摘自《奥运中的科技之光》，赵致真著。经赵致真先生授权，科学松鼠会网络发布，转载请注明。
“让我们把眼光离开运动场上那些高精尖的‘前沿科技’，去观察一下许多司空见惯的‘鸡毛蒜皮’，同样会发现有趣的知识。”
体育场馆拾零
2005年6月14，雅典国际田联超级大奖赛传来捷报，牙买加短跑名将鲍威尔以9秒77的成绩打破了男子百米世界纪录。还是这位“牙买加飞人”，2007年9月10日又在意大利城市瑞提举行的国际田联大赛中，以9秒74打破了自己保持的世界纪录。接受记者采访时鲍威尔说，“假如今天的风速再理想些，我准能跑出更好成绩。”这是一句大实话。当顺风风速每秒2米时，百米成绩能比无风时快0.15秒。鲍威尔上次打破世界纪录就占了每秒1.7米“顺风”的大便宜。而美国选手盖伊2007年6月在锐步田径大奖赛中跑出9秒76的成绩超过世界纪录时，却因为当时跑进方向的风速达到每秒2.2米，高于国际田联规定的每秒2米上限而不被承认。真可谓“成也顺风，败也顺风”了。
摘自《奥运中的科技之光》，赵致真著。经赵致真先生授权，科学松鼠会网络发布，转载请注明。
“2008年北京奥运会的国家游泳中心‘水立方’也许称得上当代科技与艺术的结晶。”
泳池哪得清如许
如果没有水波和浪花，奥运会将变得多么枯燥和单调！游泳和跳水从来是举足轻重的金牌大户，也是上座率和收视率高居榜首的热门项目。如果说坚实的地面是奥运会“陆军”角逐的战场，那么清澈晶莹的游泳池便是奥运会“水师”的用武之地了。
摘自《奥运中的科技之光》，赵致真著。经赵致真先生授权，科学松鼠会网络发布，转载请注明。
“聚乙烯、聚丙烯草株即使近距离熟视和伸出手触摸都和天然草并无二致。”
球场变革始于足下
2007年10月，NBA在中国上海和澳门的两场季前赛让无数球迷心旌摇曳、如醉如狂。两支正宗的美国职业篮球队不仅自带拉拉队，还自带专用的赛场地板，这种兴师动众的阵仗实在举世罕见。俗话说“百里不运粗”，NBA脚下的篮球地板究竟是“何方神圣”？值得不远万里空运到中国吗？
栩栩/文
这辈子没白活啊,我见了多年的偶像,李淼先生.（简介:http://baike.baidu.com/view/138408.htm）
感谢鹿兄,感谢小如妹妹,感谢松鼠会,感谢各种TV.
话说拜读李淼先生的布鸽还是在知道松鼠会之前,初翻几篇惊为天人,然后人肉了一下才发现他老人家如此内力深厚,呃.
后来看到李淼的布鸽挂在松鼠会网站上了,我就想,啊,看来松鼠会也是一个好高级的组织啊.
我去那里比较早,看见鹿兄在吃饺子.我很温情的询问鹿兄饮食起居的情况;鹿兄很温情的询问了我人身安全的情况.厄,我老人家一直情绪稳定.谢谢.
以前一直听说哥德尔是大牛,你们牛吧,我看不懂.但是郑同学竟一下子就给我科普了哥德尔不完全性定理http://baike.baidu.com/view/227841.htm
感激!
作为报答,我临场胡诌了一个”木桌上的环纹不是年轮而是分枝的印记”的伪科学来欺骗郑同学纯真幼小的心灵.呃,我老人家内心很过得去,谢谢.
Ms.Shell的同学,另一枚北师心理女出现,坐在我旁边作<同桌的你>状,心理女还怕借一支铅笔半块橡皮么?我借支笔你就内心阵阵涟漪,忘了下半截说什么么?靠!你们学心理的没有一个心理正常的:)哈哈哈
看见鹿兄安静的在读年轮,形成层,木质部,春材…我仿佛看到了融融燃烧的壁炉和童话里误吃了酵母在壁炉前睡觉被像面包一样烤大的猫…
我一文科生网友海潮前来观摩，插不上嘴，被空调熏的热死。
孔雀太帅了,谈吐和外形，让我和海潮都小鹿乱撞……晚上回去的时候我对海潮说:我好自卑的所以总抢辩,而孔师兄从容淡定,不过说不定磨砺之后我也可以像他一样.海潮说：“我要他号码（绿头盔一根手指羞涩状）。”
每次参加松鼠活动,我都能看到小如,每次我需要帮助,第一个想到的也是小如.这个故事教导我们,做人不能太善良,否则就会被人利用.谢谢.我今天是这样利用小如的,我用她替我表白.我告诉小如,我女朋友来了,然后去接海潮.海潮进来的时候,小如指着她的鼻子大喊:这是栩栩的女朋友!大家一起说,哦原来是这样。
会毕,饭局.李淼老师好平易近人啊.长白山的猎人好有趣啊.中医补肾好邪恶啊…
海潮说：“没见过比你们更变态的，一面讲环保问题一面还把空调开这么强”
摘自《奥运中的科技之光》，赵致真著。经赵致真先生授权，科学松鼠会网络发布，转载请注明。
“如何更快捷、准确、可靠地丈量距离，是体育运动的持久课题。”
明察秋毫谈测距
1968年墨西哥奥运会的头号英雄，要数美国运动员鲍勃.比蒙了。他“不朽的一跳”创造了“神话般的奇迹”，以8.90米的成绩超越世界纪录55厘米。由于几乎跳到沙坑尽头，落在当时光学测距设备的计量范围之外，以至于裁判们不得不临时找来钢卷尺反复测量与核实。这个惊人的揭晓在记分牌上显示出来时，由于比蒙对公制量度缺乏概念竟一时回不过神来，当人们告诉他8.90米等于29.25英尺，比蒙才顿时激动得长跪不起，热烈拥抱和亲吻大地。这一纪录直到23年后才被鲍威尔在东京以8.95米的成绩所打破。
摘自《奥运中的科技之光》，赵致真著。经赵致真先生授权，科学松鼠会网络发布，转载请注明。
“因此哪怕起跑确实在枪响以后，但只要时间少于0.1秒便可认定为抢跑。”
运动场上的“时间简史”
1996年亚特兰大奥运会上，英国“飞人”克里斯蒂和加拿大“黑豹”贝利的男子百米冠军之争让场内外千万人屏住了呼吸。然而戏剧性的场面出现了，克里斯蒂连续两次抢跑，比规定的起跑时间提前了约百分之一秒。裁判们经过冗长的合议，宣布取消克里斯蒂的比赛资格。于是奥运历史上留下了克里斯蒂在极度失态中愤然退场的一幕。
摘自《奥运中的科技之光》，赵致真著。经赵致真先生授权，科学松鼠会网络发布，转载请注明。
“今天的体坛明星有福了，许多厂商争相为他们量脚定做“独一无二”的运动鞋。”
运动鞋的功勋
回顾足球历史上最经典和重要的“战役”，不能不提到1954年瑞士世界杯赛匈牙利队和前联邦德国队的那场激烈拼搏。明显弱势的德国队在0比2落后的危局中绝地反击，最后以3比2取得了“几乎不可能的胜利”，成为二战后德国回归国际体育大家庭并重振民族精神的重要契机。这次反败为胜的一个关键因素，便是他们脚下穿的新款足球鞋。比赛在大雨滂沱后的范可多夫体育场进行，满地泥泞不堪，当年所向无敌的匈牙利队却被又湿又重的球鞋所折磨，守门员在最后的关键时刻滑倒。而德国队脚下的鞋则轻巧灵活并及时更换了加长的鞋钉，能在滑溜溜的赛场上增大抓地力。拍摄庆功合影的时候，德国队总教练赫尔伯格把看台上的阿迪恭恭敬敬请到身边。这是历史上唯一一张制鞋商和冠军队共享胜利喜悦的照片。
摘自《奥运中的科技之光》，赵致真著。经赵致真先生授权，科学松鼠会网络发布，转载请注明。
“体育的终极意义在于强健体魄和增进健康，运动中人的安全越来越成为现代文明重要的价值取向。”
“软硬兼施”的护身术
体育运动的魅力之一便是勇猛拼搏和激烈对抗。竞技场上到处都有速度的飞翔，力量的击打，身体的冲撞。如何确保运动员“血肉之躯”的安全，从来是体育比赛头等重要的课题。瞧瞧冰球选手们“顶盔贯甲”、全副武装的那身打扮，简直不亚于太空中的宇航员。当170克重的硬橡胶冰球以每小时160多公里的速度在场上往复弹射，平均体重80多公斤的对手在高速滑行中互相“合理冲撞”时，即使有这些头盔、护胸、护肘、护腿、护裆的全方位保护，赛场上的人身事故仍时有发生。今日的体育运动如果离开了护具，许多项目将根本无法开展。
摘自《奥运中的科技之光》，赵致真著。经赵致真先生授权，科学松鼠会网络发布，转载请注明。
“一个引人入胜的实事是，‘左撇子’运动员在对抗性竞技中具有不容置疑优势。”
格斗的艺术
有人将击剑比作“格斗的芭蕾”，有人将击剑说成“体力的象棋”。手提三尺剑，身披金属衣，在一条剑道上“狭路相逢”和“短兵相接”。击剑运动实在是动与静、刚与柔、智与勇结合的样板。轻捷灵巧的花剑，强悍威猛的重剑，劈刺兼备的佩剑，是奥运会竞赛的三大剑种。
