it impossible to explain the complexity of life in terms of mere "order"?