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  • 自然选择自然选择

    A deer mouse perched on a tree branch among green leaves in a forest setting.

    How is this deer mouse well adapted for life in the forest ?
    ::这只鹿鼠如何适应森林的生活?

    Notice how its dark coloring would allow the deer mouse to easily hide from predators on the darkened forest floor. On the other hand, deer mice that live in the nearby Sand Hills are a lighter, sand-like color. What caused the deer mice to be so well adapted to their unique environments? Natural selection.
    ::注意它的暗色颜色会如何让鹿鼠很容易地躲藏在黑暗的森林地板上的食肉动物。 另一方面,生活在附近的沙丘上的鹿鼠是一种较轻、类似沙的颜色。 是什么原因导致鹿鼠非常适合它们独特的环境? 自然选择。

    Natural Selection
    ::自然选择自然选择

    The theory of evolution by natural selection means that the inherited traits of a change over time. Inherited traits are features that are passed from one generation to the next. For example, your eye color is an inherited trait. You inherited your eye color from your parents. Inherited traits are different from acquired traits , or traits that organisms develop over a lifetime, such as strong from working out ( Figure ).
    ::自然选择的进化理论意味着随时间变化的遗传特征。 继承的特征是代代相传的特征。 例如, 你的眼睛颜色是遗传的特征。 你从父母那里继承了眼睛的颜色。 继承的特征不同于遗传的特征, 或生物在一生中形成的特征, 例如从锻炼中产生的强力( 图 ) 。

    Comparison of attached and free human earlobes, illustrating inherited traits.

    Human earlobes may be attached or free. You inherited the particular shape of your earlobes from your parents. Inherited traits are influenced by genes, which are passed on to offspring and future generations. Things not influenced by genes are not passed on to your offspring. Natural selection only operates on traits like earlobe shape that have a genetic basis, not on traits that are acquired, like a summer tan.
    ::人类耳垂可能被附着或自由。 你从父母那里继承了耳垂的特殊形状。 遗传的特性受基因的影响, 这些基因传给后代。 不受基因影响的东西不会传给后代。 自然选择只能根据诸如耳垂形状之类的特性运作,这些特性具有基因基础, 而不是根据获得的特性运作, 像夏天晒黑一样。

    Natural selection explains how organisms in a population develop traits that allow them to survive and reproduce. Natural selection means that traits that offer an advantage will most likely be passed on to offspring ; individuals with those traits have a better chance of surviving. Evolution occurs by natural selection.
    ::自然选择可以解释人口中生物是如何发展出能使其生存和繁殖的特性的。 自然选择意味着提供优势的特性最有可能传给后代;具有这些特性的个人更有可能生存。 自然选择会发生演变。

    Take the giant tortoises on the Galápagos Islands as an example. If a short-necked tortoise lives on an island with fruit located at a high level, will the short-necked tortoise survive? No, it will not, because it will not be able to reach the food it needs to survive. If all of the short necked tortoises die, and the long-necked tortoises survive, then, over time, only the long-necked trait will be passed down to offspring. All of the tortoises with long-necks will be "naturally selected" to survive. Organisms that are not well-adapted, for whatever reason, to their environment, will naturally have less of a chance of surviving and reproducing.
    ::以加拉帕戈斯群岛上的巨龟为例。如果一个短颈乌龟生活在一个具有高水平水果的岛屿上,那短颈乌龟能否生存下来? 不,它不会生存下去,因为它将无法获得生存所需的食物。 如果所有短颈乌龟都死了,长颈乌龟也能生存下来,那么,随着时间的推移,只有长颈乌龟才能传给后代。所有长颈乌龟都会“自然选择”生存下来。 不论出于何种原因,由于环境原因,不适应的有机体自然会减少生存和再生的机会。

    Every plant and animal depends on its traits to survive. Survival may include getting food, building homes, and attracting mates. Traits that allow a plant, animal, or other organism to survive and reproduce in its environment are called adaptations .
    ::每个植物和动物都依赖其特质生存。 生存可能包括获取食物、建房和吸引伴侣。 允许植物、动物或其他生物在其环境中生存和繁殖的陷阱被称为适应。

    Natural selection occurs when:
    ::自然选择发生于下列时间:

    1. There is some variation in the inherited traits of organisms within a species . Without this variation, natural selection would not be possible.
      ::物种内生物的遗传特征存在一些差异,没有这种差异,自然选择是不可能的。
    2. Some of these traits will give individuals an advantage over others in surviving and reproducing.
      ::其中一些特征将使个人在生存和再生方面比其他人更有利。
    3. These individuals will be likely to have more offspring.
      ::这些人的后代可能更多。

    Imagine how in the Arctic, dark fur makes a rabbit easy for foxes to spot and catch in the snow. Therefore, white fur is a beneficial trait that improves the chance that a rabbit will survive, reproduce, and pass the trait of white fur on to its offspring ( Figure ). Through this process of natural selection, dark fur rabbits will become uncommon over time. Rabbits will adapt to have white fur. In essence, the selection of rabbits with white fur - the beneficial trait - is a natural process.
    ::想象一下,在北极,黑毛如何让一只兔子容易被狐狸在雪中发现和捕捉。 因此,白毛是一种有益的特性,它增加了兔子生存、繁殖和将白毛特性传给后代的机会(图 ) 。 通过这一自然选择过程,黑毛兔子将随时间变化而变得罕见。 兔子将适应白毛。 本质上,选择白毛兔子 — — 有益特性 — — 是一种自然过程。

    An Arctic hare blends into the snowy landscape, showcasing its white fur for camouflage.