摘自《奥运中的科技之光》，赵致真著。经赵致真先生授权，科学松鼠会网络发布，转载请注明。
“和21分制之相比，11分制意味着更多的‘偶然性’。”
乒乓球的前世今生（下）
1979年平壤第35届世乒赛上，匈牙利队夺回了阔别27年的男子团体冠军奖杯，他们出奇制胜的一大法宝便是使用了“快速胶水”。据说是克兰帕尔在一次比赛中偶然发现重新粘贴的海绵具有魔术般的效果，击球时速度和旋转都明显增强，这一“秘密武器”很快便被各国运动员所周知和掌握，并成为乒乓球厂商的一大生意。“快速胶水”的玄机在于，其中的有机溶剂快速挥发时能渗透到球拍的海绵层，使细小的微孔结构充气和鼓胀起来，海绵层因此增厚3%至10%，“贮能模量”提高30%，“损耗模量”明显降低，击球时更富有弹性和容易“透板”。至于发出的声音格外清脆响亮，其原理可以追溯到“气穴”现象和“水锤效应”。不过这种“灌胶”的威力只能持续一两个小时，以致运动员在比赛中不得不多次反复刷胶。乒乓赛场从此也像备有“吸烟室”一样专门开设了“刷胶室”，供参赛者冒着刺鼻的气味“临阵磨枪”。 (全文…)
AS YOU tear into the wrapping paper this festive season, you might be thinking of those long weekends your loved ones spent trudging through the crowds to find that elusive perfect expression of their affection. Quaint thought, but according to UK sales figures, if last year’s festive season is anything to go by, it is likely that at least 1 in 5 of your friends and family shopped online, probably with a nice glass of wine in hand rather than a shopping bag digging into their palm. Elsewhere in the developed world, the picture is much the same.
This seismic shift in shopping habits is down to more than the mere convenience of shopping in your slippers. A new school of thought in business has emerged that claims it is all about choice. On the net, you can buy just about anything you can think of, and a lot of things you never have. Amazon alone lists millions of products, including everything from the latest New Scientist book to maternity bras, plasma TVs and a vibrating ladybird-shaped massager.
The message is simple: no matter what your taste, you will find something to satisfy it online. Gone are the days when shoppers had a limited selection of blockbusters to choose from. The internet is changing not only how we shop, but what we buy.
And yet the big sellers have never been bigger. Take the latest Harry Potter book, which on launch in 2007 sold 11 million copies in its first day, exceeding the record for the fastest-selling book - set consecutively by the previous three Potter tomes. So what’s the real deal? Is the internet really broadening our horizons? Or is it all marketing fluff masking the fact that best-sellers still rule?
The idea that the internet is transforming our buying habits was first popularised in an article written by Chris Anderson, editor-in-chief of the technology magazine Wired, in October 2004. The article, titled "The long tail", became a blog, a best-selling book and a marketing mantra.
Anderson’s premise was simple. Before the internet, even the largest retailer had physical constraints on the variety of stuff like books, CDs and DVDs it could profitably sell. Savvy store owners had to tailor their stock to maximise returns from limited shelf space, and consumers had to make do with what was on offer.
In cyberspace, by contrast, shelf space is practically unlimited and other overheads at rock bottom. Online retailers can take advantage of that to sell vast catalogues of obscure products at little or no extra cost.
Anderson postulated that this new breadth of choice was leading to a metamorphosis of the classic demand curve. Instead of a steep peak representing comparatively few big-selling items, a gentler curve spread over far more products was emerging - creating the eponymous long tail (see graph).
