The Way of Science

Evolution

The word "evolution" is used by biologists in several fundamentally different ways, and it is very important that you keep these differences clear. Here we go.

1. "Evolution" can be used to refer to specific observations (direct or indirect), measurements and experiments that demonstrate something has happened to the genetics of organisms. Remember our definition of "fact"? These are the facts of Evolution: millions of them. EVOLUTION IS FACT. Many Americans, perhaps including you, may feel uncomfortable with this statement. Alas, public education has sadly neglected teaching Evolution properly, if at all, and so it is not surprising that many of you will need convincing.
   
   
2. Millions of facts may be summarized in a relatively short statement. We will call this summary a DEFINITION of Evolution, or, as many biologists do, call it the LAW OF EVOLUTION. Remember Boyle's Law? The equation, pv = constant, is a summary of all those individual facts derived from many measurements and observations. Although our definition/law of Evolution is not completely quantitative, it still fits the concept of "natural law."
   
   
3. The biological community has accepted Evolution as fact since Darwin's publication (1859), the American public notwithstanding. We now need an EXPLANATION of how Evolution "works." What is this mechanism, and how firmly established is it? Recall, again, Boyle's Law. The explanation or mechanism behind the law is called the KINETIC THEORY OF GASSES. So here we are: the modern SYNTHETIC THEORY OF EVOLUTION tells us how those facts came to be. Please note: it's not "just a theory"! It is a powerful, well-verified and tested explanation that is predictive. It is not just a hypothesis! Many biologists say that the theory is so well tested that it can be considered "fact." For this course, though, do not scramble our definitions of fact and theory.

What we now must do is expand on each of these three concepts at length. Before embarking on that task, you need to be comfortable with one more very important idea: the concept of a SPECIES. Note: "sp." is an abbreviation for one species, and "spp." for more than one. Never use the word "specie" in this course! Why not? What does "specie" mean?

Biologists use several different definitions of this word, depending on context. Part of the reason for this apparent confusion is the difficulty of applying BREEDING CRITERIA to certain groups of organisms (fossils, e.g.). For us, this semester, here's our very important working definition of a species. A species is a population of sexual individuals who do, or could, freely exchange genes with each other by producing fertile offspring under normal conditions. In addition, such a wild population does not exchange genes with other species to any significant extent. We might then refer to a species as a reproductively isolated population with free gene flow; that is, it is one gene pool.

In class, we will examine the concept at length, and add the very important concept of subspecies. In the meantime, consider these QUESTIONS before you come to class.

1. Are all humans part of a single sp.? Is a Congo pygmy (under four feet tall) the same sp. as a Hutu (Watusi) who is over seven feet? Explain your answer.
   
   
2. Are dwarf Chihuahuas (six inches tall) part of the same species as Great Danes? Again, explain your answer.
   
   
3. Consider mules (offspring of female horses, sp #1, crossed with male donkeys, sp #2), and jennies/hinnies (the reciprocal cross, using female donkeys). Are horses and donkeys mistakenly called different spp? Explain.
   
   
4. Suppose, in a Texas pond, there are many male frogs that all look alike, and many female frogs that all look alike (with only the usual variation within each sex). In spite of these observations, biologists insist that there are two species present ("cryptic" spp.). How is this situation possible? [Hint: what do male frogs do, in the spring, to attract females?]