Lecture 11 (6/12/09): Mom...Do Birds Grow on Trees?

Complete the following sentence:

I'm stressed and sad because...

A. The Red Wings lost in Game 7.
B. Brett has taken a few days off of Blogging.
C. I have a BS110 exam on Friday (and I'm completely freaked out).
D. There's nothing good to eat in my refrigerator.

If you answered B and C, then you're in the right place. I can't do much about A at this point. But maybe the next 3 Blogs will provide some 'nourishment' for your brain, so consider these next 3 Blog posts my way of also helping you out with D (consider them the intellectual equivalent of a 'Happy Meal').

Lets get straight to the point...

You and I have a lot of work ahead of us between now and Friday morning, so we've no time to waste. To be honest with you, I think that there has been more 'information' tossed your way in Lectures 11, 12 and 13 than in any other 3 lectures all semester. So, if you're feeling a little bit more nervous about Exam 2 then Exam 1, I understand. In response, some of you might be feeling the desire to run into a dark hole and hide, fearing, with Exam 2 looming around the corner, that there's just too much knowledge to hold inside your noggin' for one exam.

If you're thinking that way, however, then you've missed an important point that I've been trying to illustrate with my Blog all semester: Another way to think about knowledge is not what's 'inside' your head, but instead what's 'outside' your head. What is there is the BS110 lectures that you can see with your eyes AND move with your hands?

Over the next couple of Blogs I'm going to once again ask you to try on some different 'glasses'-- yes, some old pairs that we've used before (like our different pairs of scale glasses), but also some new pairs that you probably didn't know you owned (or, for that matter, didn't know you needed). The notion of wearing different 'glasses' is one device that I like to use to try and persuade you that part of performing well on Prof S's exams is learning to 'see' the world like he and other biologists do. So, that brings us to one of the really important questions behind all of the material covered in Lecture 11:

• How do biologists look at--and more importantly, talk about--the amazing number of diverse life forms on our planet?

Answer #1: Taxonomies

Can you imagine how many different ways there are to talk about the living things found on Earth? A gazillion? Maybe...maybe more. This is why I inserted the image at right. Each pair of glasses is meant to represent a different way of looking at the living things found on our planet.

Let me illustrate by using my own backyard. Say I choose to wear the pink glasses from the rack...pretend that these are my "Is-it-edible?" glasses. I often classify the plants in my backyard in terms of two simple categories: those that taste good and those that don't. Among the plants in my back yard that taste good are different kinds of herbs (basil, thyme, mint, oregano, tarragon, rosemary, chives), some garlic plants, some hot pepper plants, some tomato plants, and our 3 big maple trees (my wife and I make our own maple syrup each spring).

If my wife and I had kids (which we don't), they might choose instead to organize the plants in our yard by wearing the red glasses (the "Those-plants-you-can-climb-and-those-you-can't" glasses), the yellow glasses (the "Those-plants-that-produce-fruits-good-for-throwing-at-cats-and-those-that-don't" glasses), or the green glasses (the "Those-plants-our-mom-yells-at-us-when-we-step-on-them-and-those-she-doesn't" glasses). The point is: There are so many glasses one can wear; there are so many different ways to look at the collection of living things in this world!

Most biologists, however, prefer to look at the collection of living things in this world with a couple of specific pairs of glasses. This is the idea behind many of their "taxonomies" ("taxonomy" from Greek taxis "arrangement" and -nomia "method"). Prof S told you in lecture about a one taxonomic strategy that biologists still use and value. It was the 2-name or "binomial" naming system first developed Carl Linneaus in the 1700s. In this strategy, he said that biologists like to use "morphological similarities" ("morphological" from the Greek morphe "form, shape"). In other words, biologist like to 'lump' (and 'split') groups of living things into categories based on similarities and differences in term of 'how they appear' or 'how they're built.'

If you think back to my Lecture 8 Blog ("A Biology Bedtime Story...Chapter I"), then you will recall that I used one type of taxonomy to talk about how biologists in the Galapagos often group the 13 species of Galapagos finches according to their "behavior and diet."

