Sunday, December 28, 2008
Thursday, December 25, 2008
A 3.8-billion-year-old organism was not the creature usually imagined. In LUCA, the prevailing belief is that it was a heat-loving or hyperthermophilic organism; like those odd organisms living in the hot vents along the continental ridges deep in the oceans today, above 90 degrees Celsius .
However, the new data suggests that LUCA was actually sensitive to warmer temperatures and lived in a climate below 50 degrees.
The research compared genetic information from modern organisms to characterize the ancient ancestor of all life on earth. Researchers identified common genetic traits between animals, plant, bacteria, and used them to create a tree of life with branches representing separate species. These all stemmed from the same trunk – LUCA, the genetic makeup that we then further characterized.
The RNA Connection to the Origin of Life
What this means is that in the origin of life question an important step has taken place towards reconciling conflicting ideas about LUCA. In particular, they are much more compatible with the theory of an early RNA world, where early life on Earth was composed of ribonucleic acid (RNA), rather than deoxyribonucleic acid (DNA).
RNA is particularly sensitive to heat and is unlikely to be stable in the hot temperatures of the early Earth. But the data indicate that LUCA found a cooler micro-climate to develop, which helps resolve this paradox and shows that environmental micro domains played a critical role in the development of life on Earth.
Tuesday, December 23, 2008
The RNA mechanism to overcome this thermodynamic barrier has been studied by incubating short RNA fragments in water of different temperatures and pH. Under an acidic environment and temperature lower than 70 degrees Celsius, the RNA pieces ranging from 10-24 in length could naturally fuse into larger fragments. This was generally accomplished within 14 hours.
The operation involved the RNA fragments which came together as double-stranded structures then joined at the ends. The fragments did not have to be the same size, but the efficiency of the reactions was dependent on fragment size in which case the larger the better until an optimal efficiency is reached around 100 and then it drops again.
The researchers note that this spontaneous fusing, or ligation, would a simple way for RNA to overcome initial barriers to growth and reach a biologically important size; at around 100 bases long, RNA molecules can begin to fold into functional, 3D shapes.
Saturday, December 20, 2008
The element potassium (symbol K) has three nuclides, K39, K40, and K41. Only K40 is radioactive; the other two are stable. K40 can decay in two different ways: it can break down into either calcium or argon. The ratio of calcium formed to argon formed is fixed and known. Therefore the amount of argon formed provides a direct measurement of the amount of potassium-40 present in the specimen when it was originally formed.
Because argon is an inert gas, it is not possible that it might have been in the mineral when it was first formed from molten magma. Any argon present in a mineral containing potassium-40 must have been formed as the result of radioactive decay. F, the fraction of K40 remaining, is equal to the amount of potassium-40 in the sample, divided by the sum of potassium-40 in the sample plus the calculated amount of potassium required to produce the amount of argon found. The age can then be calculated from equation (1).
In spite of the fact that it is a gas, the argon is trapped in the mineral and can't escape. (Creationists claim that argon escape renders age determinations invalid. However, any escaping argon gas would lead to a determined age younger, not older, than actual. The creationist "argon escape" theory does not support their young earth model.)
The argon age determination of the mineral can be confirmed by measuring the loss of potassium. In old rocks, there will be less potassium present than was required to form the mineral, because some of it has been transmuted to argon. The decrease in the amount of potassium required to form the original mineral has consistently confirmed the age as determined by the amount of argon formed.
Thursday, December 18, 2008
The Conventional View
Changing the Conventional View
Another way to express this is the ancestors of Native Americans who first left Siberia for greener pastures perhaps as much as 30,000 years ago, came to a standstill on Beringia – a landmass that existed during the last glacial maximum that extended from Northeastern Siberia to Western Alaska, including the Bering land bridge – and they were isolated there long enough – as much as 15,000 years – to maturate and differentiate themselves genetically from their Asian sisters.
Founding lineages or haplotypes are uniformly distributed across North and South America instead of exhibiting a nested structure from north to south. So after the Beringian standstill, the initial North to South migration occured in a swift pioneering process, not a gradual diffusion.
The investigation of the pioneering phase in the Americas, a research team, a group of geneticists from around the world, pooled their genomic datasets and then analyzed 623 complete mitochondrial DNAs (mtDNAs) from the Americas and Asia, including 20 new complete mtDNAs from the Americas and seven from Asia.
The team identified three new sub-clades that incorporate nearly all of Native American haplogroup C mtDNAs – all of them widely distributed in the New World, but absent in Asia; and they defined two additional founder groups, which differ by several mutations from the Asian-derived ancestral clades.
