Darwin’s missing links

Bold flights of a speculative mind

Recent discussions of natural selection focus on two questions: first, is natural selection a causal process or is it a statistical consequence of lower-level events? And second, is natural selection at the population level or at the level of individuals? Bouchard and Rosenberg (Br J Philos Sci, 55:693–712, 2004) argue that natural selection is causal and at the level of individuals, as opposed to Matthen and Ariew (J Philos, 99:55–83, 2002) and Walsh et al. (Philos Sci, 69:452–473, 2002), who argue that natural selection is at the population level and purely statistical. In addition to these two polar extreme positions, Millstein (Br J Philos Sci, 57:627–653, 2006) tries to steer a middle course by arguing that natural selection is a population-level causal process. I will make three points in this chapter: first, Millstein’s account of natural selection is incomplete, in the sense that nowhere in her account can one find a place for cases of natural selection-of. Second, we should prefer Brandon’s account of natural selection and drift over Millstein’s, on the grounds that her account fails to meet a plausible requirement that Brandon’s account succeeds in meeting: namely, whenever natural selection and drift operate together, a change in the strength of natural selection implies an inverse change in the strength of drift, and vice versa. Third, the prospects of the view that natural selection is a population-level causal process depend on a satisfactory solution to both the epiphenomenon and the overdetermination problems. With the help of an analogy, I will show how the two problems can be dealt with.KeywordsNatural SelectionReproductive SuccessSampling ProcessEffective Population SizeSmall OrganismThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Speciation Associated with Shifts in Migratory Behavior in an Avian Radiation.

When Charles Darwin was developing his ideas for On the Origin of Species, the most widely accepted estimates of Earth’s age were those of William Thomson (later Lord Kelvin). Kelvin used calculations involving thermodynamics to argue that Earth is only 20–100 million years old—an age far too brief to accommodate evolution by natural selection. Darwin referred to Thomson’s claim as one of his “sorest troubles,” for Darwin understood that the history of life on Earth ultimately relies on geology. Darwin suspected that Earth was much older than Thomson claimed, but Thomson’s enormous stature as a scientist obliged Darwin to reconcile his claims with Kelvin’s data. To accommodate Kelvin’s timeline, Darwin proposed pangenesis as an explanation of inheritance (i.e., every sperm and egg contained “gemmules thrown off from each different unit throughout the body”). Darwin’s explanation sped evolution while avoiding Lamarck’s quasi-spiritual sources of acquired traits. However, Darwin’s explanation of inheritance was wrong (see discussion in Moore et al. 2009a). The age of Earth remains a divisive topic in the modern evolution–creationism controversy. Whereas mainstream science has long acknowledged that Earth is approximately 4.5 billion years old, a vocal group of citizens and religious activists continue to insist that Earth is less than 10,000 years old. Although most geocentrists and flat-Earth advocates have capitulated to scientific evidence, young-Earth creationists continue to reject scientific evidence in favor of religious dictum to claim that Earth is less than 10,000 years old. These antiscience claims have been surprisingly popular with the public. For example, a Gallup Poll in early 2009 reported that “On Darwin’s [200th] Birthday, Only 4 in 10 Believe in Evolution” (Newport 2009), and Berkman et al. (2008) noted that “16% [of biology teachers] believed that human beings were created by God in their present form at one time within the last 10,000 years.” In another study, 12.5% of students were young-Earth creationists (Rutledge and Warden 2000), as are 10%–14% of biology majors (Moore and Cotner 2009). Answers in Genesis’ (AiG) Creation Museum, along with the $27 million in donations required to build it, attest to the appeal of young-Earth creationism. Indeed, AiG’s income for 2005 exceeded $13 million, and that of the Institute for Creation Research (ICR, another religious organization based on young-Earth creationism) exceeded $7 million. For comparison, the 2005 income of National Center for Science Education—the nation’s leading organization that defends the teaching of evolution in public schools—was

The year 2009 marked the 200th anniversary of Charles Darwin’s birth and the 150th anniversary of his most influential publication. Darwin transformed the biological sciences in much the same way that Nicolaus Copernicus, Galileo Galilei, and Isaac Newton, centuries earlier, transformed the physical sciences—by demonstrating that the universe operates according to natural laws that fall within the purview of rational scientific inquiry. In 1543, Copernicus published De Revolutionibus Orbium Celestium (“ On the Revolutions of the Celestial Spheres ”) that challenged conventional wisdom that the Earth was the center of creation and instead promoted the idea that natural laws govern the motion of physical objects in the universe. In 1859, in On the Origin of Species (4), Darwin developed the equally revolutionary concept that a natural but nonrandom process—natural selection—yields biological adaptations that otherwise can give the superficial impression of direct intelligent craftsmanship. Actually, Darwin barely mentioned Homo sapiens in On the Origin of Species, cautiously stating only that “much light will be thrown on the origin of man and his history.” More than a decade later, however, Darwin addressed human evolution at considerable length in The Descent of Man and Selection in Relation to Sex (5) wherein can be found many thoughtful passages, such as, “Man may be excused for feeling some pride at having risen, though not through his own exertions, to the very summit of the organic scale; and the fact of his having thus risen, instead of having been aboriginally placed there, may give him hope for a still higher destiny in the distant future.” Of course, much has been learned about humanity’s evolutionary origins and biological conditions since Darwin’s time, not least from the evidence of paleontology, comparative vertebrate biology, and genomics. An emerging field known as “anthropogeny” (6) seeks to understand the evolutionary origins … [↵][1]1To whom correspondence should be addressed. E-mail: javise{at}uci.edu. [1]: #xref-corresp-1-1

