Relating Description and Explanation: The Case of Gregor Mendel

by David Fleischacker

Description and Explanation: Mendel’s Pea Plants

One good illustration of the dynamic relationship between description and explanation is found in Mendel’s breakthrough into genetics.  Description to recall is articulating how a thing relates to us.  Explanation is relation things to things.  At least that is a starting point for defining description and explanation, we can become more precise later.

Mendel’s attentiveness to the descriptive features of pea plants provided him with a starting point that led him to his formulation of an explanatory term that gave an account for some of those features.  We know these features as phenotypes.  Every phenotype is a descriptive conjugate or set of conjugates.  The color and shape of the peas and pea pods, the flower color and their positions, as well as the size of the plant were all observable traits.  Color, shape, and size are traits that relate something to us, through our motor-sensory being. Furthermore, there is something important about the particular traits Mendel selected. Each were found in one of two forms (eg. tall or short, green or yellow), and never in some type of mixed combination.  One could as well control these traits through proper breeding.  This provided a fruitful ground for asking questions, expanding observations, building explanations, testing those explanations, and asking further questions.  It was what I would call a rich descriptive matrix.

This real reason that this matrix was rich is because it was one of those zones in the world of description that provides a starting point for launching into the world of explanation.  One finds the same kinds of zones in other scientific breakthroughs. Certain descriptive accounts of gases led to atomic theory.  Moving projectiles and other similar falling objects that had a high density and relatively low friction level provided that matrix for early modern physics. Though pea plants are not the only living thing that could have provided the zone for this breakthrough into genetics, they were Mendel’s zone.

In starting with a rich descriptive matrix, notice that one is starting with conjugates in act.  A conjugate in act just means that one is dealing with real, experienced existing descriptive traits.  In Mendel’s case, he went a bit further and counted the actual frequencies of the alternatives of the seven descriptive conjugates.  He counted how many pea plants were tall and how many were short given various crossings of parents.  He could mate two tall plants or two short plants, or a tall and a short plant, and then count the frequencies of the tall and short characteristics in the offspring.  He did this for all the traits.  He performed thousands of crosses.  Notice that in counting, he also had to organize his findings into columns allowing for the discovery of patterns.  And patterns is what he found, those patterns now familiar to all of us, namely that these traits were found, depending on the parents, in distinctive ratios — either all one trait, all the other trait, three quarters one trait and one quarter the other (3:1) or half one trait, half the other (2:2).

Notice, thus far, I have stayed entirely with descriptive conjugates.  Both the actual frequencies and the surmised ideal frequencies (eg. 3:1) are based on those descriptive features.  Explanation comes later, along with an explanatory account of the statistical frequencies. The next blog will be on how these frequencies of descriptive conjugates led to the explanatory conjugates in Mendel’s moving mind.

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