定制优秀宝宝,你准备好了吗?

你看过科幻电影《千钧一发》(Gattaca)吗?电影探讨了自由主义优生学的相关话题,其中的自由主义优生学本是一些帮助人们生育的技术,后来自然形成了这样一门学科。电影设定的时间是不久的将来,玛丽·弗里曼和安东尼奥·弗里曼夫妇走进一家医院,与医生一起决定他们的下一个宝宝应该是什么样的。 医生说:“玛丽,我们已经把你的卵子和安东尼奥的精子结合了,经过层层筛查,现在有四个胚胎可选,其中两个是健壮的男孩儿,两个是健康的女孩儿。” 此时,医生的显示屏上出现一个绿色的背景,其中有几个肥皂泡泡一样的东西互相碰撞着。 医生说:“他们肯定不会患常见的遗传病。现在要做的就是挑选一个最适合孕育的胚胎,也可以挑选性别,你们考虑过了这事儿了吗?” 玛丽说:“我们想给文森特生个弟弟,他们可以一起玩耍。”文森特是他们的第一个孩子。 医生附和了他们的决定,继续说道:“你们提出要褐色的眼睛,黑色的头发,白皙的皮肤。我斗胆排除了所有潜在的不利因素,包括过早秃顶、近视、酗酒、容易药物上瘾、暴力和肥胖倾向……” 玛丽打断他,说道:“我们确实不想让孩子生病,没问题。” 安东尼奥说:“嗯,我们在想是不是不用定得这么死,有些方面就随机而定吧。” 医生回答道:“孩子的起点自然是越高越好。要知道人类身上本来就有很多不足了,不需要再给孩子额外的困扰了。你们要记住,这个孩子还是你们的结晶,是最完美的结晶。自然怀孕一千次也生不成这么好的孩子。” 安东尼奥和马丽存在于电影里虚构的世界中,但是现实生活中了有许许多多跟他们想法相同的人,他们的愿望可能马上就能实现,其实从某方面来说,他们的愿望已经可以实现了。 1997年《千钧一发》首映时,医生们已经使用试管培养技术治疗不孕不育的男男女女十余年了。1978年,路易丝·布朗在英国诞生,她是世界首个“试管婴儿”。试管婴儿是卵子和精子在试管中受精后得来的,医生一次会制造出数个可成活的胚胎,然后将之植入女性的子宫中。首家试管婴儿诊所于1980年在美国开业,时至今日,美国已有数百家诊所提供相关服务。美国出生的婴儿中,超过1%都是通过试管受精而来。 在《千钧一发》播映的那几年,医生们正探讨另一个课题:如果可靠地使用“胚胎植入前的遗传学诊断(PGD)”帮助人们生育孩子。这项技术引起的争议更大。为了进行遗传学诊断,医生将试管受精而来的胚胎培养三天,这时胚胎有8个细胞,医生从中提取一个细胞,分析其中的DNA遗传物质,判断是否包含会引起重大疾病或衰弱的基因。有时,医生会多等两天,这时胚胎已发育成胚泡,变成一个中空的圆球,包含100多个细胞。医生提取5-20个细胞进行DNA检测。一般情况下,提取细胞后胚胎仍然可以正常发育。通过遗传学诊断,基本上可以完全排除可能因单个基因变异而患病的胚胎,如囊胞性纤维症、镰状细胞疾病、家族黑蒙性白痴、享廷顿舞蹈病,也可以完全定位唐氏综合征等因多出一条染色体而来的疾病。起初遗传学诊断主要是为那些极可能生出患病儿童的人服务的,因为有的病是家族遗传的,另外有些人身上正好出现了特定的基因变异。 有些夫妇为了救孩子的命,也使用试管受精和遗传学诊断技术生过孩子。美国至少有30家生殖诊所培育过“救星弟妹”,可以从这些孩子的脐带血中提取干细胞,用来治疗兄姐的白血病、范科尼贫血症、及其他致命疾病。患儿亲属捐献的干细胞所产生的免疫细胞,在基因上与患儿非常相似,使用这样的干细胞治疗,其成功率比使用陌生人的干细胞要高出很多。兄弟姐妹的免疫系统遗传自同样的父母,所以他们的细胞通常是完全匹配的,生殖诊所的医生也可以通过检查胚胎的DNA确保匹配。 这些诊所宣称,只有在父母们本来就想多要几个孩子的情况下才同意实行此措施,但是大部分选择这样做的父母只是绝望下的无奈之举。如此一来,一旦治疗失败怎么办?随之而来的失望之情会改变父母对“救星弟妹”的态度吗?一旦“救星弟妹”获知自身的存在只是为了救治另一个人的性命,他们的心理还能正常发育吗?2004年,茱迪·皮考特发行了小说《姐姐的守护者》,小说中13岁的救星妹妹安娜把父母告上了法庭,因为他们要求安娜为患白血病的姐姐凯特捐献肾脏。 预防疾病并不是人们选择遗传学诊断的唯一原因,借此技术,父母还可以按自己的喜好事先决定孩子的一些特征。有些父母使用遗传学诊断特意培养有残疾的孩子,如侏儒症或耳聋的孩子。在21世纪之初,一对女同性恋莎伦·杜勤诺和坎迪·麦卡洛四处寻找天生耳聋的精子捐献者,因为她们两个都有先天性耳聋。所有的精子银行都拒绝了她们的请求,他们不同意从耳聋的男子身上提取精子。最终,她们家里人认识的一个朋友捐献了精子。两人的儿子高文·麦卡洛出生于2001年11月,这个孩子几乎全聋,但是一只耳朵有些许听力。莎伦和坎迪认为耳聋并不是一种疾病或缺陷,而是一种身份、一种文化。很多医生和伦理学家却不认可,他们谴责两人故意剥夺了孩子的听觉。 这种情况毕竟不常见,一般情况下父母会花1万8千美金来决定孩子的性别。有时选择性别的目的是避免孩子患上因X染色体变异而来的疾病,女孩儿患这些病的几率较小,因为她们有两条X染色体,只要其中一条上的基因是正常的,就不会出现问题。但是大部分人跟《千钧一发》中的玛丽和安东尼奥一样,只是对男孩儿或女孩儿有偏好。有的人一连生了三个儿子,渴望有个女儿;有的人所处的文化环境严重地重男轻女。英国、加拿大及其他很多国家都禁止以医学以外的原因进行遗传学诊断,选择孩子的性别,但是这在美国是合法的。美国生殖医学会的官方政策是:“为了避免遗传疾病,可以在胚胎植入前进行性别选择,但是不能仅仅因为非医学原因进行选择。”但是2006年的一项调查表明,美国的186家生殖诊所中,58家允许父母凭喜好选择孩子的性别。这已经是7年前的数据了,最近没有相关统计,但是专家们说现在选择性别的热潮比以往任何时期都要高涨。 生殖研究所在洛杉矶、纽约、墨西哥的瓜达拉哈拉都有分部,研究所的主管杰弗里·斯坦伯格说:“美国的很多诊所允许以非医学的理由选择性别,每天都有人这么做,今天早上我们就选了三个。” 2009年,斯坦伯格对外宣布,除了性别,父母很快就能选择孩子的肤色、发色、瞳孔颜色了。给他底气的是冰岛著名生物公司“基因解码”所做的研究,该公司的科学家称,他们可以通过检测斯堪的纳维亚人的胚胎的DNA来判断其肤色、发色、瞳孔颜色。当时斯坦伯格在BBC的采访中说:“大家都得跟上潮流才行。”很多生殖学专家为此震怒。马克·休斯是胚胎植入前遗传学诊断领域的先锋,他在《圣地牙哥联合论坛报》的采访中说,斯坦伯格的想法非常荒谬,在《华尔街日报》的采访中,他说:“任何一个合法的实验室都不会这样做的,一旦这样做,他们必将被放逐。”基因解码公司的首席执行官卡利·斯蒂芬森也直白地在《华尔街日报》上表示:“我强烈反对使用这些发现来设计婴儿。”生殖研究所甚至还接到了梵蒂冈罗马教廷的电话,要求工作人员慎言慎行。斯坦伯格只好收回了自己的提案。 但是他并没有放弃,他清楚地知道父母可以在孩子出生前设计他们的外形,还有一些志同道合的医生、企业家支持他。斯坦伯格说:“我还是坚信人们应该充分利用遗传学的知识造福自身,但是我也得到了一个教训:事情得慢慢进行,很多人畏惧科学的进步。”最近,个人基因公司23andMe获得的一项专利引发了一小股狂热。该专利于9月24日审批通过,是一种通过对遗传信息的计算来选择匹配的精子或卵子的方法。23andMe公司会先把客户及数个精子或卵子捐献者的DNA进行排序,然后计算哪个人的捐献物最适合,最能达成某些条件。 该专利的说明中包括以下选择:“我想要一个结肠直肠癌发病风险低的孩子。”“一个极可能是绿眼睛的孩子”、“绝对是短跑健将”、“长命百岁”、“生病花钱的可能最小”。以上都被列为可能性,因为23andMe公司称,他们的技术在通常情况下不能确保孩子的确切特征。他们的计算基于对两个成年人的基因组的分析,DNA是从他们的血液或唾液中获取的,但是却与他们精子、卵子中的基因一致。每个成熟细胞中都有两条染色体,包括这个人的所有基因;然而精子和卵子中却只有一条染色体,染色体上分配到每个基因具体是哪一种却是随机的。