    The white fur of the Arctic hares may make it more difficult for fox and other predators to locate hares against the white snow.
    ::北极野兔的白毛可能使狐狸和其他捕食者更难在白雪上找到野兔。

    Why So Many Species?
    ::为什么有这么多物种?

    Scientists estimate that there are between 5 million and 30 million species on the planet. But why are there so many? Different species are well-adapted to live and survive in many different types of environments. As environments change over time, organisms must constantly adapt to those environments. Diversity of species increases the chance that at least some organisms adapt and survive any major changes in the environment. For example, if a natural disaster kills all of the large organisms on the planet, then the small organisms will continue to survive.
    ::科学家估计地球上有500万到3000万物种。 但为什么有这么多物种? 不同的物种非常适合在多种不同类型的环境中生存和生存。随着环境的变化,生物必须不断适应这些环境。物种的多样性增加了至少某些生物适应和生存环境任何重大变化的机会。例如,如果自然灾害杀死地球上所有大型生物,那么小生物将继续生存下去。

    Evolution Acts on the Phenotype
    ::基因型演变法

    Natural selection acts on the phenotype (the traits or characteristics) of an individual. On the other hand, natural selection does not act on the underlying genotype (the genetic makeup) of an individual. For many traits, the homozygous genotype, AA , for example, has the same phenotype as the heterozygous Aa genotype. If both an AA and Aa individual have the same phenotype, the environment cannot distinguish between them. So natural selection cannot select for a homozygous individual over a heterozygous individual. Even if the "aa" phenotype is lethal, the recessive a allele , will be maintained in the population through heterozygous Aa individuals. Furthermore, the mating of two heterozygous individuals can produce homozygous recessive ( aa ) individuals. However, natural selection can and does differentiate between dominant and recessive phenotypes.
    ::个人( 性特征或特性) 的自然选择行为 。 另一方面, 自然选择并不针对个人的基本基因类型( 基因构成) 。 对于许多特性, 单体基因类型 AA 具有与异体zygous Aa 基因类型相同的性类型 。 如果 AA 和 Aa 个人具有相同的性类型, 环境无法区分它们 。 因此自然选择无法为异体动物的个人选择同质动物 。 即使“ a” 型苯并属致命性, 休眠异性异性动物 , 也会通过异体突变人 在人群中保持。 此外, 两种异体人交配可以产生同质性( aa) 。 但是, 自然选择可以区分主体和沉息性人型 。

    Carriers
    ::承运人

    Since natural selection acts on the phenotype, if an allele causes death in a homozygous individual, aa , for example, it will not cause death in a heterozygous Aa individual. These heterozygous Aa individuals will then act as carriers of the a allele, meaning that the a allele could be passed down to offspring. People who are carriers do not express the recessive phenotype, as they have a dominant allele . This allele is said to be kept in the population's gene pool . The gene pool is the complete set of genes and alleles within a population.
    ::由于自然选择在苯类上的行为,如果一个异灵在同性古人(aa)中造成死亡,例如,如果一个同性古人(elele)在同性古人(aa)中造成死亡,那么它不会在异性古人(eterozygous Aa)中造成死亡。这些异性古人(eterozygous Aa)将随后作为异性动物的携带者,这意味着该异灵可以传给后代。作为异性克隆人的人并不表示休性芬类,因为他们有主要的异性。据说,这种异性基因将保存在人口的基因库中。基因库是人口中的一整套基因和异性基因组。

    Summary
    ::摘要

    • Evolution occurs by natural selection, the process by which organisms with traits that better enable them to adapt to their environment will tend to survive and reproduce in greater numbers. Evolution is due to differences in the survival and reproduction of individuals within a population.
      ::自然选择是进化过程的发生,在这个过程中,具有更好地适应环境特点的有机体往往能够存活并大量繁殖,而进化是由于人口中个人生存和再繁殖的差异造成的。
    • Natural selection occurs when there is some variation in the inherited traits, some of these traits will give individuals an advantage over others, and the individuals with certain traits will be more likely to have more offspring.
      ::自然选择发生在遗传特征存在某些差异时,其中一些特征将使个人比其他特征有优势,而具有某些特征的个人更有可能有更多的后代。
    • Natural selection acts on the phenotype (the traits or characteristics) of an individual, not on the underlying genotype.
      ::对个人的苯型(特征或特征)的自然选择行为,而不是对基本基因型。
    • Carriers of a trait can show no symptoms of a recessive disease and, yet, still pass it on to their offspring.
      ::一种特质的载体不能显示任何消退性疾病的症状, 并且仍然将它传递给后代。

    Review
    ::回顾

    1. What's the difference between an acquired and inherited trait?
      ::既得的和继承的特性有什么区别?
    2. Define natural selection.
      ::界定自然选择。
    3. What is an adaptation?
      ::什么是适应?
    4. What is required for natural selection to take place?
      ::进行自然选择需要什么?
    5. How many species are there on the planet?
      ::地球上有多少种物种?
    6. What's the difference between phenotype and genotype? Does natural selection act on the genotype or phenotype?
      ::苯型和基因型有什么区别?
    7. Explain how a lethal recessive gene can stay in the gene pool.
      ::解释一个致命的消亡基因 怎么能留在基因库里