‘Natural selection and the origin of species’ shows that natural selection is the mechanism of evolutionary change, which is not readily observable, but is inferred by argument from other kinds of observation. The argument is constructed from three apparently independent generalisations about the properties of organisms. The first generalisation is that individual members of any species vary from one another in manifold structural and behavioural characteristics. The second generalisation is that individual variation is to some degree hereditary — transmitted from generation to generation. The final generalisation is the Malthusian principle that organisms multiply at a rate that exceeds the capacity of the environment to carry them, with the inevitable consequence that many must die.

An animal breeder on Darwin’s birthday

“Founders” of new scholarly ideas, perspectives, or paradigms are people who advocate for such ideas before wider scholarly audiences accept them or even know they exist. Such scholars have an uphill battle. They must persuade journal and book editors to publish their work. Those gatekeepers depend on reviewers with established reputations in conventional terms, and these reviewers generally oppose anything that threatens their comfortable intellectual lives. If the idea is as stunningly simple as Darwin's natural selection theory, an innovator might have a somewhat easier time; Thomas Huxley reportedly remarked upon reading On the Origin of Species, “How extremely stupid of me not to have thought of that.” But with conceptually and methodologically broad ideas, such as the application of biologically based psychological thinking to a traditional set of disciplinary problems, it can be tough to even get a foot in the door.

Darwin television celebrations begin

Natural selection

The theme of Dr. Kuhn's paper is that Darwin's theory of evolution to explain the origin of species is inadequate, and that the 2010 decision by the Texas State Board of Education to require textbooks to present the weaknesses, as well as the strengths, of Darwin's theory was appropriate. The three limitations of Darwin's theory concern the origin of DNA, the irreducible complexity of the cell, and the paucity of transitional species. Because of these limitations, the author predicts a paradigm shift away from evolution to an alternative explanation. The intellectual problem, in my opinion, is not that evolution has “fatal defects,” but rather that it remains a suspect theory for most Americans >150 years after the publication of The Origin of Species (1859). While the Texas State Board of Education may have debated the issue for 3 full days in 2010, its recommendation in the end will probably be ignored by scientists who write textbooks. I suppose the Texas decision represents progress. Tennessee's Butler Act made it unlawful to teach evolution, giving rise to the Scopes trial in 1925, in which John T. Scopes, a high school teacher, was accused of violating that law. After an 8-day trial, a guilty verdict was reached. To embrace the idea that all forms of life, great and small, plant and animal, primate and nonprimate, were derived from a common primordial cell or organism requires a scientific perspective. The various religions, current and extinct, typically elevate humans above other forms of life. Most Homo sapiens believe that the different species on planet earth were created independently by a God, in sequential batches, placed in certain locales, with the Homo sapiens inherently superior, made in the image of the creator—thus, the resistance to the concept of evolution. With respect to the origin of DNA as a weakness of Darwinism, our knowledge of DNA, from my reading, has added to, not subtracted from, the evidence of evolution. In the 2006 preface to the 30th anniversary edition of The Selfish Gene (first published by Oxford University Press in 1976), author Richard Dawkins wrote: The correct word of the title to stress is “gene” and let me explain why. A central debate within Darwinism concerns the unit that is actually selected: what kind of entity is it that survives, or does not survive, as a consequence of natural selection. That unit will become, more or less by definition, “selfish.” … Let me repeat and expand the rationale for the word “selfish” in the title. The critical question is which level in the hierarchy of life will turn out to be the inevitably “selfish” level, at which natural selection acts? The Selfish Species? The Selfish Group? The Selfish Organism? The Selfish Ecosystem? Most of these could be argued, and most have been uncritically assumed by one or another author, but all of them are wrong. Given that the Darwinian message is going to be pithily encapsulated as The Selfish Something, that something turns out to be the gene, for cogent reasons which this book argues. The notion of “irreducible complexity” in a cell, as an argument against evolution, is beyond my present understanding. Knowing that life has existed on planet earth for billions of years, however, I suspect that there has been time enough for evolution, no matter how complex, with reducibility. With respect to transitional species, a brief glance through recent issues of National Geographic shows no paucity of data from paleontologists. Human lineage can be traced back >6 million years, with fossils discovered in East Africa from all three major phases of hominid evolution—Ardipithecus, Australopithecus, and Homo—with a divergence from living ape species (chimpanzee and bonobos) roughly 8 to 6 million years ago. Transitional species have been identified in numerous other groups. The whale, for example, accomplished an enormous transformation, with fossil evidence. Fifty million years ago it was semi-terrestrial; now it is fully aquatic. Seven billion Homo sapiens now inhabit planet earth. World population in ad 1 (the time of Christ) was about 200 million. In the struggle for survival in the next century and beyond, the hand of natural selection will be at work, I believe, and evidence of evolution, to explain the origin, modification, and behavior of species, will continue to increase. Editor's note: Gregory Dimijian, MD, is also preparing a full-length article on Darwinism, which Proceedings will publish in an upcoming issue.

