10.36 自然选择和人口 -- -- 高级
Section outline
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What's fitness?
::什么是健身吗?Does this type of fitness have anything to do with natural selection? Usually not. There are countless ways in which an organism can be more "fit," or better adapted to its habitat . And we probably do not know about most of these adaptations .
::这种类型的健康是否与自然选择有关?通常不会。生物体可以有无数种方法更适合或更适应其生境。我们可能不知道这些适应措施的大部分。Natural Selection
::自然选择自然选择While , including the bottleneck and founder effects, can cause microevolution (generational change in frequencies), its effects are mostly random. The results of genetic drift may include enhanced capabilities, but more often, they are neutral or deleterious. Natural selection depends not on chance, but on differential survival determined by an individual’s traits. Even though the variations are due to chance, the products of natural selection are usually organisms well-suited to their environment.
::尽管包括瓶颈和创建者效应在内,都可能导致微进(代际变化频率 ) , 但其影响大多是随机的。 基因漂移的结果可能包括能力的增强,但更经常地说,它们是中性的或有害的。 自然选择并不取决于机会,而取决于个人特征决定的不同生存。 尽管变异是偶然的,但自然选择的产品通常适合他们的环境。Recall that Hardy-Weinberg equilibrium requires that all individuals in a are equal in their ability to survive and successfully reproduce. As noted, however, overproduction of offspring and variation among individuals often lead to differential survival and – in other words, natural selection ( Figure ). We discussed natural selection as a part of Darwin’s theory of evolution in other concepts, but in this section, we will go deeper than Darwin could. We will explore natural selection at the level of populations – in terms of allele, genotype , and phenotype frequencies.
::回顾Hardy-Weinberg平衡要求所有个体在生存和成功繁殖能力上一律平等。 但是,正如人们所指出的,后代的过度生产和个人之间的差异往往导致不同的生存,换句话说,自然选择(图 ) 。 我们讨论自然选择是达尔文在其他概念中演进理论的一部分,但在本节中,我们将比达尔文更深入。 我们将探索人口层面的自然选择 — — 在异性、基因类型和苯型频率方面。Natural selection involves (1) heritable variation (here, giraffe neck length), (2) overproduction of offspring (3 giraffes born, not all can survive), (3) differential survival and reproduction (not enough food for all giraffes; those with shorter necks starve), and (4) gradual change in traits in the population (long-necked giraffes survive and reproduce, so their genes for long necks increase in frequency in the next generation).
::自然选择涉及1) 遗传变异(这里,长颈鹿颈长),(2) 后代的过度生产(出生的长颈鹿3人,并非所有人都能存活下来),(3) 生存和生殖差异(所有长颈鹿的食物不足;颈部较短的人挨饿),以及(4) 人口特征的逐渐变化(长颈长颈长颈鹿存活和繁殖,因此其长颈长颈的基因在下一代的频率增加)。
Acting on an Organism's Phenotype
::根据生物基因型采取行动Natural selection acts on an organism’s phenotype (appearance), which is a product of genotype and any environmental influences on . By selecting for alleles which improve survival and/or reproduction and selecting against harmful alleles, natural selection changes the proportion of alleles from one generation to the next – causing microevolution. Let’s return once more to our rabbit population. If a predator such as a hawk can see white rabbits (genotype bb ) more easily than brown rabbits ( BB and Bb ), brown rabbits are more likely than white rabbits to survive hawk . Because more brown rabbits will survive to reproduce, the next generation will probably contain a higher frequency of B alleles. Note, however, that the recessive b alleles are unlikely to disappear completely, because they can “hide” from the hawks in heterozygous brown rabbits. This is a good reminder that natural selection acts on phenotypes, rather than genotypes. The hawk - or natural selection - is unable to distinguish a BB rabbit from a Bb rabbit. The hawk is only able to distinguish a brown rabbit from a white rabbit, demonstrating how natural selection acts on the phenotype rather than the genotype of an organism.
