10.40 预防率 -- -- 先进
章节大纲
-
Fast or slow?
::快速还是慢?Which is better, the direct route or the scenic route? Each has its advantages, depending on the situation. And that describes evolution. It can be fast or slow, depending on the situation.
::哪个更好, 直接路线还是景色路线? 每一个路径都有其优势, 取决于情况。 这描述了进化。 它可以是快速的,也可以是慢的, 取决于情况。The Tempo of Speciation
::预防的温度Speciation and extinction characterize all life on earth; the clearly documents both. Two startling facts emerge from careful study of the fossil record: first, the average successful lives for “just” a few million years, and second, over 99.9% of all species that have ever lived have become extinct. The last aspects of speciation that we will consider are the tempo and pattern of species formation.
::地球上所有生命的特征是重复和灭绝;两者都有清楚的文件。 仔细研究化石记录后得出两个惊人的事实:第一,“仅仅”几百万年的平均成功寿命;第二,超过99.9%的物种已经灭绝。 我们将要考虑的物种特征的最后方面是物种形成的节奏和模式。Over time, geographic changes isolate . Small populations experience . alter individual genotypes and gene pools. New habitats form, and small groups colonize them. It is clear that evolution continues to change life. However, there is considerable debate about the rate at which speciation occurs over geologic time. Most biologists agree that single mutations seldom, if ever, cause new species in single evolutionary “leaps.” Mutations in regulatory genes, which have major effects during , may be an exception, but in general, mutations are more likely to be harmful and selected against. Except for the special case of polyploidy, speciation cannot occur within a single generation. So, what do we know about the rate and pattern of speciation?
::随着时间推移,地理变化将产生孤立。小群落经历。改变个体基因类型和基因集合。新的生境形式和小群群将它们殖民化。进化过程显然继续改变着生命。然而,对于在地质时间里发生物种特征的速度,人们争论不休。大多数生物学家都认为,单种突变很少(如果曾经发生的话)在单一进化“滴”中造成新的物种。 监管基因中的变异(在 ” 中具有重大影响)可能是一种例外,但一般来说,突变更可能是有害的,而且更可能是与之相反的。除了多球体的特殊案例外,分化不可能在一代人中发生。因此,我们对分化的速度和模式了解多少?Some evolutionary biologists consider the rate of evolution to be slow and constant, with small changes accumulating to form big changes – the idea of gradualism . Others (Niles Eldridge and Stephen Jay Gould), in response to the apparently “sudden” appearance of new forms in the fossil record, suggest that species diverge in bursts of relatively rapid change and then remain stable for relatively long periods – a model known as punctuated equilibrium . Gould maintains that both speciation and evolution occur rapidly in small, peripheral populations, whereas large, central populations remain stabilized for long periods of time. It is the large, central, stable populations which are represented in our fossil record, he argues – not the small, peripheral, evolving ones. In this model, species form as they rapidly adapt to open niches, a process referred to as adaptive radiation . The two models are compared in Figure .
::一些进化生物学家认为进化速度是缓慢和恒定的,小变化逐渐积累,形成巨大的变化 — — 渐进主义思想。 其他人(Niles Eldridge 和 Stephen Jay Gould ) , 对化石记录中新形式的明显“突然”出现的反应表明,物种在相对快速变化的连发中出现差异,然后在相对长的时期内保持稳定 — — 一种被称为“分化平衡”的模式。 古尔德认为,在小型外围人群中,分层和演化迅速发生,而大型中央人群则长期保持稳定。 他辩称,在我们的化石记录中代表着大量、中枢、稳定的人口 — — 而不是小的、外围的、不断发展的人口。 在这种模型中,物种在快速适应开放的切入点(即适应性辐射 ) 过程中的形式是不同的。 两种模型在图中进行了比较。Two views of the rate at which speciation occurs: Gradualism (top) holds that small changes accumulate gradually to form big changes. Punctuated Equilibrium (bottom) suggests that rates of change accelerate over short periods (the horizontal changes in morphology which “punctuate” the tree of life) and then stabilize for relatively long periods (the vertical lines, indicating morphology is at equilibrium). To read such an evolutionary tree, keep in mind that the top represents the present: the tips of all branches which reach the top are today’s species, and any branches that fail to reach the top represent extinctions.
