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  • 什么是物种?

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    What is a Species?
    ::什么是物种?

    Shown here are various species of the genus Musa, including the common banana. In fact, these are all "bananas." The phenotypic variations are due to genetic differences.
    ::这里展示的是穆萨人的各种物种,包括普通香蕉。事实上,这些都是“香蕉 ” 。 胎儿的变异是遗传差异造成的。

    What is a Species?
    ::什么是物种?

    avoided the use of the word evolution in his major work about evolution. The word “evolve” appears once, at the very end. He titled his work The – a process or group of processes now called . What exactly is a species? How did the millions of species which exist on earth today arise? Will they (we!) continue to change? How quickly? These are questions Darwin sought to answer – and the questions we will explore in this lesson on evolution. Darwin’s work opened the door to life’s history. This lesson will look at both the details of and modifications to his ideas, which research has made clear in the 150 years since he published The Origin .
    ::在他关于进化的主要著作中避免使用“进化”一词。“进化”一词在最后出现过一次。他将作品命名为“一个过程或一组过程 ” 。 什么是物种?今天,地球上存在的数百万物种是如何出现的?它们(我们)会继续变化吗?这些是达尔文试图回答的问题吗?这些是我们在这个进化教训中要探讨的问题。达尔文的工作打开了生命历史的大门。这个教训将审视他思想的细节和修改,在他发表《起源》150年后的这150年中,这些研究清楚地表明了这一点。

    A toddler readily recognizes that she/he is surrounded by distinct groups of individuals which we call “kinds” of plants and . Biologists refer to kinds of living things as a species - groups of individual organisms which are very similar. If we look closely, however, variations make it quite difficult to decide where to draw the lines between species. For example, are a St. Bernard and a Chihuahua similar enough to group within the same species? Just how similar must two organisms be for biologists to decide they are members of the same species? The answer to this question is not clear, even to biologists who specialize in . We will explore several, because how we define a species can help to clarify how species develop.
    ::幼儿可以轻易地认识到,她/他周围有不同的一群人,我们称之为植物和植物的“种类”。生物学家把各种生物称为一种物种——非常相似的个体生物。但是,如果我们仔细观察,变化使得很难决定物种之间的界线。例如,圣伯纳德和吉娃娃是否与同类物种的种类相当相似?生物学家要决定它们是同一物种的成员,必须有两个生物体如何相似?这个问题的答案并不明确,即使是专门研究这些生物体的生物学家也不明确。我们会探索几个物种,因为我们如何定义一个物种可以帮助澄清物种是如何发展的。

    The Biological Species Concept
    ::生物物种概念

    A widely used definition of species is the biological species concept ( Figure ), first proposed by evolutionary biologist Ernst Mayr in 1942. Mayr’s concept begins with the idea that members of a species must be similar enough that they could interbreed . Because all dogs - from a St. Bernard to a Chihuahua – are capable of interbreeding, biologists consider all dogs to be members of the same species. If you are familiar with mules, however, you know that this definition needs clarification. If horses and donkeys mate, they produce mules, but mules are sterile and cannot continue to interbreed. Therefore, the biological species concept becomes organisms similar enough to interbreed and produce fertile offspring . Horses and donkeys, therefore, are not members of the same species. As you may know, wolves and dogs can interbreed to produce viable hybrids with fertile offspring; surely, wolves and dogs are not members of the same species? The last part of the definition addresses this problem, and the complete definition becomes:
    ::1942年,进化生物学家恩斯特·梅尔首先提出了生物物种概念(Figure ) 。 Mayr的概念始于一个概念,即一个物种的成员必须足够相似,以便他们能够相互干涉。 因为从圣伯纳德到奇瓦瓦的所有狗都有能力相互交织,生物学家认为所有狗都是同一物种的成员。 但是,如果你熟悉骡子,你知道这个定义需要澄清。 如果马和驴子伴侣生产驴子,它们就会产生驴子,但骡子不育,不能继续相互交织。 因此,生物物种概念就变得与繁殖后代的有机体足够相似。 因此,马和驴子不是同一物种的成员。 正如你们可能知道的那样,狼和狗可以相互交织,与育后代产生可行的混合体;当然,狼和狗不是同一物种的成员。 定义的最后一部分是解决这个问题,完整的定义是:

    A biological species is a group of organisms similar enough that they could interbreed and produce fertile offspring under natural conditions.
    ::生物物种是一种生物体,其种类与生物体相似,在自然条件下,它们可以相互交织,产生繁殖后代。

