ANTARCTICA CONTAINS a wealth of paleontological information that is only now beginning to be collected. Some of this is hidden in rocks as fossils of plants and animals that lived there when the Antarctic continent was more temperate, but other information is found in the ice. Cores of Antarctic ice reveal climatic records for the globe in ages past. Now the Antarctic ice also yields preserved bacterial DNA hundreds of thousands to millions of years old.
Aug 15th, 2007 by Placozoan | Comments Off
Jun 19th, 2007 by Placozoan | 11 Comments »
UNFORTUNATELY THE THEORY OF EVOLUTION is not the only target of superstition and pseudoscience. In the current issue of Science I ran across a short article reporting on a web site that aims to collect information about the link between HIV and AIDS and profiles on the key figures who deny that this link exists. These people, known as AIDS denialists, claim that HIV is an innocuous virus and AIDS is brought on by stresses such as malnutrition and by the very drugs used to suppress HIV. It is bad enough when their unscientific views harm their own families, but AIDS denialists are making progress advancing their opinions in Africa in AIDS-endemic areas. Many organizations in Africa are attempting to educate people about the modes of transmission of HIV, encourage the use of condoms, and administer antivirals to people with HIV to slow disease progression and prevent prenatal infections. The denialists are working directly against these goals. It is our hope that AIDSTruth will help counter their misinformation.
Jun 13th, 2007 by Placozoan | Comments Off
NATURE REPORTS today the discovery of a bizarre 1,400 kg, surprisingly gracile bird-like dinosaur, named Gigantoraptor erlianensis. The animal is an oviraptosaur, one of a group of bird-like theropod dinosaurs. It has been placed basally in the Oviraptoridae clade, and no doubt will cause some perplexity as it has a variety of more avian traits that are missing in other early oviraptosaurs.
Jun 1st, 2007 by Placozoan | 1 Comment »
IT IS KNOWN that proteins can be broken down into various domains, often with a characteristic fold, and new proteins can be generated by splicing new domains onto an existing protein. The first ancestral domains probably evolved from the combination of genes for shorter peptides called antecedent domain segments.1
Now a new study2 attempts to elucidate the phylogeny of modern metabolic networks from their architectural details and determine which metabolic subnetworks were foundational to life. The authors examined 185 fully sequenced genomes representing all three superkingdoms. They searched for 776 folds defined by the Structural Classification of Proteins (SCOP). Only 16 of these were present in all organisms, and nine of these appeared at the base of the tree.
May 30th, 2007 by Placozoan | Comments Off
THE QUESTION of the origin of the first living organism has fascinated scientists for decades. Currently the RNA world hypothesis, which proposes RNA as the first self-reproducing molecule, is the most promising. One difficulty is that this hypothesis require a high concentration of simple organic molecules, which were probably present in low concentrations in the earliest oceans. Some suggest adsorption onto solid surfaces as one solution to this problem, now a new solution has been proposed.
There are some hypotheses that the earliest life evolved around hot springs in the ocean floor, which now harbor unusual eubacteria and archaea. These hot springs build up mineral mounds around them that are riddled with pores. Baaske and coworkers demonstrate that a simulated hydrothermal pore system under a thermal gradient (from hot spring to cold ocean) can concentrate small molecules including nucleotides up to 108 times, a hundred times higher than needed for intermolecular interaction.
May 18th, 2007 by Placozoan | 1 Comment »
I THOROUGHLY AGREE with the statement “it is well known that most biologists abhor all things mathematical” given in the article that I will cover today. The author deals with population genetics, and speeds through some basic equations in a page and a half. I will certainly not be talking about any equations today, but will attempt to restate the concepts in this fascinating paper.
The author, Michael Lynch, rejects the idea that organismal complexity arose through an adaptive mechanism (I previously discussed another paper suggesting a nonadaptive mechanism here). Key in his paper is an analysis of the differences between prokaryote and eukaryote evolution.
May 17th, 2007 by Placozoan | Comments Off
VERTEBRATE GENOMES are composed of islands of GC-rich DNA surrounded by a sea of GC-poor DNA. The GC-rich and GC-poor regions, called isochores, can be subdivided into five classes. The majority of vertebrate genes are contained in two GC-rich isochores, with the remainder spread throughout the other isochores. When compared to the genomes of fish and amphibians, the gene-rich isochores of mammals and birds are comparatively enriched in GC, while reptiles’ isochores are intermediate.
This is of interest for several reasons. First, the mutational tendency is for conversion from GC to AT as cytosine, which is commonly methylated when in a CpG dinucleotide (C followed by G), deaminates to produce thymidine. Subsequent DNA repair can then convert the GT mismatch to an AT. An increase in GC content requires a reversal of this mutational bias. Secondly, this GC increase must have occurred independently twice in order to appear in both mammals and birds.
A variety of mechanisms have been suggested for the origin of isochores, both selectionist and neutral, but no consensus has yet been reached. Now a new model has been proposed.
May 1st, 2007 by Placozoan | Comments Off
RECENT DISCOVERIES of primitive tetrapod fossils continue to shed light on the transition from sea to land (for a discussion of some recent developments see our discussion of Gogonasus). The discovery last year of the tetrapod-like fish Tiktaalik provided additional information on the development of bony, articulated forelimbs and changes in the structure of the mouth, including hints at the evolution of the first neck. In later tetrapods the culmination of these changes can be seen.
Certainly the evolution of legs was an important innovation, but perhaps more complicated were the changes that had to occur in the structure of the mouth in order to allow success on land. Once again we see the domino effect of evolutionary change. The transition from the use of pharyngeal and opercular pumping of water through gills to buccal and costal pumping of air through primitive lungs required the loss of the opercula and supporting structures. But this creates another difficulty for the transitional tetrapodomorphs. The fish that preceded the tetrapods captured prey by a suction mechanism, sealing their opercula closed and opening the mouth to draw prey in on a flood of water. Obviously any tetrapod attempting to use this method of feeding on land would be sorely disappointed. So how did biting evolve as a means of prey capture?
Apr 30th, 2007 by Placozoan | Comments Off
WE TEND to think of a genome as geared solely towards growing, feeding, and protecting its owner and the owner’s offspring. In actuality the genome is rather like a battleground, the site of both intragenomic and intergenomic warfare. The maternal and paternal genomes in a new zygote compete, with the maternal genome trying to limit resources contributed to the embryo while the paternal genome tries to wrestle away as many resources as possible for its offspring. Genetic parasites can join this war between the sexes with an ulterior motive–to propagate copies of themselves. This can be done through meiotic drive, in which an X chromosome harboring a driving gene prevents the transmission of Y chromosomes in meiosis, or through methods that actually result in the death of offspring that do not inherit the driving gene. Now some researchers are attempting to harness this genomic warfare in order to reduce the spread of malaria.
Feb 22nd, 2007 by Placozoan | Comments Off
We’ve seen it so many times on TV: the arrogant scientist or evil corporation meddles with Forces We Cannot Understand (TM) and Mother Nature lashes back with earthquakes, tsunamis, or volcanic eruptions. This time, it looks like it may actually be true, at least minus the pejorative adjectives. But the results are a lot less photogenic than Hollywood would like–450 hectares of mud.