first_img“We live in interesting times,” grinned David Penny in Nature,1 reporting on how estimates of evolutionary past based on comparative genomics (the molecular clock) is producing confusing results.  Apparently, evolutionary geneticists are going to have to make use of the theory of relativity – i.e., that how fast the clock ticks depends on the viewpoint of the observer.  “An analysis of genetic data sets from primates and birds provides firm evidence that molecular evolution is faster on shorter than on longer timescales,” his subtitle explained.  “The estimated times of various evolutionary events require a rethink” (emphasis added in all quotes).  It’s hard to give up a pet theory, he continued:The relative constancy of the rate at which DNA sequences evolve has been a treasured icon of molecular evolution for nearly 40 years.  The occurrence of such a stochastic ‘molecular clock’ was initially quite unexpected, and was explained by Motoo Kimura by assuming that most changes to amino-acid and nucleotide sequences were neutral – “neither beneficial nor injurious”, in Charles Darwin’s prescient phrase.    However, there have been several inklings that the rate of molecular evolution accelerates when measured over evolutionarily short timescales.  As they report in Molecular Biology and Evolution, Ho and colleagues have now put the evidence together.  Their analyses of primate and bird data sets reveal that there is indeed a decided acceleration of molecular evolution on short timescales.  This is an effect that demands explanation; moreover, estimates for the timing of recent events in population biology will need to be reconsidered.Penny discussed whether the phenomenon is real, whether it can be explained, and why it was not picked up earlier.  Part of the reason is no one was looking:For some reason, the continuum between population heterozygosity and long-term evolution has not been adequately studied.  Although it is a continuum, the techniques required may change as the timescale decreases.  For example, some concepts from long-term evolution (binary evolutionary trees with sequences studied only at the tips) have been extended into populations where trees are no longer binary, and ancestral sequences (at internal nodes) are still present in the population.  There are hints that a formal multiscale study is necessary, because even though the same underlying process is occurring, different features of trees are observed as the timescale changes.Lastly, he asked what are the consequences of this revelation.  Many time estimates will require recalculation – that’s one practical aspect.  “In some cases the constraints are from recent events, and it is the long-term events that require re-analysis,” he explained; “Much more remains to be done.”  The assumption of a single mutation rate is gone; “Even for nucleotides there are many ‘mutation rates’,” he pointed out.  Penny feels the solution is tractable, but the implication is that many former assumptions have been invalidated by the new data – hence his last sentence, “we live in interesting times.”1David Penny, “Evolutionary biology: Relativity for molecular clocks,” Nature 436, 183-184 (14 July 2005) | doi: 10.1038/436183a.Another evolutionary assumption has been overturned by more careful analysis; keep up the good work.  Next time, though, remove the assumption of evolution before making the observations.  Relativity applies to physics, not biology.  An evolutionary tale that requires relativity to keep its plot together has left the science department for the theater class (see 11/29/2004 entry).(Visited 14 times, 1 visits today)FacebookTwitterPinterestSave分享0last_img read more

first_imgShare Facebook Twitter Google + LinkedIn Pinterest The pattern of warmer- and wetter-than-usual weather this past winter has changed in recent months, but hopes for a warm, dry, early spring have faded. Corn growers are concerned about the amount of fall-applied nitrogen that might have been lost through the winter and how this might change nitrogen management this spring.Emerson Nafziger, University of Illinois crop scientist and Dan Schaefer of the Illinois Fertilizer and Chemical Association sampled soil around Illinois in winter and early spring to measure the amount of nitrogen that has disappeared from the top two feet of soil as a result of the winter conditions.A sample of eight fields in Vermilion County showed little change in soil nitrogen between December and February, though there was some loss of nitrate between the January and February samples. The percentage of recovered nitrogen that was in the ammonium form — the form that is safe from immediate loss due to binding with negative charges in the soil — actually went up.Nafziger also sampled fields in Urbana and Monmouth and found a considerable drop in soil nitrogen between early January and late February in both locations. Using N-Serve made little difference in the amount of nitrogen recovered or in the percentage of recovered nitrogen that was still in the ammonium form.N-Serve, a Dow nitrogen stabilizing product applied with ammonia in the fall, was applied in two neighboring fields in Champaign county. In January, 70% of the recovered nitrogen in the field with N-Serve was in the form of ammonium, compared to 53% ammonium in the field without N-Serve. By mid-March, 73% of the recovered nitrogen in the field with N-Serve was ammonium, compared with only 39% in the field without N-Serve.“We need to be cautious because this is from only a few samples, but in this case it looks like nitrapyrin (the active ingredient in N-Serve) did what it is supposed to do: keep ammonium from converting to nitrate, thereby reducing the amount of nitrogen subject to loss. Whether or not that will make a difference in how much nitrogen is available to the corn crop depends entirely on what sort of weather, soil, and crop conditions we have up to the time nitrogen uptake starts,” Nafziger explains.Overall, results were mixed across the sites and sampling times, ranging from disappearance of more than half of the nitrogen from the top two feet of soil to only small changes. The percentages of soil nitrogen present as ammonium were lower than expected, which could mean considerable potential for loss if wet weather returns.“We have little previous experience looking at soil nitrogen from fall to spring, so there’s no reason to panic at this point, or to order more fertilizer to replace what might have disappeared,” Nafziger said. “Our best strategy now is to assume that most of the nitrogen we applied last fall is still in the soil, to get the crop planted as conditions allow, and to both monitor the crop and stay tuned as we continue to monitor soil nitrogen up to the time that the crop is taking up nitrogen rapidly.”Nafziger adds that if warm and dry weather returns, there will be little N loss in the coming months If the opposite happens, producers would still have time to manage nitrogen for good yields while minimizing further loss.last_img read more

