何谓高等生物或低等生物, 即, 不同生物间有没有等级性, 是一个大问题, 既是生命科学的问题, 也是实践哲学的问题。要回答这个问题, 必须回到它的起点——达尔文的《物种起源》。本文通过梳理《物种起源》, 发现达尔文使用了大量的蕴含某种“生物等级性”的论述, 分别指向7个不同的方面或指标: (1)形态固化与功能分化的程度, (2)性状定向发育的程度, (3)生物形态的复杂程度, (4)竞争力的强弱, (5)系统发育之分化时间的早晚, (6)演化速率的高低, (7)生物分类阶元的高低。进一步的剖析显示, 这些不同的指向性, 除了指标(7), 在达尔文的演化论体系中, 彼此间大体可保持协调性与统一性, 即, 以竞争之生物关系推动的生物之系统发育的种种体现。在此框架中, 生物等级性的逻辑性是可以被理解的。但是, 进一步的考察表明, 这一理解面临着两大挑战: (1)生命科学规律的或然性, (2)宏观、动态的大演化图式(受制于外在环境的变化)之于达尔文的中观、静态的(以生物作用为主导因素)演化论的修正。在可变环境中, 演化没有目的性, 也没有方向性; 既没有先定的, 也没有可预期的; 既没有事实的, 也没有应然的。因此, 就宏观演化而言, 所谓的“生物等级性”, 往往只是一种权宜的喻象表述, 并无实体性意义, 更不存在价值意味。这个结论也构成了我们之于社会达尔文主义与自然主义环境伦理学在本体层面的批判。

Aims: What do higher or lower organisms mean, or, is there any hierarchy among different organisms, is a big question, not only of life sciences, but also of practical philosophy. To answer this question, we must return to its starting point, Darwin’s On the Origin of Species.

Progress: In this article I show that Darwin in his masterpiece used a lot of expressions that imply some meaning of “biological hierarchy” (a ladder of life), referring to seven different aspects or indicators: (1) the degrees of morphological rigidity and functional differentiation, (2) the degree of directional development of traits, (3) morphological complexity, (4) competitive strength, (5) the time of phylogenetic differentiation, (6) evolutionary rate, and (7) taxonomic rank. Further analysis demonstrates that these different indicators, except indicator (7), can generally keep consistent with each other within Darwin’s theory of evolution, that is, they are various manifestations of the phylogenetic tree driven by the biological interaction of competition. In this framework, the logic of a biological ladder can be understood.

Conclusion: Further investigation, however, shows that this understanding faces two major challenges: (1) probabilistic uncertainty pertaining to any law of life sciences and (2) a revision of Darwin’s mesoscopic-static theory of evolution, which is dominated by biological interactions, taking into account the macroscopic-dynamic evolutionary schema, which is subject to changes in the external environment. In a considerably variable environment, evolution has no goal or direction, whether predetermined or predictable, factual or desirable. Therefore, with respect to macroscopic evolution, what could be called “biological ladder” tends to be an expedient metaphorical expression with little substantial meaning, let alone axiological implications. This conclusion also constitutes the criticism of Social Darwinism and naturalistic environmental ethics on the ontological level.