To Anderson, this migration to the long tail is a journey of self-discovery for all of us. "As a teenager in the 1970s, I listened to one of the 10 radio stations on offer, but I’m not sure I really knew what my taste was." Now, he says, we are all finding out - and discovering that we like quite different things. His conclusion is summarised in the subtitle of his book: "The future of business is selling less of more".
It is an attractive hypothesis that rapidly acquired an evangelical following. But then dissenting voices emerged. The first shot across the bows came in July this year, when Anita Elberse of Harvard Business School published an analysis of music downloads and DVD-by-mail rentals in the Harvard Business Review. Her findings suggest that the long tail is far from the revolution Anderson claimed. The tail is indeed getting longer, but isn’t, as Anderson thought, growing fat with choice. Instead it is getting both flatter and thinner, filled with ever more products that sell few or no copies.
Low overheads or no overheads, that kind of long tail is not a rich man’s world, least of all for producers. Suppliers are always going to be better off concentrating on the mass-market money-spinners, says Elberse.
Her ideas have recently been backed up by another study. Will Page and Gary Eggleton at the MCPS-PRS Alliance - a UK body that collects royalties for musicians when their songs are played on air or downloaded - and Andrew Bud from the cellphone software company mBlox have analysed a year’s worth of downloads from a well-known internet music store. They found that of the 13 million tracks available, 52,000 - just 0.4 per cent - accounted for 80 per cent of downloads.
Of the 13 million tracks available, 0.4% of them account for over three-quarters of downloads
The overall pattern of demand showed nothing like the shift towards a long, fat tail postulated by Anderson. In fact, it showed the reverse: it followed what is known as a log-normal curve, characterised by a sharp spike of best-selling blockbusters that rapidly tailed off into nothing. There was an added irony to Page’s findings. If an average album holds 12 tracks, 52,000 songs equate to about 4300 CDs - according to Anderson’s Long Tail book, about the number of titles stocked by Wal-Mart, the largest bricks-and-mortar retailer in the US.
In other words, says Page, the extra choice available online is of little economic worth to the retailer. "Scarcity in conventional retailers might be a constraint," he says. "But it could also be a discipline, representing an economically optimal inventory."
Results from a study by anthropologist Alex Bentley and economist Paul Ormerod of Durham University, UK, together with anthropologist Mark Madsen of the University of Washington in Seattle, agree with Page and his colleagues’ findings (www.arxiv.org/abs/0808.1655). The researchers found that in a fashion-led market, where consumer preferences are fickle and fast-changing, the inventory size that maximises profits is actually very small - equivalent to the 10 to 20 titles often stocked in an airport bookstore.
Even for an online retailer such as Amazon, where the profit-to-overhead ratio per item is very large, the optimum inventory is likely to be considerably smaller than the millions of titles actually offered, says Ormerod. He counsels caution: "It’s a good marketing strategy to say you sell everything," he says, "but it is unlikely to be profitable on its own." Elberse agrees: "The long tail was a great idea," she says, "but as a business model it was too optimistic." The greatest attraction for shoppers, she suggests, is probably the aggressive discounts Amazon offers on its blockbuster products.
Anderson concedes that, for producers, the economics of the long tail might be shaky, but defends his central thesis: that the choices internet retailers offer open our eyes to a rich new world of possibilities - and that canny retailers can profit from that. "For most people, there’s no money in the long tail," he says. "But then, most books don’t make money. Most films don’t make money." Nevertheless, a market like this will benefit retailers like Amazon, and more importantly us consumers. We might still subsist on a staple diet of blockbusters, but we can enrich that with other titbits from the tail in a way we could not before.
So why, with the cornucopia of goodies now available to us, are blockbusters not just still here, but getting bigger? On the face of it, Anderson’s idea of a divergence of tastes in the digital era is logical. But if the long tail effect does not exist, or is not as pronounced as was thought, what is really going on?
Elberse says it’s a bit like the influence of multichannel television on the economics of sport. In the old days, if you wanted to watch soccer, you went to watch your local team in the flesh. Now, she says, in the UK you are more likely to decide to stay at home and watch Chelsea play Arsenal. This change of allegiance cuts the cash flowing into the ticket office of your local club while boosting advertising revenues for TV, which accrue disproportionately in favour of the already wealthy top clubs.
It is a phenomenon known to economists as the Matthew effect, after a quotation from the gospel of that name: "For unto every one that hath shall be given." Just as for the long tail effect, there is a plausible explanation of why it should be happening in the modern media environment: easy digital replication and efficient communication through cellphones, email and social networking sites encourage fast-moving, fast-changing fads. The result is a homogenisation of tastes that boosts the chances of popular things becoming blockbusters, making the already successful even more successful.
The winner takes it all
Duncan Watts, a sociologist at Columbia University, New York, has found evidence of just such an effect. Together with his colleagues Matthew Salganik and Peter Dodds, he tested the effect of communication and peer approval on the musical tastes of 14,000 teenage volunteers recruited online (Science, vol 311, p 854). A set of 48 songs was made available to all the volunteers, who could download whichever songs they wanted. The researchers split the volunteers into eight groups; in some, group members could see what their peers were downloading, but in others they had no such knowledge. In the socially connected groups, the winner took all: popular songs became more popular, unpopular songs more unpopular. This effect was much less pronounced in the socially isolated groups.
What’s more, there was a sting in the tail for anyone trying to predict blockbusters: in different groups, different songs tended to become the biggest hits. It is a classic butterfly effect: a small preference for a particular object can, in a highly connected community, rapidly amplify and spread its appeal. Increased social connectedness creates bigger blockbusters but makes predicting what they will be all the more difficult.
Which leads to a curious puzzle: why, when we have so much information at our fingertips, are we so concerned with what our peers like? Don’t we trust our own judgement? Watts thinks it is partly a cognitive problem. Far from liberating us, the proliferation of choice that modern technology has brought is overwhelming us - making us even more reliant on outside cues to determine what we like (see "I know what you’ll buy next summer"). "Google can deliver 100 million songs to you - but your brain hasn’t got any faster," he says.
Why, when we have so much information at our fingertips, do we care what our peers like?
Watts thinks there is a fundamental problem with ideas like the long tail: they reduce our likes and dislikes to a set of isolated, stable preferences. "There is a naive assumption that people are making decisions independently, scouring all possible choices and then optimising," he says. "But people aren’t rational in that weird economists’ sense."
Quite apart from the cognitive overload aspect, Watts thinks that the films we watch or the music we listen to is not entirely, or even mostly, about the thing being consumed. It is about the social context in which we consume it. "If you’re dating a girl who likes AC/DC, you might start listening to AC/DC. With another girlfriend, you might be listening to Aerosmith," he says.