first_imgWhen to save old windowsOne of the most wonderful aspects of our local architecture is its historic windows with their characteristic divided lite panes and historic glass. They are not only visually appealing, but their design and craftsmanship make them worthy of preservation. Unfortunately, because they are single-glazed and often in disrepair, they are also one of the largest sources of heat loss in winter and a major source of heat gain in the summer. The windows alone can be responsible for 25 to 50 percent of the energy used to heat and cool homes!… There is a point when the condition of the window clearly indicates that a replacement is necessary. When considering replacement windows, it is important to not only consider their energy efficiency, but also their appearance in terms of the pattern of the proportions of their frame and sash, the configuration of the window panes, muntin profiles, types of wood and characteristics of the glass. Search for a replacement that retains as much of the character of the historic window as possible. Juli MacDonald is an architect and accredited LEED professional who worked in Chicago for 20 years before relocating to the East Coast and eventually opening her own firm in Amesbury, Massachusetts, in 2007.Later that year she started writing the GreenBridge blog. It’s named after her firm, which concentrates on residential additions and remodels.GreenBridge Blog is a mix of project descriptions, “sustainability and efficiency” entries, which covers such topics as insulation, home office planning and green roofs, and a shorter travelogue section that details places she’s visited or conferences she’s attended.There’s nothing stiff or pedantic about the entries. MacDonald writes just enough about herself and her family to provide personal context, but does not wander so far afield we wish she’s get back on topic.The project list isn’t huge, but there are some interesting entries, including one called the “Garbage Garage.” The handsome building looks conventional, until you get into the details and find out its lower walls are rammed-earth tires, and that light in the upper gable ends comes from glass bottles laid up like cordwood and mortared in place. A visiting team from Guatemala called Long Way Home took part in the project.Another is Lamorna Cottage after a 1880s farmhouse that MacDonald and her family seem to have bought this past summer in Rockland, Maine. We’ll be traveling along as they bring the house back into livable shape.There also are links to companies that might be of interest to anyone building in New England, including Andros Energy (renewable energy systems), the Green Cocoon (insulation), and JF Jewett Farms & Co. (cabinetmakers).Here are a few excerpts: Why we should talk about toiletsWhen I first started working as an architectural intern in Rockford, Illinois, Larry, the curmudgeonly head draftsman, loved teasing me about my main job of drawing toilet rooms. He didn’t let me say ‘bathroom,’ insisting that I say ‘toilet.’ He was right – we were working on commercial toilet rooms and nobody was taking baths there… Well, it’s been a lot of years, and now I’ve got a lot to say about toilets – Do you want your toilet in a separate room? Do you like an elongated bowl for comfort? What do you think of the water-saving dual-flush models? Do you have young sons?Discussing the toilet still isn’t my favorite part of the bath design process, but it’s important, because habits and details make all the difference in a successful bathroom. I resolveOn December 12th [2009], my family lost my Grandmother, Eleanor Phillips, who lived in Fort Dodge, Iowa. I was lucky enough to be able to spend some precious time with her during her last days in the hospital. During part of that time, my cousins and I pored over Grandma’s various journals, letters and photos, and we got a wonderful sense of the fullness of her life and the way she lived and adapted throughout her 88 years.In one letter to her sister written in the 50s, she talked about ripping down discarded clothing to make braided rugs. Her journals and autobiographies described her huge love of gardening and enjoyment of the harvests. She was a farmer’s daughter, one of 6 children who knew what sharing and making-do meant, and who also knew to not leave the table without asking one sibling or parent to guard her plate. Her fondest memories of her mother included her ability to whip up the most amazing donuts for the family and to make a dress for my grandmother the night before she wore it to a dance.It was clear that she had a happy childhood – she carried a 80-year-old snapshot of a family Sunday picnic in her wallet, and in her writing she often described her many memories of her parents hugging and kissing, and her father’s desolation when her mother died at a very young age. She remembered her and her siblings’ excitement at seeing their single gift and one orange next to their plates Christmas morning.So, my resolution? To continue to carry my grandma and her lessons with me. Embrace simple and good living, enjoy family and seek happiness in the smallest things. She didn’t live her life with the intent of being ‘green’ or ‘sustainable,’ but her way of life was what so many of us strive for today. Reuse and salvageOne of my fondest memories of living in Chicago was ‘shopping’ in the alleys. My quickest walk to the train was down our 3 block alley: on one side were condo buildings and the on the other were single-family homes. It worked this way – if you didn’t want something anymore, you left it in the alley, NEXT to the garbage, sometimes with a note, and it was usually gone in a few hours. Through the years I collected a great variety of treasures. Among them: lamps, a desk, many, many chairs, my now favorite cookbook. My goal wasn’t to be green, but it really was an efficient (cheap!) and practical system.Now I use Freecycle. If you haven’t checked them out, give them a try – it is basically a local list-serve where members post items they want to give away or items they’d like to receive. It works similarly to shopping in the Chicago alley, but is a bit more civilized.In construction, the act of restoring or remodeling a home is a form of reuse and salvage. Preservation instead of demolition and new construction saves in energy and materials consumption and reduces demolition landfill. There is a great opportunity in salvaging and reusing materials for remodeling and even new construction projects, if you are aware and know where to look.last_img read more