::生物体的细胞型( 出现) 自然选择行为( 出现) 是基因型和任何环境影响的产物 。 通过选择能改善生存和(或)繁殖的异类, 并针对有害的异类选择, 自然选择会改变异类的比例, 导致微进。 让我们再次返回到我们的兔子群中。 如果像鹰这样的捕食者比棕兔( BB和Bb) 更容易看到白色兔子( genob) , 棕兔比白兔子更容易生存。 因为更多的棕兔会存活下来繁殖, 下一代可能含有更高频率的Belels。 但是, 注意, 闭类的异类虫不可能完全消失, 因为它们可以从异类的黑兔中“ ” 找到。 这很好地提醒人们, 白兔型的自然选择行为比基因型的兔子更可能无法区分BB兔子和B型兔子的繁殖。 注意, 亚型的生物学型兔子只能与亚型的兔子区别。Consider a different example, which emphasizes reproduction rather than survival: If both brown and white rabbits preferred to mate with white rabbits, the next generation’s gene pool would probably show an increase in the frequency of the b allele, because white rabbits would be more likely to reproduce successfully.
::想想另一个强调生殖而不是生存的例子:如果棕兔和白兔都愿意与白兔交配,下一代的基因库很可能显示白兔的频率增加,因为白兔更有可能成功繁殖。Although some traits are determined by a single gene , many are influenced by more than one gene (polygenic). The result of polygenic inheritance is a continuum of phenotypic values which often show a bell curve pattern of variation. Figure shows the effect of three genes, each having two alleles, on human skin color; the result is a normal distribution ranging from very dark to very light, with a peak near the middle. You can demonstrate polygenic inheritance (probably with some environmental influence) for height, ear length, or handspan by measuring your classmates and graphing the data in a similar fashion. Some curves will be flat, and others sharp – but most will resemble the normal “bell” shape.
::尽管某些特征是由单一基因决定的,但许多特征受不止一个基因(多基因)的影响。多基因继承的结果是一连串的雌性值,常常显示一个钟曲线的变化模式。 图显示了三种基因(每个基因有两个异长)对人类皮肤颜色的影响;结果的分布从非常黑暗到非常光亮,在中间附近有一个峰值。 通过测量你的同学和以类似的方式绘制数据图表,你可以看到高、耳长或手表的多基因继承(可能具有某种环境影响 ) 。 有些曲线将是平的,而另一些则很尖锐 — — 但大多数都类似于正常的“钟”形状。Given this pattern of phenotypic variation, natural selection can take three forms ( Figure ). We will use the theoretical human skin color distribution ( Figure ) to illustrate the three types of selection. Directional selection shifts the frequency curve away from the average by favoring individuals with an extreme form of the variation. The skin of early humans living in sun-rich Africa received high levels of UV radiation , which destroys vitamin B (folate) and leads to severe birth defects such as spina bifida. Selection, then, favored darker-skinned individuals, and the frequency of the darker alleles increased. After several generations, the curve would still be bell-shaped, but it would have shifted to the right, in the direction of the darker alleles. The average individual would have had darker skin as result of this microevolutionary change.
::鉴于这种视网膜变异的模式,自然选择可以采取三种形式(图 ) 。 我们将使用人类肤色分布理论(图 ) 来说明这三种选择类型。 方向选择将频率曲线从平均曲线向偏向偏向偏向偏向偏向偏向偏向偏向偏向偏向偏向偏向偏向偏向偏向偏向偏向偏向偏向偏向偏向偏向偏向向向向向向向向向向向偏向向向向向向向向偏向向向向向向偏向向向向向向向向向向向向向的曲线转移。 生活在阳光丰富的非洲早期人类的皮肤受到高紫外辐射的破坏, 维生素B ( folate) 并导致严重的先天性缺陷, 如脊柱形等 。 那么, 选择偏向偏向黑皮肤的人, 以及暗皮肤人的频率会增加。 。 在几代之后, 曲线仍然会变形, 但它会向右向偏向偏向偏向偏向偏向右, , 但向偏向偏向偏向偏向偏向偏向偏向偏向偏向偏向偏向右的偏向偏向偏向偏向偏向偏向偏向右的偏向偏向偏向偏向偏向偏向右的偏向右, 偏向偏向偏向偏向偏向偏向偏向偏向右, , 偏向偏向偏向偏向偏向偏向偏向偏向偏向偏向右的偏向偏向偏向偏向右, 但向偏向偏向偏向右的偏向偏向右, , 向右的偏向偏向偏向偏向偏向右的偏向偏向偏向右的偏向偏向偏向偏向偏向右, 偏向偏向偏向右, 。 。 , 。 。 , , 向偏向偏向偏向偏向偏向偏向偏向偏向偏向右的偏向偏向偏向偏向向向向右的偏向偏向向向向向右的偏向偏向右的偏向向向向向向右的偏向右, 向右, 向右的偏向向向向向向向向向右Three types of selection can alter allele frequencies, causing microevolution. The effect of stabilizing selection (1) is to reduce variation. Disruptive selection (2) results in two different populations, which may eventually become isolated from one another. Directional selection (3) enhances or reduces a single characteristic, such as trunk or snout length in the above example.