::分层发生速度的两种观点:渐变主义(顶部)认为小变化会逐渐累积,形成巨大的变化。 点平衡(底部)表明变化速度会在短期内加速(形态的横向变化,“突现”生命树),然后稳定在相对较长的时期(垂直线,表示形态处于平衡状态 ) 。 要阅读这样一棵进化树,请记住顶部代表当前:到达顶部的所有分支的小指点是今天的物种,而任何未能到达顶部的分支代表灭绝。In either case, species require several thousand generations – which may require several thousand years – to form. Relative to the species’ “lifespan” and the modest precision of our ability to pinpoint time within the geologic record, the differences between the two models may be minimal. Major characteristics of species could have evolved gradually over thousands of years, and we would still not be able to detect those changes on the . What we do detect are long periods of relative stability, when stabilizing selection tends to maintain equilibrium. Changes in both physiology and internal anatomy could have continued during the long periods of apparent equilibrium without our seeing them; the fossil record cannot reveal these types of changes. The debate is not about the mechanism of evolution – only its tempo.
::无论哪种情况,物种都需要几千代人 — — 这可能需要几千年 — — 才能形成。 相对于物种的 " 生命空间 " 和我们精确地确定地质记录中时间的能力,这两种模型之间的差异可能微乎其微。 物种的主要特征可能已经逐渐演变了数千年,我们仍无法检测到这些变化。 我们所发现的是长期的相对稳定时期,稳定选择往往能够保持平衡。 生理学和内部解剖学的变化本来可以在表面平衡的长时期内继续下去,而不让我们看到它们;化石记录无法揭示这些类型的变化。 辩论不是关于进化机制 — — 仅涉及其节奏。Gradualism
::渐进主义Gradualism states that small changes accumulate to form major changes. What might be considered a small, insignificant change may in itself not lead to speciation, but may increase fitness . Together, numerous similar changes, which would occur over many generations equivalent to thousands of years or more, may lead to speciation. Examples of gradualism are readily observed in the world. These changes may not be observed within the fossil record.
::渐变论指出,小的变化会积累成重大变化。 可能被视为小的、微不足道的变化本身可能不会导致分化,但可能会提高体质。 相形之下,许多类似的变化(在几代人之间,相当于数千年或更长时间)可能导致分化。 渐进主义的例子在世界上很容易观察到。 这些变化也许不会在化石记录中观察到。-
Small variations occur over time in a population of wolves. Such changes include larger ears, longer teeth, and a heightened sense of
smell
. Wolves with these helpful traits have increased fitness, allowing preferential survival. Over many generations, the traits gradually become increasingly common among the population.
::随着时间的推移,狼群会发生小的变化,这些变化包括耳朵大、牙齿长和嗅觉增强。 具有这些有益特性的狼提高了体质,允许优先生存。 在许多代人中,这些特征逐渐在人群中变得日益普遍。 -
Over the period of many generations, a population of elephants develops larger ears to help protect the elephants from the sun and keep them cool. Just like the wolf population, this larger ear is an advantageous trait and eventually becomes a physical feature of the entire population of elephants.
::在几代人的时间里,一大批大象形成更大的耳朵,帮助保护大象免受太阳的侵袭,并保持它们凉爽。 就像狼群一样,大耳朵是一种优点,最终成为整个大象群的自然特征。 -
A
is born with a longer
beak
than others in its population, which allows it to more easily forage for
inside trees, offering it an advantage over its shorter-beaked relatives, obviously increasing its fitness. Though this starts in just one bird, the advantage begins to spread throughout the population as more and more birds in the population are born with this advantageous feature, eventually resulting in the entire population of birds with longer beaks.
::人出生时的嘴比人口中其他人长,这使人更容易在树内觅食树木,使其比短嘴的亲属更有利,明显地提高了身体健康。 虽然这只是从一只鸟开始,但随着越来越多的鸟出生时具有这一有利特征,其优势开始蔓延到整个人口,最终导致所有鸟口长的鸟类。 -
Obviously, not all cats in the
genus
Panthera
, which includes lions, jaguars, leopards, and tigers, have stripes. At some point, divergence of the species needed to begin. Over a long period of time, probably well over thousands of years, tigers developed the combination of orange and black stripes, which allowed them to hide in tall grasses as they stalk their
prey
. This trait eventually became one of the distinguishing features of tigers, as the coloring on all future tigers changed to adopt the orange and black stripe coloring.