Ultimately, he thinks, our love of the blockbuster might just reflect that we humans are constantly looking out for a place to go - one where others are too. "A culture is a set of people who share beliefs, ideas and artefacts," says Watts. "Blockbusters are part of that - they make us feel we belong to something."
Anderson agrees, and says he has never said any different. "Blockbusters are always going to exist - they’re a combination of what’s genuinely awesome and banalities that appeal to the lowest common denominator. What the long tail does is break the tyranny of the blockbuster." By making it easier for all of us to access the choice available - and also with blogs, self-publishing, YouTube and the like, to produce it ourselves - the internet puts us in a better position than ever to determine ourselves what our shared tastes are.
Anderson sees the web as a gene pool from which worthy blockbusters can emerge by a process akin to natural selection. "The bluefin tuna lays maybe 3 million eggs, and three hatch. But up until now, it has been too expensive to waste life like that in media production," he says. Now, however, there is the chance that a truly commercial blockbuster can arise organically, by public acclaim, from the long tail.
The organic blockbuster? Surely that has got to taste better than the mass-produced, force-fed Christmas turkeys scheduled on TV for the next few days.
I know what you’ll buy next summer
Ever had the feeling that someone is reading your mind? If you browse through any of a growing list of online shopping sites, you might be forgiven for doing so. To boost their chances of making a sale, sites are increasingly using a technology called collaborative filtering to make an educated guess at what you might be thinking of buying.
The software beavers away behind your Amazon homepage, for example, and recommends products based on your previous purchases and clicking history. For example, after I looked up a film version of King Lear directed by Soviet film-maker Grigori Kozintsev, my Amazon homepage suggested I buy Shakespeare’s King Lear (naturally), but also Dmitri Shostakovich’s first cello concerto (because Shostakovich composed the music for several of Kozintsev’s films) and Doctor Zhivago (presumably because it is a film about Russians).
It is this sort of software that paradoxically promotes the sales of blockbusters and is responsible for homogenising choice online, say Daniel Fleder and Kartik Hosanagar of the University of Pennsylvania, Philadelphia. They outline this idea in an article to be published in the journal Management Science. To make useful recommendations, most collaborative filters must make guesses based on previous sales and ratings. But obscure products do not have much in the way of sales or ratings to go on, so the filters tend to point us towards more mainstream offerings. By following such a widget’s recommendations, I might well vastly diversify my own personal cultural experience, but I will also contribute to a decrease in system-wide diversity, adding more sales to already popular objects.
OH, THE heady days of 2007! The economy was booming, we were living it up on credit and grabbing the latest gadgets. What a difference a year makes. With the credit crunch biting, jobs vanishing and recession looming worldwide, this Christmas is looking a rather bleak affair.
Consumers said they would be spending 7 per cent less on presents this year, according to a survey at the end of October by business consultants Deloitte. That doesn’t mean you have to act like Ebeneezer Scrooge, though. Why not put your technology skills to good use and build some home-made versions of the presents you want to give but can no longer afford?
It’s easier than you might think. The web has a swarm of sites that show you how to make this year’s must-have gadgets from heaps of electronic components and old junk. So there is no excuse not to give your mum that digital photo frame she wants or your nephew a dancing teddy. Not only might you save money and keep tech junk from the dump, your friends and family are more likely to cherish a home-made present than something acquired with a wave of a bank card. At least, so says Eric Wilhelm, who has created Instructables.com, a website forum for people to share their home-made projects.
While studying for a PhD in mechanical engineering at the Massachusetts Institute of Technology, Wilhelm took up kite surfing. It was an expensive hobby, though, and Wilhelm couldn’t afford to buy his own gear. So he began designing his own, hand-sewing the kites and building the surfboards. "Half of the equipment performed beautifully, half failed spectacularly," recalls Wilhelm, who began documenting his designs on his own website.
Soon Wilhelm was inundated with notes from kite-surf dudes asking for advice, sharing their ideas and swapping photographs. Dealing with all the correspondence was time-consuming, and he realised that people like him needed a better way to share their projects online: Instructables was born.
Today the site has step-by-step instructions for 17,000 projects, with as many as 20 new ones added each day. Here you can find out how to make a robot like the one in the movie Wall-E, a flashlight from a Chapstick and an iPod speaker from a tin of mints. More than 350,000 fans rate other people’s projects, suggest improvements and add their own photographs and videos. The most popular projects have been compiled in a book, The Best of Instructables.
Of course, people have been "hacking" and modifying - "modding" - gadgets for years. "I’ve always been taking things apart," says Ilya Eigenbrot, a school principal in Montreux, Switzerland. "I want to find how things work."
Eigenbrot began when he was a student in the 1980s by fixing bits of old equipment and putting together simple computers for friends. Soon he was cannibalising all types of gadgets, including an old boom box that he turned into an in-car CD player. He began by prising the CD player from its plastic casing, then connected it to the car’s 12-volt battery via a voltage regulator and glued the whole thing to the dashboard. Magnets placed on top of the disc held it in place as it spun. "It would skip tracks as I drove," Eigenbrot admits, "but at least you could change the disc very easily."
He recommends scouring eBay for broken equipment. Then it’s just a matter of waiting until the replacement part you need to fix it comes up for sale. Alternatively, if you’re after a common gadget like a laptop, you’ll find eBay is awash with machines with cracked screens, faulty hard drives and missing keys. Buy three with different faults, strip them down, reassemble the working parts and you can have a perfect laptop for less than £20.
You don’t even have to be handy with a soldering iron to make techie gifts. With pliers, a penknife and some silicone sealant you can transform a Lego brick into a trendy USB flash memory stick. Similar designs cost a small fortune from gift catalogues, yet many companies now give away the central component - a USB stick - for free, says Ian Hampton from Oxford, UK, whose instructions are published on Instructables.
You don’t even have to be handy with a soldering iron to make techie gifts
Eigenbrot worries that the popularity of websites such as Instructables will lead to a run on components. "Supplies have dwindled in the past couple of years," he laments. "People know what they are looking for, so it’s getting harder to pick up a bargain."
For most modders and hackers, though, saving money isn’t the point. "People make things to express themselves," says Wilhelm. "It’s a backlash against mass consumerism. When you make something, you value it more and have a deeper connection with it." Better still, your loved ones will appreciate the time and effort you have put into their gifts.
Perhaps that’s just as well, because home-made isn’t always cheaper. As anyone who bakes can testify, a shop-bought cake is usually cheaper than the individual ingredients. Technology is no exception.
