Why do humans grow up so slowly? Blame the brain

first_imgHumans are late bloomers when compared with other primates—they spend almost twice as long in childhood and adolescence as chimps, gibbons, or macaques do. But why? One widely accepted but hard-to-test theory is that children’s brains consume so much energy that they divert glucose from the rest of the body, slowing growth. Now, a clever study of glucose uptake and body growth in children confirms this “expensive tissue” hypothesis.Previous studies have shown that our brains guzzle between 44% and 87% of the total energy consumed by our resting bodies during infancy and childhood. Could that be why we take so long to grow up? One way to find out is with more precise studies of brain metabolism throughout childhood, but those studies don’t exist yet. However, a new study published online today in the Proceedings of the National Academy of Sciences (PNAS) spliced together three older data sets to provide a test of this hypothesis.First, the researchers used a 1987 study of PET scans of 36 people between infancy and 30 years of age to estimate age trends in glucose uptake by three major sections of the brain. Then, to calculate how uptake varied for the entire brain, they combined that data with the brain volumes and ages of more than 400 individuals between 4.5 years of age and adulthood, gathered from a National Institutes of Health study and others. Finally, to link age and brain glucose uptake to body size, they used an age series of brain and body weights of more than 1000 individuals from birth to adulthood, gathered in 1978.Sign up for our daily newsletterGet more great content like this delivered right to you!Country *AfghanistanAland IslandsAlbaniaAlgeriaAndorraAngolaAnguillaAntarcticaAntigua and BarbudaArgentinaArmeniaArubaAustraliaAustriaAzerbaijanBahamasBahrainBangladeshBarbadosBelarusBelgiumBelizeBeninBermudaBhutanBolivia, Plurinational State ofBonaire, Sint Eustatius and SabaBosnia and HerzegovinaBotswanaBouvet IslandBrazilBritish Indian Ocean TerritoryBrunei DarussalamBulgariaBurkina FasoBurundiCambodiaCameroonCanadaCape VerdeCayman IslandsCentral African RepublicChadChileChinaChristmas IslandCocos (Keeling) IslandsColombiaComorosCongoCongo, The Democratic Republic of theCook IslandsCosta RicaCote D’IvoireCroatiaCubaCuraçaoCyprusCzech RepublicDenmarkDjiboutiDominicaDominican RepublicEcuadorEgyptEl SalvadorEquatorial GuineaEritreaEstoniaEthiopiaFalkland Islands (Malvinas)Faroe IslandsFijiFinlandFranceFrench GuianaFrench PolynesiaFrench Southern TerritoriesGabonGambiaGeorgiaGermanyGhanaGibraltarGreeceGreenlandGrenadaGuadeloupeGuatemalaGuernseyGuineaGuinea-BissauGuyanaHaitiHeard Island and Mcdonald IslandsHoly See (Vatican City State)HondurasHong KongHungaryIcelandIndiaIndonesiaIran, Islamic Republic ofIraqIrelandIsle of ManIsraelItalyJamaicaJapanJerseyJordanKazakhstanKenyaKiribatiKorea, Democratic People’s Republic ofKorea, Republic ofKuwaitKyrgyzstanLao People’s Democratic RepublicLatviaLebanonLesothoLiberiaLibyan Arab JamahiriyaLiechtensteinLithuaniaLuxembourgMacaoMacedonia, The Former Yugoslav Republic ofMadagascarMalawiMalaysiaMaldivesMaliMaltaMartiniqueMauritaniaMauritiusMayotteMexicoMoldova, Republic ofMonacoMongoliaMontenegroMontserratMoroccoMozambiqueMyanmarNamibiaNauruNepalNetherlandsNew CaledoniaNew ZealandNicaraguaNigerNigeriaNiueNorfolk IslandNorwayOmanPakistanPalestinianPanamaPapua New GuineaParaguayPeruPhilippinesPitcairnPolandPortugalQatarReunionRomaniaRussian FederationRWANDASaint Barthélemy Saint Helena, Ascension and Tristan da CunhaSaint Kitts and NevisSaint LuciaSaint Martin (French part)Saint Pierre and MiquelonSaint Vincent and the GrenadinesSamoaSan MarinoSao Tome and PrincipeSaudi ArabiaSenegalSerbiaSeychellesSierra LeoneSingaporeSint Maarten (Dutch part)SlovakiaSloveniaSolomon IslandsSomaliaSouth AfricaSouth Georgia and the South Sandwich IslandsSouth SudanSpainSri LankaSudanSurinameSvalbard and Jan MayenSwazilandSwedenSwitzerlandSyrian Arab RepublicTaiwanTajikistanTanzania, United Republic ofThailandTimor-LesteTogoTokelauTongaTrinidad and TobagoTunisiaTurkeyTurkmenistanTurks and Caicos IslandsTuvaluUgandaUkraineUnited Arab EmiratesUnited KingdomUnited StatesUruguayUzbekistanVanuatuVenezuela, Bolivarian Republic ofVietnamVirgin Islands, BritishWallis and FutunaWestern SaharaYemenZambiaZimbabweI also wish to receive emails from AAAS/Science and Science advertisers, including information on products, services and special offers which may include but are not limited to news, careers information & upcoming events.Required fields are included by an asterisk(*)The researchers, led by Christopher Kuzawa, an anthropologist at Northwestern University in Evanston, Illinois, found that when the brain demands lots of energy, body growth slows. For example, the period of highest brain glucose uptake—between 4.5 and 5 years of age—coincides with the period of lowest weight gain. This strongly suggested that the brain’s high energy needs during childhood are compensated for by slower growth.