生命史理論：進(jìn)化視角下的生命發(fā)展觀*

林鎮(zhèn)超 王 燕

(復(fù)旦大學(xué)心理學(xué)系, 上海 200433)

1 引言

以往的人類個(gè)體發(fā)展學(xué)說(shuō)習(xí)慣性地把身體結(jié)構(gòu)和生理功能的發(fā)展視為一種純粹的生物性過(guò)程,而傳統(tǒng)的心理學(xué)理論只是把上述生物性過(guò)程視為心理發(fā)展的基礎(chǔ), 相對(duì)忽視了心理因素對(duì)生物性發(fā)展的影響。

一方面, 傳統(tǒng)的生物學(xué)理所當(dāng)然地認(rèn)為人類個(gè)體會(huì)按照固定的生命歷程(life course)進(jìn)行生物性上的發(fā)展。例如, 人類嬰兒剛出生時(shí)非常被動(dòng),經(jīng)過(guò)相當(dāng)長(zhǎng)的一段成長(zhǎng)期后青春期才會(huì)到來(lái), 女性相比于男性會(huì)經(jīng)歷較長(zhǎng)的后生殖期(亦即停經(jīng))。另一方面, 盡管傳統(tǒng)的發(fā)展心理學(xué)強(qiáng)調(diào)認(rèn)知能力的發(fā)展以生理功能的發(fā)展為基礎(chǔ), 從而擺脫了身心二元論的嫌疑, 但是其依然遵循單方向作用的原則思考身體發(fā)展對(duì)心理發(fā)展的影響, 而從未系統(tǒng)地考慮心理因素對(duì)于身體發(fā)展的意義。例如,主流的心理學(xué)理論在探討兒童經(jīng)歷對(duì)個(gè)體成長(zhǎng)的影響時(shí)往往只考慮行為層面或心理層面的作用機(jī)制(例如, 母親敏感性對(duì)兒童依戀風(fēng)格的影響)。然而, 健康心理學(xué)關(guān)于心理因素作用于生理因素的研究(Matarazzo, 1980, 1982; Taylor, 1999)卻表明,身體和心理是相互作用的整體。

可見(jiàn), 傳統(tǒng)的從個(gè)體生命歷程角度進(jìn)行的研究割裂了生理與心理的統(tǒng)一, 但是越來(lái)越多的實(shí)證研究支持二者的整體性, 這是現(xiàn)有研究所忽視的最大的認(rèn)識(shí)論上的問(wèn)題。

在具體的研究領(lǐng)域, 童年經(jīng)歷、擇偶、性行為以及父母教養(yǎng)等問(wèn)題的傳統(tǒng)心理學(xué)研究, 特別是在依戀理論框架下的研究早已碩果累累。盡管依戀理論已經(jīng)成為人格發(fā)展研究、情緒發(fā)展研究、親密關(guān)系研究以及其他眾多的心理學(xué)研究的主導(dǎo)性理論框架(Mikulincer ＆amp; Shaver, 2007; Cassidy ＆amp;Shaver, 2008), 但是這些研究都共同存在一些顯而易見(jiàn)的問(wèn)題。第一, 過(guò)分關(guān)注個(gè)體成長(zhǎng)的人際環(huán)境而忽視客觀的物質(zhì)條件(例如, 父親工作的穩(wěn)定性或者家庭居住場(chǎng)所的穩(wěn)定性), 實(shí)證研究早已表明, 后者的個(gè)體差異也非常明顯且對(duì)個(gè)體的發(fā)展同樣具有重要影響(Belsky, Steinberg, ＆amp; Draper,1991; Chisholm, 1996a, 1999b; Edgarton, 1992; Foley,1992); 第二, 過(guò)分強(qiáng)調(diào)依戀對(duì)于個(gè)體生存(甚至種群的生存)而言的進(jìn)化意義, 而忽視絕大多數(shù)進(jìn)化理論特別注重的繁衍功能(Belsky, 2007; Belsky et al., 1991; Chisholm, 1996, 1999a, 1999b)。

