Thinking Exercise 1: Origins

Consider the following:

1
Centre of origin -----------------------------> Present Distribution


Ancestor -------------------------------------> Descendant


Plesiomorphy --------------------------------> Apomorphy

2
Each of these statements refers to a particular subject, namely an area, a taxon and a character-state. The arrow in each example indicates a transformation of some kind. For instance, taxa disperse away from a centre of origin; descendant taxa originate from ancestors and; plesiomorphic character-states transform into derived states.

3
The transformations are supported by dispersal ability, transitional fossils and plesiomorphic or apomorphic states respectively.

4
Finally, all three statements are assumed apriori to any data undergoing analysis and together form a synthesis, namely a taxon has an ancestor that dispersed from a single center of origin.

Problem 1 Dispersal ability

Just because an organism can disperse does not mean it has or will do so in the future. The seeds of alpine plants most likely are able to survive extended periods in salt water. Having this physiological tolerance to salt water does not mean for example that they have (or will) be transported from the Australian Alps, across the Tasman Sea and up into the New Zealand Alps. The same is true for rafting animals. A set number of animals are most likely able to survive extended periods rafting across seaways. Again, this does not mean that this is likely to occur.

Problem 2 Ancestors and Transitional Forms

Ancestors or transitional fossils are designated rather than real. Archaeopteryx was at one time a descendant. Since its demise in the Jurassic, it has become an ancestor and a transitional fossil without actually changing form. Transitional fossils, like ancestors, are simply terms assigned to designated forms.

Problem 3 Plesiomorphic and Apomorphic

Character-states, like transitional fossils and ancestors, are designated to be either plesiomorphic or apomorphic. The states themselves are fixed in time and space. An ancestor has plesiomorphic traits whereas a descendant has apomorphic states. The states may have a transitional form.

Qualifiers

Centers of origin, ancestors, transitional forms, apomorphic and plesimorphic character-states are all artificial designations. We have no objective or empirical way of knowing where an area is a center of origin, whether a fossil is an ancestor or whether a trait is apomorphic. These designations, however, are essential as they qualify the statements made above (1). Moreover, these qualifiers are assumed before examining data.

Data

Data are not neutral and are essentially theory / hypothesis laden. More important, data are not necessarily informative. Whether our data are informative is another matter entirely. If we use uninformative data in the above statements we are left with the same uninformative data. For instance, if a paraphyletic group is placed into each the above statements we will end up with multiple centers of origin for a single group and multiple ancestors of a single group. This would contradict our hypothesis of a single ancestor originating from a single area.

Teleology

In order for a taxon to be a descendant it requires an ancestor. If we had the means to go back in time and find this ancestor, we will find a descendant with apomorphic character-states, which has an ancestor and a center of origin. We can repeat this process again and again, but yet we will never find an ancestor, a plesiomorphic character-state or a center of origin. The reason is that these are all subjective hypothetical qualifiers that are needed to justify a theory. They are a means to an end. These metaphysical or teleological hypotheses are immune to empirical analysis.

Solution

The notion of transformation is hierarchical, particularly when it is assumed that one is a modification of the other (e.g., plesiomorphy -> apomorphy). To think otherwise is to have plesiomorphy and apomorphy as phenetic constructs requiring a method to unite (transform) them. Therefore:

Centre of origin --------------------------------> Centre of origin
-------------------------------------------------> Present Distribution

That is, for areas the occupation will be inclusive (descendant distributions = sum of all ancestral areas)

Ancestor --------------------------------------> Ancestor
-----------------------------------------------> Descendant

For ancestors the descendant will be inclusive (descendant characters = sum of all ancestral characters)

Plesiomorphy --------------------------> Plesiomorphy
---------------------------------------> Apomorphy

For apomorphy, plesiomorphic characters are included (with the apomorphy).