因此,每个精子和卵子所含的基因组合都是独一无二的。如果不破坏精子和卵子,科学家是无法对其中的DNA进行排序的。 23andMe公司的发言人凯瑟琳·阿法瑞恩在声明中说:“起初我们在介绍这种工具、申请专利的时候也想过它可能被生殖诊所使用,但是我们从未做过这方面的研究,以后也不会做。”无论如何,医生已经可以用遗传学诊断技术达成23andMe公司提出的一些设想了,现在的父母已经可以像电影中的弗里曼夫妇一样选择一些东西了。即使现在达不到目的,不久的将来也肯定可以。 从2009年斯坦伯格的提案遭到反对以来,研究人员对哪些基因控制人体哪些地方的颜色已经有了更深入的了解。荷兰伊拉斯姆斯大学医学中心的法医遗传学家曼弗雷德·凯瑟和同事已经发表了多项研究,他们通过检测DNA精确地判断出人的瞳孔颜色及发色。他们的测试方法还无法识到所有的颜色,但是已经足够辨别棕色、蓝色和蓝棕混合的瞳色了,他们还能辨别棕色、黑色、金色、红色的头发。他们的研究旨在破案,但是生殖诊所的医生可以轻易地将这些方法用于胚胎植入前的遗传学诊断。根据现有的研究,曼弗雷德认为科学家很快就能够准确地通过DNA判断人的肤色了。他还说,在过一段时间,科学家们也许就能够推断出人们的发质、脸形、身高等信息了。 目前已经可以通过基因分析判断胚胎是不是会出现一些生理上的奇特现象,这些现象对有的人来说很迷人,对有的人来说却很平常。例如,某人会不会出现“亚裔脸潮红”。ALDH2这个基因控制着一种叫做乙醛脱氢酶的酶,它可以把酒精代谢产生的有毒副产品转化成良性的酸。如果某人的两个ALDH2基因只有一个发挥作用或者都不发挥作用,那么他喝酒后就会恶心、脸红。50%的东亚人的乙醛脱氢酶不活跃。基因测试还可以比较轻易地判断胚胎的耳垢是否会浓稠,因为这是由一个单一的基因决定的。该基因的一种形态使耳朵分泌粘稠的琥珀色耳垢,另一种形态使耳朵分泌干的、灰色薄片状耳垢。还有一种基因,可以单独决定人能不能忍受苦味的食物,如球芽甘蓝、咖啡、卷心菜等等。 这些例子中,基因和人体特征之间的联系都比较直观易懂,其实大部分基因是复杂而难以理解的。人体的大部分体表特征,哪怕是看起来很简单的耳垂形状、酒窝、发旋都受到多个基因的交叉影响,大大超乎研究者的想象,成了难解的谜题。正因如此,直到最近科学家们才能够准确地通过DNA判断眼睛、头发的颜色。在高中你可能接触后孟德尔的遗传学说,说眼睛的颜色是由一个或两个显性的棕色基因或两个隐性蓝色基因决定的。事实上,影响瞳孔颜色的基因超过10个。所以,想要知道智力、性格这种复杂的潜力,可能永远也研究不出可用的基因测试方法了。在可以预见的将来,定制的宝宝也许只能确定一些基本的外形特征,比如脸和身体的颜色及形状,但是对于很多父母来说这可是相当重要。 使用试管受精和胚胎植入前遗传学诊断的方式来定制宝宝还是有很多局限的,说到底遗传学诊断并不能按照父母的要求主动地改变胚胎的DNA,父母只能从培育出的数个胚胎中挑选出他们认为最好的那个。而且医生只能给从女性卵巢中提取的卵子授精,多了没有。目前,为了进行试管受精,平均可以采集8-15个卵子,这已经能够给父母很多选择了,但是还不足以确保某个胚胎同时具备父母想要的多个特征。 但是,科学家还在继续从各个方面研究人类的基因组,他们肯定还能发现新的基因联系,也许相关技术还不足以确保某个特征,但是至少能够提高可能性。23andMe公司称,通过给DNA排序,可以了解你身上的60个“特征”,其中很多都是体格特征或某种天赋。随着这些知识的不断揭露,有些人可能经不住诱惑,即使相关研究还在初期阶段他们也敢尝试。生殖诊所可以利用这些发现,谨慎地给父母一些新的选择,他们不仅能选择孩子的性别,还能让天平稍稍倾斜,就像《千钧一发》中的医生说的那样,让“孩子的起点越高越好”。人们会口耳相传,一些富裕的父母可能会认为,他们的选择将决定孩子要面对完全未知的未来,还是至少在某个方面有了优势。1997年《千钧一发》在剧场上映的时候,剧中的很多方面还不可能实现,现在已经实现一部分了。今日我们的社会之所以无法成为电影中的那样,问题不在于科学技术的发展,而是在于人们对相关科技的态度,这是更为微妙的一个领域。 2003年,白宫科学技术政策办公室的法医学助理专管塔尼娅·西蒙切利写道:“胚胎植入前的遗传学诊断技术得以自由发展,因此父母和生殖学专家对孩子的基因控制水平越来越高,达到了前所未有的程度。事实上,如果有所谓一个接一个的虚假因果关系形成的‘滑坡谬论’,这就是一例。遗传学诊断技术的发展,加上克隆和基因工程技术,带来了新的优生学潮流。当年纳粹党人通过国家推行类似的优生学,而这个新潮流却是个人和市场导向的。孩子正成为客户定制的商品。” 在市场导向的优生学潮流中,所谓的英才教育将被彻底消灭。坚持不懈、适应力强、自我完善这些素质将败给人们所认为的天赋才能,败给由基因保证的成功。在《千钧一发》中,虽然法律禁止对基因进行歧视,那个世界中的人却是清楚地分为两个阶层的。“合法者”拥有正确的基因、最好的工作、最高的生活质量;“不合法者”是自然生育的,他们只能做下贱的工作,相对来说很贫困。电影中的优生学还有一定的风险,即可能制造出一大群基因类似的人,相对于基因多样的人群,他们更容易患某些疾病、更容易发生某些基因突变。 然而,电影会不会是未来真实世界的预演?我们对此有信心吗? 斯坦伯格说:“人们的需求正在上升,人们的想法越来越倾向于自由主义,将来几乎每个胚胎都要经过遗传学诊断。”

Are We Too Close to Making Gattaca a Reality?

The Freemans are characters in the science fiction film Gattaca, which explores liberal eugenics as an unintended consequence of certain technologies meant to assist human reproduction. Sometime in the not-too-distant future, Marie and Antonio Freeman step into a doctor’s office to design their next child. “Your extracted eggs, Marie, have been fertilized with Antonio’s sperm,” the doctor says. “After screening we’re left with, as you see, two healthy boys and two very healthy girls.” A monitor displays what looks like soap bubbles that bumped into each other on a green background. “Naturally, no critical predispositions to any of the major heritable diseases,” the doctor says. “All that remains is to select the most compatible candidate. We might as well start with gender—have you given it any thought?” “We would want Vincent to have a brother, you know, to play with,” Marie says, referring to her first child. Acknowledging this, the doctor continues: “You have specified hazel