承認(rèn)、贊美達(dá)爾文的自然選擇進(jìn)化論思想(Bowlby, 1991)并將其作為理論基礎(chǔ), 是依戀理論歷久彌新, 牢牢占據(jù)學(xué)術(shù)主流的根本原因。不幸的是, 當(dāng)Bowlby著手研究依戀的時(shí)候, 人們對(duì)進(jìn)化的認(rèn)識(shí)依然只停留在達(dá)爾文時(shí)代的現(xiàn)象學(xué)和解剖學(xué)水平。因而, 依戀理論需要在更高一個(gè)層面來(lái)整合進(jìn)化學(xué)領(lǐng)域的新進(jìn)展并重新審視依戀的進(jìn)化性功能(Simpson ＆amp; Belsky, 2008)。

針對(duì)上述問(wèn)題, 本文將從進(jìn)化的角度系統(tǒng)地介紹一種可能的、比較綜合的生命發(fā)展理論：生命史理論(life history theory; Belsky, 2007; Belsky,2010; Belsky et al., 1991; see also Charnov, 1993;Daan ＆amp; Tinbergen, 1997; Roff, 1992, 2002; Stearns,1992)。它既對(duì)傳統(tǒng)的依戀研究進(jìn)行了擴(kuò)展, 又解決了生理與心理統(tǒng)一性的問(wèn)題。更確切地說(shuō), 生命史理論并非是一個(gè)完整的理論, 而是一個(gè)有待充實(shí)的、龐大的理論框架。

2 生命史理論

如何在關(guān)乎生存和繁衍的各種生命活動(dòng)中有效地分配時(shí)間、資源和能量, 是地球上每一個(gè)有機(jī)體都必須面臨的最基本的挑戰(zhàn)(Charnov, 1993;MacArthur ＆amp; Wilson, 1967; Roff, 1992, 2002;Schaffer, 1983; Stearns, 1992)。例如, 過(guò)多地參與社會(huì)競(jìng)爭(zhēng)會(huì)影響有機(jī)體的免疫能力, 在教養(yǎng)子女上的付出會(huì)占用個(gè)體尋求新配偶的時(shí)間和資源。對(duì)此, 進(jìn)化學(xué)家和生態(tài)學(xué)家提出了生命史理論來(lái)對(duì)這個(gè)問(wèn)題進(jìn)行“怎么樣(how)”和“為什么(why)”兩個(gè)層面的回答。

在分配時(shí)間、資源和能量的過(guò)程中, 個(gè)體必須在軀體努力(somatic effort)和繁衍努力(reproductive effort)之間做出適應(yīng)于特定環(huán)境的最基本的權(quán)衡(Griskevicius, Delton, Robertson ＆amp;Tybur, 2011; Griskevicius, Tybur, Delton, ＆amp; Robertson,2011)。軀體努力是指?jìng)€(gè)體在維持和發(fā)展生理系統(tǒng)和物化資本(embodied capital; 例如, 知識(shí)、技能)上的投入, 可細(xì)分為軀體的維持(bodily maintenance)和成長(zhǎng)(growth)兩個(gè)維度; 繁衍努力是指?jìng)€(gè)體在同性競(jìng)爭(zhēng)、求偶、繁衍以及子女教養(yǎng)上的投入, 可進(jìn)一步分為擇偶(mating)和后代教養(yǎng)(parenting)兩個(gè)方面(Kaplan ＆amp; Gangestad, 2005; Griskevicius,Delton et al., 2011; Griskevicius, Tybur et al., 2011;Simpson, Griskevicius, Kuo, Sung, ＆amp; Collins, 2012)。這兩者是既相互關(guān)聯(lián)但又存在資源分配矛盾的不同的生命發(fā)展方向。