A Universal Struggle for Life? A comparative study of the reception of Darwinism among religious thinkers in the Anglo-Saxon world and in the Middle East in the second half of the 19th century Sacha Aellen How was Darwinism and its potential implications experienced by religious thinkers in the 19th century? What features of the perception of Darwinism were local, depending on specific socio-political situations, and which ones were not? These are the questions I tried to answer in my Master Thesis that I submitted last summer. Let us start with the beginning: what exactly is Darwinism? Mostly contained in two of Charles Darwin's books -The Origins of Species and Descent of Man (1871) -, Darwinism is an evolutionary theory composed of two particularly crucial features. First, living beings all share a common ancestry. Through time, they have developed genetic modifications that created divisions between species but they all have a common origin. Second, the living beings that are...

I read the article ‘Paul Broca: from fame to shame?’ with great interest.1 Its balanced presentation compels the readership to weigh in on one view or the other—especially since the title ends in a question mark! Broca, born and raised in the Bordeaux region of France, was unquestionably one of the great clinical neuroanatomists of the 19th century. This recognition led to naming a neuroscience building at the University of Bordeaux after him; this decision is now questioned because of his beliefs in physical anthropology.1 The Broca example is more useful to study if we begin by placing his ideas into the context of his time. Before race became ‘a baseless social construct,’1 intellectual elite and religious scholars had already been discussing the origin of ‘mankind’ (note, the use of the currently preferred term ‘humankind’ would be anachronistic) for centuries. Charles Darwin’s Origin of species by means of natural selection, or the preservation of favoured races in the struggle for life was published in 1859 and his second major work on evolution, The descent of man, and selection in relation to sex, was published in 1871. These works, and their spirited discussion among religious and secular scholars, quickly and radically changed thoughts about mankind’s origin. These discussions in Paris were further complicated by an ongoing battle between secular savants and the Roman Catholic Church; as the 19th century progressed, French society became progressively more secular.2,3 Contemporary scholars, who were not strictly wedded to a literal interpretation of creationism, were split between two opposing, but not directly testable, theories: monogenism (humanity had a single origin) and polygenism (human races are of different origins). Monogenism was compatible with scientific variations on creationism that were proliferating; polygenism was incompatible and almost uniformly embraced by secular French scholars by the 1820s. Atheist members of the lay public favoured polygenism because it contradicted the biblical account of human creation and because it appeared more scientific. It should be remembered that Broca had founded a society of ‘freethinkers’ (at the time, essentially a synonym for atheists) in Paris in 1848 and the Société d’anthropologie de Paris in 1859, the year Darwin published Origin of species.2,3

The species is the fundamental or basic unit of organic or biological diversity, usually characterised as a group of individuals or populations of individuals with interbreeding or genealogical relationships. Understanding the nature of species can be challenging when considering sexual versus asexual organisms. Identifying species is also challenging, for example, when studying the fossil record, or when speciation is not yet complete. Speciation is the process leading to the formation or origin of species. As such, speciation is the process by which reproductive and/or genealogical boundaries form around groups of organisms. Commonly understood forces of evolution causing divergence in phenotypes contribute to the formation of species. Geographic, ecological, behavioural and genetic factors are also important to understanding how the process works. Key Concepts: Species are fundamental units of biodiversity but can be defined in different ways, from either a prospective (future) or retrospective (historical) perspective. Speciation is the study of how new species form and may be brought about by a multitude of phenotypic changes. The causes of speciation are complex and likely include a diversity of evolutionary forces such as natural selection, sexual selection and genetic drift that lead to divergence in phenotype. Divergence in specific phenotypes is important to speciation if they directly or indirectly cause a reduction in gene flow between newly forming species. The genetics of speciation is the study of the genetic basis of phenotypic evolution that leads to a reduction in gene flow between newly forming species.

Art and evolution