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Being, doing, developing, evolving – what origins of life researchers might have overlooked?

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Posted November 20, 2013
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Single celled organisms use chemotaxis as a navigation system

Single celled organisms use chemotaxis as a navigation system

The early days of life is a heavily discussed topic by the modern scientists. So far, two main theories have taken the lead in the origin of life research, emphasizing the self-maintenance and self-replication properties of protocells (i.e. metabolism-first and replication-first hypotheses). While the former suggests that any self-producing chemical system can qualify as life, as long as it is bounded and self-organized, the latter insists that life could not exist without at least a primitive ”code”, that could be replicated and passed to “offspring”. Lately, however, the two theories are beginning to merge, and a recent study shows that other dimensions of life – such as motility – should not be overlooked either.

The living beings of modern day share one feature: animals are defined by the ability to move to survive, plants grow or climb towards the sun, fungi extend their hyphae over thousands of square meters. Even single-celled organisms, like bacteria and protists, use chemotaxis for directional movement in response to nutrients, other attractants or away from harmful substances. Should the earliest forms of life have been any different, considering the role that motility has in every modern being?

Autocatalytic reactive spots (black) move away from their waste products (shades of grey) in a reaction-diffusion system

Autocatalytic reactive spots (black) move away from their waste products (shades of grey) in a reaction-diffusion system

The scientists explore this idea by looking into a simple reaction-diffusion system, which exhibits basic dissipative behavior. These molecular systems share many of the theoretical qualities of life, although they are still far from a living cell: they are self-producing, as long as there is unrestricted molecular supply, they are precarious in nature, meaning they will become extinct if disrupted significantly (“death”), and, most important of all, they are capable of adaptive behavior, much as the modern cells and organisms.

Reactive spots (grey) move away from their "tails" (black) – “parasitic” reactants that regulate the “population” and spatial distribution of spots (much as a conventional symbiotic relationship would)

Reactive spots (grey) move away from their “tails” (black) – “parasitic” reactants that regulate the “population” and spatial distribution of spots (much as a conventional symbiotic relationship would)

Theoretical models reveal that these reactive units form far from a static system. Instead, the chemical reactants move in a highly structured fashion in response to environmental changes. It should be noted that reactive spots are shown to “run” from their own waste products, which could be detrimental, or even form “parasitic” relationships with other reactants, which highly influence their spatial distribution.

The scientists demonstrate that, although relatively basic, not-membrane-bound and otherwise far from a living cell, reactive spots exhibit much of the adaptive behavior and directive exploration of modern cells. This brings the idea of a motile protocell into question and encourages scientist to look for a unified and more universal theory of the origin of life on Earth.

Source: www.technology.org

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