后达尔文时代何去何从

1882年达尔文去世前,至少让他感到满意的是,进化论被自然科学界所接受了。达尔文的科学巨著《物种起源》论证了两个问题：第一,物种是可变的,生物是进化的。当时绝大部分生物学家都相继接受了这个事实,进化论从此取代神创论,成为生物学研究的基石。第二,自然选择是生物进化的动力。对于这一重要思想,当时的生物学家和地质学家都心存疑虑,所以,适者生存是进化机制的思想,只吸引了少数追随者。     

乌龟寿星曾是达尔文的宠物吗？

2006年6月22日，一只176岁的乌龟在澳大利亚一家动物园去世，一些人相信，这只乌龟是英国生物学家查尔斯·达尔文从美洲厄瓜多尔加拉帕戈斯群岛带回欧洲的，它在达尔文推出进化论过程中起过一定作用。这只传奇乌龟叫哈莉叶，虽然哈莉叶已经去世，但是它的身世还是个谜，不过这丝毫不影响它成为明星，这位老寿星总是能吸引众多参观者的目光。     

达尔文雀——"自然选择"与"适应"的经典例证

1831年,达尔参加了一次为期五年的环球旅行,他乘坐“贝格尔号”游历了巴西、南美洲的东海岸和西海岸、新西兰、澳大利亚和塔斯马尼亚岛;最后经过印度洋,绕过非洲好望角,横渡大西洋,再回到巴西。他在这次科学旅行中,仔细地观察了所到各处的地质矿物、生态环境和生物类型,发现了很多有趣的现象。     

走近达尔文(2)--达尔文与拉马克

提起“物竞天择,适生存”,我们必然会想起达尔;而提到达尔,我们又必定会想到拉马克。在生物进化理论的历史上,这二的名字代表了永不磨灭的辉煌。     

生物进化研究的回顾与展望

生物进化是自然科学的永恒之迷。随着历史的发展和科学的进步,生物进化思想从早期的萌芽,到自然选择学说、新达尔文主义,从现代综合理论,到分子进化的中性学说。再到新灾变论和点断平衡论等。当前,由于生物学各分支学科的飞速发展．它们就各自的研究对象在宏观和微观上不断地拓展和深入,并在不同的层次上形成了广泛的交叉、渗透和融合,现代的进化生物学研究从宏观的表型到微观的分子,从群体遗传改变的微进化到成种事件以及地史上生物类群谱系演化的宏进化,从直接的化石证据到基于形态性状、分子证据和环境变迁的综合推理,从基于遗传基础的比较基因组学到演化机理的进化发育生物学等。可以预见,在新的世纪里,在哲学和具体方法论(如系统论、控制论和信息论)的指导下,在生命科学、其他自然科学乃至社会科学工作者的通力合作下,综合遗传、发育和进化等研究领域的各种理论成果,生物进化理论即将出现也一定会出现的一个新的大综合和新的大统一。     

加拉帕戈斯群岛山雀仍在进化中——达尔文进化论找到新证据

岛类为了争食可以从“大嘴”变成“小嘴”。美国科学家经过长期对加拉帕戈斯群岛鸟类的研究证实,激发达尔文产生进化论思想的鸟类仍在进化中。这一研究成果也为达尔文的进化论提供了新的证据。14日出版的《科学》杂志公布了这个研究成果。■大喙变小喙由美国普林斯顿大学生物学     

达尔文与《物种起源》

现代生物学之父查尔斯·达尔文（Charles Darwin）于1809年2月12日出生于英国什鲁斯伯里一个富裕的中产阶级家庭，他的祖父伊拉兹马斯·达尔文（Erasmus Darwin，1731—1802）和父亲罗伯特·达尔文（Robert Darwin，1766—1848）都是很成功的医生，积累了大笔财产。很巧的是，伊拉兹马斯·达尔文是进化论先驱，     

达尔文进化论的科学本质与贡献

自达尔文1859年发表《物种起源》一书以来,“进化”已逐渐成为生物学文献中出现频率最高的词汇之一。随着科学界对生物进化现象的认识逐渐深入,人们对达尔文进化论的理解也在不断深化和提高。从魏斯曼等人提出“新达尔文主义：到摩尔根等人以“粒子遗传”替代“融合遗传”的概念以及费希尔、霍尔丹和赖特等人创立群体遗传学,     

进化与适应观培养的单元教学设计——以“生命起源和生物进化”为例

以“生命起源和生物进化”为例,阐述了进化与适应观培养的单元教学设计。通过纵向上注重任务解构—活动设计—概念建构一致性,横向上注重任务间环环相扣和素养发展层层递进,构建了网络型单元教学体系,进而聚焦系统知识和素养培育,提升学科育人价值。教学实践表明,在单元教学设计中注重提升教学设计站位,从学科育人的视角创设情境,通过一体化的单元教学设计网络实现核心素养落地,具有很好的教学效果。     

走近达尔文(1)--《物种起源》与达尔文的进化理论

1859年达尔《物种起源》一书首版面世,首次系统全面地论述了达尔自己的进化论思想,书中引用了很多古生物学、地质学和生物学等方面的证据,详实可信,使科学的进化理论第一次在宗教神学所包围的大的社会环境下旗帜鲜明地被确立下来,不再是以前较软弱、不够完善的理论假说或思想萌芽了。此后,越来越多的人了解、接受了达尔的进化思想,并使之不断发展、完善,产生了系统的进化理论体系——达尔主义。     

Sisyphean evolution in Darwin's finches

The trajectory of speciation involves geographic isolation of ancestral populations followed by divergence by natural selection, genetic drift or sexual selection. Once started, the process may experience fits and starts, as sometimes diverging populations intermittently reconnect. In theory populations might cycle between stages of differentiation and never attain species status, a process we refer to as Sisyphean evolution. We argue that the six putative ground finch species (genus Geospiza) of the Galápagos Islands represent a dramatic example of Sisyphean evolution that has been confused with the standard model of speciation. The dynamic environment of the Galápagos, closely spaced islands, and frequent dispersal and introgression have prevented the completion of the speciation process. We suggest that morphological clusters represent locally adapted ecomorphs, which might mimic, and have been confused with, species, but these ecomorphs do not form separate gene pools and are ephemeral in space and time. Thus the pattern of morphological, behavioural and genetic variation supports recognition of a single species of Geospiza, which we suggest should be recognized as Darwin's ground finch (Geospiza magnirostris). We argue that instead of providing an icon of insular speciation and adaptive radiation, which is featured in nearly every textbook on evolutionary biology, Darwin's ground finch represents a potentially more interesting phenomenon, one of transient morphs trapped in an unpredictable cycle of Sisyphean evolution. Instead of revealing details of the origin of species, the mechanisms underlying the transient occurrence of ecomorphs provide one of the best illustrations of the antagonistic effects of natural selection and introgression.     

Divergence and evolution in Darwin's finches

The medium and large ground finches of the Galapagos archipelago Geospiza fortis and G. magnirostris are distinguished by their different body size and bill dimensions on most of the islands where they both occur. On the island of Indefatigable this distinction is not complete and a group of birds with intermediate bill dimensions is present. The origin of this group could be explained by sympatric divergence of G. fortis or by hybridization, between this species and G. magnirostris . Although the conditions for sympatric divergence are severe it seems likely that strong disruptive selection for different optimal bill sizes may be operating on G. fortis , due to the presence of several ecological niches, separate categories of size and hardness of seeds the birds eat. It is suggested that islands in the Galapagos archipelago, and perhaps other oceanic islands, may provide conditions extremely conducive to sympatric divergence, or even sympatric speciation.     

Convergent evolution of Darwin's finches caused by introgressive hybridization and selection

Abstract Between 1973 and 2003 mean morphological features of the cactus finch, Geospiza scandens, and the medium ground finch, G. fortis, populations on the Galápagos island of Daphne Major were subject to fluctuating directional selection. An increase in bluntness or robustness in the beak of G. scandens after 1990 can only partly be explained by selection. We use 16 microsatellite loci to test predictions of the previously proposed hypothesis that introgressive hybridization contributed to the trend, resulting in genes flowing predominantly from G. fortis to G. scandens. To identify F₁ hybrids and backcrosses we use pedigrees where known, supplemented by the results of assignment tests based on 14 autosomal loci when parents were not known. We analyze changes in morphology and allelic composition in the two populations over a period of 15–20 years. With samples that included F₁ hybrids and backcrosses, the G. scandens population became more similar to the G. fortis population both genetically and morphologically. Gene flow between species was estimated to be three times greater from G. fortis to G. scandens than in the opposite direction, resulting in a 20% reduction in the genetic difference between the species. Nevertheless, removing identified F₁ hybrids and backcrosses from the total sample and reanalyzing the traits did not eliminate the convergence. The two species also converged in beak shape by 22.2% and in body size by 45.5%. A combination of introgressive hybridization and selection jointly provide the best explanation of convergence in morphology and genetic constitution under the changed ecological conditions following a major El Niño event in 1983. The study illustrates how species without postmating barriers to gene exchange can alternate between convergence and divergence when environmental conditions oscillate.     

