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Lesson 9the origin of species

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Charles Darwin and the Origin of Species

Charles Robert Darwin(1809.02.12 － 1882.04.19), who is the father of the theory of origin of species.

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Background information This article is about Charles Darwin's book.

It introduced the theory that populations evolve over

the course of generations through a process of

natural selection. Darwin's book was the

culmination of evidence he had accumulated on the

voyage of the Beagle in the 1830s and expanded

through continuing investigations and experiments

after his return.

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Background information

In biology, evolution is the changes in the inherited traits of a population of organisms from one generation to the next. These changes are caused by a combination of three main processes: variation, reproduction, and selection.

Genes that are passed on to an organism's offspring produce the inherited traits that are the basis of evolution. These traits vary within populations, with organisms showing heritable differences in their traits.

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Background information

When organisms reproduce, their offspring may have new or altered traits. These new traits arise in two main ways: either from mutations in genes, or from the transfer of genes between populations and between species.

In species that reproduce sexually, new combinations of genes are also produced by genetic recombination, which can increase variation between organisms. Evolution occurs when these heritable differences become more common or rare in a population.

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Background information Two major mechanisms drive evolution.

The first is natural selection, a process causing heritable traits that are helpful for survival and reproduction to become more common in a population, and harmful traits to become more rare.

This occurs because individuals with advantageous traits are more likely to reproduce, so that more individuals in the next generation inherit these traits. Over many generations, adaptations occur through a combination of successive, small, random changes in traits, and natural selection of those variants best-suited for their environment.

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Background information

The second major mechanism is genetic drift, an independent process that produces random changes in the frequency of traits in a population.

Genetic drift results from the role probability plays in whether a given trait will be passed on as individuals survive and reproduce. Though the changes produced in any one generation by drift and selection are small, differences accumulate with each subsequent generation and can, over time, cause substantial changes in the organisms. This process can culminate in the emergence of new species.

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Glossary

allopatric speciation 异域物种形成，异地物质形成 [ ] Allopatric speciation: the new species arises from a

population that is geographically separated

allo- 或 all- [] ( 前缀 ), 表示“分歧，不同”之义

其它的 , 不同的 allopatric. 分布在邻近不同地区的 同分异构的 allocholesterol. 异胆固醇

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sympatric speciation

[]

同域物种形成，同地物质形成，分布区重叠物质形成 sym- pref ( 用在字母 b, m, p 之前 ) = syn- 　表示“共 , 合”

之义

synecology 　群体生态学； syncarp 　合心皮果； sympatric 　同域的

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polyploid []n. 倍数体 , 有多倍染色体 adj. 多倍体

的

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analogy[] 相似，同功 convergence [] n. 集中 , 收敛 ;( 生物学 ) 趋同 convergent adj.

divergence []

n. 分歧 ;( 生物学 ) 趋异 divergent adj.

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homology []n. 同源性，同种性，同系性

phalange[]n. 　 [ 解 ] 指骨 , 趾骨

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cline []n.[ 生 ] 梯度变异，变异群，渐变群

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evolution

convergent evolution

divergent evolution

parallel evolution

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extinction[]

In biology and ecology, extinction is the c

essation of existence of a species or grou

p of taxa. The moment of extinction is ge

nerally considered to be the death of the

last individual of that species.

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hybrid sterility

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macroevolution &microevolution macroevolution[]//macro-

n.( 动、植物的 ) 宏 ( 观 ) 进化 , 种外进化 , 大进化　

microevolution[]//micro-

n. 微进化 , 种内进化

Macroevolution is the origin of new taxonomic

groups, as opposed to microevolution, which is

genetic variation between generations within a

species.

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genetic drift 遗传漂变

Random fluctuations in the frequency of the

appearance of a gene in a small, isolated

population, presumably owing to chance

rather than natural selection.

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gene flow 基因流动

Transfer of genes from one population to

another of the same species, as by

migration or the dispersal of seeds and

pollen.

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phylogeny [] 种系发生，系统发生，系统发育

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Punctuated equilibrium

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reproductive isolation

An important concept in evolutionary biology, reproductive isolation is a category of mechanisms that prevent two or more populations from exchanging genes.

Reproductive isolation can occur either by preventing fertilization, or by the creation of a degenerate or sterile hybrid, such as the case with the common mule.

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1 how biologists define a species

A species is a population or group of popul

ations whose members have the potential to i

nterbreed with one another and produce viabl

e offspring, but who cannot produce viable of

fspring with other species.

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The biological species concept is based on inter-fertility, rather than physical similarity.

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Alternative concepts of species

a.  Ecological species concept

- Species are defined by their use of environmen

tal resources; their ecological niche (e.g. species

that are defined by their food source such as butt

erflies with certain flowers).

niche 小生境，生物居所的特定区间

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Alternative concepts of species

b.  pluralistic species concept

- Factors that are most important for the

maintenance of individuals as a species

vary.  These factors include reproductive

isolation, i.e. not being in the same area so

mating is precluded.                 

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Alternative concepts of species

c.  Morphological ( 形态学 )species concept

- Species are characterized according to a unique set of structural features.  This is still the most widely used concept by taxonomists( 分类学家 ).

d.  Genealogical species concept genealogical[]adj.宗谱的 , 系谱的 , 家系的 - Recognizes species are sets of organisms with unique

genetic histories. This idea is based often on molecular analyses such as DNA sequences.