為了更形象地描述軀體努力和繁衍努力之間的關(guān)系, Kenrick和Luce (2000)將這個(gè)最基本的生命史權(quán)衡類比于一個(gè)銀行賬戶。軀體努力類似于存款, 而繁衍努力則代表取款?！按婵睢迸c“取款”是相互關(guān)聯(lián)的：一個(gè)更大的存款有利于將來(lái)的取款, 就好比一個(gè)有機(jī)體為了將來(lái)更好地繁衍而不斷提高軀體資本的積累(例如, 保持身體健康、獲取高學(xué)歷、得到體面的工作有利于提高追求高質(zhì)量配偶的成功率并為后代的生養(yǎng)提供堅(jiān)實(shí)的物質(zhì)保障)。然而, “存款”與“取款”之間的銜接又有時(shí)間風(fēng)險(xiǎn)：在不穩(wěn)定的環(huán)境中, 戰(zhàn)爭(zhēng)動(dòng)亂、經(jīng)濟(jì)波動(dòng)等都可能導(dǎo)致存款努力所希望達(dá)到的預(yù)期破滅(例如, 繁衍后代之前就死于戰(zhàn)爭(zhēng))。因而, 在特定環(huán)境中, 與其承受巨大的風(fēng)險(xiǎn)繼續(xù)去“存款”, 不如把有限的精力和資源及時(shí)地投入到繁衍任務(wù)中。

權(quán)衡的傾向或者過(guò)程可以被概念化為生命史策略(life history strategy)或繁衍策略(reproductive strategy), 其是一個(gè)以“快策略”和“慢策略”為兩極的連續(xù)譜系。在快策略的一端, 個(gè)體更早地性成熟, 更早地發(fā)生性行為, 有更多的性伴侶, 以及生育更多的子女, 在后代教養(yǎng)上投入更少; 而在慢策略的一端, 個(gè)體更注重身體培養(yǎng)和技能發(fā)展,較遲開(kāi)始性行為, 更注重后代的質(zhì)量而非數(shù)量,更注重后代的教養(yǎng)(Belsky, 2010; Belsky, Houts, ＆amp;Fearon, 2010; Ellis, 2004; Griskevicius, Delton et al., 2011; Griskevicius, Tybur et al., 2011; Kaplan ＆amp;Gangestad, 2005; Simpson et al., 2012)。此外, 生命史策略和其他許多個(gè)體變量都存在關(guān)聯(lián)(L. Ellis,1988; Ellis, McFadyen-Ketchum, Dodge, Pettit, ＆amp;Bates, 1999; Figueredo et al., 2006; Figueredo,Vásquez, Brumbach, ＆amp; Schneider, 2004, 2007; Kruger＆amp; Nesse, 2006; Nettle, 2010; Wilson ＆amp; Daly, 2004),例如, 人格特質(zhì)(Figueredo et al., 2004)。

自然選擇偏好于那些做出最佳權(quán)衡的個(gè)體(Schaffer, 1983)。在這里, 所謂“最佳”就是指最具有適應(yīng)性(adaptive), 在進(jìn)化視角下的意義并非指?jìng)€(gè)體的心理健康(例如, 幸福感), 而是強(qiáng)調(diào)個(gè)體能否把基因成功地遺傳下去(Belsky, Schlomer, ＆amp;Ellis, 2012; Charnov, 1993; MacArthur ＆amp; Wilson,1967; Roff, 1992, 2002; Schaffer, 1983; Stearns,1992)。特定繁衍策略的選擇使得個(gè)體適應(yīng)于不同的生活環(huán)境(Belsky et al., 2012; Ellis, Figueredo,Brumbach, ＆amp; Schlomer, 2009)。例如, 在貧窮、動(dòng)亂的環(huán)境中更早生育子女有利于提高基因遺傳的概率, 從而避免個(gè)體在繁衍之前就死于惡劣環(huán)境。

生命史策略的選擇既有物種間的差異, 也有種群內(nèi)的個(gè)體差異。一般而言, 大多數(shù)人類個(gè)體都是以一種相當(dāng)慢的生命史策略來(lái)展開(kāi)生命軌跡(Gladden, Sisco, ＆amp; Figueredo, 2008; Kaplan, Hill,Lancaster, ＆amp; Hurtado, 2000), 而其他物種, 鼩例如鼱(shrew)則會(huì)采取快策略。無(wú)論是物種間的差異抑或是種群內(nèi)的個(gè)體差異, 特定生命史策略的選擇體現(xiàn)的依舊是生物的適應(yīng)性。

