DNA dating: How molecular clocks are refining human evolution's timeline
Traditionally researchers built timelines of human prehistory based on fossils and artifacts, which can be directly dated with methods such as. problem by reconciling the fossil record of species diversity with modern DNA samples. Date: September 20, ; Source: University of Pennsylvania. Since genetic material (like DNA) decays rapidly, the molecular clock method can 't date very old fossils. It's mainly useful for figuring out how long ago living.Fossils and dating methods (ANT)
The Secret Life of Dung Moa, the giant flightless birds of New Zealand, may have been extinct for at least years, but their dung is surprisingly resilient. On cave floors and buried in shelters, researchers found dung from the moa, with some of the samples being 15 cm nearly six inches in length. The contents of the droppings give more than a window into the giant bird's eating habits—they preserve a record of what the long-gone moa's ecosystem was like.
The arid conditions of New Zealand caves provide the perfect place for poo preservation. Australia should, too, the researchers say, but the droppings of ancient marsupials just haven't turned up. As professor Alan Cooper says, "A key question for us is 'where has all the Australian poo gone?
Nuclear Forensics If you think your metal detector has uncovered some treasures, try finding vintage plutonium in the backyard. Jon Schwantes of the Pacific Northwest National Laboratory was called in to analyze a sample of plutonium accidentally discovered in a safe during the cleanup of the Hanford nuclear site in Washington.
Science and Evolution: Accuracy of Fossils and Dating Methods
One clue was the "signature" left by the reactor—every reactor's is different. The fingerprint of this discarded material led him to a reactor not in Hanford, but in Oak Ridge, TN. It also led him to the conclusion that it was created inmeaning it was created during the Manhattan Project, making it one of the world's oldest-known samples of enriched plutonium. Chemical Warfare A pile of skeletons probably wouldn't tell us much more than the obvious.
But University of Leicester archaeologist Simon James sees evidence that, to him, dates the first known chemical warfare attack back to A. In that year, Persians attacked a Roman garrison at Dura-Europos in Syria; when they tried to mine under the walls, Romans tried to counter by mining under the Persian tunnels. Archaeologists found the pile of Roman bodies in one of the tunnels, but no cause of death.
James thinks it was asphyxiation. In the tunnels, he says, there was bitumen and sulfur—materials that, when burned, give off toxic gas.
So, he says, the Persians probably used chemical warfare to do in their rivals. The Magnetic Fields One classical way to date objects is to take note of what strata of rock they occupy—rocks come in layers, with the oldest at the bottom.
But those rocks also carry less obvious information—their magnetic signatures. The Earth's magnetic field varies all the time, by both strength and orientation. At the time rocks form, however, their magnetic materials acquire the particular orientation of the planet's magnetism at the time, giving geologists a window into the Earth's magnetic past. Ice Cores You've probably heard about ice cores, but what are they exactly?
Ice sheets are laid down in layers, and the layer corresponding to each year is a little different. The important thing for climate researchers is that the oxygen isotopes present in a layer can help show what the temperature was that year. So by extracting a cylindrical core sample containing layers that go way back, they can build a model of the climate of the past. Pollen Finally, pollen is good for something besides making you sneeze.
However, these methods require ancient remains to have certain elements or preservation conditions, and that is not always the case.
Moreover, relevant fossils or artifacts have not been discovered for all milestones in human evolution. Analyzing DNA from present-day and ancient genomes provides a complementary approach for dating evolutionary events. Because certain genetic changes occur at a steady rate per generation, they provide an estimate of the time elapsed.
Molecular clocks are becoming more sophisticated, thanks to improved DNA sequencing, analytical tools and a better understanding of the biological processes behind genetic changes. By applying these methods to the ever-growing database of DNA from diverse populations both present-day and ancientgeneticists are helping to build a more refined timeline of human evolution. How DNA accumulates changes Molecular clocks are based on two key biological processes that are the source of all heritable variation: DNA image via www.
These changes will be inherited by future generations if they occur in eggs, sperm or their cellular precursors the germline. Most result from mistakes when DNA copies itself during cell division, although other types of mutations occur spontaneously or from exposure to hazards like radiation and chemicals.
10 Methods Scientists Use to Date Things
In a single human genome, there are about 70 nucleotide changes per generation — minuscule in a genome made up of six billion letters. But in aggregate, over many generations, these changes lead to substantial evolutionary variation.
Scientists can use mutations to estimate the timing of branches in our evolutionary tree. Then, knowing the rate of these changes, they can calculate the time needed to accumulate that many differences.
Comparison of DNA between you and your sibling would show relatively few mutational differences because you share ancestors — mom and dad — just one generation ago.
However, there are millions of differences between humans and chimpanzees ; our last common ancestor lived over six million years ago. Bits of the chromosomes from your mom and your dad recombine as your DNA prepares to be passed on.
Dating Techniques | stihotvorenia.info
Chromosomes image via www. Recombinationalso known as crossing-over, is the other main way DNA accumulates changes over time. It leads to shuffling of the two copies of the genome one from each parentwhich are bundled into chromosomes. In humans, about 36 recombination events occur per generation, one or two per chromosome. As this happens every generation, segments inherited from a particular individual get broken into smaller and smaller chunks.
Based on the size of these chunks and frequency of crossovers, geneticists can estimate how long ago that individual was your ancestor. Gene flow between divergent populations leads to chromosomes with mosaic ancestry. As recombination occurs in each generation, the bits of Neanderthal ancestry in modern human genomes becomes smaller and smaller over time.
Bridget Alex, CC BY-ND Building timelines based on changes Genetic changes from mutation and recombination provide two distinct clocks, each suited for dating different evolutionary events and timescales. Because mutations accumulate so slowly, this clock works better for very ancient events, like evolutionary splits between species.
The recombination clock, on the other hand, ticks at a rate appropriate for dates within the lastyears. The case of Neanderthals illustrates how the mutation and recombination clocks can be used together to help us untangle complicated ancestral relationships. Geneticists estimate that there are 1. Applying the mutation clock to this count suggests the groups initially split betweenandyears ago. At that time, a population — the common ancestors of both human groups — separated geographically and genetically.
Some individuals of the group migrated to Eurasia and over time evolved into Neanderthals. Those who stayed in Africa became anatomically modern humans.
An evolutionary tree displays the divergence and interbreeding dates that researchers estimated with molecular clock methods for these groups. Modern humans eventually spread to Eurasia and mated with Neanderthals. Applying the recombination clock to Neanderthal DNA retained in present-day humans, researchers estimate that the groups interbred between 54, and 40, years ago.