Evidence for Evolution

Convergent and Divergent Evolution

The Story...Toby was a young adventurous Joey who lived in the Australian outback with his Mum, Dad and three sisters. Toby loved hearing stories was interested in hearing more about his heritage. He became interested in developing his understanding of how Kangaroos have evolved over time and where they came from.

Toby

Toby’s parents were not able to tell him much except that their family had been living in Alice Springs for the past 100 years. This did not satisfy Tody’s intrigue and so he set out determined to find some more answers. Joey had no idea of where to begin his investigation but knew that his teachers at school always had answers. So his first stop was to visit his favourite teacher at school Mr Amos. Mr Amos was Toby’s science teacher and Joey recalled learning about ancestry the previous term. Toby thought that Mr Amos must be able to help him out somehow! Off Joey went in search of Mr Amos and hopefully some answers!

Mr Amos

Hi Mr Amos!Hi Toby. To what do I owe this pleasure of have you visit me on your day off?”

Well Mr Amos I’m trying to research my ancestry and figure out where they came from but I need your help because I don’t know where to start!”

Well Joey I’m very impressed that you are so interested in your ancestry. Do you remember what we talked about last term when we were learning about ancestry.

Do I ever Mr Amos. We learnt about how species

evolve and palaeontologists who look at comparative

anatomy to figure out major lineages of species.

Very good Joey. I’m very impressed with how much you remember.”

Thank you Mr Amos but how will this help me figure out my ancestry?”

Well Joey it just so happens that a close friend of mine, Samantha, is a palaeontologist who I’m sure would be more than happy to have a look into your ancestry with you.

Gees Mr Amos that would be fantastic! Thank-you! No worries Joey. I’m glad I

could help. Good luck in your quest for information!”

So off Toby went to meet Samantha. He was very excited about this as the prospect of finally learning something about his ancestry was in close reach!

Samantha greeted Toby with open arms. She was very excited to see him as Mr Amos had called ahead and informed her that Toby was on his way over. Samantha loved visitors and embraced any opportunity she had to talk about her love and passion of palaeontology. Samantha had a particular interest in the area of comparative anatomy and so was very keen to look into Toby’s ancestry and determine how comparative anatomy has played a part in the evolution of Toby’s family.

Samantha

Why hello young Toby! I’m very excited that you have come to visit me and that you have taken an interest in my work. Let’s start by providing you with some background information about comparative anatomy so you know how and why its used.

Sounds good Samantha. I’m very interested to learn about anything to do with ancestry.

1. Alright lets get started! Comparative anatomy is about establishing relationships on the basis of structural similarities and differences. Palaeontologists research comparative anatomy as a means of determining how closely related species are.

2. It is assumed that groups with little in common have diverged from a common ancestor much earlier in geological history compared to groups that have a lot in common.

3. Comparative anatomists look for structures in species which although may serve different functions are fundamentally similar, and therefore suggests a common origin. These are called homologous structures.

Wow like how its believed that tree

Kangaroos evolved from Possums because they

both use their tails .

That’s a perfect example Toby. Great work! Comparative anatomists look at three things when trying to determine whether or not two structures or homologous or not. These are their relative positions, gross morphology, studying the shape and general appearance or form of an organism and histological appearance, the appearance of the tissues of the body of an organism.

Cool so they look at things like the shape of a kangaroos tail and how this has evolved as well as the development of the embryo to determine how different structures may have similarities.”

Exactly right Toby. Your showing a fantastic

understanding already!” Animals are said to evolve in two different ways. These are referred to as

divergent and convergent evolution. Divergent evolution occurs when the same species splits into two or more

descendant species due to developing new characteristics to enable them to

survive in their new and differing habitats.

This means that species that were once similar or related then

become more and more dissimilar. The newly produced organisms

have certain features in common with each other and with the

ancestral stock from which they arose and this forms the basis of

what we call homology.

So this is like what they say has happened with our pouch. It evolved

from another species and Kangaroos adapted it to enable survival in their

new environment.

1. Exactly right. That’s a perfect example of divergent evolution Toby.

We call the result of divergent evolution adaptive radiation, the

process whereby populations move into new environments and undergo rapid evolution as they adapt to the

unexploited habitats.2. Comparative anatomists

construct evolutionary trees which illustrates adaptive radiation in

which branches represent separate lines of descent from a common ancestor. The more similar two

organisms are, the more recently they are assumed to have diverged.

3. The other type of evolution, convergent , occurs when complete organisms (or their parts) come to

resemble each other more closely than their ancestors (or ancestral

structures) did, as a result of their sharing similar environments.

The anatomical similarity between species is said not to

be caused by common ancestry but by the fact that structures

that perform the same functions are likely to resemble one

another to a degree. These structures are described as

analogous.

So like how both Kangaroos and Wombats have both

evolved to have sharp claws for digging in Australia’s dry climate. Their claws are an analogous structure. And an

example of convergent evolution would again be

possums and tree kangaroos.

Excellent! You’ve got a really good

understanding now. I think I have given you enough information to

do a bit of your own investigating! Good

luck!

Thanks Samantha! You have been a great help!

The End