由于自然選擇塑造了環(huán)境敏感性(environmentally sensitive)的生命發(fā)展系統(tǒng), 個(gè)體會(huì)選擇特定的生命史策略從而適應(yīng)于不同的成長(zhǎng)環(huán)境(Belsky et al., 1991; Boyce ＆amp; Ellis, 2005; Ellis et al., 2009)。值得注意的是, 對(duì)環(huán)境的敏感性和易感性存在個(gè)體差異, 和其他心理行為變量一樣,生命史策略同樣受到遺傳和基因的影響(Figueredo et al., 2004)。生命史權(quán)衡是熔鑄于成長(zhǎng)經(jīng)歷的、經(jīng)由基因和環(huán)境共同調(diào)節(jié)的動(dòng)態(tài)過(guò)程(Bakermans-Kranenburg, van IJzendoorn, Pijlman, Mesman, ＆amp;Juffer, 2008; Belsky ＆amp; Hartman, 2014; Belsky ＆amp;Pluess, 2009a, 2009b, 2011, 2013; Ellis, Boyce,Belsky, Bakermans-Kranenburg, ＆amp; Van IJzendoorn,2011; Pluess ＆amp; Belsky, 2010, 2013)。

3 童年經(jīng)歷和繁衍策略

在微觀層面上, 個(gè)體如何做出特定的生命史策略選擇？抑或說(shuō), 生命史策略是如何形成和發(fā)展的？

早在1982年, 人類學(xué)家Draper和Harpending(1982)就提供了一個(gè)頗具創(chuàng)新性的進(jìn)化學(xué)模型用以解釋父親缺失(father absence)對(duì)女孩成長(zhǎng)的影響。借鑒Trivers (1974)的親代投資理論, Draper和Harpending (1982)認(rèn)為, 作為表征家庭社會(huì)地位的核心人物, 父親缺失意味著個(gè)體無(wú)法接受良好的教養(yǎng)、未來(lái)成長(zhǎng)條件的惡化, 這些預(yù)期促使女孩更早地性成熟, 特別是月經(jīng)初潮的提前到來(lái), 從而有利于其從其他男性身上更早更多地獲取資源。

盡管Draper和Harpending (1982)的理論模型缺乏系統(tǒng)性, 以至于無(wú)法解釋更多現(xiàn)象并做出其他合理預(yù)測(cè), 但是, 一個(gè)非常具有啟發(fā)性的嶄新的問(wèn)題卻進(jìn)入了心理學(xué)研究的視角：早期經(jīng)歷如何影響個(gè)體的繁衍策略？

對(duì)此, Belsky, Steinberg和Draper (1991)在整合依戀理論、社會(huì)化理論、社會(huì)學(xué)習(xí)理論等相關(guān)學(xué)科知識(shí)的基礎(chǔ)上, 借鑒進(jìn)化學(xué)領(lǐng)域的“生命史”概念(see Charnov, 1993; Roff, 1992, 2002; Stearns,1992)提出了一個(gè)全新的生命發(fā)展模型。他們認(rèn)為,兒童將依戀視為感知環(huán)境條件的線索(Belsky,2007, 2010; Belsky ＆amp; Fearon, 2002, 2008; Belsky et al., 1991; Simpson ＆amp; Belsky, 2008; Simpson et al.,2012)。如果兒童的照料者有能力投入時(shí)間、精力、資源從而實(shí)現(xiàn)所謂的敏感性、盡責(zé)性, 那么個(gè)體所處的生活環(huán)境就有可能是資源豐富的并且是安全穩(wěn)定的, 個(gè)體也就相應(yīng)地形成安全依戀的內(nèi)部工作模式(internal working model; Bowlby, 1973)。特別地, 嬰兒沒(méi)有能力去評(píng)估它所處的環(huán)境, 但是它能判斷照料者是否滿足它們的生理和情感要求(Del Giudice, 2009a; Simpson ＆amp; Belsky, 2008)。

Belsky等人(1991, 2007)由此提出了一個(gè)相對(duì)籠統(tǒng)的發(fā)展路徑：(1)早期的家庭背景(family context; 例如, 父母婚姻狀態(tài)、經(jīng)濟(jì)條件、社會(huì)環(huán)境); (2)早期的撫養(yǎng)經(jīng)歷(childrearing experiences;例如, 照料者的敏感水平、盡責(zé)性); (3)心理和行為的發(fā)展(psychological/behavioral development;例如, 依戀模式、內(nèi)部工作模式); (4)軀體的發(fā)展(somatic development; 例如, 何時(shí)性成熟); (5)特定繁衍策略的選擇。

