Another concept I want to discuss is the idea of population thinking. This was an idea that was put forth by Ernst Mayr. Ernst Mayr is the author of this book and I reread this a few years ago. This is actually a very classic work. This was published in the 1960s but it really never quite came out.
goes out of date. And I went through here, you know, a few years ago and reread this and made lots of notes. And one of the things that really struck me when I reread this book is the idea of population thinking that Meyer talks about. And he contrasts this with typological thinking. And so I want you to think in terms of populations.
And it keeps coming back to populations, because populations are very important in biology. And this is what Meyer says about populations. The assumptions of population thinking are diametrically opposed to that of the typologist.
The populationist stresses the uniqueness of everything in the organic world. What is true for the human species that no two individuals are alike? is equally true for all other species of animals and plants. All organisms are composed of unique features and can be described collectively only in statistical terms. Individuals form populations of which we can determine the arithmetic mean and the statistics of variation.
Averages are merely statistical abstractions. Only the individuals of which the populations are composed have reality. And Meyer goes on to say, The ultimate conclusions of the population thinker and of the typologist are precisely the opposite.
For the typologist, the type is real and the variation is an illusion. For the populationist, the type or the average is an abstraction and only the variation is real. No two ways of looking at nature could be more different.
So he's contrasting typological thinking, the idea that there is an ideal organism, with population thinking, the idea that we're really looking at a population of varying organisms. So, as an example of this, if we were to think about typological thinking, this is the idea that there is an ideal of something, and we, say if you're a drawing of a starling, and this might be something that you're going to draw. you would find, for example, in a field guide. You might go to a field guide, and you would look in there, and you would find an illustration of a starling and a description of a starling, and it would tell you what to look for to identify a starling. would expect if you saw one that that's what it would look like you would have certain traits that define a starling and if you go out into the real world and you look at starlings and here's a flock of starlings you would find a bunch of birds that look very similar to this ideal the what we might have seen in the field guide but they're not all the same just like all humans are not the same all starlings are not the same some will be a little bigger some a little smaller some with a little different colors, some with a longer bell or a shorter bell, different characteristics in their feathers, different genes, different biochemical characteristics.
They all vary in different ways because they're all individuals in a population. And so typological thinking is that there is an ideal of every species and that the individuals are somehow falling short of the ideal. They don't have necessarily the defining traits. And Meyer wants us to avoid that kind of typological thinking. The population thinking turns that on its head.
Population thinking, we start with the real population, the real population of individuals, of starlings, or humans, or... Norway maple trees or whatever we're talking about is a real population with variation. And from that, it varies in lots of different ways, but from that we can come up with, as he said, statistics of variation we can say on average this is kind of what a starling looks like but that is an abstract concept you will not find a starling that looks exactly like this one in the picture all the starlings look different and in various ways So the abstract type isn't an ideal, it isn't even real, it's just an abstraction taken from the real population.
So population thinking is the idea that the population is real rather than the type is real and that the population, individuals in the population are different. So when you think about organisms, I want you to think about populations. When you get up in the morning, I want you to think about biological populations. When you see an organism, when you see a bird, when you see a lizard, when you see an animal or a plant on TV, when you see a...
An animal or a plant that you eat for your meal for breakfast or lunch, I want you to think about that organism as being part of a population. When you see your friends, I want you to think about them as being part of a population, with individuals that vary, and that the population is real. And I want to finish up briefly talking about species. Species are...
very difficult to define exactly what a species is. It's often difficult to determine exactly what the species boundaries are. And there's lots of different concepts of exactly how you define a species. But there are some general criteria that we can think of that define a species. Members of the same species share a common descent.
They are the tip of the... of the evolutionary tree. They are the leaves, the twigs at the end of the tree. They're the smallest distinct groupings of the evolutionary tree. They form a reproductive community.
They reproduce with each other. They produce offspring like themselves. They form a distinct gene pool and they form an ecological unit. They fill a niche in the ecosystem and interact in certain ways. ways with other organisms.
In a lot of cases there's very complex ways that organisms interact. Here's a group of salamanders of the genus Ensatina that look very different. You can see that there are areas, it says, where two subspecies occupy the same territory but do not interbreed. There's an area of smooth inter-gradation between subspecies.
or an area in which two closely adjacent subspecies hybridize. And at various times these have been considered by biologists to be a single species or to be multiple species. And they interact in various complex ways and it's difficult to look at these organisms and to figure out whether they are in fact more than one species.
Traditionally, species have been defined morphologically. By morphology we mean simply what do they look like and we still use that in field guides. How do you recognize a species? Typically it's by what it looks like.
Going back to Ernst Mayr again. Ernst Mayr put forth what's called the biological species concept. He says species are groups of interbreeding natural populations that are reproductively isolated from other such groups. So these are groups of populations that interbreed and they do not breed with other groups. Remember the importance in evolutionary biology of distinguishing between individuals, populations, and species.