eyes, dark hair and fair skin. I have taken the liberty of eradicating any potentially prejudicial conditions: premature baldness, myopia, alcoholism and addictive susceptibility, propensity for violence and obesity—” “We didn’t want—I mean, diseases, yes,” Marie interrupts. “Right, we were wondering if it’s good to leave a few things to chance,” Antonio says. “You want to give your child the best possible start,” the doctor replies. “Believe me, we have enough imperfection built-in already. Your child doesn’t need any additional burdens. And keep in mind, this child is still you, simply the best of you. You could conceive naturally a thousand times and never get such a result.” Although Antonio and Marie do not exist outside the movie’s imaginary universe, their real-life counterparts could be walking among us sooner than we think—and, in a sense, they already are. When Gattaca premiered in 1997, doctors had been using laboratory techniques to help women and men overcome infertility for more than a decade. In 1978, Louise Brown of the U.K. became the world’s first “test tube baby”—the first person conceived through in vitro fertilization (IVF), a procedure in which sperm and eggs are combined in the lab to create several viable embryos that are subsequently implanted in a woman’s womb. The first IVF clinic opened in the U.S. in 1980. Today, hundreds of fertility clinics in the country offer IVF and more than one percent of children born in the U.S. are conceived this way. In the years surrounding Gattaca’s release, doctors were also talking about how to responsibly use another, more controversial technique to help people have children: preimplantation genetic diagnosis (PGD). In this procedure, clinicians vacuum up one of eight cells in a three-day-old embryo created through IVF and analyze the DNA within to find genes associated with debilitating and potentially fatal diseases. Sometimes, doctors wait two more days, when the embryo has become what is known as a blastocyst—a mostly hollow ball of around 100 cells—and collect between 5 and 20 cells for DNA analysis. In most cases, this extraction does not significantly disturb the embryo’s development. PGD can identify embryos that will almost certainly develop disorders caused by a mutation in a single gene, such as cystic fibrosis, sickle cell disease, Tay-Sachs and Huntington’s, as well as disorders that result from an extra chromosome, such as Down syndrome. From its earliest days, PGD has been principally intended for people who have a high risk of conceiving a child with a particular disorder, because it runs in the family or because they happen to harbor a certain genetic mutation. Couples have also created one child through IVF-PGD in order to save another. At least 30 fertility clinics in the U.S. will help parents conceive a “savior sibling”—a child whose umblical cord blood can be harvested as a source of stem cells to treat leukemia, Fanconi anemia or another terrible illness in his or her older sibling. An infusion of stem cells donated by a relative whose immune cells are genetically similar to those of the sick child has a much better chance of succeeding than cells from a stranger. Siblings inherit their immune system genes from the same parents, so they are sometimes an almost exact immunological match—something