In almost every single class dedicated to the study of natural sciences (biology especially), a central “dogma” has always been engrained into our minds – that mutations associated with mental/physical retardations and the like are “un-natural”, often embraced with a negative connotation synonymous with “detriment”. Even within the social context, we tend to view those with stunted/impaired morphological development in a pitying/negative light. It is from this aforementioned springboard, that I became increasingly interested in function of body plans, ultimately leading me to ask the question: Are there any “natural” forms of morphological retardation shared by the human species? And the answer was …
Paedomorphosis – the developmental processes in which adults retain body plans seen in the infant stage, most commonly associated with A. progenesis (acceleration of sexual maturity) or B. neoteny (retardation of body parts). My initial exposure to this particular biological concept came from my best friend — Campbell’s AP Biology textbook (Chapter 34), in which the most basic explanation of paedomorphosis was provided. Prior to research, I knew that the aforementioned was associated with the natural alteration of body plans (early sexual maturation or retardation of physical development), most likely naturally selected for. I was also aware of its significant presence within the amphibian and reptilian classes, but that was pretty much all. The next leap was to expand my knowledge on paedomorphosis, with a “twist” – the application of the principle to the human species. Interestingly enough, paedomorphosis in the human sense “refers to the phylogenetic processes that lead to the evolution of facial underdevelopment. The paedomorphic feature, then, is one that has evolved through changes in the timing and rate of development and is species specific” (Wehr, 2005). The article, “Three theories for facial paedomorphosis in human evolution and the preference for facial underdevelopment”, then continues to provide explanations to why natural selection has facilitated paedomorphosis in humans specifically. According to Dr. Wehr, underdevelopment of the human facial structure allows for the “mimicry associated with youth and fertility, while also being a necessary antecedent to brain expansion and human cognition” (Wehr 2005) — all characteristics that increase the functionality and reproductive success of human individuals. Further, the author discusses different attraction oriented studies observing our biological affinity to larger eyes, smaller noses, and shorter chins – all characteristics seen in the infant stages of our species. Hence through Wehr’s article, I have answered my original question regarding “natural” body retardation; I have learned that the paedomorphic process in humans was most commonly associated with the underdevelopment of faces, and is positively correlated with the sexual success that the look of “youthful fertility” brings about. Like all beautifully written research papers, Dr. Wehr’s study in human paedomorphology incited a plethora of additional questions such as: “Evolutionarily wise, are there any other anthropoids that exhibit facial under-development ?” and “how does the facial structure differ, if a person is afflicted with a condition that prevents natural paedomorphosis?”. These questions and more will continue to fuel my interest in the biological concept of paedomorphosis, as we continue our exploration in the study of body plans.
Wehr, P. (2005). Three Theories For Facial Paedomorphosis in Human Evolution and the Preference for Facial Underdevelopment. Retrieved from https://circle.ubc.ca/bitstream/handle/2429/16943/ubc_2005-104554.pdf?sequence=1
For further information, visit https://circle.ubc.ca/bitstream/handle/2429/16943/ubc_2005-104554.pdf?sequence=1
Exactly like how humans have specific preferences in the way they select mates, animals in nature can do the same thing. During my freshman year of biology, I was alterted to a species of bird that was enthralled with long tail feathers. Females would choose to reproduce with the individuals that had the longest and most vibrant rears. The question of effectiveness was completely irrelevant; over time, the species’ tail feathers became so long that their ability of flight was impaired. In addition to breeding themselves a crucial lack of maneuverability, their color proved to be quite inadequate at effectively camoflaging thier vulnerable selves from predators.
Just like in contemporary society, sexual selection can bring harm to a species without much possibility for biological improvement.
I’ve never heard of paedomorphosis until reading your blog, and it is quite interesting. Natural impediment to the normal function of body parts is always fascinating, but paedomorphosis can actually have some positives. Like you said, it can result in younger and more fertile facial features (whether this is truly worth it is up to the individual). However I do still have questions even after reading about this. First, how common is paedomorphosis in humans? It would be interesting to understand if it is as plentifully expressed in humans as it is in reptiles and amphibians. Also, is there a way to try to lessen the effects of it? Like Alex said, difficulty to reproduce can harm a species. I’m not sure if this is really a disease, but if so, then being able to lessen these effects could help stop paedomorphosis “symptoms” in different species.
Similar to Varun, I had never heard of paedomorphosis until reading your blog, and there are a few things that are somewhat unclear to me. First, you mention Neoteny, the retardation of body parts. Does this mean body parts are slow to fully develop, or are slow to age and therefore retain their functionality longer? Also, how would it be determined that someone has paedomorphosis, because couldn’t it easily be mistaken for consistent care of the body, or just little exposure to excessive wear?