::三种选择可以改变所有频率,导致微变。稳定选择(1)的效果是减少差异。干扰选择(2)导致两种不同的人口,最终可能相互隔离。方向选择(3)提高或减少一个单一特征,如上述例子中的干线或鼻孔长度。Natural Selection and Human Migration
::自然选择和人口迁移As humans migrated into the northern hemisphere, excessive UV radiation was no longer a problem, but the relative lack of sunlight led to lower levels of vitamin D 3 , normally synthesized in the skin and necessary for calcium absorption and growth. Thus, selection in the north favored lighter-skinned individuals – another example of directional selection. However, if we consider the as a whole at that time, disruptive selection would describe the microevolution taking place. In northern climates, alleles for light skin would be favored, and in southern climates alleles for dark skin would be favored, resulting in two distinct peaks in the distribution of skin color phenotypes and their corresponding genotypes. Keep in mind that the “three gene – dark/light” model is an oversimplification of the genetics underlying skin color, but the adaptive values are real, and the model allows us to illustrate how microevolution works. Note that a map of human skin colors supports this type of selection to some extent ( Figure ).
::随着人类迁移到北半球,过分的紫外线辐射已不再是一个问题,但相对缺乏阳光导致维生素D3水平较低,这种维生素D3通常在皮肤中合成,对于吸收和生长钙是必需的。 因此,在北方,选择更喜欢皮肤较轻的人 — — 这是方向选择的另一个例子。 但是,如果当时从整体上考虑,破坏性选择将描述正在发生的微变。 在北方气候中,光皮肤的光谱会更受欢迎,而在南方气候中,暗皮肤的光谱会更受欢迎,导致皮肤色型及其对应基因型的分布出现两个截然不同的峰值。 牢记“ 三个基因- 黑暗/ 光” 模型是皮肤色下的遗传基因的过度简单化,但适应值是真实的,模型允许我们说明微变效果是如何起作用的。 注意人类皮肤图在某种程度上支持这种选择( 图示 ) 。The distribution of skin colors at least partially supports disruptive selection – for lighter skin in the north, to allow sunlight to form vitamin D 3 in the skin, and for darker skin toward the equator to prevent UV radiation from breaking down vitamin B-folate.
::皮肤颜色的分布至少部分地支持了干扰选择 — — 北部较轻的皮肤,允许阳光在皮肤中形成维生素D3, 以及更暗的皮肤向赤道的皮肤,以防止紫外线辐射破坏维生素B泡沫。Today, extensive , mobility, and intermarriage in the human population may be changing selective pressures on skin color once again. For the sake of argument, let’s make the somewhat unrealistic assumption that mixing becomes complete and that all people will be sufficiently mobile that they experience intermediate levels of sunlight. These conditions would select against both extremely dark skin (too little vitamin D 3 ) and extremely light skin (too little vitamin B-folate). The result would be a taller, narrower distribution – less diversity - about the same mean, a phenomenon known as stabilizing selection . Although our example is perhaps unrealistic, stabilizing selection is probably the most common form of natural selection, preventing form and function from straying away from a “proven” norm.
::如今,人口的广泛、流动性和异性通婚可能再次改变了对肤色的选择性压力。 为了论证,让我们假设混合是完全的,所有人都有足够的流动性,能够体验到中等水平的阳光。 这些条件既针对极暗皮肤(维生素D3太少 ) , 也针对极浅皮肤(维生素B-folate太少 ) 。 其结果将是更高、更窄的分布 — — 更少的多样性 — — 大约为同一平均值 — 一种被称为稳定选择的现象。 尽管我们的例子也许不切实际,但稳定选择可能是最常见的自然选择形式,防止形式和功能偏离“被证实”的规范。Stabilizing Selection
::稳定选择选择Stabilizing selection can lead to the preservation of harmful alleles. A famous example, which we considered in earlier lessons, is sickle-cell anemia ( Figure ). The gene for Beta- hemoglobin - half of the oxygen-carrying in our - has two alleles, which we will call Hgb-A and Hgb-S. Individuals having two copies of the Hgb-S allele suffer from sickle-cell anemia, a potentially lethal disease in which sickled clog capillaries and cannot carry oxygen efficiently. In equatorial regions, individuals with two copies of Hgb-A become infected with Plasmodium parasites and often die from malaria . However, individuals with one copy of each allele (the heterozygous genotype) escape both causes of death; although they may experience slight sickling at high altitudes, they do not suffer from full-blown anemia, and malaria parasites cannot infect their red blood cells . Stabilizing selection has maintained the frequencies of both alleles, even though each is potentially lethal in the homozygous state.