doctors at fertility clinics can determine by looking at an embryo’s DNA. Nominally, clinics agree to help parents in this way only if the couple had always intended to have several children. But some parents in this situation undoubtedly alter their original family plan out of desperation. So what happens if the treatment fails? How will the inevitable disappointment change the way parents feel about their second child? And how does learning that one’s entire existence hinges on saving someone else’s life warp the psychological development of a child or young adult? In Jodi Picoult’s 2004 novel My Sister’s Keeper, thirteen-year-old savior sibling Anna sues her parents for medical emancipation when they ask her to donate a kidney to her older sister Kate, who has leukemia. Preventing and treating diseases are not the only reasons people have turned to pre-implantation genetic diagnosis. PGD also makes it possible for parents to predetermine characteristics of a child to suit their personal preferences. In a few cases, people have used PGD to guarantee that a child will have what many others would consider a disability, such as dwarfism or deafness. In the early 2000s, lesbian couple Sharon Duchesneau and Candy McCullough—both deaf from birth—visited one sperm bank after another searching for a donor who was also congenitally deaf. All the banks declined their request or said they did not take sperm from deaf men, but the couple got what they were looking for from a family friend. Their son, Gauvin McCullough, was born in November 2001; he is mostly deaf but has some hearing in one ear. Deafness, the couple argued, is not a medical condition or defect—it is an identity, a culture. Many doctors and ethicists disagreed, berating Duchesneau and McCullough for deliberately depriving a child of one of his primary senses. Much more commonly, hopeful parents in the past decade have been paying upwards of $18,000 to choose the sex of their child. Sometimes the purpose of such sex selection is avoiding a disease caused by a mutation on the X chromosome: girls are much less likely to have these illnesses because they have two X chromosomes, so one typical copy of the relevant gene can compensate for its mutated counterpart. Like Marie and Antonio Freeman in Gattaca, however, many couples simply want a boy or a girl. Perhaps they have had three boys in a row and long for a girl. Or maybe their culture values sons far more than daughters. Although the U.K., Canada and many other countries have prohibited non-medical sex selection through PGD, the practice is legal in the U.S. The official policy of the American Society of Reproductive Medicine is as follows: “Whereas preimplantation sex selection is appropriate to avoid the birth of children with genetic disorders, it is not acceptable when used solely for nonmedical reasons.” Yet in a 2006 survey of 186 U.S. fertility clinics, 58 allowed parents to choose sex as a matter of preference. And that was seven years ago. More recent statistics are scarce, but fertility experts confirm that sex selection is more prevalent now than ever. “A lot of U.S. clinics offer non-medical sex selection,” says Jeffrey Steinberg, director of The Fertility Institutes, which has branches in Los Angeles, New York and Guadalajara, Mexico. “We do it every single