Introduction to Evolution

INTRODUCTION:

This lesson introduces the most important connecting concept in all of the life sciences. As one famous geneticist, Theodosius Dobzhansky, once said, “Nothing in biology makes sense except in the light of evolution. Without that light, it becomes a pile of sundry facts, some of them interesting or curious, but making no meaningful picture as a whole." The purpose here is to introduce the basics of this concept early to students so as to provide a “meaningful picture” and framework for all further studies. Hence, this should be viewed as foundation work relevant to virtually the whole KS2 unit on “Life processes and living things,” including growth and reproduction, variation and classification, adaptation, feeding relationships, etc. The lesson takes a direct approach: first with a hands-on introduction to fossils and what they tell us about geological time and how life has changed, then a discussion of pictures showing some transitional forms that have been found in the fossil record. This is then followed by a fun worksheet, completed under the leadership of the teacher, which illustrates the basic idea of natural selection. Finally, a web video on the earliest primates helps make the connection with human evolution.

TEACHING:

Ask if anyone in the room has any fossils? Bring out yours, describe each one a bit and pass them around to each table. Does anyone know how fossils are made? There are basically 3 different ways:

1) Sometimes small animals or insects can get trapped in tree sap, which then hardens to eventually form amber. 2) An impression, like footprints, is left on wet sand or clay and, after a very long time, this can turn to rock.

Relevant KS2 Links: SC1 1a, 2b, 2l; SC2 1a, 5b, 5c Plus basic foundation to provide context for essentially all of the life sciences

Suggested Year Group:

3-4

EQUIPMENT • A small collection of fossils of different ages, preferably ones where

you know approximately how old they are. These can be purchased in museums or nature shops or from the web if you don’t have some of your own;

• A large printout of the accompanying pictures (or an OHP projection or electronic version for SmartBoards); • Copies of the accompanying worksheet for each student and

various coloured pencils; • A board to draw on yourself;

Base Concepts Conveyed: Living things have similar characteristics because they are related, which means they have a common ancestor. Populations can change due to selection by predators. Lots of small changes over a very long period of time can lead to big changes.

Assumes Introduction to Atoms

How are fossils made?

3) Remember the experiment we did with copper coins? We found that some vinegar and salt could be used to remove atoms of copper from the surface of the coins to make them shiny. And what happened when we put in some iron nails? Right, the nails became dark because some of the copper atoms swapped placed with some of the iron atoms in the nail. Well, something a bit similar can happen where atoms in the rock get dissolved in water and, if that water is in contact with shells or bones for a very long time, some of these atoms can swap places with those in the shell or bone, so they gradually turn to stone.

How long do you think it takes these processes to happen? Typically many millions of years! Talk about how old some of your fossils are. These are very big numbers! How fast can you count? If you started counting to a million and didn’t stop to eat or to sleep, it would take over a month (some people actually tried this: a team of 3 took turns so the others could rest )! That’s only one million, and fossils we find can go back many hundreds of millions of years. How do we know that’s true? Does anyone know how we can tell how old fossils are? One way is to look around today to see how long it takes the earth to move around and begin to form features that will eventually become valleys and mountains and volcanoes. From that we can work out how long it must take, which turns out to be millions of years. So, if we found fossils in layers of rock that go underneath mountains, they must have been there even before the mountain! So fossils can tell us what sort of living things were around a very long time ago. And one thing we can tell straight away, is that the shape of life has changed over the years and many creatures that lived long ago (like dinosaurs) are no longer alive. At the same time, there are some animals alive today that weren’t around long ago. In fact, if we go back before just 200 thousand years ago, we can’t find any fossils of bones from modern humans… though there are bones of animals similar to humans that are no longer alive today! If we go much, much further back - about 400 million years ago, there were no land animals, only creatures in the sea. What does that suggest about where life came from? Here is a very interesting type of fish that comes from around that time (show the picture of the tiktaalik). What does it look like? What kind of animal is that!? It looks like something in between a fish and a 4-legged land animal! What does that suggest? Here is a photograph of a very famous fossil (show the picture of the archaeopteryx skeleton). Its head got bent back when it died, but see the bony tail here and the long, sharp claws? Here’s a close-up photo of the skull from another such fossil (show the picture of the archaeopteryx skull). What do you see in the mouth? Right, sharp teeth! This is definitely a small dinosaur. But look back at the original photo of the skeleton again… what else do you see? Feathers! Here is a photo of a model scientists have made to show what they think this creature looked like (show the picture). What does it remind you of? A bird! But this lived about 150 million years ago, before there were any other birds around (there are no fossils of birds dating to before this), and it looks like something between a dinosaur and a bird. What does this suggest? It seems that, somehow, animals have gradually changed: fish changed into land animals and dinosaurs changed into birds (so, in a sense, dinosaurs are still around)! But how and why does this happen? Let’s see if we can work this out together:

How old are fossils?