::稳定选择可导致保存有害的病源。我们在早期的教训中曾考虑过的一个著名例子是镰状细胞贫血(Figure )。Beta-hemoglobin的基因 -- -- 我们含氧量的一半 -- -- 有两个异源,我们称其为汞-A和汞-S。 具有两份汞-S allele的个人可能患有镰状细胞贫血,一种可能是致命的疾病,在这种疾病中,有病菌阻塞,不能有效地携带氧气。在赤道地区,有两份汞-A的人感染了疟原寄生虫,并经常死于疟疾。然而,每个异源(异源基因型)的基因基因都可避免两种死亡原因;尽管他们可能在高空经历轻度的生病,但他们不会患全热性贫血,而且疟疾寄生虫无法感染其红血细胞。稳定的选择保持了这两种异源的频率,尽管在同系菌状态下,每种人都有潜在的致命性。The distribution of malaria (left) correlates closely with the distribution of the sickle-cell allele (right). Because the heterozygous genotype confers immunity to malaria, this allele, which is lethal in the homozygous condition, persists in environments where malaria is common. Thus, natural selection can occasionally result in persistence of harmful alleles.
::疟疾(左)的分布与镰状细胞(右)的分布密切相关。 因为异体兹古斯基因型赋予疟疾豁免权,因此,在同质古斯病条件下致命的这种异体在疟疾常见的环境中持续存在,因此,自然选择有时会导致有害的异体持续存在。Selection for a particular trait may also select for other traits which do not directly affect fitness – if, for example, genes are linked, or if a single gene influences several different traits.
::特定特性的选择也可以选择不直接影响身体健康的其他特性 — — 例如,如果基因是相连的,或者如果一个单一的基因影响几种不同的特性。Fitness
::适合性Another way to look at natural selection is in terms of fitness - the ability of an organism with a certain genotype to reproduce. Fitness can be measured as the proportion of that organism’s genes in all of the next generation’s genes. When differences in individual genotypes affect fitness, the genotypes with higher fitness become more common. This change in genotype frequencies is natural selection.
::研究自然选择的另一种方法就是从健康的角度来看待自然选择 — — 一个具有某种基因型的有机体繁殖能力。 健康性可以用该生物体基因在下一代所有基因中的比例来衡量。 当个体基因型的差异影响健康性时,健康性较高的基因型会变得更加常见。 基因型频率的这种变化是自然选择的。Kin Selection
::选择金币An intriguing corollary of genotype selection is kin selection . Behaviors which sacrifice reproductive success or even survival can actually increase fitness if they promote the survival and reproduction of close relatives who share a significant proportion of the same genes. Examples include subordinate male turkeys, who help their dominant brothers display to potential mates ( Figure ), and honeybee workers, who spend their lives collecting pollen and raising young to ensure that their mother, the queen, reproduces successfully ( Figure ).
::基因型选择的一个令人感兴趣的必然结果就是选择亲属。 牺牲生殖成功甚至生存的牺牲行为如果能够促进拥有相同基因相当大比例的近亲的生存和繁殖,实际上可以提高健康。 例子包括下属男性火鸡,他们帮助其占优势的弟弟向潜在伴侣展示(图 ) , 蜜蜂工人,他们花一生的时间收集花粉和养育年幼者,以确保母后成功繁殖(图 ) 。Wild turkeys display in groups of closely related individuals, but only alpha males eventually mate. Subordinate males sacrifice their chance to reproduce, even chasing away other males to promote their dominant brothers’ success, because this behavior increases the chance that the genes they share will be represented in the next generation. This means of increasing gene frequency is kin selection.
::野生火鸡在紧密关联的个人群体中出现,但最终只有阿尔法男性交配。 屈从的雄性牺牲了繁殖机会,甚至追逐其他雄性以促其占优势的兄弟成功,因为这种行为增加了他们共享的基因在下一代中代表的可能性。 增加基因频率的手段是亲属选择。Many social insects also illustrate kin selection. These honeybee workers are sterile. They spend their lives collecting pollen, feeding larvae, and cleaning and defending the hive. With no chance of reproductive success of their own, they dedicate their lives to the reproductive success of the hive’s queen – their mother – who shares 50% of her genes with each of them.