在此基礎(chǔ)上, 兩個(gè)截然不同的、帶有原型(prototype)性質(zhì)的發(fā)展軌跡被用以闡明生命史策略的兩個(gè)典型取向。數(shù)量取向(quantity-oriented)的繁衍策略產(chǎn)生于具有非常多負(fù)性應(yīng)激源的家庭環(huán)境中(例如, 家庭關(guān)系不和、婚姻破裂、經(jīng)濟(jì)拮據(jù)), 相應(yīng)地, 非安全型的依戀模式和機(jī)會(huì)主義的人際關(guān)系取向就會(huì)形成, 從而促成一系列快策略的結(jié)果(例如, 青春期的提前到來(lái), 對(duì)短期配偶關(guān)系的偏好, 養(yǎng)育更多子女但缺乏相應(yīng)的親代投資)。相反, 質(zhì)量取向(quality- oriented)的繁衍策略形成于良好的撫養(yǎng)環(huán)境(例如, 夫妻關(guān)系和諧, 經(jīng)濟(jì)條件殷實(shí)), 敏感的、盡責(zé)的、有積極情感的父母教養(yǎng)行為會(huì)促使個(gè)體形成安全型依戀風(fēng)格、互惠型的人際關(guān)系取向, 青春期和首次性行為的時(shí)間也就推遲了。值得注意的是, 數(shù)量取向和質(zhì)量取向只是繁衍策略連續(xù)譜系上的兩個(gè)極端, 五階段的發(fā)展路徑也只是對(duì)理論所涉及的主要領(lǐng)域的一種抽象概括, 并沒(méi)有限定嚴(yán)格的因果次序(Belsky,2007, 2010; Belsky et al., 1991)。例如, 不良的成長(zhǎng)環(huán)境不一定會(huì)導(dǎo)致非安全型依戀。

可見(jiàn), 相較于以往的發(fā)展心理學(xué)理論, 特別是社會(huì)化理論, 生命史理論有兩個(gè)最為明顯的創(chuàng)新點(diǎn)：第一, 摒棄大多數(shù)理論“貼標(biāo)簽”的傳統(tǒng), 不對(duì)依戀類型和人際關(guān)系模式做價(jià)值判斷和倫理取舍, 而是強(qiáng)調(diào)特定的生命史策略對(duì)環(huán)境的適應(yīng)性;第二, 從個(gè)體發(fā)展的角度提出心理影響生理的假設(shè), 具體而言, 就是早期經(jīng)歷對(duì)性成熟時(shí)間的影響(Belsky, 2010; Belsky et al., 2010)。

有趣的是, 早期經(jīng)歷對(duì)性成熟時(shí)間的影響集中體現(xiàn)在女性的身上, 特別是關(guān)乎女性月經(jīng)初潮的時(shí)間(Belsky, 2010; Ellis, 2004; see also Del Giudice, 2011; Draper ＆amp; Harpending, 1982)。需要說(shuō)明的是, 這并非是由于對(duì)男性性成熟的測(cè)量存在困難而導(dǎo)致的研究數(shù)據(jù)的偏誤(Belsky et al.,2007; Del Giudice, 2009a)。事實(shí)上, Ellis和Essex(2007)已經(jīng)發(fā)現(xiàn), 無(wú)論針對(duì)男性抑或是女性, 都可以把腎上腺功能初現(xiàn)(adrenarche)作為衡量性成熟時(shí)間的指標(biāo)(腎上腺功能初現(xiàn)是青春期的最初階段; Auchus ＆amp; Rainey, 2004; Herdt ＆amp; McClintock,2000; Ibanez, Dimartino-Nardi, Potau, ＆amp; Saenger,2000)。例如, Ellis和Essex (2007)發(fā)現(xiàn), 低質(zhì)量的父母教養(yǎng)和高水平的婚姻沖突會(huì)導(dǎo)致兒童在6至7歲時(shí)就腎上腺功能初現(xiàn)(see also Ellis, 2004)。