How do we know their age?

Has life always looked the same?

Where did land animals come from?

Where did birds come from?

Refers to ‘Introduction to Atoms’

ACTIVITY: Pass out the sheets on Silly Bungos to everyone in the class. Ask someone to read the first short paragraph (in bold) out loud to the rest of the class, which talks about how the one-eyed Silly Bungo fish are always getting eaten by Slurp Gobblers, so they have to hide behind small red rocks. Ask everyone in the class to concentrate, and try to really picture this in their heads. Now, read the next part, which says that when baby fish are born, some will grow to be a bit bigger and some a bit smaller than their parents… just like with people. In the space below this, they should draw pictures of which type of fish that would have a better chance of not getting eaten by the Slurp Gobbler. See who drew big fish or small fish and discuss why they think these would survive best. Help them realise that smaller fish can hide better. Draw this on the board yourself, with an arrow pointing from the original Silly Bungo to this one. Now read the next part, which says some Silly Bungo fish might be born yellow and some red, just like people can have skin tones that might be slightly different to that of their parents. Again, in the space below this, have them draw pictures of the type of fish that would have a better chance of not being eaten and discuss their reasons. Small red fish can certainly hide very well behind small red rocks! Draw this on the board yourself, with an arrow from the previous Silly Bungo drawing. Finally, read the last part, which says that some Silly Bungos might be born with no eyes and some with an extra one on the other side of their heads. Once more, have them draw pictures of the type of fish that could best survive being eaten. Discuss their reasoning again. You should finally end up with small, red, two-eyed fish. Draw this on the board yourself, with another arrow from the previous drawing. So, there you have it: random differences, like we know happen with people (you’re not exactly like your parents or brothers or sisters, are you?), can get preferentially selected because it allows an animal to survive better in its environment compared to another animal. And, over many, many, many generations, this can lead to big changes in what animals look like. And that goes for us too! Show the picture of different animal limbs compared with those of a modern human. See if the students can spot the similarities. This shows how we must all be related, all being part of the same chain of evolution . Is that it though? Have we finally stopped evolving now? What do you think? Show the chart of American and European average heights over the years. Back around 1700, Americans were about 5 cm taller than Europeans on average. But today, the average European is taller than the average American. This is believed to be the result of Europeans now having a healthier diet. The point is that, even over a few hundred years, the characteristics of different human populations are still changing, even if only by a little bit, so we are still evolving even today. Imagine the size of changes that could happen over a million years!

PLENARY: Watch the Nova Science Now episode on the earliest primates and discuss: http://www.pbs.org/wgbh/nova/sciencenow/0303/02.html

Have we stopped evolving now?

How can small differences be “naturally selected?”

Why did the form of animals change?

Quick Reference

o Pass around fossils. How are they made? Three ways: 1. Tree sap hardens to rock (Amber) 2. Impressions on wet clay harden to rock 3. Atoms in bone/shell replaced by atoms from minerals dissolved in water

o How old are fossils? Many millions of years. Some are hundreds of millions of years old. o How long would it take to count to just one million? Over a month! o How do we know they’re that old?

One way: fossils beneath geologic features that took a very long time to create. o Fossils show different animals lived then that aren’t alive now, though some look similar. o Show picture of Tiktaalik. Fish? Land animal? What does this suggest? o Show pictures of Archaeoptryx. Dinosaur? Bird? What does this suggest? o Perhaps fish changed into land animals and dinosaurs into birds! But how? o Pass out Silly Bungo worksheet. Read each section aloud to class. o Discuss each drawing and draw evolution to small, red, two-eyed fish. o Discuss general evolution of animals, including humans. o Watch web video on the earliest primates and discuss.

Archaeopteryx (150 million years old)

Silly Bungos Imagine that the Silly Bungo fish live at the bottom of the sea. They are coloured white and have only one eye on the side of their head. They live in fear of the huge, dreaded Slurp Gobbler, which sneaks up and eats Silly Bungos! The only defence a Silly Bungo has is to hide behind the small, red rocks that lie around where they live. This is tricky, because the Silly Bungos are just a bit larger than the rocks, so it’s difficult to hide!

When the Silly Bungos lay their eggs and baby fish are born, some of them grow up to be a little bit bigger and some a little bit smaller than their parents. Draw a picture of the types of these Silly Bungos you think have a better chance to survive the Slurp Gobbler:

When these survivors produce their own baby fish, most of them are white, like their parents. But, once in a while, some are born yellow and some are born red. Draw a picture of the types of Silly Bungos you think have a better chance to survive:

And when these survivors produce baby fish of their own, most of them have one eye, just like their parents. But, once in a while, some are born with no eyes at all and some are born with an extra eye on the other side of their head, to give them 2. Draw a picture of the types of Silly Bungos that now have the best chance of surviving: