Chapter Three: Mechanisms of Change
Some notes to stimulate your appetite to think about the mechanisms of change and how to prepare for chapter three quiz.
In chapter two, we are introduced to evidence regarding showing change with time. The premise is this, from direct and indirect evidence; there are observations that show a change with time. This process of change with time can be shown in adaptations in populations of organisms. We have noted that this process can be shown using concepts such as speciation and isolation mechanisms. Basically, keep one species away from another and allow mating only to occur within this population, the chances are that a unique species will evolve. In chapter three, we begin to hypothesize about the mechanism that causes this change.
Historical note:
Though some philosophers have suggested that we learn nothing from observing history, the case is not the same for observing fossils. We begin with the notion that all species are fixed. No that does not mean neutered but that all species were put on the earth at a specific time and in a specific place. From a western philosophical point of view, those folks that were busy classifying nature never challenged this idea. Biologists were in fact part of a field of inquiry known as natural history and sometimes grouped with natural philosophers. For many years, “Naturalists” were quite content to just identify and classify and to create some universal means to classify all living things. Then the inquiry into how things worked began. The scientific method created a method of thinking to examine the world. Forces such as gravity and energy became the field of inquiry for scientists. From this inquiry came “laws” and interpretations of chemical and physical forces. As naturalist began to observe more history of organisms upon the earth, the inquiry began to follow the same pattern of questioning. What was going on? Why did organisms become extinct? Why were animals different? Were there unknown forces within nature, like the forces of gravity and Newtonian physics?
So lets look into the text to answer the following:
Who started asking questions about the fixity of species and how could this questioning affect how people perceived fossils?
Once a question is asked, more will follow.
So who proposed the idea of adaptations, the law of use and disuse?
Why do you suppose he used a term such as “law”?
Let’s make a few observations such as”: a heron has long legs, some insects are resistant to insecticides,and some organisms have thick skin or fur.
How could we explain these adaptations from Lamarck and Darwin’s point of view?
Now lets get logical and examine some of the ideas proposed by both Lamarck and Darwin.
Here are some statements, can you identify ones that Darwin would support or Lamarck would support?
Which Statements can be used with the other to create an argument?
Many types of variations exist within a species
Members of a species tend to increase in a geometric ration from generation to generation (example 2:4:8:16: 32)
Some variations have more survival value than others
Organisms in a population reproduce, but the population tends to remain constant
There is a struggle for survival
Organisms are able to adapt to their environment when they inherit variations that have been developed by their parents through use and disuse of certain organs
How would Darwin use some of these statements to support his mechanism of change?
With both Darwin and Lamarck, we have a key problem to consider: Does the environment affect how an organism evolves, or does the organism have a means to adapt to the environment?
One of the key issues is the notion of choice. If we accept the idea that the environment is selecting species, then does the notion of “free will” and “choice” have a place in human thought?
So let’s look outside the realm of the human mind. Organisms on the planet have genetic material. This material allows organisms to display traits. This information, first shown by an inventive monk named Mendel remained unknown to both Lamarck and Darwin. While both were looking for a source of change, either within the organism or due to the environment, neither of them knew about the origin and transmission of variation.
Darwin did consider domestic animal breeding and noted how humans could artificially select traits, but he still didn’t know about the source of these traits. He did suggest that through artificial breeding of animals, humans could “select” a desirable trait. However he was still in a muddle about the origins of traits or why some organisms produced infertile young. For example, the notion of a “hybrid”…which is a product of a cross of two species and in some cases can be infertile such as a donkey and horse was a mystery to Darwin. Darwin did note the formation of species, and the multiplication of species or speciation. He suggested that this process was gradual with time. Yet the more evidence that was brought forth challenged this portion of his idea. Can you define and show examples of the idea known as “punctuated equilibrium”?
Now here is the challenge…
Darwin suggested that his observations about finches in the Galapagos islands was an example of the process of evolution and that by noting this process, the mechanism for natural selection could be illustrated
First of all…who offered the idea of a struggle for existence and natural selection to Darwin?
Now by using some of the terminology such as:
Isolation mechanisms
Speciation
Hybrid
Competition
Predators
Can you describe what occurred with the finches and why they changed with time? Remember to break up you explanation into two parts…the observations that showed a process and the concepts that explain the mechanism.
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