不過(guò), 即使是以腎上腺功能初現(xiàn)作為衡量指標(biāo), 早期經(jīng)歷對(duì)性成熟時(shí)間的影響依然主要體現(xiàn)在女性身上。對(duì)此, Del Giudice和Belsky (2010)指出：對(duì)于女性而言, 最重要的生命史權(quán)衡在于軀體努力和繁衍努力之間; 而對(duì)于男性, 擇偶與親代投資之間的權(quán)衡更為重要。因而, 相較于男性的青春期, 女性的青春期更能體現(xiàn)個(gè)體的生命史策略, 更加容易受到早期經(jīng)歷的影響。

這種生命史權(quán)衡的性別差異是通過(guò)成人依戀風(fēng)格的性別差異來(lái)實(shí)現(xiàn)的(Del Giudice, 2008,2009a, 2009b, 2009c, 2011; Del Giudice ＆amp; Belsky,2010)：盡管兒童早期的依戀風(fēng)格沒(méi)有性別差異,但隨著年齡的增長(zhǎng), 男性更多地表現(xiàn)出回避型依戀, 而女性在中等壓力情境下更多地表現(xiàn)為焦慮型依戀, 在高壓力情境下才會(huì)往回避型依戀轉(zhuǎn)變。顯而易見(jiàn), 回避型依戀使得男性表現(xiàn)得更加堅(jiān)強(qiáng)、好斗, 有利于其投身社會(huì)競(jìng)爭(zhēng)從而獲取資源, 焦慮型依戀促使女性更加注重和男性伴侶的聯(lián)結(jié)從而能從伴侶身上獲得更多資源, 生命史權(quán)衡的性別差異具有進(jìn)化意義上的適應(yīng)性(Chisholm,1996, 1999a, 1999b; Davis, Shaver, ＆amp; Vernon, 2004;Del Giudice, 2011; Del Giudice ＆amp; Belsky, 2010,2011)。

綜上所述, 性成熟時(shí)間是生命史理論區(qū)別于其他人類發(fā)展理論的核心變量(Belsky, 2010), 它有力地揭示了早期經(jīng)歷影響個(gè)體繁衍策略的基本路徑。值得注意的是, 生命史策略和依戀相互印證：前者偏向于行為學(xué)上的測(cè)量, 而后者偏重于心理學(xué)上的解釋; 前者反映了后者的進(jìn)化學(xué)機(jī)理,而后者為前者建構(gòu)了存在的載體。至此, 生命史理論從宏觀角度的“why”和微觀角度的“how”系統(tǒng)地揭示了人類個(gè)體的生命史現(xiàn)象。

4 對(duì)環(huán)境線索的感知和利用

盡管生命史理論仍以依戀作為個(gè)體心理終身發(fā)展的核心, 但它的解釋范疇并不拘囿于與依戀有關(guān)的現(xiàn)象, 甚至不局限于心理現(xiàn)象。部分研究甚至從經(jīng)濟(jì)學(xué)角度、社會(huì)學(xué)角度給予了實(shí)證支持。

在經(jīng)濟(jì)衰退時(shí)期, 人們幾乎在所有消費(fèi)品上的開(kāi)銷都會(huì)有所減少(Bohlen, Carlotti, ＆amp; Mihas,2010; Katona, 1974), 然而, 女性在美容產(chǎn)品上的開(kāi)支卻會(huì)有所增加(Koehn, 2001; Elliott, 2008)。這種反常的行為經(jīng)濟(jì)學(xué)現(xiàn)象被一些新聞?dòng)浾哒{(diào)侃為“口紅效應(yīng)” (lipstick effect; Koehn, 2001)。借鑒生命史理論的解釋框架, Hill, Rodeheffer, Griskevicius,Durante和White (2012)認(rèn)為, 女性在美容產(chǎn)品上的反常投入是為了提高其在擇偶時(shí)的吸引力, 以期求得資源豐富的配偶。一方面, 在經(jīng)濟(jì)衰退時(shí)期, 高質(zhì)量的男性的數(shù)量會(huì)減少, 加劇了女性間的競(jìng)爭(zhēng); 另一方面, 在經(jīng)濟(jì)衰退時(shí)期, 高質(zhì)量的男性更能保證后代繁衍中的親代投入(Buss, 1994;Clutton-Brock, 2009; Cotton, Small, ＆amp; Pomiankowski,2006; Jennions ＆amp; Petrie, 1997; Symons, 1979)。