“This is a very, very cool paper,” says Karin Isler, a biological anthropologist at the University of Zurich in Switzerland. “It very convincingly shows that the conflicting demands of the brain’s and the body’s energy requirements for growth are met, in humans, by a temporal sequence of delayed growth.”The expensive tissue hypothesis was first proposed in 1995 by anthropologists Leslie Aiello of New York’s Wenner-Gren Foundation for Anthropological Research and Peter Wheeler of the United Kingdom’s Liverpool John Moores University. Although it was initially thought that bigger brains were supported by smaller digestive systems, later studies revealed that other mechanisms could also be at work. Isler and primatologist Carel Van Schaik from the University of Zurich suggested that energy-rich diets, delayed growth and reproduction, and energy-efficient locomotion could also help feed the energy-hungry brain. Humans show signs of all three: We cook our food and eat meat, boosting caloric intake; we grow up more slowly and reproduce later; and we walk on two feet, saving energy compared with quadrupedal chimpanzees. The PNAS study supports the trade-off between delayed growth and larger brains, Isler says.The ideal next step would be to see if a similar trade-off with growth happens in other primates, too. But that will hard, Kuzawa says. “Obtaining PET data on brain glucose use across the full growing years in other closely related primates would be fascinating but difficult, and likely impossible for the more relevant comparative species like chimpanzees,” he says.*Correction, 26 August, 11:56 a.m.: An earlier version of the story incorrectly stated that the study sample sizes were 400 and 1000, although they were higher. The article has been amended to reflect this.last_img read more

Winter Soldiers: How The Ice Stupa Team Is Saving Glaciers The World Over

first_imgWhen Sonam Wangchuk, an education activist and engineer, invited crowd-funding on the internet for his Ice Stupa project back in 2014, he wrote in his usual cheeky flair: “It only makes sense to invite global contribution to help solve the problems we are facing here in the mountains, since whether we like it or not, we receive more than our fair share of the impact of your other global (warming) contributions.”The good-natured jibe aside, he is right. The beginnings of climate change are experienced clearly in the mountainous regions. It is seen in their receding glaciers, erratic run-off streams that local communities depend on, and meltwater lakes, which are dammed precariously by moraines and lead to flooding when the compressed sediments are unable to hold back the huge volume of water. The flooding of glacial meltwater lakes is a real threat all over the world — from the Himalayas to the Andes in Peru.The alarming receding of glaciers that was causing a water crisis in the desert mountains of Ladakh made Sonam Wangchuk step in with his Ice Stupa project. Wangchuk, like most inhabitants of the region, realized that there was too much water in winter when they don’t need it, and too little during the farming season when the farmers rely on melting snow to grow wheat, barley and vegetables.The Ice Stupa ProjectThe ice stupa, Wangchuk had told a group of volunteers, which the author was a part of, is a thing of “functional beauty”. “Ice stupas are important in more ways than one,” Wangchuk said. “They can be used to green mountain deserts, mitigate disaster, and restore livelihood of mountain communities. They also work as a tourist attraction.”Shaped like a Buddhist stupa, the ice stupa is a structure built to combat the mountain desert’s water crisis. The ice structure, adorned with sea buckthorn bushes and prayer flags, and dominating the Ladakhi village of Phyang, can store up to 1.7 million liters of water. The idea is that the water released by the glaciers in the pre-farming season can be stored in the form of an ice structure and released during the summer months when the farmers need it. With the ice structure’s capacity to store water, the water can not only be used for farming but also to effectively green the deserts. As of now, 5,000 willow trees are growing under the patronage of the ice stupa.The idea came from a civil engineer, Chewang Norphel, who wanted to store the glacial run-off water by grafting ice terraces. Norphel diverted the water from the main glacial streams via canals to catchment areas that are shaded from the sun. Ice terraces, however, came with limitations. They needed to be higher in altitude, and villagers were required to regularly climb up the mountain to maintain it. Also, come summer and they would have little control over the melting of water.Wangchuk merely sought ways to improve Norphel’s artificial glacier design. The engineer, on whom the character of Aamir Khan was based in the hit Hindi film, 3 Iditos, realized that by reducing the surface area exposed to the sun and warm winds, the ice structure can last longer — even at lower altitudes. How an ice stupa works is simple.