Steven A Benner
Foundation for Applied Molecular Evolution, PO Box 13174, Gainesville, FL 32604, USA
author email corresponding author email
BMC Biology 2010, 8:77doi:10.1186/1741-7007-8-77
The electronic version of this article is the complete one and can be found online at: http://www.biomedcentral.com/1741-7007/8/77
Received: 7 June 2010
Accepted: 9 June 2010
Published: 14 June 2010
© 2010 Benner; licensee BioMed Central Ltd.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Recent achievements in synthetic biology have raised the question of what we mean by 'life'. Is a definition possible?
Yes, one can always write out a definition for an abstract concept like 'life'. But a definition has value only if it is set within the context of a theory that gives its terms meaning, as Carol Cleland and Chris Chyba argue in their paper published in 2002. And a definition is most useful if it provides what a scientist needs.
For example?
Well, water can be defined as a molecule built from two atoms of hydrogen and one atom of water. But this definition must be set in the context of atomic theory from chemistry to have meaning. Further, for a scientist wishing to identify water, this definition may be less useful than an operational definition - for example, that water is a substance that freezes at 0°C, boils at 100°C, has a density of 1 gram per cubic centimeter, and the like.
How does this apply to life?
Consider this definition from a group of scientists empanelled by NASA in 1994 who suggested that life could be defined as a 'self-sustaining chemical system capable of Darwinian evolution'.
Self-sustaining? But doesn't most life need to eat something from outside itself?
Yes. But the panelists, when asked, pointed out that 'self-sustaining' was not used to mean that the life must not eat. Rather, the term means only that life must not need to be provided its sustenance through the action of an intelligent being, a gardener or a keeper.
Aren't you just defining life as we know it? Is this not a bit Earth-o-centric?
This definition is grounded in a deeply held theory of life, as I argue in my book Life, the Universe and the Scientific Method. It tells us what we definers believe about what is possible in reality and what is not. Thus, we can conceive, and many science fiction authors have conceived, of life made from pure energy or not requiring Darwinian evolution to exist. Surely, if we encountered such beings during a real (not fictional) star trek, and if they were to talk to us (as aliens generally do in science fiction), we would instantly revise our definition to include them. We do not do so now because we do not believe that they could possibly exist. That is, we believe that anything that has the attributes of life would be chemical and would have come to exist via Darwinian evolution. Admittedly, those beliefs are based on our knowledge of Earth life, and of no other.
Are those beliefs justifiable from any other perspective?
One can do an interesting thought experiment. In a few years, we may be able to identify DNA sequences that prospectively help our children survive, and gain the technology that allows these sequences to be placed into our germ lines to generate mutant children that are fitter by design. If this happens, then our species will start to escape Darwinian mechanisms for improving our genes. The good news is that we will no longer need to see children die of genetic disease; a large number of bad mutations is the Darwinian cost of a few good ones. With gene therapy, we may imaginably be able to scan the germ line for deleterious genes and remove them.
Will this mean that we are no longer 'life'?
By this definition, yes: Darwinian evolution does not allow prospective mutation. Through this technology, humankind would be able to evolve in a more Lamarckian way. But this scenario is not implausible. So perhaps we should start thinking now about a better definition-theory of life.
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UMA PERGUNTA INDISCRETA DESTE BLOGGER:
Se os cientistas até hoje não sabem definir o que é vida, qual é mesmo nome da ciência que estuda a vida ainda não definida pela ciência? Agnobiologia??? Como pode existir uma ciência assim que não sabemos definir seu objeto de estudos e pesquisas? Ou é intencional somente para favorecer agendas ideológicas e aéticas???
Sei lá, mas acho que hoje em dia está prevalecendo uma burrice imensa passando por ciência.
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UMA PERGUNTA INDISCRETA DESTE BLOGGER:
Se os cientistas até hoje não sabem definir o que é vida, qual é mesmo nome da ciência que estuda a vida ainda não definida pela ciência? Agnobiologia??? Como pode existir uma ciência assim que não sabemos definir seu objeto de estudos e pesquisas? Ou é intencional somente para favorecer agendas ideológicas e aéticas???
Sei lá, mas acho que hoje em dia está prevalecendo uma burrice imensa passando por ciência.
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