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    The species is the smallest group or level used to classify living things. As for all levels, the goal of classification is to show evolutionary relationships. A biological species is defined as a group of organisms similar enough to reproduce and have fertile offspring under natural conditions. A mating between a horse and a donkey produces a mule, but the mule is sterile, so the horse and donkey are not considered members of the same species. On the other hand, dogs and wolves can interbreed successfully, but because they do not do so in nature, they are not classified as members of the same species.
    ::物种是用来对生物进行分类的最小组或级。 至于所有层次,分类的目标是显示进化关系。生物物种被定义为一种在自然条件下足以繁殖和生育后代的生物。马与驴交配会产生驴子,但骡子不育,因此马和驴子不被认为是同一物种的成员。另一方面,狗和狼可以成功地进行交织,但由于它们没有这样做,它们不被列为同一物种的成员。

    This definition serves the goal of defining members of a species as individuals which are still undergoing evolution – they form a distinct yet potentially common gene pool . You will learn much more about classification in the other concepts, but here it is important to realize that one of the primary goals of classification is to show evolutionary history – patterns of common ancestry. This makes the biological species – a functionally reproducing unit – an important foundation of classification. Closely related species descended from relatively recent common ancestors , and distantly related species descended from more distant common ancestors. The emphasis the biological species concept places on successful fits this goal of classification quite well.
    ::这一定义的目的是将物种成员定义为仍在演变中的个人 — — 它们构成一个独特但潜在的共同基因库。 你会更多地了解其他概念中的分类,但在此必须认识到,分类的主要目标之一是展示进化历史 — — 共同祖先模式。 这使得生物物种 — — 一个功能再生单位 — — 成为分类的重要基础。 密切相关的物种来自较近的常见祖先,与远远的共同祖先相联的物种。 生物物种概念的强调非常符合这一分类目标。

    Another advantage of the biological concept is that it has the potential to explain how speciation occurred – that is, how two closely related groups of organisms became different species through reproductive isolation . Members of two species may appear very similar, yet fail to interbreed because of reproductive barriers . Barriers to reproduction may either prevent mating , or prevent of a fertilized egg after mating. Elaborate behaviors, including the blinking pattern of fireflies or the songs of , are often required to elicit mating behavior – and limit mating to members of a species ( Figure ). Different breeding seasons, such as flowering dates, can also prevent interbreeding. Molecular differences between even closely related species may prevent or pollen from actually fertilizing eggs. Once the eggs are fertilized, may be so incompatible that and cannot proceed normally; if the zygote cannot develop, offspring do not survive. All of these barriers between species work to ensure successful reproduction within species, keeping specific, useful adaptations “in the family;" thus, they are a logical way for us to distinguish members of one species from members of another.
    ::生物概念的另一个好处是,它有可能解释物种特征是如何发生的 — — 即两个密切相关的生物组如何通过生殖隔离而成为不同的物种。 两个物种的成员可能看起来非常相似,但因生殖障碍而不能相互干扰。 生殖障碍可能阻止交配,或防止交配后受精蛋的受精。 精心设计的行为,包括闪烁的萤火虫模式或歌曲,往往需要引起交配行为 — — 并限制与物种成员的交配(Figure ) 。 不同的繁殖季节,如开花日期,也可以防止相互交织。 即使是密切相关的物种之间的分子差异也可能防止或授粉蛋实际受精。 一旦卵受精,这种差异可能非常不相容,并且无法正常地进行; 如果酶不能发育,后代就不会存活下来。 所有这些物种之间的障碍都有助于确保物种内部的成功繁殖,“在家族中”保持具体的、有用的适应。 因此,它们是我们区分一个物种的成员和另一个物种成员的合乎逻辑的方法。

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    The Western Meadowlark (left) and the Eastern Meadowlark (right) appear morphologically identical. However, geography and songs serve as reproductive barriers to interbreeding, so the two are considered to be separate species.
    ::西米多拉尔克(左)和东米多拉尔克(右)看起来形态相同。 但是,地理和歌曲是影响生育的阻碍,因此两者被认为是不同的物种。

    Although the biological species concept is extremely helpful in evolutionary thinking it has serious limitations for practical use. For organisms that reproduce asexually – including all and - the definition is entirely unworkable. Nor can we detect whether or not organisms would have been able to interbreed – whether or not they coexisted. Biologists must rely on structure and (if available) biochemical similarities to classify fossils and most microorganisms.
    ::尽管生物物种概念在进化思维中极有帮助,但它在实际应用方面有着严重的局限性。 对于性繁殖的生物 — — 包括所有生物和所有生物 — — 定义是完全行不通的。 我们也无法发现生物是否能够相互融合 — — 不论它们是否共存。 生物学家必须依靠结构和(如果有的话)生化相似性来对化石和大多数微生物进行分类。

