人类肥胖是进化中出现的错误
进化论宣称：物竞天择，适者生存。然而，我们可以将如今最严重的一些健康问题归咎于人类的进化，如癌症、肥胖症、糖尿病和心血管疾病等。
2009年一项盖洛普(Gallup)民意测验发现，44%的美国人相信，上帝在过去一万年间创造出有着如今这个模样的人类，而且他们中的许多人还认为，人体的设计是完美无瑕的。
不过，大多数科学家──包括生物学家、人类学家、古生物学家和遗传学家──都认为，21世纪的人类身体是一系列妥协的产物，是我们祖先为适应不断变化的环境所做出的应急性演化的结果。
“从很多方面来说，我们的身体为适应人类社会的现代化进程而做出了错误的演化。”耶鲁大学(Yale University)进化生物学家斯特恩斯(Stephen Stearns)说道。他和该领域的其他科学家正在督促各大医学院在培养研究现代疾病的医生时引入更多的进化学理论。
举例而言，免疫系统旨在帮助人体抵抗疟疾和霍乱等流行病，这类疾病都是伴随着人类城市化进程而产生的。根据“卫生假设”(hygiene hypothesis)理论，哮喘和各类自身免疫病的患病人群在不断增长，原因在于如今人类所处的环境更为清洁，人体免疫系统没有接触到足够多的外部挑战，反而与人体自身的生理系统打起仗来。
肥胖症现在如此普遍，也有其史前时期的人类进化根源。我们的祖先靠打猎和采集植物果实为生，摄取其中的养份和蛋白质，因此他们身材修长，擅长长途奔跑。大约一万年前，人类进入农业社会时期，主流的饮食结构也相应转向碳水化合物较为丰富的食物。早期的农业耕作者卡路里摄入较多，但营养不足，男性的平均身高从1米75下降到1米60，女性的平均身高从1米65下降到1米52。新陈代谢方面的演化是以千年纪为时间轴的，但较近期转入农业社会的人口群体，如波利尼西亚人和印第安人，现在患上肥胖症和II型糖尿病的比率最高。
哥伦比亚大学医学中心(Columbia University Medical Center)的肥胖症专家雷贝尔(Rudolph Leibel)称，甚至连“溜溜球节食”（yo-yo dieting，即体重反复增减）这一现象也脱离不了进化的影响。他是“瘦素”(leptin)的发现者之一，这种荷尔蒙通常能向人体发出停止进食的信号。当人们节食时，体内瘦素水平急剧减少，启动一连串生理变化，导致人体燃烧更少的卡路里并恢复原先的体重。“这在饥荒时期很管用，如今却已不合时宜。” 雷贝尔教授说道。
由于人类遭受猛兽袭击的威胁减少以及抵御疾病能力的提高，其寿命变得更长，从而给细胞发生病变提供更多的机会。生殖性肿瘤可能就是人类寿命延长和社会文化演变的产物。在以往的历史长河中，女性终其一生一般只有100次月经周期，因为频繁的怀孕和哺乳活动会阻止月经来潮。如今，女性一般都要经历400 次月经周期，从而给卵巢带来更大的压力，并导致乳房承受更多的荷尔蒙分泌波动。
攻击或逃离的反应机制(fight-or-flight mechanism)是祖先留给我们的最著名遗产之一。当人类大脑感知到危险时，这种反应机制会促使身体分泌肾上腺素、皮质醇和其他荷尔蒙，导致肌肉紧张、血管收缩、消化道放缓以及心跳加速。在我们祖先逃离猛口象的时候，这种机制很有用，但如今人们往往在电脑旁边工作，反而变得有害无利。
甚至连焦虑型噩梦──如梦到没有复习就参加考试，或者从悬崖摔下来──可能也有祖先留下的影子。因为在古代，人们必须在晚上守夜，以防止猛兽的攻击。哈佛大学(Harvard University)心理学家及《梦境》(Dreams)杂志的编辑巴雷特(Deirdre Barrett)说道。
研究全世界范围遗传变异的科学家们表示，在过去一万年到四万年间，人类约有1,800个基因（占人类基因组的7%左右）已在发生快速演变，其中很多基因演变所带来的影响我们还不太清楚，但研究人员已经发现，有几项变异能令人类更适宜生存并凭借遗传得以存续。
较近期的许多基因突变是人类对传染疾病所做出的反应，尤其是当人们开始大规模聚居的时候。在非洲，过去一万年来出现了25种新的基因变种以及一个全新的血型，以帮助人们抵抗疟疾的侵扰。现在，约有10%的欧洲人出现基因变异，使其能对艾滋病病毒免疫。
然而，很多对人类有利的进化也伴随着一些弊端。举例而言，我们很早就知道，让一些非洲人免受疟疾侵扰的基因变异会让他们更易患上镰状细胞性贫血。那些让早期非洲人保留体内盐分以防在热带气候环境下脱水的基因，现在却让一些美国黑人容易患上高血压病。
在人类发展历史中，人体的一些组成部分曾经发挥过有利作用，如今却在拖我们的后腿。德州理工大学(Texas Tech University)的遗传学家海尔德(Lewis I. Held Jr.)将这种现象称为“bislagiatt”，这个词由“但当时觉得是个好主意”(but it seemed like a good idea at the time)所对应的英文单词首字母缩写组成。
在其著作《人体解剖学怪谈》(Quirks of Human Anatomy)中，海尔德教授列举了这类“时过境迁”的人体部件，如男性睾丸，它们悬挂在体表之外，因为精子在温度稍低的环境下更易成长，但这使得男性更容易遭受生殖器创伤。
对女性来说，产妇的狭窄骨盆（目的是支撑身体直立行走）与新生儿的大脑袋（有助于婴儿今后的认知发展）存在不匹配的情形，从而导致分娩是一个痛苦而且有时候很危险的过程。
科学家认为，阑尾是灵长类动物体内的一个发酵温床，有助于肠道有益细菌的繁殖。然而，由于人类饮食的多样化以及很少再吃生食，阑尾对人体的作用越来越小。
人类的嘴部也存在进化不平衡的问题。我们的祖先进入农业社会后，饮食结构从肉类和植物为主转为碳水化合物为主，因此牙齿出现较大程度的缩小。然而，人类下巴的缩小幅度更大，让智齿几乎变得没有用处，反而让现代人的脸部显得有些拥挤。
那么，为什么长期的人类进化没有改正这些弊病？“人体的很多功能还没有触发物竞天择的进化规则，”海尔德教授说道。也就是说，它们在人类进入生育年龄前所造成的问题还不够大，不影响人类的生存，因此就一代代地遗传下去了。一些专家认为，智齿和阑尾可能正在慢慢退出，有些婴儿出生时就没有智齿和阑尾，因为它们有时候会引起威胁生命的细菌感染。
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