text: The chemical chain of events that led to the origin of life on Earth is likely forever lost to the mists of time. But some of our earliest ancestors—including the microbial Eve from which all modern cells descended—left behind traces in the genes they passed to their descendants. To track these shared genes, geneticists have surveyed nearly 2000 genomes of modern microbes. Now, researchers report that they’ve used this sort of genome mining to reveal new insights about the daily life of our last universal common ancestor, or LUCA. The results suggest that LUCA was a heat-loving microbe that fed on hydrogen gas and lived in a world devoid of oxygen, bolstering strong suspicions that life on Earth formed in and around hydrothermal vents such as those found near undersea volcanoes. 
   
   Today, the cells that make up all life on Earth are clustered into three broad groups: bacteria, archaea, and eukaryotes. The first two comprise prokaryotes—cells without a nucleus. A distant union between these two formed eukaryotes—cells with a nucleus that make up all the complex multicellular organisms including plants and animals. 
   
   Genetic studies to date have revealed some tantalizing clues about LUCA. Most evidence suggests that, like modern cells, LUCA stored genetic information using DNA. It also built proteins and used adenosine triphosphate as its currency for energy. But it has been harder for geneticists to know other details of LUCA’s lifestyle. One major complication: Microbes not only pass genes to their progeny, but also swap them among their neighbors in a process called horizontal gene transfer. This makes it hard to tell whether genes shared by separate microbes reflect a shared lineage or whether some bugs were just better at spreading their genetic material far and wide. And that makes it harder to pin down LUCA’s lifestyle. 
   
   To get closer to doing just that, researchers led by William Martin, an evolutionary biologist at Heinrich Heine University in Dusseldorf, Germany, took a more stringent approach to identifying genes that were likely inherited. Rather than looking for genes shared by a single species bacteria and archaea, they searched for those shared by at least two species of bacteria and two archaea. This gave them an initial count of some 6 million genes grouped into more than 286,000 related gene families. Further analysis revealed that only 355 of these gene families were broadly distributed across all modern organisms, and thus could be tracked from an ancestral species through all of its descendants. That made the 355 gene families likely LUCA candidates. 
   
   As Martin and his colleagues report in today’s issue of Nature Microbiology , these genes aren’t randomly scattered throughout modern organisms, but fall into distinct groups that reflect LUCA’s likely metabolism. Most notably, they reveal that LUCA was an anaerobe that grew in an environment devoid of the oxygen that most cells today require. That jibes with what scientists know about Earth 4 billion years ago, a period known as the late heavy bombardment. Not long after the planet’s formation, meteors and comets rained steadily down, the seas periodically boiled away, and the atmosphere lacked oxygen. The gene scans also show that LUCA was almost certainly a heat-loving “thermophile” that fed on hydrogen gas (H 2 ), as others have proposed. Today, many microbes produce H 2 . But because LUCA preceded them, it would have had to belly up to a geological source of hydrogen, such as a hydrothermal vent like those found near an undersea volcano. ||||| The concept of a last universal common ancestor of all cells (LUCA, or the progenote) is central to the study of early evolution and life's origin, yet information about how and where LUCA lived is lacking. We investigated all clusters and phylogenetic trees for 6.1 million protein coding genes from sequenced prokaryotic genomes in order to reconstruct the microbial ecology of LUCA. Among 286,514 protein clusters, we identified 355 protein families (∼0.1%) that trace to LUCA by phylogenetic criteria. Because these proteins are not universally distributed, they can shed light on LUCA's physiology. Their functions, properties and prosthetic groups depict LUCA as anaerobic, CO 2 -fixing, H 2 -dependent with a Wood–Ljungdahl pathway, N 2 -fixing and thermophilic. LUCA's biochemistry was replete with FeS clusters and radical reaction mechanisms. Its cofactors reveal dependence upon transition metals, flavins, S-adenosyl methionine, coenzyme A, ferredoxin, molybdopterin, corrins and selenium. Its genetic code required nucleoside modifications and S-adenosyl methionine-dependent methylations. The 355 phylogenies identify clostridia and methanogens, whose modern lifestyles resemble that of LUCA, as basal among their respective domains. LUCA inhabited a geochemically active environment rich in H 2 , CO 2 and iron. The data support the theory of an autotrophic origin of life involving the Wood–Ljungdahl pathway in a hydrothermal setting. ||||| A surprisingly specific genetic portrait of the ancestor of all living things has been generated by scientists who say that the likeness sheds considerable light on the mystery of how life first emerged on Earth. 
   
   This venerable ancestor was a single-cell, bacterium-like organism. But it has a grand name, or at least an acronym. It is known as Luca, the Last Universal Common Ancestor, and is estimated to have lived some four billion years ago, when Earth was a mere 560 million years old. 
   
   The new finding sharpens the debate between those who believe life began in some extreme environment, such as in deep sea vents or the flanks of volcanoes, and others who favor more normal settings, such as the “warm little pond” proposed by Darwin. 
   
   The nature of the earliest ancestor of all living things has long been uncertain because the three great domains of life seemed to have no common point of origin. The domains are those of the bacteria, the archaea and the eukaryotes. Archaea are bacteria-like organisms but with a different metabolism, and the eukaryotes include all plants and animals.
target: – The first name on your family tree—in fact, on the family tree of every living creature—should technically be LUCA. As the New York Times explains, the acronym stands for the Last Universal Common Ancestor, an organism that lived about 4 billion years ago and became the ancestor of all life forms. Now, a new study in Nature Microbiology provides what its authors say is evidence that settles the debate about where this first life began: near hydrothermal vents, like those found near deep-sea volcanoes. Researchers at Germany's Heinrich Heine University say their genetic sleuthing has revealed that LUCA was tailor-made to live in such an environment—it was essentially "a heat-loving microbe that fed on hydrogen gas and lived in a world devoid of oxygen," in the words of Science. To figure out this genetic profile, the scientists examined 6 million genes associated with two simple and ancient forms of life, bacteria and archaea. After identifying genes that were shared between the two groups, they whittled the figure down to 355 gene families that met their criteria for having originated in LUCA, their joint ancestor. “It was flabbergasting to us that we found as many as we did,” says lead researcher William Martin. This smaller group of genes allowed them to create a snapshot of sorts of LUCA, one hailed as "remarkable" by a UCLA evolutionary biologist. But don't expect the debate to end. The study “is all very interesting, but it has nothing to do with the actual origin of life,” Cambridge chemist John Sutherland tells the Times. (In less ancient but still ancient news, the remains of more real-life hobbits have been found.)