    The Morphological Species Concept
    ::病理物种概念

    Alternatives to the biological species concept emphasize the characteristics and processes which unite, rather than divide (reproductive barriers), species. We will look at just a few in order to gain insight into evolutionary thought. A much more practical definition is the morphological species concept , which groups organisms based on structural and biochemical similarities. Recent advances in molecular biology , such as comparison, have strengthened this means of clarifying evolutionary relationships. Biologists probably use this method more than any other to differentiate species in nature, despite its limitations in confirming the potential for interbreeding.
    ::生物物种概念的替代方法强调将物种(生殖障碍)和物种联系在一起的特征和过程,而不是分割(生殖障碍),我们将只看几个,以便深入了解进化思想。一个更实际得多的定义是形态物种概念,即根据结构和生化相似性将生物群集起来。分子生物学的最近进展,例如比较,加强了这种澄清进化关系的手段。生物学家可能比任何其他人更多地使用这种方法来区分自然物种,尽管在确认异种间繁殖潜力方面存在着局限性。

    The Ecological Species Concept
    ::生态物种概念

    The ecological species concept focuses on a group’s common ecological niche – the set of environmental conditions and resources used or required by the group. This concept is based on the idea that ecological and evolutionary processes divide resources in such a way that individuals can most efficiently adapt to use those resources as a group . All members of a species, then, have a unique set of adaptations to a particular set of environmental conditions. Note that both the morphological and ecological definitions “work” for asexually reproducing organisms and many fossils. However, they do not help to explain how two closely related groups became different species, as the biological definition does.
    ::生态物种概念侧重于一个群体共同的生态优势 — — 该群体使用或需要的一系列环境条件和资源。 这一概念基于这样一种理念,即生态和进化过程将资源分化,使个人能够最有效地适应这些资源作为一个群体使用。 因此,一个物种的所有成员都有一套独特的适应特定环境条件的方法。 注意形态和生态定义对性再生生物和许多化石的“工作 ” 。 但是,它们无助于解释两个密切相关的群体是如何成为不同的物种的,正如生物定义那样。

    The Evolutionary Species Concept
    ::进化物种概念

    The last concept we will consider has the potential to clarify the path of speciation, or evolutionary history – that primary goal of classification. The genealogical or evolutionary species concept defines a species as a group of organisms with a unique genetic history – a group which shares common ancestry without divergence. A species, according to this concept, is a group which forms one tip on the branching tree of life’s history. Modern technology which compares DNA and sequences makes this definition workable, but still, the mechanism of speciation is not defined.
    ::我们所要考虑的最后一个概念有可能澄清物种划分或进化历史的路径 — — 即这一首要分类目标。 基因学或进化物种概念将物种定义为具有独特遗传史的生物群 — — 拥有共同的祖先,没有差异的物种群。 根据这一概念,一个物种组在生命历史的分支树上形成一丝一毫。 比较DNA和序列的现代技术使得这一定义可行,但是仍然没有界定物种划分机制。

    Ideally, all of these ways of determining exactly which individuals make up a species would merge; all make valid points about the idea of a species, and all seek the common goal of defining a new, unique unit of life in space and time. Practically, however, each has its own usefulness for different purposes. If we were working in the field, we would undoubtedly use the morphological concept. However, as we explore the idea of speciation mentally and through lab models, we will adopt the biological species concept as our working definition.
    ::最理想的是,所有确定具体由哪些人构成的物种将合并的方法;所有方法都对物种的概念提出正确的意见,并且都寻求在时空上界定新的、独特的生命单位的共同目标。然而,实际上,每一种方法都有其自身的不同用途。如果我们在实地工作,我们无疑会使用形态概念。然而,当我们探索精神和实验室模型的分化概念时,我们将采用生物物种概念作为我们的工作定义。

    Humans, One Species?
    ::人类,一个物种?