::很明显,在豹形动物中,并非所有的猫都有条纹,它们包括狮子、美洲豹、豹和老虎。在某个时候,物种的差异需要开始。在很长一段时间里,老虎们发展了橙色和黑色条纹的结合,在它们跟踪猎物时,它们可以躲在高草中。这一特征最终成为老虎的显著特征之一,因为未来所有老虎的颜色都改变为橙色和黑色条纹颜色。 -
Small variations appear over a long period of time among a population of penguins. A population of penguins has thousands to millions of individuals. When resources are limited, any advantage that increases fitness is beneficial. Variations among individuals include thicker coats of down that allow them to survive in very cold climates. Penguins with these traits survive much better than those with thinner down coats, leading to the changes becoming standard among all penguins.
::长期以来,企鹅群中出现了小的变化。企鹅群中有数千至数百万人。当资源有限时,任何提高健康水平的优势都是有益的。个人之间的差异包括更厚的下层外套,这使他们能在非常寒冷的气候下生存。具有这些特征的企鹅的生存能力比穿更薄的外衣的企鹅要好得多,从而导致所有企鹅之间的变化成为标准。 -
The relationship between
flowers
and their
pollinators
is obviously important. What happens if a flower is able to attract more pollinators? A species of flowers adapts over time to attract more bees, a change encoded in the flower's
that allows the flowers to spread its
pollen
further and increase the size of the population. The
adaptation
is advantageous to the flowers and, after a long period passes, the flowers all gradually adopt the adaptation.
::花及其授粉者之间的关系显然很重要。 如果花能吸引更多的授粉者,会发生什么情况? 花种会随着时间的流逝而变化,以吸引更多的蜜蜂,花朵的编码会改变,使花朵能够进一步传播花粉,增加人口规模。 适应有利于花朵,在经过很长一段时间之后,花朵会逐渐采用适应方法。
Punctuated Equilibrium
::标点平衡Proponents of either model admit that the pace of evolution probably changes from one set of conditions to another. Lake Victoria in East Africa, for example, is just a million years old, and yet it is home to more than 300 species of cichlid found nowhere else ( Figure ). Genetic analysis shows that all of them descended from a single ancestral “founder” species; this is relatively rapid evolution. Without , that species expanded across the huge Lake, and suited individual populations to exploit the many different food sources and habitats present in the Lake. Cichlid evolution is an example of adaptive radiation similar to that of Darwin’s finches and Hawaiian honeycreepers, discussed in the Evolution concepts. The fossil record shows similar opportunities for accelerated evolution after . The extinction of the dinosaurs opened an abundance of ecological niches, soon occupied by radiating birds and mammals . Speciation may accelerate not only with a major increase in available niches, but also with the appearance of new adaptations, such as legs or wings , which allow a group to enter a variety of new niches. In contrast, long periods of environmental stability may slow the pace of speciation.
::这两种模型的支持者都承认进化速度可能从一组条件变化到另一组条件。 例如,东非的维多利亚湖(Victoria Lake)只有100万年的历史,然而它却拥有300多种在其他地方都找不到的cichlid物种(图 )。基因分析显示,所有这些物种都来自一个祖传的“创始人”物种;这是相对快速的演变。没有这种物种,这些物种会跨越巨大的湖泊,并适合个体种群来利用湖中存在的许多不同的食物来源和生境。Cichlid的进化是适应性辐射的一个例子,类似于进化概念中讨论的达尔文的芬切和夏威夷蜂蜜猎人。化史表明类似的机会在进化后加速进化。恐龙的灭绝打开了大量的生态位置,很快被散热的鸟类和哺乳动物所占据。 拼凑的步伐可能不仅随着现有位置的大幅增长而加快,而且随着新的适应性(例如腿和翅膀)的出现,使得一个群体能够进入各种新位置。相反,环境稳定度的漫长时期可能会减缓。You can see that both evolution and our investigations into how evolution funcitons are ongoing works in progress. We have come a long way in understanding “the origin of species” since , but questions remain. Exactly what is selected - genes, genotypes, phenotypes , or individuals – is still debated; some, such as Stephen Jay Gould, accept that selection acts at multiple levels. Exactly how fast speciation occurs also remains under discussion; both gradualism and punctuated equilibrium models have merit. Several definitions of a species today serve different purposes; eventually, they should merge into a single clear picture of this basic unit of evolution.
