White, J., Tollini, C.D., Collie, W.A., Strueber, M.B., Strueber, L.H., and Ward, J.W. (2009) Evolution and University-level Anthropology Textbooks: The “Missing Link”? Evo. Edu. Outreach 2:722–737 [doi: 10.1007/s12052-009-0176-6]The authors refer to an earlier study by Linhart (1997) who examined definitions of evolution in biology textbooks.
Abstract: Although studies analyzing the content of evolution curriculum usually focus on courses within the context of a biological sciences department or program, research must also address students and courses outside of the biological sciences. For example, using data solely from biological courses will not fully represent the scope of coverage of evolution in university education, as other fields, like anthropology, also utilize evolutionary principles. We analyzed the content of 31 university-level anthropology textbooks for the following: (1) presence of a definition of evolution in various sections of the textbooks, (2) accuracy and consistency of the definitions provided in the textbook sections, and (3) differences between textbooks for cultural and physical anthropology. Results of this study suggest that anthropology textbooks do not necessarily (1) provide a single definition of evolution or (2) provide an accurate, “baseline” definition of evolution when present. Additionally, substantive differences were observed between definitions provided in different sections within a single textbook, as well as between textbooks written for cultural anthropology and physical anthropology/archaeology courses. Given the inclusion of anthropology courses in general education curriculum at the university-level, we conclude that this situation may further exacerbate the misunderstanding of the basic tenets of evolution that university students have been repeatedly shown to demonstrate. We stress the role of the instructor in choosing textbooks that provide accurate information for students, as well as the responsibility they hold in providing a concise, accurate definition of evolution in social sciences courses.
In our literature search, we were able to locate only one study that directly addressed the coverage of evolution in textbooks. Linhart (1997) focused on textbooks designed for one of the following six courses in the biological sciences: general biology (for majors and non-majors), evolution, genetics, paleontology, ecology, and systematics. He restricted his sample to 50 textbooks that had multiple editions and a sizable market share, and he located at least some of these textbooks using colleagues’ recommendations. He analyzed the content of the glossary entry for evolution in each textbook, as well as the material in any pages listed in an index entry for evolution, and compared these data against a definition of evolution he constructed after reviewing the literature:I agree with the problems that Linhart outlines and I agree that evolution needs to be defined as a process that involves genetic change and populations. It's very important that evolution should be defined in a way that allows for multiple mechanisms such as natural selection and random genetic drift.
Evolution is said to have occurred within a species, lineage, or population when measurable changes in various morphological, physiological, behavioral, or biochemical characteristics can be detected. These characteristics must be at least partly under genetic control. The genetic change(s) can occur as aWhile he found variation between the textbooks written for the six different courses in his sample, his findings indicated that the majority of all of the textbooks equated evolution with natural selection or adaptation and did not describe evolution in much detail. Linhart (1997) expressed much concern regarding the content of the definition of evolution in these textbooks, arguing that many students will have an inaccurate or incomplete view of evolution unless they are provided with additional material.
consequence of processes such as migration, mutation, genetic drift or bottleneck, natural selection, and nonrandom mating. Genetic changes within different populations of a species can lead to differences among lineages, and sometimes to the origin of new species...Evolution is not a synonym of natural selection. Nor is evolution a process that leads inevitably to increased or improved adaptation, or to greater reproductive success. Evolution does not imply a progressively closer fit between a population and its environment. Finally, evolution does not involve predictable or irrevocable changes from simple to more complex forms or toward some sort of perfection (Linhart 1997: 387).
Most of the biology textbooks I've read do an adequate job of defining evolution but I haven't covered as many textbooks as Linhart.
It's disappointing that biology textbooks and anthropology textbooks do such a poor job of defining—and presumably explaining—evolution. Is it any wonder that the general public is scientifically illiterate when we can't even get it right in the textbooks?
Linhart, Y. (1997) The teaching of evolution: we need to do better. Bioscience 47:385–91.
"Evolution is said to have occurred within a species, lineage, or population when measurable changes in various morphological, physiological, behavioral, or biochemical characteristics can be detected."
ReplyDeleteAnd you're, um, okay with this?
I like it, but it would appear to exclude things like point mutations in junk DNA, which would constitute > 90% of the "evolution" as measured by your preferred definition.
I've often thought that we find it difficult to talk about evolution because we lack suitable words to capture the concept; I guess we are not going to invent a new language though.
ReplyDeleteWhile anthropologists will probably be mainly interested in populations changing over time, I would suggest that they need to understand the basic evolutionary process first... even if it seems harsh and mechanical.
My (inexpert) try at defining biological evolution would be something like:
Evolution is the collective term for the variations arising from differential survival of imperfectly replicating molecules. Typical outcomes, past and present, include collections of replicating material in viruses, single celled organisms, multi-celled organisms, and collections of similar organisms in populations and species.
I know it is a cumbersome definition, but we know that individuals don't evolve. I would also suggest that populations don't evolve - the genetic material collectively expressed through the individuals in the population does.
Am I being too picky? Or do we risk misleading ourselves by talking loosely about genes 'for' particular traits and the evolving traits of a population? Before you know it we'll be talking about how populations change over time and introducing a teleological bias to our debates.
