McShea Daniel W
Museum of Paleontology, University of Michigan, Ann Arbor, Michigan, 48109.
Evolution. 1993 Jun;47(3):730-740. doi: 10.1111/j.1558-5646.1993.tb01229.x.
The notion that morphological complexity increases in evolution is widely accepted in biology and paleontology. Several possible explanations have been offered for this trend, among them the suggestion that it has an active forcing mechanism, such as natural selection or the second law of thermodynamics. No such mechanism has yet been empirically demonstrated, but testing is possible: if a forcing mechanism has operated, the expectation is that complexity would have increased in evolutionary lineages more frequently than it decreased. However, a quantitative analysis of changes in the complexity of the vertebral column in a random sample of mammalian lineages reveals a nearly equal number of increases and decreases. This finding raises the possibility that no forcing mechanism exists, or at least that it may not be as powerful or pervasive as has been assumed. The finding also highlights the need for more empirical tests.
形态复杂性在进化过程中会增加这一观点在生物学和古生物学中被广泛接受。针对这一趋势，人们提出了几种可能的解释，其中包括它具有一种主动推动机制的观点，比如自然选择或热力学第二定律。然而，尚未有这样的机制得到实证证明，但进行测试是可行的：如果存在一种推动机制，那么可以预期在进化谱系中复杂性增加的情况会比减少的情况更频繁。然而，对哺乳动物谱系随机样本中脊柱复杂性变化的定量分析显示，增加和减少的数量几乎相等。这一发现增加了不存在推动机制的可能性，或者至少表明它可能不像人们所设想的那样强大或普遍。这一发现还凸显了进行更多实证测试的必要性。
