盖娅假说:在争议中发展

Gaia hypothesis: developing in disputes

自从1972年Lovelock提出盖娅假说已经过去了40年,但围绕它的争议却从未停止过。盖娅假说在反对者的批评中与支持者的证明中不断发展。当前,最极端形式的盖娅假说基本上已被摒弃,尤其是那种明显带有目的论的说法。弱盖娅提出的"有机体可以影响他们的环境,有机体与环境的反馈耦合可以塑造两者的进化"这两个观点也已经是普遍接受的事实。除此之外,盖娅假说提出的其他3个命题却饱受争议。(1)内在平衡的盖娅:生物调节反馈有助于环境的内在平衡。反对者认为,生物反馈稳定全球环境的说法,与冰芯记录和大量的气候反馈研究结果相矛盾的。支持者认为,地球生物-环境系统的内在平衡可以产生于正负反馈的混合。盖娅假说关心的是地球几十亿年的历史,盖娅假说在较短时间尺度内可证伪,并不意味着其在较长时间尺度内也可证伪。(2)最优的盖娅:生物调节环境,使环境更加适合生物的生存。关于有机体的繁荣主要是由于他们对环境的改变,还是由于他们对环境的适应,目前尚未有结论。但盖娅的支持者认为,当生物-环境系统受到干扰或崩溃时,主导过程将显现。拥有较强环境反馈的系统,将易于快速过渡到新的状态,而由适应主导的过程将改变得较为平缓。反对者同意生物通过生物调节作用影响环境条件以使自身受益,但是生物首先要适应环境条件通过自然选择才能得以繁荣发展的。地球形成这样的环境条件,很可能纯粹是一种运气。(3)自然选择的盖娅:生物调节反馈产生于达尔文式的自然选择。反对者认为,"自然选择支持促进生命效应"的说法并非普遍有效,只有当遗传特征赋予携带者繁殖优势时,自然选择才会支持它。自然选择是机制,而非原则。支持者认为自然选择并不是盖娅系统环境调节的必要条件;基于副产品的自然选择,可以解决许多进化论学者提出的物种合作中的欺骗问题;自然选择并不总是支持促进生命的效应,但在当遗传特征使携带者相对非携带者受益时,自然选择可以使特征携带者产生进化优势。虽然争议依然存在并将持续下去,但作为假说生产者,盖娅假说已经证明了它的价值。但是在人类活动对生物圈影响不断增强的背景下,盖娅假说必须与人类活动相结合,否则必然走向衰落,并被其他理论或假说所替代。在此基础上,未来盖娅假说的研究者们需要继续努力探索可以应用于生物圈的一般性原则,并坚持系统性的思考方法。在具体的方法方面,可以利用系统度量指标;建立新的模型,尤其是建立关于生物地球化学循环过程的机理模型;搞清楚不同尺度过程的成本与收益。

Forty years ago Lovelock introduced the Gaia hypothesis and the criticisms by opponents and support by proponents are continuously developing. Currently, the extreme teleological version of Gaia has been ignored. The weak form of the Gaia hypothesis, which has been generally accepted, are the views that life collectively has a significant effect on earth＇s environment and the feedback coupling system of life and environment can shape their coevolution. However, three other Gaia propositions are strongly debated： the Homeostatic Gala, the Optimal Gaia, and the Gaia based on natural selection. The Homeostatic Gaia states that biologically mediated feedbacks contribute to environmental homeostasis. Opponents argue this proposition contradicts ice core records and the findings of climatic feedback research. Proponents argue the homeostasis of the earth＇s biota-environment system results from a combination of positive and negative feedbacks. The primary concern of the Gaia hypothesis is focused on billions years of the earth history. Although the Gaia hypothesis can be falsified in relatively short timescales, that does not indicate it can be falsified in longer timescales. The Optimal Gaia states that life regulates the physical and chemical environment to meet the biosphere＇s needs. Although a conclusion has not been formed regarding alteration of or adaption to the environment, proponents assert that when the biota- environment system is perturbed or collapses, the dominant effect will appear. A system with strong environmental feedback will be prone to rapid transitions between states, whereas one where adaptation dominates will change more slowly. Opponents agree life can benefit itself by the biologically mediated effect on the environmental condition, but they claim life should firstly adapt to the environmental condition by natural selection. It is very likely the earth evolved to this environmental condition only by chance. The last proposition, Gaia based on natural selection, specifies that biologically medicated feedbacks come from Darwinian natural selection. The opponents argue the statement that life-enhancing effects are favored by natural selection, but this is not always valid, except when a heritage trait confers a reproductive advantage to its carrier. Natural selection is a mechanism, not a principle. Proponents believe that natural selection is not an essential condition to environmental regulation. Natural selection based on by-products can resolve the cheat issue in interspecific cooperation raised by many evolutionists. Proponents acknowledge natural selection does not always favor life-enhancing effects, however, when a heritage trait benefits its carriers compared to non-carriers, natural selection can confer an evolutionary advantage to carriers. Disputes continue, but as a hypothesis generator, the Gaia hypothesis has proven its worth. Since the industrial revolution, the impact of human activities on the biosphere has been constantly enhanced. Under this situation, the Gaia hypothesis must incorporate human activities or it will decline and be substituted by other theories or hypotheses. In the future, scientists researching the Gaia hypothesis should strive to explore the general principle, which can apply to the whole biosphere and insist on systematic thinking. In terms of specific methods, consideration to experimenting with biosphere-scale metrics, such as GPP and cycling ratio is recommended. Scientists must build new mathematic models and particularly new mechanic models with addressed on different scales when discussing life benefiting the regards to biogeochemistry. Costs and benefits need to be environment