Monday, May 14, 2012

Next Generation Science Standards: Evolution

Next Generation Science Standards is an organization dedicated to developing new K12 science standards for schools in the United States. The partners are the American National Research Council, The American Association for the Advancement of Science (AAAS), The National Science Teachers Association (NSTA), and Achieve, a nonprofit education reform organization.

The draft standards are posted on the website and you are invited to make comments until June 1st. Let's see what the new standards have to say about teaching evolution.

Here's what should be taught in middle school.
LS4.A: Evidence of Common Ancestry and Diversity
  • Fossils are mineral replacements, preserved remains, or traces of organisms that lived in the past. Thousands of layers of sedimentary rock not only provide evidence of the history of the Earth itself but also of changes in organisms whose fossil remains have been found in those layers. (a)
  • The collection of fossils and their placement in chronological order (e.g., through the location of the sedimentary layers in which they are found or through radioactive dating) is known as the fossil record. It documents the existence, diversity, extinction, and change of many life forms throughout the history of life on Earth. Because of the conditions necessary for their preservation, not all types of organisms that existed in the past have left fossils that can be retrieved. (c)
  • Anatomical similarities and differences between various organisms living today, and between them and organisms in the fossil record, enable the reconstruction of evolutionary history and the inference of lines of evolutionary descent. (b)
  • Comparison of the embryological development of different species also reveals similarities that show relationships not evident in the fully-formed anatomy. (d)
LS4.B: Natural Selection
  • Genetic variations among individuals in a population give some individual an advantage in surviving and reproducing in their environment. This is known as natural selection. It leads to the predominance of certain traits in a population, and the suppression of others. (e),(f)
LS4.C: Adaptation
  • Adaptation by natural selection acting over generations is one important process by which species change over time in response to changes in environmental conditions. (g)
  • Traits that support successful survival and reproduction in the new environment become more common; those that do not become less common. Thus, the distribution of traits in a population changes. (f)
  • In separated populations with different conditions, the changes can be large enough that the populations, provided they remain separated (a process called reproductive isolation), evolve to be separate species. (g)
Not bad, all things considered. I'd like to add that some evolution occurs by the chance increase in certain traits in a population, a process known as random genetic drift. Drift is part of the standards in my province of Ontario.

I'd also like to delete "in response to changes in environmental conditions" and "in the new environment" from LS4.C. The idea that natural selection only occurs when the environment changes is a common misconception and there's no reason to perpetuate that misconception.

Here are the high school standards.
LS4.A: Evidence of Common Ancestry and Diversity
  • Genetic information, like the fossil record, also provides evidence of evolution. DNA sequences vary among species, but there are many overlaps; in fact, the ongoing branching that produces multiple lines of descent can be inferred by comparing the DNA sequences of different organisms. Such information is also derivable from the similarities and differences in amino acid sequences and from anatomical and embryological evidence. (e)
LS4.B: Natural Selection
  • Natural selection occurs only if there is both (1) variation in the genetic information between organisms in a population and (2) variation in the expression of that genetic information—that is, trait variation—that leads to differences in performance among individuals. (a),(c)
  • The traits that positively affect survival are more likely to be reproduced, and thus are more common in the population. (b),(c),(d),(f)
LS4.C: Adaptation
  • Natural selection is the result of four factors: (1) the potential for a species to increase in number, (2) the genetic variation of individuals in a species due to mutation and sexual reproduction, (3) competition for an environment’s limited supply of the resources that individuals need in order to survive and reproduce, and (4) the ensuing proliferation of those organisms that are better able to survive and reproduce in that environment. (a)
  • Natural selection leads to adaptation, that is, to a population dominated by organisms that are anatomically, behaviorally, and physiologically well suited to survive and reproduce in a specific environment. That is, the differential survival and reproduction of organisms in a population that have an advantageous heritable trait leads to an increase in the proportion of individuals in future generations that have the trait and to a decrease in the proportion of individuals that do not. (b),(c),(f)
  • Adaptation also means that the distribution of traits in a population can change when conditions change. (d)
  • Changes in the physical environment, whether naturally occurring or human induced, have thus contributed to the expansion of some species, the emergence of new distinct species as populations diverge under different conditions, and the decline–and sometimes the extinction–of some species. (d)
  • Species become extinct because they can no longer survive and reproduce in their altered environment. If members cannot adjust to change that is too fast or drastic, the opportunity for the species’ evolution is lost. (d)
I have more of a problem with the high school standards. High school students must learn about random genetic drift, especially if they are comparing sequences since most of the changes they will see are nearly neutral changes that have been fixed by drift.

I think the standards should specifically mention that selection can occur in a constant environment since no organisms are perfectly adapted.

I hope the standards include specific attention to the relationship between humans and other species as shown by the combination of sequence comparisons, anatomical similarities, and the fossil record.