Below is this behavior/diet taxonomy, which is based on a) where the birds spend most of their time, and b) what they typically eat:

• Group A: The finches that live in trees and eat fruits and bugs.
• Group B: The finches that live in trees, but are strict vegetarians (i.e., no bugs!).
• Group C: The finches that live in trees, but they don't look and act like the other groups of tree finches...they actually look and act more like a different genera of birds (like the "warblers").
• Group D: The finches that spend most of their time hopping on the ground.

Do you see one of those branching 'tree' diagrams in the bulleted Groups up above? No, you don't. That's because taxonomies aren't always necessarily concerned with how groups of organisms are related--genetically speaking, that is--to one another. As soon as we start talking about how groups of organisms are related to one another in terms of their 'origins'...or their genetics...or their genes...or their DNA...or their actual base pairs (G, C, A, T)...then we're entering the realm of "phylogenies" ("phylogeny" from Greek phylon "race" and -geneia "origin").

Answer #2: Phylogenies

Why do I have only one pair of glasses at right when in talking about taxonomies I had many?

That's because looking at living things in terms of phylogenies involves a very specialized type of scientific glasses. I've decided to make them X-Ray glasses because--as Prof S mentioned in class--phylogenies try to lump and split groups of organisms according to their "evolutionary history." So, in order to get a sense of how organisms evolved in the past, you sort of need a pair of glasses that are capable of 'penetrating' things like the fossil record or--as is becoming increasingly common in 21st century science--'peeking at' and comparing the DNA of different living species.

In modern-day science, classifying organisms based on their evolutionary history basically means showing how today's living things could be related to each other and to organisms that lived in the past.

And this, is when these branching tree-looking diagrams come into play...

Galapagos Finches: Who is most closely related to whom?

At right (click on it to make it bigger), you can see a phylogeny for 14 species of birds found in the Galapagos (this includes the 13 species of finches mentioned above).

If you were to associate "time" with this tree diagram? How would you do it?

Well, hopefully you realize that the far left of the tree, "the trunk," represents the (hypothetical) common ancestor of all 14 of these Galapagos bird species. That means that in looking at the diagram from left to right, we are basically marching forward with our eyes through time! At the far right is the so-called "present-day" and at the far left is some point in the "past."

Can you identify the "branch points" or "nodes" in this diagram? How many are there? Do you see any places where "polytomy" occurred? These are a few of the terms that Prof S went over in class, so hopefully you can answer these types of questions quite easily...Yes? No?

Now, take a look at the tree diagram below at left. This is where taxonomy meets phylogeny. The caption in the upper left of the diagram says it all...

Here, I'll translate it for you: 'When we look at the DNA sequences of as many as 15 different species of Galapagos finches, it so happens that how we think they are related--phylogenically speaking--is actually quite similar to how we might group or arrange them--taxonomically speaking--according to things such as the way they feed.'

The black branches (i.e., U-shaped lines) of these two tree diagrams are nearly identical, but notice that the tree diagram at left has colored boxes. The colored boxes represent the taxonomy-part of this representation: they represent the "feeding approaches" of the Galapagos finches. The black lines represent the phylogeny-part of this representation: they represent the "relatedness" of the Galapagos finches.

I know, I know...You're thinking: 'First there was 13 finch species, then there was 14 species...now there's 15? What's the deal?'

By now, however, these differing numbers of species shouldn't surprise you in the least! Why? Because you know that there are many different ways to say what counts as a species. The Biological Species Concept is one way...The Ecological Species Concept is another way...it's highly likely that the web sources where I gathered these different images from were made by people using different concepts for what counts as a separate species of Galapagos finch.

Or, it may be the case that this last image represents newer (or older) developments in our phylogenic understanding of finches. It's possible that the 15 finch species have been somewhat 'lumped,' or that the 13 species have been somewhat 'split.'

Looking ahead...

Tonight we've only scratched the surface of all of the different ideas that are wrapped up or 'hidden' within things like the tree diagrams. In the Lecture 12 Blog, we'll look closely at how the ideas in Lecture 12 connect to those presented in Lecture 11...

• HERE'S A HINT: the key connection between Lectures 11 & 12 is 'In The Trees...', but maybe you can't see it just yet.

My guess is that you soon will be able to understand my hint...but it will require that you go out and secure a couple of additional pairs of glasses to put on.