Teaching Evolution 6/5: Skeletons in the Family Tree

 I’ve decided to add a quick post which fits in nicely with the set of five I made the other week. Basically, a bunch of interesting things showed up in science news online, more or less simultaneously, and I thought it was worth adding a new post instead of amending an old one.

One bit of news is that there is some evidence to suggest that humans bred with Neanderthals. This was reported in New Scientist, and the accompanying editorial was pretty good too. An interesting aspect is that Neanderthal DNA shows up in all human populations not descended from ancestral Africans. This nicely illustrates the problems with the whole concept of a species as a distinct, separate group of individuals. Things are a little more complicated than that.

The SciencePunk website puts the human family tree in perspective by linking to some work estimating just how closely related we are to other modern species. Describing chimpanzees, gorillas and so on as cousins is a helpful shorthand, but this article makes the relationship a little more specific. It links to the Tree of Life website, which although not recently updated shows the wider genetic connections between diverse species. The page on us (Homo, naturally) includes links both popular and academic.

Not so much our family tree (in an immediate sense), but still something that students may be interested in. On Not Exactly Rocket Science, Ed Yong’s excellent science interpretation blog, a paper was referenced which gives more evidence that feathers were first used for warmth, not flying. A study has shown that the bones were probably not strong enough to support powered flight. Please note, I’ve carefully stated this as ‘used for’ not ‘evolved for’ as that is just asking for trouble with determinism…

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Teaching Evolution 5/5 – Resources

Hopefully the posts this week have given a few ideas about how to make the teaching of evolution a little more interactive – it is, after all, fairly hard to show evolution happening in a school science lab. Today I’m going to share a few resources that have not featured so far, split between books and websites (some for us as teachers, some for the students to ‘do’ something).

Books

Bill Bryson’s book, A Brief History of Nearly Everything, is fantastic. It includes his discussions with creationists, as well as some great discussion of the main features of evolution, as observed and as documented in the fossil record. The illustrated version is a treat if you can afford it.

Richard Dawkins is a bit like Marmite, you either love him or hate him. I find myself defending his views a fair bit and must admit that he is strongest when discussing science rather than religion. He has a gift for annoying people and although I often agree whole-heartedly with his views, the way he expresses them is not always constructive. His books are many and varied, and in most cases probably a bit tricky for the average student, but I really enjoy them. He’s got plenty on evolutionary theory but I’d suggest that The Blind Watchmaker and The Greatest Show On Earth are probably good places to begin. Unweaving the Rainbow is also excellent, a collection of essays that provide some very vivid examples and quotes. 

I first read Matt Ridley’s The Origins Of Virtue when at University the first time. It was my first exposure to really good science writing and it still sits on my shelf today. For teachers, I’d suggest that Genome might be more accessible, unless you’re particularly interested in sociobiological explanations for altruistic behaviour. (Trust me, it’s more interesting than it sounds.) He followed up a lot of Dawkins’ early ideas, applying them to humans and human behaviour. If this kind of thing sounds good, try Jared Diamond. His recent Guns Germs and Steel was a great book, the history of the whole human race, and I’m sorry I missed the TV show.

Web – Activities for students

One I have tried out is from the University of Colorado, a sim based on the changing characteristics of wolves and rabbits in an ecosystem. Like all their others (listed on the website) it’s research based but allows students to spot and manipulate patterns of change.

Evolution Lab is another activity, based on imaginary organisms that ‘grab’ passing food. Over time students can observe effects on phenotype and so track evolutionary change.

The Peppered Moth is a standard example of natural selection in the UK, a case which happened quickly enough for us to notice. (As in most similar examples, it was a fairly dramatic change caused by human activites, albeit one which has since been reversed.) A simulation is found here, which I tracked down through an excellent blog run by an American biologist.

With Darwin’s recent birthday, there’s been a load of stuff available. Survival Rivals is a site with online activities, linked to documentation they’ll sent out to UK schools for free. It’s funded by the Wellcome Trust and there’s one activity for each of KS3, 4 and 5.

YouTube is an excellent resource, assuming your school network makes it available. I’m sure that Evolution Primer #1 is just the tip of the iceberg for useful introductions. I’m sure there are lots of other resources and evolution simulations about – it’s just the sort of thing Flash is good for! Please post in the comments if you have an particular favourites.

Web – Ideas

Although there are some difficulties in teaching evolutionary theory in the UK, our problems are nothing compared to the USA. The American Civil Liberties Union has a FAQ about ‘intelligent design’, the latest attempt to give creationism a coat of paint and call it a scientific theory. (It isn’t.)

One of many, the Evolution FAQ has some useful, short definitions and ideas. Along with Talk Origins (which has grown out of a Usenet group), it provides some excellent suggestions for countering arguments from intelligent design. As previous posts this week have discussed, humans do not think in geological timescales. This can make it hard to grasp the time available for generations of natural selection. Rejecting evolution (or anything else) on this basis is called the Argument from Personal Incredulity.