Griskevicius等人(2011)則發(fā)現(xiàn), 實(shí)驗(yàn)室情境中虛擬的環(huán)境線索同樣能啟動(dòng)個(gè)體做出特定的生命史權(quán)衡：在面臨死亡的威脅和資源匱乏的情境中, 個(gè)體的生命史策略會(huì)發(fā)生轉(zhuǎn)變。特別地, 對(duì)于那些童年時(shí)成長(zhǎng)于貧窮家庭的個(gè)體而言, 死亡威脅相關(guān)的線索會(huì)促使其更加注重當(dāng)下的生活(value the present), 更加追求眼前的利益, 更愿意投身風(fēng)險(xiǎn)行為; 相反, 那些童年時(shí)成長(zhǎng)于富裕家庭的個(gè)體則會(huì)因此更加注重未來(lái)的發(fā)展并避免更多的風(fēng)險(xiǎn), 表現(xiàn)出所謂的“延遲滿足(delayed rewards)”。Chisholm (1999b)認(rèn)為, 死亡相關(guān)的線索會(huì)促使個(gè)體有意識(shí)地或無(wú)意識(shí)地產(chǎn)生與繁衍相關(guān)的預(yù)期(Promislow ＆amp; Harvey, 1990; Wilson ＆amp;Daly, 1997), 從而影響生命史權(quán)衡。

近期一項(xiàng)研究還發(fā)現(xiàn)(Dunkel, Mathes, ＆amp;Beaver, 2013), 壽命預(yù)期會(huì)影響個(gè)體的自我控制(self-control), 進(jìn)而影響其犯罪意向。壽命預(yù)期為5個(gè)月、5年、50年的個(gè)體, 其自我控制的水平依次遞增, 相應(yīng)地, 犯罪意向的分?jǐn)?shù)依次遞減。研究結(jié)果進(jìn)一步表明, 當(dāng)壽命預(yù)期很短的時(shí)候, 生命史策略更能解釋個(gè)體的自我控制和犯罪意向。

可見(jiàn), 盡管繁衍策略主要形成于個(gè)體生命早期的 5至 7年, 但是它依然持續(xù)地受到當(dāng)下經(jīng)歷的鞏固、調(diào)整和重塑(Del Giudice ＆amp; Belsky, 2011;Simpson et al., 2012), 無(wú)論當(dāng)下環(huán)境信息是真實(shí)的還是實(shí)驗(yàn)室啟動(dòng)的。這種生命史策略的轉(zhuǎn)變體現(xiàn)了個(gè)體的決策動(dòng)機(jī)：企圖利用所感知到的環(huán)境信息來(lái)做出最恰當(dāng)?shù)男袨闆Q策從而適應(yīng)于環(huán)境變化, 實(shí)現(xiàn)利益最大化。進(jìn)一步地, 并非所有的環(huán)境線索的效價(jià)都是相同的, 人們對(duì)生存和繁衍更緊密相關(guān)的環(huán)境線索更敏感(李宏利, 陸慧菁, 張雷,2011)。

總之, 以上研究從依戀以外的角度論證了生命史理論的要義：通過(guò)感知和利用環(huán)境線索來(lái)做出最具有適應(yīng)性的權(quán)衡。

5 反思與總結(jié)

未來(lái)的研究需要注意兩個(gè)問(wèn)題：(1)深入挖掘人類社會(huì)規(guī)范在生命史權(quán)衡中的意義; (2)探索實(shí)證研究的新方法, 擴(kuò)展實(shí)證研究的新路徑。

