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Pregnancy Timeline by SemestersFemale Reproductive SystemFertilizationThe Appearance of SomitesFirst TrimesterSecond TrimesterThird TrimesterFetal liver is producing blood cellsHead may position into pelvisBrain convolutions beginFull TermWhite fat begins to be madeWhite fat begins to be madeHead may position into pelvisImmune system beginningImmune system beginningPeriod of rapid brain growthBrain convolutions beginLungs begin to produce surfactantSensory brain waves begin to activateSensory brain waves begin to activateInner Ear Bones HardenBone marrow starts making blood cellsBone marrow starts making blood cellsBrown fat surrounds lymphatic systemFetal sexual organs visibleFinger and toe prints appearFinger and toe prints appearHeartbeat can be detectedHeartbeat can be detectedBasic Brain Structure in PlaceThe Appearance of SomitesFirst Detectable Brain WavesA Four Chambered HeartBeginning Cerebral HemispheresEnd of Embryonic PeriodEnd of Embryonic PeriodFirst Thin Layer of Skin AppearsThird TrimesterDevelopmental Timeline
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April 24, 2012--------News Archive Return to: News Alerts


"...the earliest cells were rickety assemblies whose parts were
constantly malfunctioning and breaking down..."

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The Roots and Early Branches of the Tree of Life

Researchers have traced the tree of life back to a single ancestral form

A study published in PLoS Computational Biology maps the development of life-sustaining chemistry to the history of early life. Researchers Rogier Braakman and Eric Smith of the Santa Fe Institute traced the six methods of carbon fixation seen in modern life back to a single ancestral form.

Carbon fixation – life's mechanism for making carbon dioxide biologically useful – forms the biggest bridge between Earth's non-living chemistry and its biosphere.

All organisms that fix carbon do so in one of six ways. These six mechanisms overlap, but it was previously unclear which of the six came first and how their development interweaved with environmental and biological changes.

Braakman and Smith used a method that creates "trees" of evolutionary relatedness based on genetic sequences and metabolic traits. From this, they were able to reconstruct the complete early evolutionary history of biological carbon–fixation, relating all ways in which life today performs this function.

The earliest form of carbon fixation identified achieved a special kind of built-in robustness – not seen in modern cells – by layering multiple carbon-fixing mechanisms.

This allowed early life to compensate for a lack of control over its internal chemistry, and form a template for the earliest major branches in the tree of life. For example, the first major life-form split came with the appearance of oxygen, causing the ancestors of blue–green algae and most bacteria to separate from Archaea, which are the other major early group of single-celled microorganisms.

"It seems likely that the earliest cells were rickety assemblies whose parts were constantly malfunctioning and breaking down," explains Smith. "How can any metabolism be sustained with such shaky support? The key is concurrent and constant redundancy."

Once early cells had more refined enzymes and membranes, there was greater control over metabolic chemistry. Minimization of energy (ATP) was used to create biomass, changes in oxygen levels and alkalinity directed life's unfolding.

The environment drove major divergences in predictable ways, in contrast to the common belief that chance dominated evolutionary innovation.

"Mapping cell function onto genetic history gives us a clear picture of the physiology that led to the major foundational divergences of evolution," explains Braakman. "This highlights the central role of basic chemistry and physics in driving early evolution."

With the ancestral form uncovered, and evolutionary drivers pinned to branching points in the tree, the researchers now want to make the study more mathematically formal and further analyze the early evolution of metabolism.

This work was supported in part by the NSF FIBR grant nr. 0526747 - The Emergence of Life: From Geochemistry to the Genetic Code. ES is further supported by Insight Venture Partners. RB is further supported by an Omidyar Fellowship. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

CITATION: Braakman R, Smith E (2012) The Emergence and Early Evolution of Biological Carbon-Fixation. PLoS Comput Biol 8(4): e1002455. doi:10.1371/journal.pcbi.1002455

PLoS Computational Biology features works of exceptional significance that further our understanding of living systems at all scales through the application of computational methods. All works published in PLoS Computational Biology are open access. Everything is immediately available subject only to the condition that the original authorship and source are properly attributed. Copyright is retained.

The Public Library of Science (PLoS) is a non-profit organization of scientists and physicians committed to making the world's scientific and medical literature a freely available public resource. For more information, visit http://www.plos.org.

Original article: http://www.eurekalert.org/pub_releases/2012-04/plos-ftr041612.php