Be inventive, though, and your home-made presents could even earn you money. Two years ago Joe Langevin, an electronics graduate from Seattle, launched the website Hack N Mod (www.hacknmod.com) for people to share their hacked and modified gadgets. He pays $40 to anyone who submits an original project that he features on his website. Who knows, you could be one of the few making a profit this credit-crunch Christmas.
Pimp my present
Autonomous Cookie Monster
Awww, some hackers just can’t resist a cuddly toy. The Toy Retailers Association in the UK and Ireland has picked an all-singing, all-dancing version of the Sesame Street character Elmo as one of its top toys for Christmas, but a more heavyweight Sesame Street character could give Elmo a run for his money - the autonomous Cookie Monster.One modder on Hackaday.com took a Cookie Monster soft toy and removed the stuffing. He then wrapped the fur around the legs and torso of a walking robot toy. To make the Cookie Monster’s arms and head move, he inserted servo motors, like those in a remote-controlled plane, and added wheels to his feet. To help the Cookie Monster build up a rough picture of its environment and avoid obstacles he also hid an ultrasonic distance sensor inside its mouth. Finally he added a programmable micro-controller to coordinate its movements before sewing Cookie Monster back up. For details, see www.tinyurl.com/66unc6.
Nintendo Wii balance board
Nintendo’s Wii games console has already provided rich pickings to hackers and modders. So they couldn’t fail to rise to the challenge this year as the world went crazy for the Wii Fit exercise system. Wii Fit users stand on a wireless Balance Board that detects their centre of balance and relays this information to the console, which can then simulate anything from a yoga instructor to a virtual pair of skis. Over 2 million systems were sold between July and September, and even now you’ll be hard pushed to find one in stock. In the US, online retailer Amazon is limiting the number of Wii Fits each household can buy to three - presumably to prevent people buying them up by the dozen to sell on eBay.You can cut out the queues - and beat the eBay profiteers - by doing what Californian blogger Mike Sylvester did. He has built his own version of the balance board after spending $20 on materials from his local hardware store. Its key component is the standard motion-sensing "Wiimote" wireless controller for the Wii. This he places inside some foam pipe insulation glued to the top of a laminate board. Textured tape on the board’s surface prevents players sliding off, and more pipe insulation is glued to the edges to stop the board damaging the floor. To make a fulcrum, Sylvester glues tennis balls to the board’s underside. You’ll need to reprogram the Wiimote too, but soon you could be snowboarding down a hillside with the best of them. For details, see www.tinyurl.com/2fj2c4.
Digital photo frame
Instructables.com has step-by-step instructions for several different home-made frames, including a 10-inch design made from parts that you should find on eBay for around $100. This may not seem any cheaper than a ready-made version until you consider that you could make one using a 17-inch screen for about the same cost. A ready-made frame that big will set you back around $400.You’ll need to be comfortable taking apart electronics for this one, though, as its key ingredients are the LCD screen and hard drive from a laptop. You also need a touch-sensitive screen the same size as the LCD display, two sheets of Perspex (Plexiglas), some screws and lots of double-sided sticky tape. For details see www.tinyurl.com/6qaw44.
iPod speakers and cellphone charger
Share your playlists for less. Instructables contributor Justin Seiter has built an iPod speaker from a musical greeting card, a pair of old headphones and an empty cereal packet. Inside cards that play a tune when opened, you’ll find a loudspeaker. Remove it and connect it to the wires of the headphones. The headphone jack then plugs into the iPod as usual. Not loud enough? To amplify the music, cut a hole for the speaker in the cereal box. Who’d have thought Rice Krispies could do more than snap, crackle and pop? For details, see www.tinyurl.com/5rkz5n.The same project site also shows you how you can make your own portable USB charger for your iPod, cellphone or digital camera using two AA batteries enclosed within an empty tin of mints. For details, see www.tinyurl.com/253zcv.
iPhone
OK, so you won’t fool anyone with this poor man’s iPhone, but it’s still fun to make and doesn’t require a degree in electronics. It involves gluing together an old cellphone and Apple’s first-generation iPod Nano, so you can both make calls and listen to the music you’ve downloaded from iTunes. According to the tutorial on Instructables, you need to carve out part of the cellphone’s innards to make room for the iPod, which you then glue inside. However, New Scientist staff were impressed with an even cruder version made by winding a rubber band around an iPod and cellphone placed back to back. Would you want one for Christmas, though? For details, see www.tinyurl.com/3297qu.
Segway
Remember the Segway, the ride-on, self-balancing scooter that was going to revolutionise the way we travel - and didn’t? A new Segway will set you back around $6000, but Geoffrey Bennett can make you look ridiculous for far less. His home-made version is put together from two second-hand electric wheelchair motors, with the gearbox, hub, wheel and tyre attached, plus a gyroscope and accelerometer picked up from an electronics store. Bennett’s device is powered by six 12-volt batteries and styled using two planks of wood, a broomstick and gaffer tape. For details, see www.tinyurl.com/5tre2u.
摘自《奥运中的科技之光》，赵致真著。经赵致真先生授权，科学松鼠会网络发布，转载请注明。
“没有一种球像乒乓球那样，将花样百出的旋转作为常规技术形态和基本‘杀伤’手段。”
乒乓球的前世今生（上）
作为奥运会正式比赛项目，乒乓球直到1988年才姗姗来迟。但它的人气之旺、魅力之大却在奥运赛场一路攀升。2000年悉尼奥运会上，乒乓球是第四个将所有门票售罄的竞赛项目。鲜为人知的是，国际乒联早在1937年便通过了参加奥运会的决议，但谨慎而自尊的蒙塔古主席由于担心乒乓球水准不高会遭到拒绝而未能付诸实施，谁知这一拖延就是50年。
What if our universe didn’t emerge from nothing, but is a recycled version of one that went before?
Anil Ananthaswamy investigates
ABHAY ASHTEKAR remembers his reaction the first time he saw the universe bounce. “I was taken aback,” he says. He was watching a simulation of the universe rewind towards the big bang. Mostly the universe behaved as expected, becoming smaller and denser as the galaxies converged. But then, instead of reaching the big bang “singularity”, the universe bounced and started expanding again. What on earth was happening?
Ashtekar wanted to be sure of what he was seeing, so he asked his colleagues to sit on the result for six months before publishing it in 2006. And no wonder. The theory that the recycled universe was based on, called loop quantum cosmology (LQC), had managed to illuminate the very birth of the universe – something even Einstein’s general theory of relativity fails to do.