day. We did three this morning.” In 2009 Steinberg announced that he would soon give parents the option to choose their child’s skin color, hair color and eye color in addition to sex. He based this claim on studies in which scientists at deCode Genetics in Iceland suggested they could identify the skin, hair and eye color of a Scandinavian by looking at his or her DNA. “It’s time for everyone to pull their heads out of the sand,” Steinberg proclaimed to the BBC at the time. Many fertility specialists were outraged. Mark Hughes, a pioneer of pre-implantation genetic diagnosis, told the San Diego Union-Tribune that the whole idea was absurd and the Wall Street Journal quoted him as saying that “no legitimate lab would get into it and, if they did, they’d be ostracized.” Likewise, Kari Stefansson, chief executive of deCode, did not mince words with the WSJ: “I vehemently oppose the use of these discoveries for tailor-making children,” he said. Fertility Institutes even received a call from the Vatican urging its staff to think more carefully. Steinberg withdrew his proposal. But that does not mean he and other likeminded clinicians and entrepreneurs have forgotten about the possibility of parents molding their children before birth. “I’m still very much in favor of using genetics for all it can offer us,” Steinberg says, “but I learned a lesson: you really have to take things very, very slowly, because science is scary to a lot of people.” Most recently, a minor furor erupted over a patent awarded to the personal genomics company 23andMe. The patent in question, issued on September 24th, describes a method of “gamete donor selection based on genetic calculations.” 23andMe would first sequence the DNA of a man or woman who wants a baby as well as the DNA of several potential sperm or egg donors. Then, the company would calculate which pairing of hopeful parent and donor would most likely result in a child with various traits. Illustrations in the patent depict drop down menus with choices like: “I prefer a child with Low Risk of Colorectal Cancer; “High Probability of Green Eyes;” “100% Likely Sprinter;” and “Longest Expected Life Span” or “Least Expected Life Cost of Health Care.” All the choices are presented as probabilities because, in most cases, the technique 23andMe describes could not guarantee that a child will or will not have a certain trait. Their calculations would be based on an analysis of two adults’ genomes using DNA derived from blood or saliva, which does reflect the genes inside those adults’ sperm and eggs. Every adult cell in the human body has two copies of every gene in that person’s genome; in contrast, sperm and eggs have only one copy of each gene and which copy is assigned to which gamete is randomly determined. Consequently, every gamete ends up with a unique set of genes. Scientists have no way of sequencing the DNA inside an individual sperm or egg without destroying it. “When we originally introduced the tool and filed the patent there was some thinking the feature could have applications for fertility clinics. But we’ve never pursued the idea, and have no plans to do so,” 23andMe spokeswoman Catherine Afarian said in a prepared statement. Nevertheless, doctors using PGD can already—or will soon be able to—accomplish at least some of what 23andMe