所謂的“適應(yīng)性”本身就是一種動(dòng)態(tài)的建構(gòu),它根植于人與環(huán)境的互動(dòng)模式。從這個(gè)角度講,人類個(gè)體的生命史權(quán)衡要遠(yuǎn)比其他哺乳動(dòng)物復(fù)雜,因?yàn)槿祟惿鐣?huì)并非是單純的物理性生態(tài)系統(tǒng)(Figueredo ＆amp; Jacobs, 2010)。例如, Sherman,Figueredo和Funder (2013)認(rèn)為, 慢策略更加具有社會(huì)適應(yīng)性, 因?yàn)槿祟惿鐣?huì)的規(guī)范(normativeness)本來(lái)就是主要由慢策略的個(gè)體(或群體)所建立的。這些慢策略的個(gè)體往往出生于優(yōu)越的上層社會(huì),偏好親社會(huì)行為(prosocial behavior), 并且往往是社會(huì)規(guī)則的制定者, 因而, 親社會(huì)行為模式往往是他們所推崇的, 進(jìn)而使得他們能從中獲利。簡(jiǎn)言之, 當(dāng)借鑒生命史理論來(lái)思考個(gè)體的發(fā)展的時(shí)候, 研究者必須清醒地意識(shí)到社會(huì)性動(dòng)物不僅要面對(duì)自然選擇的壓力, 而且其行為還要受限于由其創(chuàng)生的社會(huì)規(guī)范。未來(lái)的研究不應(yīng)當(dāng)只是純粹地把進(jìn)化學(xué)的理論從動(dòng)物界延伸到人類社會(huì), 而需要更多地強(qiáng)調(diào)人類及人類社會(huì)自身的特殊性。

然而, 盡管生命史理論的研究發(fā)現(xiàn)成長(zhǎng)于不良環(huán)境的個(gè)體更容易做出一些不被社會(huì)規(guī)范所接受的行為, 但是我們并非要戴著有色眼鏡去區(qū)別對(duì)待成長(zhǎng)于不同環(huán)境的個(gè)體, 相反, 我們需要借助一些努力來(lái)扭轉(zhuǎn)、規(guī)避這些現(xiàn)象。雖然生命史策略是個(gè)體的無(wú)意識(shí)偏好(Kenrick, Griskevicius,Neuberg, ＆amp; Schaller, 2010; Simpson, Griskevicius,＆amp; Kim, 2011; Simpson et al., 2012), 但是, 我們卻不能否認(rèn)意識(shí)層面的思考和社會(huì)教化的作用(Geronimus, 1996)。生命史理論的研究并沒(méi)有取代人們對(duì)于價(jià)值觀的思考(Belsky et al., 2012), 恰恰相反, 它為這種思考提供了一個(gè)著力點(diǎn)：人保留了“人”作為動(dòng)物的基本屬性, 但是人應(yīng)當(dāng)有“人”所特有的思考和追求。

不過(guò), 當(dāng)文化因素被納入研究范疇的時(shí)候,問(wèn)題隨之復(fù)雜：快策略和慢策略如何在社會(huì)規(guī)范體系下被重新定義？例如, 在中國(guó), 計(jì)劃生育政策的實(shí)施會(huì)影響到人們的繁衍策略。

上述問(wèn)題的懸而未決使得相關(guān)的實(shí)證研究具有相當(dāng)大的局限性。量化生命史策略的最大的困難就在于：生命史權(quán)衡在個(gè)體生命史歷程中是動(dòng)態(tài)的、情境性的, 在人類發(fā)展歷程中同樣是動(dòng)態(tài)的、情境性的。例如, 現(xiàn)代化進(jìn)程使得人們初婚的時(shí)間不斷推遲, 東方文明比西方社會(huì)在性態(tài)度上更加保守, 動(dòng)亂貧窮的環(huán)境和穩(wěn)定富足的環(huán)境可以在一個(gè)相對(duì)較小的區(qū)域共存。因而, 對(duì)生命史策略的量化必須強(qiáng)調(diào)大數(shù)據(jù)思維, 建構(gòu)一個(gè)能夠不斷更新的常模。更重要的是, 生命史理論的實(shí)證研究需要探索新方法、新路徑。如何在實(shí)驗(yàn)室情境下設(shè)計(jì)巧妙的實(shí)驗(yàn)區(qū)分不同生命史策略的個(gè)體, 抑或說(shuō)如何更準(zhǔn)確地評(píng)估個(gè)體的生命史權(quán)衡傾向, 是未來(lái)研究亟需解決的問(wèn)題。

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