If you have students giving specific arguments based on religious beliefs – and some may be given tuition in a religious setting or at home – then it is worth doing some reading yourself. There are a lot of classic arguments (the eye, for example) that we have excellent evidence for, and there is a list of responses to creationist claims; this is also at Talk Origins.

Recently a group calling themselves Truth In Science have sent out ‘textbooks’ to UK schools, giving the intelligent design arguments. Fortunately most science departments noticed the major issues with the book, which exploits the UK curriculum focus on discussing how science works. Check out the website of the British Centre for Science Education for more information.

Update: A recent comment in Nature summarises one of the major objections to ‘intelligent design; – we, like so many other organisms, appear to have been designed very badly! (I’m currently trying to recall where I first read a quote, I think from a biologist, that only an idiot would put the playground next to the sewer…)

Hopefully this week’s activities have been interesting as well as useful. I’d really appreciate any comments, positive and constructive. I’d be particularly grateful for any feedback about using the activites with students, as that will help me improve them.

Teaching Evolution 4/5 – Timescales

Many people, including students – and probably teachers, too – struggle with the idea that all living things are related to each other. We certainly struggle with the thought that we have close relatives, chimpanzees, who seem to us to be so different. Even when I point out that so much of the similarities are invisible to us, my students can’t cope with the thought that there’s been enough time for natural selection to cause the noticeable differences. The difficulty is that we can’t grasp the time involved.

The Earth is old. I mean, really, really old. And when we say this to kids, they think it means a few thousand years old. A few might start thinking in millions. What we need to do is put the age of the Earth, put the ‘clock’ of evolution, in perspective. I have several ways of doing this, but they’re inspired by one of Richard Dawkins‘ analogies (quote tracked down on a forum on his website).

“Fling your arms wide in an expansive gesture to span all of evolution from its origin at your left fingertip to today at your right fingertip. All the way across your midline to well past your right shoulder, life consists of nothing but bacteria. Many-celled, invertebrate life flowers somewhere around your right elbow. The dinosaurs originate in the middle of your right palm, and go extinct around your last finger joint. The whole story of Homo sapiens and our predecessor Homo erectus is contained in the thickness of one nail-clipping. As for recorded history; as for the Sumerians, the Babylonians, the Jewish patriarchs, the legions of Rome, the Christian Fathers, the dynasties of Pharaohs, the Laws of the Medes and Persians which never change; as for Troy and the Greeks, Helen and Achilles and Agamemnon dead; as for Napoleon and Hitler, the Beatles and the Spice Girls, they and everyone that knew them are blown away in the dust from one light stroke of a nail-file.”

(This version from Unweaving The Rainbow, many similar ones around.)

On the spur of the moment in a lesson, I produced a list of landmark times for one of my classes. Slightly tidied (and corrected, I must admit) it starts in the present day and goes back in larger and larger steps.

now – 2010

60 years ago – 1950CE – post WW2, rationing, no electronics, cars still a rare luxury in the UK.

600 years ago – 1400CE – Middle Ages, the time of knights and castles, peasants and Robin Hood.

6 000 years ago – 4000BCE – the first cities (Ur), before Stonehenge and the Pyramids.

60 000 years ago – humans migrating ‘Out of Africa’ to every continent except Antarctica.

600 000 years ago – Homo Heidelbergensis using tools, weapons, possibly clothes and language.

6 000 000 years ago – common ancestor of humans and chimpanzees.

60 000 000 years ago – dinosaurs RIP, mammals taking over on land.

600 000 000 years ago – the most complex lifeform on Earth was probably a worm.

It might be interesting and/or useful to give these points to students and challenge them to show the timeline using pictures – research lesson anybody? Alternatively produce a powerpoint yourself and use it as a starter or plenary.

You can find some nice animations online, such as the Prehistoric Timeline at the National Geographic website. A few other useful resources will be posted tomorrow but I’ll finish with an Excel sheet (disguised as an Word document) I’ve played with. Type the room you have available into the appropriate box and it will tell you the correct distance from the origin for all kinds of ‘landmarks’. This could be prepared ahead of time, or students could be given the values and asked to attach masking tape signs at the appropriate points on a piece of string (e.g. 4.6m of string equal to 4600 million years would put all human and protohuman history, up to tool use, in the last centimetre).

Activity: timeline saved as docx – once open, you can edit the Excel sheet assuming you have the software.

Teaching Evolution 3/5 – Non-Random Selection

This post – and activity – is a follow up from yesterday’s, looking at mutation. I’ve found that students often struggle with randomness and, short of loaning them Mlodinow’s excellent book, it’s hard to fix their problems. Instead, I focus on separating the concepts of variation and selection.

Variation always happens during reproduction. In asexual reproduction it is caused by mutations, mistakes in copying the instructions that make up the genome. For humans and other organisms that reproduce sexually most variation (in the short term) is caused by the shuffling of the genes during meiosis. We can treat this kind of variation – or the effects of it, in changing characteristics – as effectively random changes that affect an original characteristic.