LQC has been tantalising physicists since 2003 with the idea that our universe could conceivably have emerged from the collapse of a previous universe. Now the theory is poised to make predictions we can actually test. If they are verified, the big bang will give way to a big bounce and we will finally know the quantum structure of space-time. Instead of a universe that emerged from a point of infinite density, we will have one that recycles, possibly through an eternal series of expansions and contractions, with no beginning and no end.
LQC is in fact the first tangible application of another theory called loop quantum gravity, which cunningly combines Einstein’s theory of gravity with quantum mechanics. We need theories like this to work out what happens when microscopic volumes experience an extreme gravitational force, as happened near the big bang, for example. In the mid 1980s,Ashtekar rewrote the equations of general relativity in a quantum-mechanical framework. Together with theoretical physicists Lee Smolin and Carlo Rovelli, Ashtekar later used this framework to show that the fabric of space-time is woven from loops of gravitational field lines. Zoom out far enough and space appears smooth and unbroken, but a closer look reveals that space comes in indivisible chunks, or quanta, 10-35 square metres in size.
In 2000, Martin Bojowald, then a postdoc with Ashtekar at the Pennsylvania State University in University Park, used loop quantum gravity to create a simple model of the universe. LQC was born.
Bojowald’s major realisation was that unlike general relativity, the physics of LQC did not break down at the big bang.
“Einstein’s relativity fails to explain the very birth of the universe”
Cosmologists dread the singularity because at this point gravity becomes infinite, along with the temperature and density of the universe. As its equations cannot cope with such infinities, general relativity fails to describe what happens at the big bang. Bojowald’s work showed how to avoid the hated singularity, albeit mathematically. “I was very impressed by it,” says Ashtekar, “and still am.”
Jerzy Lewandowski of the University of Warsaw in Poland, along with Bojowald, Ashtekar and two more of his postdocs, Parampreet Singh and Tomasz Pawlowski, went on to improve on the idea. Singh and Pawlowski developed computer simulations of the universe according to LQC, and that’s when they saw the universe bounce. When they ran time backwards, instead of becoming infinitely dense at the big bang, the universe stopped collapsing and reversed direction. The big bang singularity had truly disappeared (Physical Review Letters, vol 96, p 141301).
But the celebration was short-lived. When the team used LQC to look at the behaviour of our universe long after expansion began, they were in for a shock – it started to collapse, challenging everything we know about the cosmos. “This was a complete departure from general relativity,” says Singh, who is now at the Perimeter Institute for Theoretical Physics in Waterloo, Canada. “It was blatantly wrong.”
Ashtekar took it hard. “I was pretty depressed,” he says. “It didn’t bode well for LQC.” However, after more feverish mathematics, Ashtekar, Singh and Pawlowski solved the problem. Early versions of the theory described the evolution of the universe in terms of quanta of area, but a closer look revealed a subtle error. Ashtekar, Singh and Pawlowski corrected this and found that the calculations now involved tiny volumes of space.
It made a crucial difference. Now the universe according to LQC agreed brilliantly with general relativity when expansion was well advanced, while still eliminating the singularity at the big bang. Rovelli, based at the University of the Mediterranean in Marseille, France, was impressed. “This was a very big deal,” he says. “Everyone had hoped that once we learned to treat the quantum universe correctly, the big bang singularity would disappear. But it had never happened before.”
Physicist Claus Kiefer at the University of Cologne in Germany, who has written extensively about the subject, agrees. “It is really a new perspective on how we can view the early universe,” he says. “Now, you have a theory that can give you a natural explanation for a singularity-free universe.” He adds that while competing theories of quantum gravity, such as string theory, have their own insights to offer cosmology, none of these theories has fully embraced quantum mechanics.
Will our universe bounce?
According to the big bounce picture formulated by theoretical physicist Abhay Ashtekar and others, the cosmos grew from the collapse of a pre-existing universe. Will the same fate await us?
It depends. We used to think that the universe was dominated by the gravity of its stars and other matter: either the universe is dense enough for gravity to halt the expansion from the big bang and pull everything back, or else it isn’t, in which case the expansion would carry on forever. However, observations of distant supernovae in the past 10 years have challenged that view. They show not just that the universe is expanding, but also that the expansion is speeding up due to a mysterious repulsive force that cosmologists call “dark energy”. So if the universe fails to contract, has it already bounced its last bounce?
Perhaps not. Cosmologists are still very much in the dark about dark energy. Some theoretical models speculate that the nature of dark energy could change over time, switching from a repulsive to an attractive force that behaves much like gravity. If that happens, the universe will stop expanding and the galaxies will begin to rush together. A question mark also hangs over the universe’s matter and energy density, which we have not measured with sufficient accuracy to be sure that the universe will not eventually stop expanding. If it turns out to be a smidgen greater than current observations, then it is a recipe for cosmic collapse.
According to the big bounce, in both scenarios the universe will eventually collapse until it reaches the highest density allowed by the theory. At this point, the universe will rebound and begin expanding again – the ultimate in cosmic recycling.
If LQC turns out to be right, our universe emerged from a pre-existing universe that had been expanding before contracting due to gravity. As all the matter squeezed into a microscopic volume, this universe approached the so-called Planck density, 5.1 × 1096 kilograms per cubic metre. At this stage, it stopped contracting and rebounded, giving us our universe.
“You cannot reach the Planck density. It is forbidden by theory,” says Singh. According to Bojowald, that is because an extraordinary repulsive force develops in the fabric of spacetime at densities equivalent to compressing a trillion solar masses down to the size of a proton. At this point, the quanta of spacetime cannot be squeezed any further. The compressed space-time reacts by exerting an outward force strong enough to repulse gravity. This momentary act of repulsion causes the universe to rebound. From then on, the universe keeps expanding because of the inertia of the big bounce. Nothing can slow it down – except gravity.
LQC also illuminates another mysterious phase of our universe. In classical cosmology, a phenomenon called inflation caused the universe to expand at incredible speed in the first fractions of a second after the big bang. This inflationary phase is needed to explain why the temperature of faraway regions of the universe is almost identical, even though heat should not have had time to spread that far – the so-called horizon problem. It also explains why the universe is so finely balanced between expanding forever and contracting eventually under gravity – the flatness problem. Cosmologists invoke a particle called the inflaton to make inflation happen, but precious little is known about it.
Cosmic recall
More importantly, even less is known about the pre-inflationary universe. Cosmologists have always assumed that they could ignore quantum effects and regard space-time as smooth at the onset of inflation, as general relativity requires. This had always been an educated guess – until now. LQC shows that at the time inflation begins, space-time can be treated as smooth. “This is not an assumption any more,” says Singh. “It’s actually a prediction from loop quantum cosmology.”