The simplest definition is usually the best: Evolution is a change in gene frequency in a population.
ReplyDeleteCharles Darwin used the phrase "descent with modification" to describe evolution. We can now measure genetic evolution at the molecular level--change in DNA sequences.
ReplyDeleteEvolution involves the interaction of two sets of natural processes each generation. The set of non-adaptive processes includes both mutations and sampling error. The set of adaptive processes includes what Darwin called natural selection and sexual selection.
Evolution can be best understood as the product of natural (including sexual) slection superimposed on the non-adptive processes of mutation and sampling error each generation.
Scientists as well as the general public need a better understanding of these natural processes.
The following is my provisional proposed description of how natural (including sexual)selection operates.
Charles Darwin (1859:62) used the metaphor “Struggle for Existence” to describe the ecological interactions that individual organisms have with (1) the physical conditions of the environment, (2) individuals of other species, and (3) individuals of the same species. These ecological interactions cause the natural (including sexual) selection of hereditary variations, that is, cause the selective survival of genes, the selective exponential multiplication of genes and the selective recombination of genes via mate choice that affect adaptations (designs) for survival and reproductive success each generation.
The adaptations we observe today are the product of natural selection operating on genetic variation produced by mutations, sampling error (genetic drift) and selective recombination (via selective mating) over billions of generations.
The simplest definition is usually the best: Evolution is a change in gene frequency in a population.
ReplyDeleteI have a problem with that because language and culture may or may not have a strict gene analogue or equivalent. Yet, they still act as an evolutionary system. So evolution is something different than merely change in gene frequencies, that definition only applies to a biological system. A good definition of evolution would work for language and cultural systems as well...
Psi Wavefunction says,
ReplyDeleteI have a problem with that because language and culture may or may not have a strict gene analogue or equivalent. Yet, they still act as an evolutionary system.
In this context we're only talking about biological evolution. The definition refers only to biological evolution of the sort that's normally covered in a evolutionary biology course.
But you knew that, didn't you?
Carl,
ReplyDeleteThere's much more to random genetic drift than the phrase "sampling errors." The founder effect is one obvious example.
The other problem with using a term like "sampling errors" is that it's hard to convey the notion of fixation by random genetic drift based only on the notion of sampling errors.
Your concept of natural selection is not very helpful. A true understanding of evolution involves the knowledge that beneficial alleles can be lost and detrimental alleles can be gained. You need to incorporate the stochastic component of natural selection into your understanding of evolution.
The other problem with your concept of natural selection is that it places too much emphasis on the traditional idea of environment as something that is external to the organism. There are many kinds of adaptive changes at the molecular and cellular level that don't really conform to the idea of "ecological interactions."
In your final sentence you say,
The adaptations we observe today are the product of natural selection operating on genetic variation produced by mutations, sampling error (genetic drift) and selective recombination (via selective mating) over billions of generations.
This seems to imply that fixation of alleles by random genetic drift is just an example of "genetic variation." That's not correct. Random genetic drift eliminates variation as does natural selection. It just takes longer.
Larry,
ReplyDeleteAlthough you insist that all who use evolution should stick to the post-"modern synthesis" version (i.e. change in gene frequency in a population), many are using a definition that predates our understanding of genetics.
Is this wrong or right?
As long as when talking to the public, we start off by explicitly stating our post-"modern synthesis" definition, or else I fear that we will be talking over their heads, and you can see why. They are not using the term in the same way that we do.
And why would this be the case that evolution has various definitions? Once you pointed out that the definition of "singularity" is defined by physicists and everyone respects that - the same should apply to evolution. However unlike singularity, the meaning of evolution has changed overtime. When Erasmus Darwin used the term, I am sure he did not use our current definition. When Charles Darwin used the term I am sure he meant "decent with phenotypic modification". Thus in most minds evolution = natural selection. (Although I do admit that phenotypic modifications that propagate in a population also arise from neutral selection or propagate even despite negative selection.)
Alex Palazzo asks,
ReplyDeleteAlthough you insist that all who use evolution should stick to the post-"modern synthesis" version (i.e. change in gene frequency in a population), many are using a definition that predates our understanding of genetics.
Is this wrong or right?
The Modern Synthesis—which was established in the 1940s—transformed our thinking about evolution by moving it from a nineteenth century natural history perspective to a twentieth century view that incorporated genetics and modern scientific thinking.
The definition of evolution as a change in the frequency of alleles in a population is a product of early 20th century genetics and this definition was very much a part of the Modern Synthesis. (In spite of hold-outs like Ernst Mayr.)
So, is it right that we had a modernized definition of evolution that took account of new science that was unknown to Darwin? Yes.
As long as when talking to the public, we start off by explicitly stating our post-"modern synthesis" definition, or else I fear that we will be talking over their heads, and you can see why. They are not using the term in the same way that we do.
One of the important roles of a scientist is to educate the general public. If the average person misunderstands evolution then our job is to teach them the correct understanding. It's ridiculous to avoid the correct definition of evolution just because the general public doesn't know about it.
I don't think there are two equivalent definitions of evolution. I think that the minimal definition of evolution is a change in the hereditary characteristics (alleles) in a population over time. I think that "descent with modification" is not only fuzzy and wishy-washy, but also dead wrong in some cases.