proposes and give parents a few of the choices the Freemans made about their second son. Since Steinberg’s contentious proposal in 2009, researchers have developed a much clearer understanding of the various genes responsible for the pigments in our bodies. Forensic geneticist Manfred Kayser of Erasmus MC and his colleagues have published many studies in which they have accurately identified people’s eye and hair color by looking at their DNA. Their tests cannot recognize every possible shade, but they are specific enough to distinguish between brown, blue and mottled brown-blue eyes, as well as brown, black, blonde and red hair. Such studies are intended to help solve crimes, but clinicians at fertility clinics could easily adapt the strategies for PGD. Based on ongoing research, Manfred thinks he and other scientists will soon be able to confidently identify skin color by looking at someone’s genes as well. In the more distant future, he adds, researchers will probably learn enough to deduce the texture of a person’s hair, the shape of his or her face, and the person’s height. Today, genetic analysis can also reveal the likelihood of various quirks of human biology that some people find fascinating and others might consider trivial. Take, for example, the probability that someone will experience “Asian glow.” The ALDH2 gene codes for an enzyme named aldehyde dehydrogenase that converts a toxic byproduct of alcohol metabolism into a benign acid. People with only one or no working copies of the gene feel nauseated and flush red when they drink alcohol. Around 50 percent of East Asians have underactive aldehyde dehydrogenases. Earwax consistency is also relatively easy to predict with a genetic test because it is controlled by a single gene: one version of the gene produces sticky amber ear wax; the other makes dry, gray, flaky earwax. A single gene also largely determines one’s ability to taste certain bitter compounds commonly found in Brussels sprouts, coffee, cabbage and other foods. These examples of relatively straightforward relationships between genes and traits are exceptions to the daunting complexity of human genetics. Most characteristics of the human body—even seemingly simple ones like earlobe attachment, dimples and hair whorls—have stumped researchers with far more convoluted genetics than they anticipated. That’s why confidently reporting eye and hair color based on DNA is a relatively recent accomplishment. In high school, you may have learned that eye color is a simple Mendelian trait in which one or two dominant copies of a gene produces brown eyes whereas two recessive versions result in blue eyes. In fact, more than a dozen genes likely interact to determine the hue of your iris. So, when it comes to something as multi-faceted as intelligence or personality, we may never have a particularly useful predictive genetic test. For the foreseeable future, then, any possibility of designer babies may be limited to rather basic—though, to many parents, important—human features: essentially, the shape and color of a child’s face and body. IVF presents another set of barriers to tailor-making children through PGD. After all, PGD does not entail actively engineering DNA inside an embryo to fit parents’ specifications; rather, parents select what they consider the