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Thursday, April 11, 2013

Next Generation Science Standards

The Next Generation Science Standards are a set of recommendations for teaching science to public school children in the USA. The standards were made up by representatives from the National Research Council and 26 states. The standards have been extensively reviewed and many drafts were posted on the web.

You can look at the final version at DCI Arrangements of the Next Generation Science Standards.

Let's look at the High School Section on Biological Evolution : Unity and Diversity. Let me know what you think.

HS-LS4 Biological Evolution: Unity and Diversity

Students who demonstrate understanding can:

HS-LS4-1. Communicate scientific information that common ancestry and biological evolution are supported by multiple lines of empirical evidence. [Clarification Statement: Emphasis is on a conceptual understanding of the role each line of evidence has relating to common ancestry and biological evolution. Examples of evidence could include similarities in DNA sequences, anatomical structures, and order of appearance of structures in embryological development.}

HS-LS4-2. Construct an explanation based on evidence that the process of evolution primarily results from four factors: (1) the potential for a species to increase in number, (2) the heritable genetic variation of individuals in a species due to mutation and sexual reproduction, (3) competition for limited resources, and (4) the proliferation of those organisms that are better able to survive and reproduce in the environment. [Clarification Statement: Emphasis is on using evidence to explain the influence each of the four factors has on number of organisms, behaviors, morphology, or physiology in terms of ability to compete for limited resources and subsequent survival of individuals and adaptation of species. Examples of evidence could include mathematical models such as simple distribution graphs and proportional reasoning.] [Assessment Boundary: Assessment does not include other mechanisms of evolution, such as genetic drift, gene flow through migration, and co-evolution.]

HS-LS4-3. Apply concepts of statistics and probability to support explanations that organisms with an advantageous heritable trait tend to increase in proportion to organisms lacking this trait. [Clarification Statement: Emphasis is on analyzing shifts in numerical distribution of traits and using these shifts as evidence to support explanations.] [Assessment Boundary: Assessment is limited to basic statistical and graphical analysis. Assessment does not include allele frequency calculations.]

HS-LS4-4. Construct an explanation based on evidence for how natural selection leads to adaptation of populations. [Clarification Statement: Emphasis is on using data to provide evidence for how specific biotic and abiotic differences in ecosystems ( such as ranges of seasonal temperature, long-term climate change, acidity, light, geographic barriers, or evolution of other organisms) contribute to a change in gene frequency over time, leading to adaptation of populations.]

HS-LS4-5. Evaluate the evidence supporting claims that changes in environmental conditions may result in: (1) increases in the number of individuals of some species, (2) the emergence of new species over time , and (3) the extinction of other species. [Clarification Statement: Emphasis is on determining cause and effect relationships for how changes to the environment such as deforestation, fishing, application of fertilizers, drought, flood, and the rate of change of the environment affect distribution or disappearance of traits in species.]

HS-LS4-6. Create or revise a simulation to test a solution to mitigate adverse impacts of human activity on biodiversity. * [Clarification Statement: Emphasis is on designing solutions for a proposed problem related to threatened or endangered species, or to genetic variation of organisms for multiple species.]


  1. Obviously there is a huge problem in outcome 2: in cases where the effect of one of factors (3) or (4) is small, factor (2) just leads to genetic drift. It is necessary to understand this _before_ moving on to more advanced concepts such as adaptation, especially if students are expected to move on to applying concepts of statistics and probability (outcome 3).

    Drift is the simple (default) case that happens in the absence of further complications - calling it an "other mechanism" is wrong, and treating it as a concept that is somehow more advanced (to the point of being explicitly excluded from the curriculum) is worse.

    In general the outcomes seem too advanced and much too vague - I have no idea how the students are meant to achieve them when the curriculum cuts corners on the basic mechanisms.

  2. My thoughts—

    1.Specifically consider the evolution of man & chimp from a common ape ancestor.
    2.Introduce pseudogenes, jumping genes and the like as sources of DNA having no primeval adaptive function.
    3.Include biological clock from non-functional DNA, showing how it independently confirms the timing (from fossils) of the man-chimp split. I think the logic of the mathematics is simple enough for high schoolers to grasp.

    HS-LS4-2: Caveat-
    Ecological adaptiveness measured in external phenotypes is due mainly to coding DNA as distinct from non-functional DNA, such as pseudogenes.

    HS-LS4-5: Caveats-
    1.Animals and Plants may co-evolve. Changes in ‘environmental conditions’ are not necessary for either neutral or adaptive evolution.
    2.Adaptive evolution in a species may result in reduction in the number of individuals, as when insects become rare when they adapt to be more efficient at eating their host plants all up.

  3. Nothing or very little about drift or stochastic events, all about selection and adaptation. That needs to be changed, evolution can't be properly understood without it.

  4. I can see why they would want to start with getting the students to understand natural selection. Too many students come away from their biology courses with the idea that there is some magical drive toward perfection, but don't get it that the changes happen by changes of gene and genotype frequencies owing to current fitness. (This is reinforced by television documentaries on Nature that feature impressive narrators declaring how Nature makes sure everything works out efficiently).

    Asking the students to master genetic drift and stochastic processes of evolution first is not a great idea. In my theoretical population genetics course (a graduate course) the students have the hardest time with the last half of the course, which is about genetic drift and its interaction with other forces. I think that the educators who drew this up were understandably desperate to get the students to focus on understanding how natural selection works.

    1. I'm not sure I agree. I think something like the following gets the bare basics of the concept across quite well, and could be conveyed to a high school class in a matter of minutes:

      If high school graduates were required to understand only that much, it would still be a great improvement over the current situation.

    2. It's interesting that they seem to be emphasizing environmental issues in the guidelines. I presume this is their attempt to make the study of evolution seem pertinent to "real world" issues, but I'm not sure how successful that will be.

    3. @Joe Felsenstein,

      Random genetic drift and the rudiments of population genetics are requirements in the biology curriculum of Ontario high schools. I don't think the failure rate of our students is greater than that of American students.

      Why in the world would your GRADUATE students have trouble understanding random genetic drift? They should have learned all about it as undergraduates, no? The longer we put off teaching this stuff the harder it will be to change students' misconceptions.

  5. I agree with lutesuite and I used precisely that UC Berkeley page to discuss genetic drift with my high schoolers. They got it.

    I'm glad to see that I already am doing what these standards outline. I'm student teaching now and, except for some emphasis on history of evolutionary thought, my unit fit perfectly.

    The environmental emphasis runs through the entire curriculum, in some other sciences too.

    1. Darn, this was supposed to be in response to Joe's comment.

  6. The NGSS are meant to be the floor....not the ceiling. They are meant to represent the foundation in terms of 1: practices of science 2: core ideas 3: cross cutting concepts [i'm not going to explain]. They are a set of performance standards to assess and there is no reason teachers cannot go deeper. Ultimately is drift a FOUNDATION knowledge to generally understand evolution? That is the debate. Do ALL graduates truly need to understand drift? Is it AS important as natural selection and descent with modification? It will ALWAYS be a debate - there is no 'correct' side to this as the members who generated the standards are every bit as aware of this limitation as you are. The very fact they put the boundary into the descriptor illustrates this. It was a judgement call. Being a foundation, there are more courses many students are free to take to continue to deepen their understanding. As for Ontario...only those students taking SBIU3/SBI4U [perhaps SBI4C] would here about drift AND evolution is generally speaking not in the curriculum AT ALL unless a student takes those courses. If you want to criticize curricula then ALL curricula have judgement calls.