The models developed by Ashtekar, Singh, Bojowald and Pawlowski represent an enormous step forward. This is the first time that a theory is able to make predictions about what was happening prior to inflation, while correctly predicting what happens postinflation. “To do both of these things at the same time has been difficult,” says Ashtekar.
If the universe we inhabit emerged from a previous cosmos, can we know something about the universe that preceded ours? LQC simulations show that it too would have had stars and galaxies. But opinions differ when it comes to the quantum phase just before and after the big bounce, when it is impossible to pin down the volume of the universe due to quantum fluctuations. Bojowald’s calculations show that some of the information about the earlier universe is wiped out as it goes through the big bounce. In other words, there is no “cosmic recall” (Nature Physics, vol 3, p 523).
In contrast, another detailed analysis done by Singh and Alejandro Corichi, of the
“The pre-existing universe was squeezed into a microscopic volume”
Autonomous National University of Mexico in Michoacán, suggests otherwise (Physical Review Letters, vol 100, p 161302).
Ashtekar likens the spirited spat among his former postdocs and students to watching his children squabble. “It’s much ado about nothing,” he says. Though arguments about the universe possibly having a cosmic recall may be of philosophical interest, they are premature. “We should be worrying about making contact with experiments today.”
That day may be near. The researchers’ first target is the cosmic microwave background (CMB), a radiation released long after the universe’s quantum phase. Even
though the CMB originated 370,000 years after the big bang, its seeds were laid out much earlier, says Bojowald. “That could be a period when quantum gravity effects might play a role.”
Bojowald has discovered that such effects would have dominated when, according to LQC, the universe went through a short phase of accelerated expansion before the onset of inflation. Dubbed superinflation, it occurred due to the immense repulsive forces of the high-density quantum universe rather than the presence of inflatons. Exactly how this phase might affect the CMB is unclear, but already there are hints that LQC might predict something different from classical cosmology. “This is what we are going to work on in the next two years. We are going to find robust predictions,” says Singh.
Meanwhile, Ed Copeland of the University of Nottingham, UK, and his colleagues have shown that superinflation can produce the kind of quantum fluctuations in the fabric of space-time that eventually became seeds for the formation of galaxies and clusters of galaxies. This suggests that superinflation might make inflation unnecessary, thus removing what has essentially always been an add-on to standard cosmological theory. It is early days for superinflation, though, because it cannot yet solve the horizon and flatness problems that inflation so elegantly resolves.
Copeland says that future experiments might reveal whether our universe underwent inflation or superinflation by looking for a pattern of gravitational waves that only inflation could have created. These ripples in the fabric of space-time would have polarised the CMB, though the effect is too faint for today’s instruments to detect. Things might change next year, however, when the European Space Agency launches the Planck satellite, promising the most detailed view of the microwave background to date. Copeland’s work suggests that superinflation would suppress the production of gravitational waves at cosmological scales, and that there would be no such imprint in the CMB. “If you do detect them, it would probably count against LQC,” he says.
Kiefer cautions that all the predictions of LQC are subject to one big caveat. The predictions of classical cosmology come from solving the equations of general relativity, albeit with certain simplifying assumptions about the universe. Ideally, LQC should be put on the same footing – all its equations should be derived from loop quantum gravity. Instead, Bojowald and others obtained LQC by starting with an idealised universe derived from general relativity and then using techniques from loop quantum gravity to quantise gravity in the model. “From a physicist’s point of view, it is fully justified,” says Kiefer. “Mathematicians perhaps would not be amused.”
Rovelli agrees. To put LQC on a firmer foundation, he and his colleague Francesca Vidotto have been working to reconcile it with loop quantum gravity (www.arxiv.org/ abs/0805.4585v1). “The conclusion is very positive,” says Rovelli. “We are able to recover the equations of LQC, starting with something much closer to loop quantum gravity.”
No wonder Rovelli is looking forward to upcoming experiments that could vindicate the theory. “I hope before dying to know whether loop quantum gravity is correct or not,” he says. For a man who turned 50 only recently, he is being unduly pessimistic. A raft of experiments, of which Planck is only the first, will soon be measuring the CMB and looking for gravitational waves. A revolution in our notions of how our universe began may be closer than he thinks. ~
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Why do women lose their ability to bear children long before they grow old? Daughters-in-law may be to blame, discovers Alison Motluk
IT FLIES in the face of natural selection, yet in humans it seems fixed and universal: at around age 50, not far past the midpoint of life, normal healthy women lose their capacity to bear children. Following a decade of gentle winding down, the whole reproductive system screeches to a halt. It is as though, after a few years of wearing bifocals, all women suddenly went blind.
Menopause is a mystery. It leaves women with 20, 30, perhaps even 50 years of life – squandered time in evolutionary terms, because no further genes can be passed on. Yet the selection pressure for menopause must have been strong: there are no known pockets of women around the world who do not go through it. All the evidence suggests menopause has been around a long time, and that the age at which it hits has changed little. Increased longevity seems not to have budged our closing hours. Nor, apparently, has lifestyle; it hits hunter-gatherers at pretty much the same age as hip New Yorkers.
In an attempt to explain this phenomenon, anthropologists suggest that menopause lets women see their last child through to maturity, or that it enables them to provide for their grandchildren. Both ideas make evolutionary sense, since they allow mothers to pass on more of their genes to subsequent generations. But when the numbers are crunched, they just don’t seem enough to explain why women would forgo turning out a few more babies of their own. “The sums don’t add up – the benefits aren’t sufficient to stop breeding,” says Michael Cant from the University of Exeter at Penryn, UK. “There’s a missing piece of the puzzle.” As a zoologist, whose main work has been in banded mongooses and paper wasps, he had an idea about what that missing piece might be. Put bluntly, he suspects that daughters-in-law could be to blame.
Change, not decay
Humans are odd. Elsewhere in the animal kingdom, reproductive senescence tends to set in alongside other bodily deterioration: Females just churn out fewer young in the same way that, for instance, the heart pumps blood a little less efficiently, the ears hear a little less sharply and the skin becomes less elastic. Growing old is like that for humans too – with the singular exception of female fertility. Whereas average life expectancy for women in the developed world is about 80 and among hunter-gatherers about 65 or 70, the mean last birth, in populations that do not use contraceptives, is just 38. By age 51, half of women have ceased ovulating, menstruating and producing the high levels of oestrogen associated with fertility; by age 60, more than 99 per cent have made the transition.