The source of mutations is covered in another section (LS3.B).

It would be nice to describe the differences between the fact of evolution and evolutionary theory.


8 comments :

  1. Being very much a non-expert in these matters, it was, however, my impression that the dominate form of evolution is due to allopatric speciation, e.g. when a relatively small founder population becomes separated from the main population and is subject to different environments that cause a change in allele frequencies of the founder population. As I understand it, eventually, the genomes of the founder population become sufficiently different from the main population so that interbreeding can no longer take place, e.g. speciation.

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  2. my impression that the dominate form of evolution is due to allopatric speciation, e.g. when a relatively small founder population becomes separated from the main population and is subject to different environments that cause a change in allele frequencies of the founder population

    What you have described isn't allopatric speciation, exactly, but a special form of it called peripatric speciation. In plain vanilla allopatric speciation there is no particular requirement that populations be unequal in size, or that the larger one be called the "main" population, or that the smaller one is the one that turns into a new species. It's just that populations genetically isolated from each other (by geography, behavior, or whatever) diverge, and if they diverge enough, we count them as separate species. Divergence can be assisted by selection in different environments, or if you wait long enough, drift will do the job. Sufficient divergence of the right sort produces pre- or post-mating isolation. And selection against hybrids can cause reinforcement of isolation in sympatry.

    The standards say almost nothing about speciation, just "In separated populations with different conditions, the changes can be large enough that the populations, provided they remain separated (a process called reproductive isolation), evolve to be separate species." I presume Larry is complaining about the assumption that only selection is responsible for adaptation and that only adaptation is responsible for speciation, and he's right to do so. But I don't see your complaint as valid or even much relevant to the little they do say.

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  3. I'm surprised by the prominence given to the fossil record, and that there is no mention made of biogeography. I have no problem with the fossil record, and I understand that it can be easier for kids to grasp than other kinds of evidence of evolution, but I am sometimes concerned that the general public thinks that all there is to evolution is the study of fossils.

    TomS

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  4. It would be nice to describe the differences between the fact of evolution and evolutionary theory. LM

    Wouldn't it. As well as that evolutionary science proposes to study just about the most complex phenomenon of any science, on the basis of extremely fragmentary historical evidence from billions of years and jillions of organisms in the past. I'd include that those facts necessitate any conclusions, including natural selection, being seen as extremely contingent and likely to be modified as other evidence is discovered. You could use it to teach what science is, what it isn't, what it was invented to do and how it restricts what it looks at to do that.

    It would be nice if somewhere in the science curriculum if students could be introduced to the idea that science is a human invention, that it doesn't have a disembodied existence of its own and that it exists in no other place than human minds. That other phenomena such as history have found other means to study things that science can't contain and that those are the appropriate ways to study those things, consulting scientific findings as useful, would be nice too.

    Though I'd hope that in all of this students learn something about the practical importance of disinfection, inoculation, adequate nutrition, contraception, disease prevention etc. That those aren't sacrificed for studying the hot button of evolution, which very few of the students will ever have the slightest need of as compared to other biological topics. Most students in the United States will get one biology course in high school, if that.

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    Replies
    1. It would be nice if somewhere in the science curriculum if students could be introduced to the idea that science is a human invention, that it doesn't have a disembodied existence of its own and that it exists in no other place than human minds.

      I don't think people tout it as anything other than a human invention (religion, on the other hand ...). Science is a human attempt to investigate regularities in the assumed 'real world' - one investigator communicates their findings to others, who can repeat, disconfirm or build upon that work. If there is no regularity, it can't be repeated - which is where some confusion between evolution-as-history and evolution-as-process comes in. But I'm not sure what ill your corrective to current teaching is designed to address.

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    2. Another comment from a thought criminal ..
      That other phenomena such as history have found other means to study things that science can't contain and that those are the appropriate ways to study those things, consulting scientific findings as useful, would be nice too.

      As far as I know, historians use the scientific way of knowing to investigate historical questions. What "other means" are you talking about?

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  5. The basic for evolution is the history of life, and history of life is a much better topic for middle school and high school than natural selection and adaptation. My experience is than first year students get the idea that natural selection can do and will do anything, that everything is adaptive, put into their heads in school. Such evolution is a boring topic in school. Fossils are exciting.

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  6. Middle school standards could add that species change in time in response to each other (bees and flowers) and changing environments. The claim that something like climate must change for evolution to happen is outrageous. Biogeography should also be included, for it explains why continents and islands have peculiar biotas (and Ark biology is over the top). In the high school standards, genetic drift would fit in nicely with DNA phylogeny. It also seems wise to talk about sexual selection for weapons and ornamentation. A brief mention of social adaptations (herds vs. African wild dogs) and within family altruism (bees) would help dispel the notion that social evolution is beyond understanding.

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