    What about humans? Are we all members of the same species? According to the biological species concept, the answer is a resounding yes. Despite our differences in appearance, culture, and location on planet Earth, any human female is capable of producing fertile offspring with any human male. Therefore, all humans are members of the same biological species. In contrast, humans and chimpanzees do not interbreed even when they share the same territory, so biologists consider chimpanzees to be a distinct species. Before we leave the “species problem” and Homo sapiens , it is worth noting that all of the various definitions of species confirm the unity of the human species. DNA sequences, chemistry, anatomy, ecological resources, and reproductive ability all reveal similarities which unite us as a single species with common ancestry. In fact, the most recent and precise method of comparison – DNA sequences – shows that somewhere between 1 in 100 and 1 in 1,000 base pairs differ, on average, between one human and the next. Based on this analysis, we humans are 99.9% identical. The differences which seem so great to us (skin color, facial features, build, personality) are important for recognition of individuals, and a few may adapt us to particular regions of the Earth, but overall, we are vastly more similar to than different from each other; we are one species.
    ::人类呢? 人类呢? 我们都是同一物种的成员吗?根据生物物种概念,答案是肯定的。根据生物物种概念,答案是肯定的。尽管我们在地球上的外观、文化和位置上存在差异,但任何人类女性都有能力与任何男性生出肥沃的后代。因此,所有人类都是同一生物物种的成员。相比之下,人类和黑猩猩即使拥有相同的地域,也没有相互交织。相反,人类和黑猩猩即使拥有相同的地域,生物学家也认为黑猩猩是一种不同的物种。在我们离开“物种问题”和智人之前,值得指出的是,物种的所有不同定义都证实了人类物种的团结性。DNA序列、化学、解剖学、生态资源和生殖能力都揭示了相似性,而我们作为一个有着共同祖先的单一物种。 相比之下,最近和精确的比较方法 — DNA序列 — 表明, 平均在1:1:1到1 000对基本对之间,人类和下一个智人之间有差异。基于这一分析,我们人类是99.9 % , 人类是人类的所有物种定义都证实了人类的团结。 。 DNA序列、化学、解说、解说、生态资源、生态资源和生殖能力都显示了相似性特征之间的差异。

    Although we may not learn exactly how we came to be a separate species, we can gain some insight by looking closely at what is known of the process of speciation. What do we know now – that Darwin did not know - about “the origin of species?"
    ::尽管我们也许没有确切地知道我们是如何成为一个单独物种的,但通过仔细观察人们所知道的物种特征过程,我们可以得到一些深刻的洞察力。 我们现在知道的是什么,达尔文不知道什么是“物种起源 ” ?

    Summary
    ::摘要

    • Ever since Darwin’s publication of The Origin of Species , biologists have continued to work out the details of how species originate – the foundation of evolutionary process.
      ::自达尔文出版《物种起源》以来,生物学家一直在研究物种起源的细节 — — 这是进化过程的基础。
    • A species is the smallest group of organisms into which biologists classify living things.
      ::物种是生物学家将生物分类的最小的生物群。
    • A biological species is a group of organisms that can interbreed to produce fertile offspring under natural conditions. This is probably the most widely accepted definition of a species.
      ::生物物种是一种有机体,可以在自然条件下相互交织,产生肥沃的后代,这可能是对物种最普遍接受的定义。
    • A morphological species groups organisms based on extensive structural and biochemical similarities. This is probably the most practical definition for use in the field.
      ::基于广泛的结构和生化相似性的形态物种组生物体,这可能是实地使用的最实际的定义。
    • A genealogical or evolutionary species includes organisms which share a recent, unique common ancestor. This is the goal of all classification; the only question is how to recognize members.
      ::基因物种或进化物种包括具有最近独特共同祖先的生物,这是所有分类的目标;唯一的问题是如何识别成员。
    • An ecological species groups organisms together if they share a unique set of adaptations to a particular set of environmental conditions.
      ::生态物种组生物如果具有一套针对特定环境条件的独特适应性,它们就共同组成一个生态物种组生物体。
    • Ideally, all four definitions would merge to recognize a true species.
      ::理想的情况是,所有四个定义都将合并,承认一个真正的物种。
    • All humans are members of the same biological species because all races and cultures can and do intermarry and our DNA is 99.9% identical.
      ::所有人都是同一生物物种的成员,因为所有种族和文化都能够并进行婚姻间交流,我们的DNA是99.9%完全相同的。

    Review
    ::回顾

    1. Define the biological species concept and analyze its usefulness.
      ::界定生物物种概念并分析其效用。
    2. Compare the biological species concept to morphological, genealogical, and ecological concepts.
      ::将生物物种概念与形态学、基因学和生态概念作比较。
    3. Analyze the reasons why biologists consider all humans to be members of the same species.
      ::分析生物学家为什么认为人类都是同一物种的成员。