deconstructing ‘processes & patterns of evolution’

A while ago my friend Heather, who’s a biology teacher, asked if I would write something on answering questions in the ‘processes & patterns of evolution’ paper (AS90717). Here you are, Heather – I finally got around to it 🙂

You’re probably all familiar with the Achievement Standard document, but the assessment specifications are also useful in highlighting other things that are important. The standard tends to be quite pared down, & the specifications document is a place where the examiner can indicate areas that they think are significant. For example, the current assessment specification for AS90717 says:

There will be an emphasis on groups that contain New Zealand examples, eg ratites, Nothofagus.
But I think it’s also important for you to recognise that (going on past papers) they aren’t going to restrict themselves to New Zealand examples only. And that makes a lot of sense – it’s not just a New Zealand phenomenon & there’s so much exciting research going on elsewhere. And – just as important – the examiner is not expecting you to be aware of the details of the material that they use as context for a question. That’s just the background information. What they do want to see from you is the ability to apply your understanding of evolutionary processes & patterns to explaining the data that they provide. 
The concept of natural selection and its role in speciation should be clearly understood. 
What’s being looked for here is an understanding of how natural selection operates. I know from teachers – & I see it sometimes in my students here as well – that there’s a bit of a tendency among students to say "it evolved through natural selection" & leave things at that. But that’s not going to be sufficient because it doesn’t address the how of the question.
For example, in the 2004 Scholarship paper there was a question about the evolution of different fish (from memory, flounder, angler fish, & seahorse). Apparently a lot of students provided the sort of general non-answer that I’ve just given. But what they should have done (& what the successful candidates did do) was break it down: spelling out how natural selection might bring about change within a given population. 
To do this, you might start by saying that all the individual fish in that population will be different (variation). Some of that variation will have a genetic component – it will be heritable. If a variation in a particular feature (e.g. body shape, or colour) makes it more likely that an individual possessing it survives (e.g. is less likely to be picked up by a predator, or is better at competing for a resource) & reproduces, and it has a genetic component, then the individual will pass that feature on to at least some of its offspring. If individuals with that feature consistently produce, on average, more offspring than individuals without it, over time the feature will spread through the population (differential reproductive success).
And one of the key messages there is that evolution involves changes in the gene pool of a population:
Candidates should understand that evolutionary change at the level of species and populations reflects underlying changes in allele frequencies of the evolving populations.
You also need to think about the role of the environment in driving evolution, both within populations and at the species level:
The significance of environmental changes, such as glacial/interglacial periods and associated changes in sea level, and their effects on speciation should be clearly understood.
These environmental changes can both select for (and against) individuals with a particular set of characteristics. And they can also be instrumental in the early stages of speciation, when geographically isolated populations can then go on to evolve intrinsic isolating mechanisms (e.g. differences in behaviour or structure) that reduce or prevent interbreeding when the populations come back into contact with each other. Last year’s L3 paper asked you to think about this in terms of the dreaded cockroaches!
Reproductive isolating mechanisms need to be considered in terms of how they contribute to speciation.
And of course, you need to be able to integrate all this: if you understand how evolutionary processes operate, then you should be able to apply that understanding to explain the various patterns of evolution: convergent and divergent evolution, and adaptive radiation, for example. It’s quite doable – but you do need to read the questions carefully, and think about how to apply your existing knowledge to the novel contexts that you’ll meet in the exam. (And don’t be thrown by the fact that they are novel!) Go for it!


2 thoughts on “deconstructing ‘processes & patterns of evolution’”

  • Tessa Lambert says:

    I have just been reading your blog in preparation for my schol exam on saturday, and came across this blog that I believe was written for my biology teacher Dr Meikle. She has always encourage us to read your blog and it has indeed been very helpful! So thank you!

  • Alison Campbell says:

    Hi Tessa 🙂 You’re right, I wrote it for Dr Meikle. (We were at uni together, many moons ago.) I’m really glad to hear that the blog’s been helpful – I’ve always hoped it would be & it makes my day to hear that you’ve found it so. Best wishes for your exams, and for your future study.

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