Excerpt for evidence of evolution assignment
Senter, P., Ambrocio, Z., Andrade, J.B., Foust, K.K., Gaston, J.E., Lewis, RP., Liniewski, R.M., Ragin, B.A., Robinson, K.L., Stanley, S.G. 2015. Vestigial Biological Structures: A Classroom-Applicable Test of Creationist Hypotheses. American Biology Teacher, v77 n2 p99-106 Feb 2015
|
" INTRODUCTION. Many organisms possess biological structures that are recognizable as degenerate versions of their homologs in related organisms and that do not perform the functions that those homologs perform. For example, degenerate eyes in blind cave fishes and cave salamanders are useless for vision (Eigenmann, 1900), and degenerate limbs in numerous lizard species are useless for locomotion (Moch & Senter, 2011). Such degenerate structures are called “vestigial structures” because they are vestiges (remnants) of ancestral structures. Biologists recognize vestigial structures as evidence for biological evolution (Starr & Taggart, 2004; Reece et al., 2011). For example, blind cave fishes and salamanders arguably have eyes only because they inherited them from sighted ancestors. Until recently the human and ape appendix has been considered a vestigial organ, a remnant of a much larger ancestral cecum. A cecum is a side branch of the large intestine that houses bacteria that break down cellulose, enhancing the digestion of plant matter in herbivorous mammals (Kardong, 2011). However, an anatomical study of primates showed that the appendix of humans and apes is not a remnant of a cecum but is instead an evolutionarily new structure with no homolog in lower primates (Scott, 1980). It appears to function as a protective reservoir for beneficial bacteria that inhabit the colon, a microbial “Noah’s ark” from which beneficial bacteria can repopulate the colon if a disease decimates them (Bollinger et al., 2007). The recognition of the appendix as vestigial ceased not because it has a function but because it is a newly evolved structure instead of a vestige of an ancestral structure.
A structure does not have to be useless or functionless to be a vestige. Even so, scientists generally hesitate to use the term “vestigial” for a structure unless it has lost its most salient previous function. For example, the degenerate pelves of whales currently function as anchors for reproductive structures but are considered vestigial because they have lost their previous function as anchors for hindlimbs that are used in locomotion (SimõesLopes & Gutstein, 2004). Likewise, the degenerate ink glands of certain marine snails store algal pigments but are considered vestigial because they have lost their previous function as organs of ink production (Prince & Johnson, 2006). Anti-evolution authors have long insisted that all structures previously identified as vestigial are actually misidentified as such (e.g., Morris, 1974; Koop & Schaeffer, 1987; Bergman & Howe, 1990; Bergman, 2000; Menton, 2010). According to the their argument, no truly vestigial biological structures exist. Rather, in each case, the structure is functional but its function was unknown when it was labeled as vestigial. Such authors fail to understand that a structure can have a function and yet be a vestige. |
Click for link to original paper.
Texas blind salamander (Eurycea rathbuni) with vestigial eyes, small black dots of pigment below the skin. They are accompanied by a vestigial optic nerve that no longer carries impulses to the brain.
The vestigial pelvis in marine mammals is a hold-over from their weight-bearing terrestrial ancestors. Some evidence points to derived function in reproduction.
|
Nevertheless, some of these authors have noticed something that is worth noticing: Lists of vestigial structures in biology textbooks have dwindled through thedecades. These authors use this as evidence that scientists have lost confidence in the existence of vestigial structures or that scientists cannot find more examples of valid vestigial structures (Koop & Schaeffer, 1987; Bergman & Howe, 1990; Bergman, 2000). As one author puts it, “vestigial organs…have now been thoroughly discredited” (Bergman, 2010, p. 63). Indeed, lists of vestigial biological structures in current biology textbooks are usually quite short, with only one to three examples (e.g., Starr & Taggart, 2004; Reece et al., 2011). This is the case even in textbooks for evolution classes (e.g., Ridley, 2004; Kardong, 2008), one of which does not mention vestigial structures at all (Volpe & Rosenbaum, 2000). It is therefore worth testing the YEC hypotheses that biologists have lost confidence in the existence of vestigial structures and that more examples than those in short textbook lists cannot be found. Both hypotheses make the same prediction: that a review of recent primary scientific literature will find only a small number of examples (or none) of biological structures that are identified as vestigial. This is because scientists primarily communicate via primary literature (technical journals, etc.), not textbooks."