Two main hypotheses have been put forward to explain human menopause. The “mother hypothesis” suggests that at a certain point, a mother will do better in the genetic stakes by avoiding the risks associated with childbirth and additional child-rearing and instead concentrate on raising the kids she already has. This idea recognises the fact that human mothering is particularly demanding. We are able to produce babies at shorter intervals than other primates, and ours are born extremely needy: it takes them more than a decade to become independent. There is no doubt that motherless children are less likely to survive and that childbirth is risky. However, a woman who dies in childbirth compromises the survival chances of at most two or three dependent children, whereas early reproductive senescence guarantees that every woman forgoes the opportunity to produce at least two or three more babies. Even if menopause made sense in the light of the mother hypothesis, it need not happen so early: most women, both now and historically, not only live well past the maturity of their last born, they also see their grandchildren mature.
Is menopause the ghost of competition between successive generations?
Which leads to the second theory, the “grandmother hypothesis” . This suggests that a healthy grandmother, who is not burdened with dependent offspring, helps ensure the survival of her genes by contributing to the care of her extended genetic brood, her grandchildren. There is evidence that grandmothers really do make a difference to the survival chances of their grandchildren (Nature, vol 428, p 178) , but is this enough to compensate for the children they did not bear themselves? A woman passes on 50 per cent of her genes to her own child and only 25 per cent to a grandchild, so she would have to make a very substantial contribution indeed. Kim Hill at Arizona State University in Mesa and Magdalena Hurtado at the University of New Mexico in Albuquerque, calculated the genetic benefits of grandmothering as compared to continued reproduction for older women in the Ache tribe of Paraguay and concluded that they simply weren’t big enough to explain why women cease to reproduce so young (Human Nature, vol 2, p 315).
Even when the mother and grandmother benefits are added together, they are too small to justify such an early end of fertility, says Thomas Kirkwood, a gerontologist at the University of Newcastle, UK (BioEssays, vol 23, p 282). That’s where Cant’s idea comes in (Proceedings of the National Academy of Sciences, vol 105, p 5332).
Intrigued by this whole menopause debate, Cant and his colleague Rufus Johnstone at the University of Cambridge, UK, noted a striking oversight. Researchers were looking at the benefits and costs to the postmenopausal females, says Cant, but no one seemed to consider the costs to other women of the group. His work as a zoologist had made him mindful of the fact that in societies where females cooperate over child-rearing – where food is shared and non-mothers step in to assist in the care of young – you have to consider the costs and benefits to all the females, because all of them will be competing for the same scarce resources. “Reproductive competition has been overlooked in human studies,” says Cant. “It might give us insight into why women stop breeding when they do.”
The first clue that they could be onto something came when Cant and Johnstone mapped out the overlap in reproductive years between human generations. “It was such a striking pattern,” says Cant. “Although human mothers may survive for the majority of their daughters’ lifespan, they will continue to reproduce for at most a small fraction of their daughters’ reproductive span.” This sets humans apart from most primates (see diagram, right) but reproductive separation is found in other mammals. In mearcats and naked mole rats, for instance, mothers and daughters do not reproduce at the same time either. But here it’s the younger females that forgo reproducing in deference to the older ones. What is most unusual about humans, says Cant, is that it’s the other way round.
He and Johnstone were convinced that this lack of reproductive overlap in humans evolved to minimise reproductive conflict between the generations. So they began to study patterns of human dispersal, which determines the relationships between competing females within a social unit.
In most mammals, young males leave and join another group while young females stay with their mother. As they reach sexual maturity, females are highly related to the group, so have an incentive, in evolutionary terms, to help their mothers and aunts raise their siblings and cousins, rather than producing babies of their own. But humans seem to have evolved a different pattern.
According to Cant and Johnstone, several lines of evidence, including mitochondrial DNA and Y chromosome analysis, as well as studies of modern hunter-gatherers, suggest that in our ancestors it was overwhelmingly the females who moved. So older women were competing for resources with young women who had come from elsewhere. Cant points out that when a young woman leaves her family group and joins another, she is unrelated to anyone in her new home and is thus insensitive to the costs she might inflict on the older females by having children. As females age, however, they are increasingly related to the group, and have less to lose and more to gain by helping with the care and provisioning of the younger generation.
Did menopause evolve because older women found it less costly in evolutionary terms to forgo reproduction than their daughters-in-law did? “A system in which females become more related to their group as they age has this predicted outcome,” says Cant. He calls menopause the “ghost of reproductive competitions past”.
Menopause on–off switch
Wendy Saltzman, at the University of California, Riverside, is intrigued by the idea. In marmosets, the species she studies, subordinate females do not ovulate or copulate, in what she believes is a response to the threat of infanticide from more dominant individuals. However, there is a key difference between this and menopause: the marmoset’s condition is self-imposed and females can switch things back on when it is in their interest to do so, whereas menopause leaves women with no choice. “Why this inflexible reproductive shutoff instead of a plastic system?” she wonders.
Saltzman also questions how competitive human females actually are. “I would need to be convinced that there really was intensive competition,” she says. This doubt is shared by Sarah Blaffer Hrdy, an anthropologist at the University of California at Davis. “Not only is there no evidence of reproductive suppression,” she says, “There is reason to think women in small groups would benefit from the presence of a co-breeding female.”
There are also questions surrounding the issue of female dispersal. For one thing, this happens in two other primate species, yet they lack menopause. Our closest relatives, chimps and bonobos, both show the same migration pattern as ancestral humans, but instead of experiencing menopause, female fertility seems merely to decline slowly with age. However, Cant points out that unlike humans, they are not cooperative breeders so the same competition dynamics do not apply.
A second objection is harder to dismiss. Kristen Hawkes, at the University of Utah in Salt Lake City, disputes whether human migration patterns are really female-biased as Cant describes them. “He misrepresents the human data he cites.” She says that studies of modern hunter-gatherers show that many young females only leave their natal home after they have had a couple of babies, a detail that doesn’t fit well with the model proposed by Cant and Johnstone. Hrdy also takes issue with this. “Hunter-gatherers are famously flexible in their residence patterns,” she notes.
If all that weren’t bad enough, there is also the anomaly of killer whales – possibly the only other animal with clear-cut menopause followed by many more years of life. Killer whale society does not have female dispersal: both females and males stay with the natal group, and simply breed with members of other pods as they cross paths. Nevertheless, says Cant, in this case too, females become more related to their group as they age, giving older females greater incentives to forgo reproduction than younger females.
Cant and Johnstone are staunch in the face of their critics. “Female dispersal leads to asymmetry which leads to reproductive competition. But maybe that’s not the only, or even the main, driving force,” says Cant, and if the female dispersal idea fails,“the reproductive competition theory could still be right”. ~