Proponents of intelligent design often point to the random nature of variation as ‘proof’ that evolution couldn’t work. This is best addressed by pointing out that selection is the true friving force behind evolution, and it is clearly not random. It is true that sometimes a slow impala escapes a cheetah or a furry wolf still gets chilly, but on average those individuals with the characteristics best suited to their situation will survive and thrive. This is not random. On the contrary, it is both predictable and reproducible in statistical terms.

The first time I tried this I asked students to use the random number function of their calculators to model variation. We used even numbers for an increase in height, odd numbers for a decrease. We then ‘selected’ the offspring that were taller, imagining a situation where this would be an advantage. Over generations, the whole population became taller on average. My new version uses dice to simulate the changes but the selection works the same way. The printable activity consists of four pages:

1. Teachers’ guide including answers to questions
2. Instruction sheet with questions (if laminated this can be reused)
3. Data sheet for students to write on their results
4. Answer sheet for questions if required (could be turned into differentiated writing frame)

printable: giraffes as pdf

Please let me know if you find this useful or have any comments, especially any problems you had with it. I will give one health warning: This simulation works much faster than variation would change height in nature, in all but the most extreme environments!

Teaching Evolution 2/5 – Mutations

Nobody understands mistakes like kids. Unless, of course, you mean the teachers who have to correct them. I find my students get very interested in the idea of mutation and starting from the media version – X-Men for example – we work towards a more accurate description, of a mistake that is made during the copying of genes in cell division. I find it useful to mention mutations in body cells and their causes (chemical triggers such as tar and benzene, viruses like HPV and nuclear radiation). With an articulate, curious class, this can turn into a lesson of its own!

With a new individual that has an altered gene compared to the parents, there are two possibilities. If in ‘non-coding’ or junk DNA, there will be absolutely no effect. (Variations in these sections are used for DNA fingerprinting, which students can learn about by doing a Nova Interactive.) If it is in ‘coding’ DNA, those sections that actually do something, then there are several possible outcomes:

• it makes exactly the same protein – no observable change
• it makes a similar protein that does effectively the same job
• it makes a protein which does the job slightly better or worse
• it doesn’t make a protein at all (and the organism can’t survive)

Most mutations that cause any effect at all, cause a negative effect. The example – explained better in the powerpoint linked below – is that if we change a random letter on a page of a book, it is unlikely to make the book better. These mutations are random, not deliberate. The chances of a mutation improving the functioning of a protein or cell is small, to say the least.

In my activity – Evolution In Other Words as ppt – students start with a word and ‘mutate’ it by changing one letter at a time. I’m playing with ways of making this more random, perhaps by using Scrabble tiles. The idea is that students will see not only that mutation can happen, but that after a few ‘generations’ it is hard to see relationships, both between ‘ancestor’ and ‘descendant’ words, and between ‘cousins’ – words which diverged by changing a different letter. Depending on how much of the powerpoint is used, students can also be prepared for concepts such as selection and speciation.

What’s interesting to me is that many surviving mutations will appear to be survival-neutral – they don’t make an organism better or worse at surviving. I often give the contrasting examples of fur colour and eye colour. Different colours of fur are clearly relevant for survival in the wild, but eye colour, as long as it is not linked to eyesight, shouldn’t matter. This is a nice way to introduce the concept that sometimes the advantages of a characteristic are difficult to observe, subtle or non-existent.

Teaching Evolution 1/5 – Basics

After the recent, fairly epic post about using homeopathy to teach ‘how science works’, and the time spent turning it into a (hopefully useful) scheme available as a pdf, I’m trying five shorter posts again this week. Instead of books, however, I’ll be sharing some ideas for teaching what can be one of the trickier topics, evolution. I’d like to emphasize that it’s tricky not because it’s difficult in itself, but because of the manufactroversy we see mentioned in the media and the mind-boggling time scales often involved. I really enjoy teaching evolution and my aim is that the following posts will show how it can be fun, rather than difficult.

A lot of evolutionary ideas make intuitive sense to students. I start by discussing adaptations, putting them in the context of a characteristic, some aspect of anatomy or behaviour, that gives an advantage over other individuals. This is an opportunity to remind students of the importance of linking structure and function – in this case, the adaptation itself with the advantage it offers. More able students may understand quickly that these advantages also come with a ‘cost’, while others may need a little time to deal with this.

Comparing different animals that have similar adaptations (such as teeth and claws for hunting) and animals in apparently similar situations that have different solutions to the same problem (foxes are solitary hunters/scavengers while wolves are pack predators) can be illuminating. You may choose to consider how humans fit into this context, or leave this discussion for a later time. I tend to finish the ideas of adaptations by summing it up. I suggest that to be Successful, an individual must have the Three S Factors.

• Survival (avoid being eaten, freeze to death or similar)
• Snacks (get enough food)
• Shagging/Sex (have offspring)

Funnily enough, this seems to be an idea that sticks in their heads! Once we’ve covered the background, it’s time to move on to random variation within a population, followed by selection pressure. Some thoughts on teaching these will be appearing later this week.