The Species Problem
Houston, we have a problem. . . - no, not a space problem, but a species problem. In fact, this problem has been around just about ever since scientists first attempted to classify living organisms. The concept of species is something that most of us may take for granted, but it is far from being a clear-cut concept. You'd think that the question would have been settled when Darwin wrote his book, On The Origin Of Species. The surprise is that not only has the species problem not been resolved, it has become even more convoluted over time!
As a plant breeder, I have had to be concerned with species and varieties of the plants I work with. I've tended to assume that if two plants can interbreed and produce fertile offspring, they are the same genus. However, my breeding experience does not match the classification that scientists have applied to the plants I work with. Some feel that plants of the same species can interbreed and produce fertile offspring, but to me that seems self-evident. After all, if plants of the same species cannot interbreed, than no evolution of any kind can take place! Of course, this line of thought implies that two plants which are different species cannot interbreed and produce fertile offspring. In my breeding experience, I have found this to be true in some cases and false in other cases.
The next consideration, for me, was that if you have two specimens of the same species and cross-fertilize them, the offspring should look just like the parents. If the offspring are all different, that is a clue that you are working with hybrids, not species. But consider that from the so-called ?biological? species concept, originally articulated by Theodosius Dobzhansky and Ernst Mayr in the 1930s and 40s, on through to current thought, you can find in the literature as many as 21 (that's twenty-one) different concepts of what a species really is! A Google search for "the species problem" yields a diversity of references and points of view on this topic and demonstrates vividly how far from consensus the scientific community is on this question.
So does this question of what a species is really matter? After all, we just want to know what to call our plants, so why not just come up with a name for each plant and leave it at that? The reason is that this problem is the underpinning of evolutionary biology. Speciation, understood as a fundamental evolutionary process, has little meaning if we have no reliable means of differentiating between species. I present this here to point out the real difficulties faced by scientists every day when working with different types of organisms, and especially when trying to go beyond observed facts to hypotheses and theories advanced by them to explain those facts.
In my breeding work, I try, with deliberate intent, to recombine different characteristics of what may be different species in an effort to develop an entirely new or novel plant. To do so successfully, I need to find what I call a breeding pathway, a combination of plant types or species, that will allow me to advance towards my goal while continuing to yield fertile offspring. Some crosses I've done do yield interesting offspring, but they are sterile, so the pathway is a dead end. In my work with plants in the genus Alocasia; some "species" cross freely in both directions, others cross in only one direction, and some won't cross at all. Some that cross in only one direction have fertile offspring, while others that cross in only one direction have sterile offspring. So far I haven't seen enough consistency in the way crosses work to enable me to say for sure if I am working with different species or merely different varieties of the same species.
I'll provide a few examples of where the designation of species appears to fall short of being sound. Two plants I've wanted to breed with are Alocasia wentii and Alocasia hypnosa. See my previous article, Alocasia hypnosa for more information about that plant. To my dismay, I discovered that while both plants bloom, neither of them produces any pollen! So sexual reproduction is not possible in these plants. To me, sterile plants may indicate that they are the result of some hybridization attempt, either natural or artificial. This is my viewpoint because I have produced similarly sterile hybrids from my own breeding work. However, such hybrids should not be considered as new species.
So you see that the species problem is not just a question of what kind of foundation the theory of evolution is built upon, but of whether one can be successful at improving or modifying plants via hybridization.
Photo credit: LariAnn Garner