::你可以看到,进化过程和我们对进化真菌是如何在不断起作用的调查都在进行之中。我们从那时以来在理解“物种起源”方面已经取得了长足的进展,但问题依然存在。 所选择的基因、基因类型、苯型或个人等,仍然在争论;有些,例如斯蒂芬·杰伊·古尔德(Stephen Jay Gould),承认在多个层面的选择行为。 精确地说,分解速度也还在讨论之中;渐进主义和分化平衡模式都有其优点。 如今,对一个物种的若干定义服务于不同的目的;最终,它们应该合并为这一基本进化单元的单一清晰图景。Behind these disagreements, however, lies a powerfully reinforced theory of evolution and an increasingly detailed story of life on Earth. By any definition, humans form a single species, increasingly united by mobility, common genes, and common resources. We and the millions of species whom we share the Earth with today all arose from a single common ancestor billions of years ago – through deep time and the myriad of instances of allopatric and sympatric speciation . Amazing adaptive logic was most often a result of directional, stabilizing, and disruptive environmental forces selecting for favorable variations and against unfavorable ones. Chance played a major role – through mutation, , genetic drift, and much environmental change. The pace of speciation probably varied – from gradual change, to rapid change, to long periods of stability. Both speciation and extinction continue today – and will continue into the future, although we cannot predict the direction, because chance determines so much of the direction evolution takes. As a unique species, we are significantly influencing the amount of extinction – and may consequently affect the rate of speciation, as well. That, however, is a topic for a later concept.
::然而,在这些分歧背后,存在着一种强有力的进化理论和越来越详细的地球生命故事。 不论从任何意义上讲,人类形成一个单一的物种,并日益通过流动性、共同基因和共同资源而团结在一起。 我们和我们共同拥有今天的数以百万计的物种都来自于一个共同的祖先,数十亿年前 — — 经历了深刻的时间和无数的异族和异族异族和异族异族异族现象。 惊人的适应逻辑往往是选择有利变异和不利于不利变异的环境力量的结果。 机会通过突变、遗传漂移和许多环境变化发挥了主要作用。 探险的速度可能各不相同 — — 从逐渐变化到迅速变化,到长期的稳定时期。 探险和灭绝现象今天仍在继续,并且会持续到未来,尽管我们无法预测方向,因为机会决定了方向演变的如此之大。 作为一个独特的物种,我们正极大地影响着灭绝的程度,并因此可能会影响探险的速度。 然而,这是一个后来的话题。Summary
::摘要-
The Gradualism model of speciation holds that small changes accumulate to form big changes.
::分化的渐进主义模式认为,小变化会累积成大变化。 -
The Punctuated Equilibrium model suggests that rates of change accelerate over short periods in small, peripheral populations and then stabilize for long periods in large, central populations.
::标定的平衡模式表明,在短时期内,小型外围人口的变化速度加快,然后在大中部人口长期稳定。 -
Differences between the two may be minimal, because gradual change can occur over thousands of years without our ability to detect it in the fossil record.
::两者之间的差别可能微乎其微,因为逐步变化可能持续数千年,而我们却没有能力在化石记录中发现。 -
Conditions that may accelerate speciation are mass extinctions and the formation of new habitats (e.g. volcanic islands) because both create a sudden availability of many “empty” niches.
::可能加速物种分布的条件是大规模灭绝和形成新的生境(如火山岛),因为两者都造成许多“空”空地突然出现。 -
Evolution of a major new adaptation, such as legs or wings, may also accelerate speciation by suiting a species to multiple new habitats.
::诸如腿或翅膀等重大新适应的演进也可能通过使物种适应多个新生境而加快物种的分化。 -
Long periods of environmental stability may slow the rate of speciation.
::长期的环境稳定可能会减缓物种划分的速度。
Review
::回顾-
Compare and contrast the gradualist and punctuated equilibrium models of evolutionary change. Give examples which support each.
::比较和对比进化变化的渐进和标点平衡模型。 给出支持每种变化的示例 。
-
Small variations occur over time in a population of wolves. Such changes include larger ears, longer teeth, and a heightened sense of
smell
. Wolves with these helpful traits have increased fitness, allowing preferential survival. Over many generations, the traits gradually become increasingly common among the population.