Did the migration occur quickly or slowly? Migration may have occured 30,000 years ago, but the earliest archeological evidence is that it occurred only 15,000 years ago.
First the ancestors of Native Americans peopled Beringia before the Last Glacial Maximum, but remained locally isolated – likely because of ecological barriers – until entering the Americas 15,000 years before the present (the Beringian incubation model, BIM).
The team set out to test the two hypotheses: one, that Native Americans’ ancestors moved directly from Northeast Asia to the Americas; the other, that Native American ancestors were isolated from other Northeast Asian populations for a significant period of time before moving rapidly into the Americas all the way down to Tierra del Fuego.
The data supports the second hypothesis: The ancestors of Native Americans peopled Beringia before the Last Glacial Maximum, but remained locally isolated until entering the Americas at 15,000 years before the present. So they moved into the Americas quickly.
Saturday, December 13, 2008
At the Max-Planck Institute for Evolutionary Anthropology in Germany scientists have reconstructed the genome sequence. They sequenced the Neanderthal mitochondria—powerhouses of the cell with their own DNA including 13 protein-coding genes—nearly 35 times over. This coverage allowed them to sort out those differences between the Neanderthal and human genomes resulting from damage to the degraded DNA extracted from ancient bone versus true evolutionary changes.
This new sequence and its analysis confirms that the mitochondria of Neanderthals falls outside the variation found in humans today and it provides no evidence of integration between the two lineages although it remains a possibility. It also shows that the last common ancestor of Neanderthals and humans lived about 660,000 years ago, give or take 140,000 years.
The new sequence revealed that the Neanderthals have fewer evolutionary changes overall, but a greater number that alter the amino acid building blocks of proteins. This means that the Neanderthals had a smaller population size than humans do, which makes natural selection less effective in removing mutations.
That notion is consistent with arguments made by other scientists based upon the geological record. Anthropologists argue there were a few thousand Neanderthals that roamed over Europe 40,000 years ago. That smaller population might have been the result of the smaller size of Europe compared to Africa. Another geological issue was that the Neanderthals also would have had to deal with repeated glaciations.
Tuesday, December 2, 2008
Researcher working with an international team of geneticists and anthropologists, have produced new genetic evidence that's likely to hearten proponents of the land bridge theory. The study, is one of the most comprehensive analyses so far among efforts to use genetic data to shed light on the topic.
The researchers examined genetic variation at 678 key locations or markers in the DNA of present-day members of 29 Native American populations across North, Central and South America. They also analyzed data from two Siberian groups. The analysis shows:
- genetic diversity, as well as genetic similarity to the Siberian groups, decreases the farther a native population is from the Bering Strait -- adding to existing archaeological and genetic evidence that the ancestors of native North and South Americans came by the northwest route.
- a unique genetic variant is widespread in Native Americans across both American continents -- suggesting that the first humans in the Americas came in a single migration or multiple waves from a single source, not in waves of migrations from different sources. The variant, which is not part of a gene and has no biological function, has not been found in genetic studies of people elsewhere in the world except eastern Siberia.
The researchers say the variant likely occurred shortly prior to migration to the Americas, or immediately afterwards.
The Genetic Markers for North American Populations originate in East Asia
There is reasonably clear genetic evidence that the most likely candidate for the source of Native American populations is somewhere in east Asia, the research concludes. If there were a large number of migrations, and most of the source groups didn't have the variant, then you would not see the widespread presence of the mutation in the Americas.
Studies with Genetic Markers
Researchers studied the same set of 678 genetic markers used in the new study in 50 populations around the world, to learn which populations are genetically similar and what migration patterns might explain the similarities. For North and South America, the current research breaks new ground by looking at a large number of native populations using a large number of markers.
The pattern the research uncovered -- that as the founding populations moved south from the Bering Strait, genetic diversity declined -- is what one would expect when migration is relatively recent. There has not been time yet for mutations that typically occur over longer periods to diversify the gene pool.
The study also found that:
- The study's findings hint at supporting evidence for scientists who believe early inhabitants followed the coasts to spread south into South America, rather than moving in waves across the interior.
- Assuming a migration route along the coast provides a slightly better fit with the pattern that are seen in genetic diversity.
- Populations in the Andes and Central America showed genetic similarities.
- Populations from western South America showed more genetic variation than populations from eastern South America.
- Among closely related populations, the ones more similar linguistically were also more similar genetically.