Exploring possible human influences on the evolution of Darwin's finches

Humans are an increasingly common influence on the evolution of natural populations. Potential arenas of influence include altered evolutionary trajectories within populations and modifications of the process of divergence among populations. We consider this second arena in the medium ground finch (Geospiza fortis) on Santa Cruz Island, Galápagos, Ecuador. Our study compared the G. fortis population at a relatively undisturbed site, El Garrapatero, to the population at a severely disturbed site, Academy Bay, which is immediately adjacent to the town of Puerto Ayora. The El Garrapatero population currently shows beak size bimodality that is tied to assortative mating and disruptive selection, whereas the Academy Bay population was historically bimodal but has lost this property in conjunction with a dramatic increase in local human population density. We here evaluate potential ecological-adaptive drivers of the differences in modality by quantifying relationships between morphology (beak and head dimensions), functional performance (bite force), and environmental characteristics (diet). Our main finding is that associations among these variables are generally weaker at Academy Bay than at El Garrapatero, possibly because novel foods are used at the former site irrespective of individual morphology and performance. These results are consistent with the hypothesis that the rugged adaptive landscapes promoting and maintaining diversification in nature can be smoothed by human activities, thus hindering ongoing adaptive radiation.     

Inbreeding and interbreeding in Darwin's finches

Studies of inbreeding and interspecific hybridization are generally pursued separately with different metrics. There is a need to integrate them because they have the common goal of seeking an understanding of the genetic and ecological basis of fitness variation in populations. We use mean expected heterozygosity as an axis of variation on which to compare the fitness of inbreeding and hybridizing Darwin's finches (Geospiza scandens and G. fortis) relative to the fitness of matched outbred controls. We find that relative fitness of inbred finches is less than one in the 1991 cohorts of both species. Inbreeding depression is stronger in the species (G. scandens) with the lower genetically effective population size. Relative fitness of hybrids (backcrosses) in the same cohort of G. scandens is greater than one. Evidence of heterosis in G. fortis is mixed. Thus the two interbreeding species displayed somewhat different fitness patterns under the same set of environmental conditions. Hybridization may enhance fitness to different degrees by counteracting the effects of inbreeding depression, by other additive and nonadditive genetic effects, and by producing phenotypes well suited to exploit particular ecological conditions.     

Fission and fusion of Darwin's finches populations

This study addresses the causes and evolutionary consequences of introgressive hybridization in the sympatric species of Darwin's ground finches (Geospiza) on the small island of Daphne Major in the Galápagos archipelago. Hybridization occurs rarely (less than 2% of breeding pairs) but persistently across years, usually as a result of imprinting on the song of another species. Hybrids survive well under some ecological conditions, but not others. Hybrids mate according to song type. The resulting introgression increases phenotypic and genetic variation in the backcrossed populations. Effects of introgression on beak shape are determined by the underlying developmental genetic pathways. Introgressive hybridization has been widespread throughout the archipelago in the recent past, and may have been a persistent feature throughout the early history of the radiation, episodically affecting both the speed and direction of evolution. We discuss how fission through selection and fusion through introgression in contemporary Darwin's finch populations may be a reflection of processes occurring in other young radiations. We propose that introgression has the largest effect on the evolution of interbreeding species after they have diverged in morphology, but before the point is reached when genetic incompatibilities incur a severe fitness cost.     

On the origin of Darwin's finches

Darwin's finches comprise a group of 15 species endemic to the Galápagos (14 species) and Cocos (1 species) Islands in the Pacific Ocean. The group is monophyletic and originated from an ancestral species that reached the Galápagos Archipelago from Central or South America. Descendants of this ancestor on the Archipelago then colonized Cocos Island. In the present study, we used sequences of two mitochondrial (mt) DNA segments (922 bp of the cytochrome b gene and 1,082 bp of the control region), as well as two nuclear markers (830 bp of numt2, consisting of 140 bp of mtDNA control region and 690 bp of flanking nuclear DNA; and 740 bp of numt3, consisting of 420 bp of mt cytochrome b sequence flanked by 320 bp of nuclear DNA) to identify the species group most closely related to the Darwin's finches. To this end, we analyzed the sequences of 28 species representing the main groups (tribes) of the family Fringillidae, as well as 2 outgroup species and 13 species of Darwin's finches. In addition, we used mtDNA cytochrome b sequences of some 180 additional Fringillidae species from the database for phylogeny reconstruction by maximum-parsimony, maximum-likelihood, minimum-evolution, and neighbor-joining methods. The study identifies the grassquit genus Tiaris, and specifically the species Tiaris obscura, as the nearest living relative of Darwin's finches among the species surveyed. Darwin's finches diverged from the Tiaris group shortly after the various extant species of Tiaris diverged from one another. The initial adaptive radiation of the Tiaris group apparently occurred on the Caribbean islands and then spread to Central and South America, from where the ancestors of Darwin's finches departed for the Galápagos Islands approximately 2.3 MYA, at the time of the dramatic climatic changes associated with the closure of the Panamanian isthmus and the onset of Pleistocene glaciation.