most desirable genetic package from a group of successfully fertilized embryos. And clinicians can only fertilize as many eggs as they collect from a woman’s ovaries Currently, IVF retrieves between 8 and 15 eggs on average—enough to provide parents with quite a few options, but not a large enough number to ensure that any one embryo will have more than a handful of desired traits. As scientists continue to examine the human genome from every angle, however, they will undoubtedly uncover new genetic associations that—if they cannot promise a particular feature—will at least divulge a probability. 23andMe claims that, by sequencing your DNA, it can tell you something interesting about 60 “traits,” many of which are physical characteristics or talents of some kind. As that type of knowledge continues to surface, some people will not be able to resist it, even when it rests only on a few preliminary studies. A clinic could take advantage of these insights to discreetly give couples the option of choosing more than just the sex of their child through PGD, framing it as a way to tip the scales, to—as the doctor in Gattaca says—give one’s child “the best possible start.” One couple would tell another. Some parents—especially the wealthy—may begin to believe they have a choice between leaving their child’s future completely to chance and helping that child in at least some small way. When Gattaca appeared in theaters in 1997, much of what the film depicted was not yet possible. Now, some of it is. What separates our society from a proto-Gattaca today is not so much scientific understanding or technology as people’s attitudes towards that technology—a much more delicate membrane. “Unfettered development of PGD applications is providing parents and fertility specialists an increasing and unprecedented level of control over the genetic make-up of their children,” wrote Tania Simoncelli, Assistant Director for Forensic Sciences within the White House Office of Science and Technology Policy, in 2003. “Indeed, if ever there was a case for a ‘slippery slope,’ this is it. Advances in PGD, together with cloning and genetic engineering, are tending towards a new era of eugenics. Unlike the state-sponsored eugenics of the Nazi era, this new eugenics is an individual, market-based eugenics, where children are increasingly regarded as made-to order consumer products.” An era of market-based eugenics would exterminate any lingering notions of meritocracy. Perseverance, adaptability, and self-improvement would become subordinate to what people would see as innate talent and near certain prosperity preordained by one’s genes. Despite laws meant to prevent genetic discrimination, the world of Gattaca is a highly stratified one with two distinct classes: the valids—who have the right genes, the most prestigious jobs and the highest quality of life—and the in-valids, who were conceived in the typical fashion and are relegated to menial work and relative poverty. Eugenics also risks creating a genetically homogenous population that is far more vulnerable to disease and freak deleterious mutations than a diverse one. But that could never happen this side of the silver screen, right? “The demand is up,” Steinberg says. “People are liberalizing. You will see PGD done on almost every embryo in the future.”