章节大纲

  • lesson content

    How can a river influence evolution?
    ::河流如何影响进化?

    Imagine a group of small organisms , such as mice, that become separated by a mighty river. This group has now become isolated and formed two separate groups. The groups are obviously no longer able to breed together. Over many generations, each group will evolve separately, eventually forming two completely new of mice.
    ::想象一下小生物群,如小鼠,被一条强大的河流隔开。这个小生物群现在已经变得孤立,组成了两个不同的组。这些组显然不再能够一起繁殖。在许多代人中,每个组将分别演变,最终形成两个全新的小鼠。

    An Overview of Speciation
    ::特征概述

    occurs at the boundary between microevolution and . At what point do the changes in allele frequencies , due to microevolution, add up to define a new and separate species?
    ::微进和微进之间的边界发生。由于微进导致的Alle频率变化在什么时间点加上一个新的和单独的物种定义?

    Ernst Mayr, who developed the biological species concept , also identified two essential components of speciation. For two to evolve into separate species, they must experience:
    ::Ernst Mayr开发了生物物种概念,也确定了物种划分的两个基本组成部分。

    1. Isolation
      ::孤立
    2. Genetic divergence
      ::遗传差异

    Isolation limits which would tend to maintain uniformity between the two populations. Physical separation by a barrier limits and prevents interbreeding, but differing environmental conditions may also provide a form of isolation. Isolation increases the chance that two populations will take separate microevolutionary pathways. Returning to our white and brown rabbits, a difference in altitude (and thus a difference in temperature) might separate two parts of a population so that albino individuals will be favored higher on a mountain where snow frequently accumulates, but brown individuals would be favored down toward the valleys, where snow rarely covers the ground.
    ::隔离限制往往会维持两种人口的统一性。 隔离限制会维持两种人口之间的统一性。 隔离限制会通过屏障限制进行实际隔离,防止相互交错,但不同的环境条件也可能提供一种隔离形式。 隔离增加了两个人口采取单独微进途径的可能性。 回到我们的白兔和棕兔身上,高度差异(因此温度差异)可能会将一个人口的两个部分分离开来,这样白种人会在雪常积聚的山上得到更高的青睐,但棕色人会被偏向山谷,那里很少有雪覆盖地面的山谷。

    Although the two rabbit populations might be isolated by environmental differences, they would not become separate species unless enough genetic differences accumulate to prevent successful interbreeding. Genetic divergence is more likely if populations are small, increasing the chance of . Even in large populations, however, environmental differences may result in large genetic differences which prevent interbreeding. In our rabbit populations, for example, selection for white rabbits might be accompanied by mate selection based on white coat color. If mate preferences were heritable and sufficiently strong, interbreeding between the brown and white populations would cease, and the two populations would become two species.
    ::尽管两种兔子种群可能因环境差异而被隔离,但它们不会成为单独的物种,除非有足够的遗传差异累积起来,以防止成功相互交织。如果种群数量小,遗传差异就更有可能出现,从而增加出现这种差异的可能性。然而,即使在大量种群中,环境差异也可能导致巨大的遗传差异,从而防止了相互交织。例如,在我们的兔子种群中,选择白兔子时可能同时根据白大衣颜色选择配偶。如果配偶的偏好具有遗传性和足够强,则褐色和白色种群之间的相互交织会停止,而这两种种群将变成两种物种。

    Speciation results in two groups of individuals, each more closely adapted to local environmental conditions than the larger parent population. Although speciation may not always result in a better fit between a species and its environment (remember that genetic drift increases the influence of chance), over time, tends to increase fitness . A species’ adaptations to both physical and living environments increase the chance that the species will survive. The millions of species that exist today are each carefully attuned to a particular niche . And, just as variation within a species ensures that some individuals will survive environmental change, a great diversity of species increases the chance that at least some organisms will survive major changes in the environment.
    ::物种特征的特征表现为两组人,每组人比较大的母种群更适合当地的环境条件。 虽然物种特征不一定总能导致物种与环境之间的更好适应(记住基因漂移会增加机会的影响 ) , 随着时间的推移, 物种的特征往往会提高健康。 物种对物理和生活环境的适应增加了物种生存的可能性。 当今存在的数百万物种都仔细地适应了特定的位置。 而正如物种内部的变化能确保某些物种在环境变化中存活下来一样,物种的多样性增加了至少某些生物在环境发生重大变化时生存下去的机会。

    Isolation and genetic divergence are both prerequisites for speciation, but they are so closely related that sometimes it is difficult to distinguish one from the other. Physical isolation may encourage genetic divergence, but many evolutionary biologists believe that reproductive isolation can result from genetic divergence alone. That leads us to two major categories of speciation – one based on geographic isolation, and the other based on reproductive isolation alone. These two categories, and examples of speciation from each, are the topic of the next section.
    ::隔离和遗传差异是分化的前提,但两者密切相关,有时很难区分。 物理隔离可能鼓励遗传差异,但许多进化生物学家认为生殖隔离只能由遗传差异造成。 这导致我们分为两大类:一类基于地理隔离,另一类则仅基于生殖隔离。 这两类以及每种类型的分化例子是下一节的主题。

    Summary
    ::摘要

    • For populations to become separate species, they must experience isolation and genetic divergence.
      ::为使种群成为独立的物种,它们必须经历孤立和遗传差异。
    • Isolation can be physical or environmental, but it must be accompanied by heritable reproductive isolation, which requires genetic divergence.
      ::隔离可以是物理隔离,也可以是环境隔离,但必须伴随遗传性生殖隔离,这就要求存在遗传差异。
    • The result of speciation is usually two groups of individuals, each more closely adapted to local environmental conditions than the larger parent population.
      ::物种划分的结果通常是两组人,每一组人比较大的父母人口更密切地适应当地环境条件。

    Review
    ::回顾

    1. Describe two conditions that can lead to speciation.
      ::描述导致分层的两个条件。
    2. Explain the results of speciation in terms of adaptation, chance, and changes in the environment.
      ::解释在适应、机会和环境变化方面的分层结果。