Amazing stuff! The researchers were using a "relaxed molecular clock" and they support a "complexified ... sequence" called CALM! I like British humor! 😊
"Complex life began to develop earlier, and over a longer span of time, than previously believed, a new study has revealed. The research sheds new light on the conditions needed for early organisms to evolve and challenges several long-standing scientific theories in this area. ..."
"... the research indicates that complex organisms evolved long before there were substantial levels of oxygen in the atmosphere, something which had previously been considered a prerequisite to the evolution of complex life. ...
team has developed a new way of probing these questions, by extending on the ‘molecular clocks’ method which is used to estimate how long ago two species shared a common ancestor.
“The approach was two-fold: by collecting sequence data from hundreds of species and combining this with known fossil evidence, we were able to create a time-resolved tree of life. We could then apply this framework to better resolve the timing of historical events within individual gene families,” ...
By collecting evidence from multiple gene families (more than a hundred in total) in multiple biological systems and focusing on the features which distinguish eukaryotes from prokaryotes, the team were able to begin to piece together the developmental pathway for complex life.
Surprisingly the researchers found evidence that the transition began almost 2.9 billion years ago – almost a billion years earlier than by some other estimates – suggesting that the nucleus and other internal structures appear to have evolved significantly before mitochondria. ..."
From the abstract:
"The origin of eukaryotes was a formative but poorly understood event in the history of life. Current hypotheses of eukaryogenesis differ principally in the timing of mitochondrial endosymbiosis relative to the acquisition of other eukaryote novelties.
Discriminating among these hypotheses has been challenging, because there are no living lineages representative of intermediate steps within eukaryogenesis. However, many eukaryotic cell functions are contingent on genes that emerged from duplication events during eukaryogenesis. Consequently, the timescale of these duplications can provide insights into the sequence of steps in the evolutionary assembly of the eukaryotic cell.
Here we show, using a relaxed molecular clock, that the process of eukaryogenesis spanned the Mesoarchaean to late Palaeoproterozoic eras.
Within these constraints, we dated the timing of these gene duplications, revealing that the eukaryotic host cell already had complex cellular features before mitochondrial endosymbiosis, including an elaborated cytoskeleton, membrane trafficking, endomembrane, phagocytotic machinery and a nucleus, all between 3.0 and 2.25 billion years ago, after which mitochondrial endosymbiosis occurred.
Our results enable us to reject mitochondrion-early scenarios of eukaryogenesis, instead supporting a complexified-archaean, late-mitochondrion sequence for the assembly of eukaryote characteristics.
Our inference of a complex archaeal host cell is compatible with hypotheses on the adaptive benefits of syntrophy in oceans that would have remained largely anoxic for more than a billion years."
Complex life developed earlier than previously thought, new study reveals (original news release) "Complex life began to develop earlier, and over a longer span of time, than previously believed, a groundbreaking new study has revealed. The research sheds new light on the conditions needed for early organisms to evolve and challenges several long-standing scientific theories in this area."
Fig. 1: Time-resolved species tree and gene duplications by prokaryotic origin.
Fig. 2: Key gene duplications defining the cytoskeleton and nuclear compartment.
The team has proposed a new evidence-based scenario for the emergence of complex life they have called ‘CALM’ - Complex Archaeon, Late Mitochondrion
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