Pracrise Listening 38 - Thấm Tâm Vy

Nội dung text: Pracrise Listening 38 - Thấm Tâm Vy

1. Diet and evolution Symbiosis High-carb footprint An underground marketplace Modern humans may be evolving to deal with carbohydrate-rich diets Fungi, it turns out, are canny traders of nutrients to plants It is easy to assume that the long march of evolution has halted in modern man—that In the soil where plants’ roots meet fungal hyphae, there are trading posts of a type the safe, disease-free lives people now lead mean natural selection no longer operates on that came into being more than 200 million years ago—long before people got around to much of Homo sapiens. It is an attractive idea. Frances Brodsky of University College, engaging in similar activities. London and her colleagues, however, beg to differ. A paper they have just published in These meeting places are the exchanges where plants provide fungi with nutrient eLife suggests that diet, at least, is still a selective pressure. Dr Brodsky and her team molecules, such as sugars and fats, that they make by photosynthesis, in exchange for study proteins called clathrins. These are involved in a range of matters physiological, raw materials like nitrates and phosphates, which fungi are adept at collecting from the but one of the molecules the team is investigating, encoded by a gene called CLTCL1, surrounding area. is concerned with the regulation of blood-sugar levels. CLTCL1 comes in two forms, That much is well established. Botanists have long wondered, however, how the one more efficient than the other at encouraging the removal of glucose from the blood. details change when resources become patchy, and thus scarce in some places and The team decided to look into the evolutionary history behind this. To do so they abundant in others. A study just published in Current Biology by Toby Kiers of the Free analysed the relevant DNA in 2,504 human genomes taken from a database called the University of Amsterdam suggests that, like cunning merchants who know how to make 1000 Genomes Project. a profit, fungi exploit resource scarcity by marking up their prices. They demand more This project has collected samples from 26 human populations around the world. They nutrients from plants in return for their valuable mineral commodities. also looked at chimpanzee DNA, and at fossil DNA from two extinct species of human, Such canniness has long been suspected. But proving it means tracking the raw Neanderthals and Denisovans. Putting all this information together they deduced two materials as they are collected and distributed. That has proved tricky. Dr Kiers, though, things. First, just under half of people alive today carry the more efficient version of the thought she could do it using structures called quantum dots. gene. Second, this version is also a more recent version of the gene. It seems to have A quantum dot is a mote of matter a few nanometres across. It is made of a started spreading during the Neolithic—the moment when humans started farming semiconducting material capable of fluorescing when struck by ultraviolet rays, and cereals. different sorts of dot fluoresce in different colours. Dr Kiers theorised that if she and her Dr Brodsky suspects this is no coincidence. A cereal-based diet is far richer in team attached quantum dots to particles of phosphate then they might be able to track carbohydrates than the diet of a huntergatherer. Once digested, those carbs will end up those particles around as they were collected by fungi and passed along to plants. as glucose in the bloodstream. An inability to control high blood sugar is known as Matthew Whiteside, a member of her team, developed the technique, tested it and found diabetes. And diabetes can be fatal. So a better way of removing glucose from the blood that she was right. After sowing a Petri dish that played host to fungal hyphae and carrot and into storage cells will be favoured by natural selection. A gene variant encouraging roots with tagged phosphates Dr Whiteside found that he could, after sufficient time had this would probably spread quite rapidly through a population of farmers. passed, spot the tagged phosphates inside both hyphae and roots by shining ultraviolet There is, in fact, already one known example of something similar having happened— light on them. the persistence into adulthood of the ability to digest lactose, a sugar found in milk. Dr Kiers then arranged for some patches of the Petri dish “garden” in which the fungi Human children produce an enzyme, lactase, that lets them do this. Usually, this and carrots were growing to be rich in phosphates, and some to be poor. She also capacity is lost in adults. But populations descended from those that domesticated milk- arranged for the phosphates in the rich zones to be tagged with dots that would fluoresce producing animals such as goats and cattle often retain lactose-digestion into adulthood. blue when bombarded with ultraviolet light and for those in the poor zones to fluoresce Whether the efficient form of CLTCL1 really is still becoming more abundant— and red. As she monitored the collection and trading of the phosphates from fungi to carrots people are thus evolving—is impossible to say at the moment. One thing which remains she found that the fungi enthusiastically transported them across the hyphal network to be confirmed is that those with the less effective version actually do have problems from areas of abundance to zones of scarcity. regulating their blood-sugar levels. If that turns out to be true, though, and given that Moreover, though she was unable to measure directly what price the carrots paid for even today diabetes kills many people, the chances are good that this piece of evolution their phosphates, she managed to do so indirectly. She found that hyphae growing in is still a work in progress.  [The Economist, UK, June 7th, 2019] resource-poor patches put on more weight per unit of phosphate transferred to nearby roots than did those in patches of abundance. This, she argues, makes it clear that fungi Note: – genome: bộ di truyền – patchy: loang lổ – commodities: hàng trao đổi –mote: hạt in zones of scarcity are marking up the price of their products.  [The Economist, UK, June 7th, 2019 – hyphae: sợi nấm Thẩm Tâm Vy, June 7th, 2019 PRACTISE LISTENING 38