“Water maintains its level. If, say, water is piped 30 m upstream, it would rise 30 m from the ground when it reaches the village. Since the pipe is upstream, the water flows down to the village because of gravity,” Wangchuk’s video uploaded on his YouTube page explains. As the water jets out from the pipe, which is narrower at the opening (picture a hose) in Ladakh’s winter nights with temperatures close to -40 degree Celsius, the water freezes by the time it reaches the ground.The sea buckthorn plants help scatter the droplets, making it easier for water to freeze as it comes down. The ice forms layer by layer on the dome structure built by volunteers who come to work on the project during Ladakh’s harsh winters. The dome structure which has plastic sheets, distributes the weight evenly, as the ice rises to the sky, taking the natural shape of a cone.True to his blithe demeanor, Wangchuk admitted candidly that the prayer flags on the ice stupa have less to do with religion and more with the fact that it breaks warm wind. At 78.4 feet, the ice stupa made this year is one of the tallest man-made ice structures.Tackling Glacial Meltwater Lakes — From Sikkim to PeruLike the Lake Palcacocha in Peru, the Lhonak Lake in Sikkim was considered dangerous for years. In 2013, scientists from the National Remote Sensing Centre published a report in the Current Science journal, saying that the meltwater lake formed, dammed by loose soil and glacial debris, in northern Sikkim could cause devastation downstream.In 2016, the Sikkim government approached Wangchuk for help with Lhonak Lake. Around that time, Wangchuk had publicly criticized the handling of the Phugtal flash floods in Zanskar region by the National Disaster Management Authority. He had asked the government agencies not to blast the debris holding the lake formed in Phugtal and instead siphon the water off to drain the lake. His advice was ignored, and while people downstream were evacuated, the eventual flash flood caused by blasting the debris destroyed 12 bridges and fields of villagers.The Sikkim government wanted Wangchuk to use the siphon technique to drain the water from Lhonak lake to make the threat of flash floods in the state impotent.In September 2016, Wangchuk and his Ice Stupa team, along with help from the military, embarked on a three-week expedition and installed three pipes to drain the Lhonak lake. The idea then struck him that the water that has been siphoned off can be used to re-glaciate the region by making ice stupas. The team hopes to implement it in Sikkim, and in Andes, Peru, as well.The initial groundwork was done in Phinaya, Peru, in August this year. Surya Balasubramanium and Darren Thomas Clark, from the Ice Stupa team, went on a recce, and tested the capabilities of water cannon for ice formation and the capability of the ice to survive the hot days in Peru. They came back from the recce, flushed with success. Clark wrote about it on his Facebook page: “Despite the unfavorably warm conditions near Phinaya, Peru (Altitude 5000 meters, 17,000 ft.), we were able to build 2 glacier bases in two nights. We proved that our techniques for building glaciers can work in the Andes, and we will be back next year for a full scale build in the best location possible.”Peru will have a full scale ice stupa next year to mitigate the risks of glacial meltwater lakes.The MortAlive ProjectMorteratsch Glacier, one of Switzerland’s prime attractions, is seeing a yearly loss of 15 million tonnes of ice. This is where the MortAlive Project, which started independently under Prof Hans Oerlemans, comes in. The project creates an artificial snow cover for the glacier in summer to delay the retreat of the glacier. “Our studies show that in 20 years we can build back the glacier to how it is now,” Balasubramanium, who is now part of the project, says.The artificial snow-making and ice stupas are being used in conjunction so that the team can do more than slow down the glacier’s retreat. “This winter, it will be built near the Morteratsch Bahnhof, one of the stops of the Glacier Express train,” Balasubramanium told Little India.The first ice stupa of Switzerland was built in Van Rosel last winter. The design from Ladakh was adapted slightly in Switzerland, with the team using live twigs. “As expected, the twigs were alive and growing again when the ice started melting,” Balasubramanium added.Not just for tourism, ice stupas are being planned in the country as a water solution for alpine huts.This winter, the ice stupa built in Ladakh is expected to have an additional snow cover to delay its melting and to make it more attractive as a tourist spot.As climate change bares its teeth as a reality, the world is coming together to fight the effects, one ice stupa at a time. Related Itemsartificial glacierglacier graftingIce stupaice stupa Ladakhice stupa Switzerlandice stupa Van RoselLittle IndiaMortAlive projectSonam Wangchuklast_img read more