Section of Evolution and Ecology, One Shields Avenue, University of California, Davis, California 95616 USA.
Am J Bot. 2003 Jun;90(6):954-6. doi: 10.3732/ajb.90.6.954.
Heckman et al. (Science 293: 1129-1133) used sequences obtained from GenBank to infer divergence times in fungi and green plants. They estimated that the crown group of land plants originated in the Precambrian, at 703 ± 45 mya, a date much older than dates implied by the fossils, which are no older than about 450 mya. This paper presents an analysis of an entirely different set of sequence data from 27 plastid protein-coding genes in 10 land plants and a green algal outgroup. It uses a calibration point closer to the origin of land plants and inference methods that do not assume a molecular clock. This leads to estimates ranging from 425 to 490 mya, which brackets the age suggested by the fossil record. Possible explanations for the differing conclusions in the two studies include differences in calibration points and use of single-copy plastid genes rather than nuclear gene families.
赫克曼等人（Science 293:1129-1133）利用从 GenBank 获取的序列推断真菌和绿色植物的分歧时间。他们估计，陆地植物的冠群起源于前寒武纪，大约在 703±45 百万年前，这一日期远早于化石所暗示的日期，化石的年龄不超过大约 450 百万年前。本文介绍了对来自 10 种陆地植物和一种绿色藻类外类群的 27 种质体蛋白编码基因的完全不同的数据集的分析。它使用了一个更接近陆地植物起源的校准点和不假设分子钟的推断方法。这导致的估计范围在 425 到 490 百万年前，与化石记录所暗示的年龄相符。这两项研究得出不同结论的可能解释包括校准点的差异以及使用单拷贝的质体基因而不是核基因家族。