::许多社会昆虫也展示了亲属选择。 这些蜜蜂工人不育。 他们花一生的时间收集花粉、喂幼虫、打扫和捍卫蜂巢。 在自己没有生育成功机会的情况下,他们把生命献给蜂巢女王 — — 他们的母亲 — — 的生育成功,后者与每个蜂巢分享50%的基因。We have looked carefully at equilibrium populations and at possible disruptions of equilibrium which cause microevolution – a generational change in a population’s allele frequencies :
::我们仔细研究均衡人口和可能造成微变的均衡中断情况,-
, together with
, are the ultimate sources of variation, and are important causes of microevolution in microorganisms.
::与微生物一起是变异的最终来源,也是微生物微变的重要原因。 -
can accelerate microevolution by importing new, already successful alleles into the population.
::可以通过向人口输入新的、已经取得成功的灵长类来加速微演化。 -
Genetic drift can increase the effect of chance variations in small populations.
::基因漂移可增加小人群机会变化的影响。 -
Natural selection can be directional, disruptive, or stabilizing.
::自然选择可以是方向性的、破坏性的或稳定的。 -
Specialized types of selection, such as mate selection and kin selection, can cause microevolution.
::特殊选择类型,如配偶选择和亲属选择,可导致微进。
Evolutionary biologists are not yet in agreement regarding the relative importance of each type of selection to the , although most would agree that natural selection is the primary force in microevolution. In the next lesson, we will apply our understanding of microevolutionary processes to that “mystery of mysteries,” as Darwin and Herschel called it: the origin of .
::进化生物学家尚未就每种选择的相对重要性达成一致,尽管大多数人会同意自然选择是微进的主要力量。 在下一个教训中,我们将将我们对微进过程的理解应用到达尔文和赫歇尔称之为“神秘神秘”的“神秘之谜 ” ( 达尔文和赫歇尔称之为“神秘之谜 ” : 其起源 ” 。Summary
::摘要-
Natural selection occurs in populations of any size and results are more likely to adapt a population to its environment.
::自然选择发生在任何规模的人口中,结果更有可能使人口适应环境。 -
Natural selection acts on phenotypic variations; some phenotypic variations may include environmental effects which are not heritable.
::自然选择行为涉及地貌差异;有些地貌差异可能包括不可遗传的环境影响。 -
Evolution is a result of natural selection and is measured as a change in allele frequencies.
::进化是自然选择的结果,是用阿列斯频率的变化来衡量的。 -
For a trait whose genetic basis is polygenic, the pattern of phenotypic variation usually forms a bell curve about an average value.
::对于遗传基础为多基因的特征,视位变化模式通常形成一个平均值的钟曲线。 -
Directional selection results in a shift of allele frequencies toward one extreme.
::方向选择的结果是将Alle频率向一个极端转移。 -
Disruptive selection favors both extremes over the average phenotypic value.
::干扰性选择优于两种极端,优于平均胸前值。 -
Stabilizing selection maintains or narrows existing variation in phenotype.
::稳定选择维持或缩小目前苯型的变异。 -
Fitness is the ability of an organism with a certain genotype to reproduce successfully.
::适合性是具有某种基因型的生物体成功繁殖的能力。 -
Because alleles often affect more than one trait in different ways, or have different effects in different environments, natural selection can sometimes lead to the persistence of harmful or even lethal alleles.
::由于所有物往往以不同的方式影响一个以上的特性,或在不同环境中产生不同的影响,自然选择有时会导致有害甚至致命的物种持续存在。 -
Kin selection involves the sacrifice an individual's own reproductive potential in order to help a close relative reproduce successfully.
::选择坚果涉及牺牲个人自己的生育潜力,以帮助近亲成功繁殖。
Review
::回顾-
Use the distribution of phenotypes for a trait whose genetic basis is polygenic to interpret directional, disruptive, and stabilizing patterns of selection.
::使用苯型的分布,用于遗传基础为多源的特性,解释选择的方向性、破坏性和稳定性模式。 -
Describe how natural selection can sometimes lead to the persistence of harmful or even lethal alleles. Include an example.
::说明自然选择有时会如何导致有害甚至致命的排流物的持续存在。 -
Describe kin selection. Give an example.
::描述亲属选择。 例如 。
-
, together with
, are the ultimate sources of variation, and are important causes of microevolution in microorganisms.
