Aristotle and Modern Conceptions of the Aging Process of Animals
By: Jordan Phillips
Philosophy of Science
Introduction
There are many perennial questions in philosophy of science. One of them is how do we account for aging and for differences in life spans between species. Why, for example, can turtles live for over a century, while mice only live for a handful of years. This fits best into the subcategory of philosophy of biology. Aristotle reflected on this question in a brief work titled “On Length and Shortness of Life.” His work has stark differences to conceptions from modern biology. I will use four sources to demonstrate these contemporary perspectives. The first is a video commentary. The second is a standard pathology textbook. The third is the standard college biology textbook. And finally, a video from an anatomy trainer. In this paper, I will do two things. First, I will summarize both Aristotle and modern scientific thought on aging. Second, I will compare and contrast these visions.
Aristotle on Aging
Aristotle begins answering this question in a surprisingly modern way. While Aristotle doesn’t have as deep of an understanding of the material world as we do, he begins analyzing this question by looking at the material causes of natural objects. He wants to point out that matter acts in two relevant ways here. Some types of matter seem to cycle between generation and decay, while other types of matter pass away in modes unique to themselves. To the former category, he says, “Hence it is natural to infer that everything else arising from them and decomposed of them should share in the same nature, in all cases where things are not, like a house, a composite unity formed by the synthesis of many things.” This is a stunningly modern statement. He is saying that to understand the decaying of a living thing over its lifetime, we have to look primarily at the material causes of that decay. Towards the latter category, he gives the example of the health of a body is only a logical question in regard to a body that is alive. In this way, the matter of health is reliant on the matter of the body as a whole.
Next, Aristotle goes on to describe matter’s relationship to change. He says, “all things are at all times in a state of transition and are coming into being or passing away.” So, a material substance like a plant or an animal is limited to a finite amount of time by its very nature. Aristotle argues that this is because matter is immediately followed by contrariety. Inherent in matter is rivalry, competition and change.
Now that Aristotle has laid out the principles of the material world, he is ready to apply it to living things. He uses examples from his vast study of living things to discount false perspectives on this issue. For example, he excludes the possibility that larger organisms always outlive smaller animals, since horses have shorter lives than humans. He does this to compare size, sanguinity, and terrestrial vs aquatic species to show that none of these, in themselves, is the principle of what makes an organism live longer than another. While this is the case, he thinks there are general patterns of lifespan given these traits. He thinks in general, your largest plants have the longest life span, sanguineous animals live longer than ones with open circulatory systems, and that land animals live longer than sea animals. Also, he thinks that larger animals generally live longer than smaller animals.
From these observations, he starts to look for a cause. He thinks that in general young and healthy organisms are “humid and warm,” while old age makes animals “dry and cold, and so is a corpse.” (466a18-20). From this observation, he infers that there must be a fluid in animals that is less and less available throughout an organism's life, and that this fluid is given in amounts depending on the type of organism that it is. This, he thinks, explains why large plants and animals (in general) live longer. They are larger, and so can store more of this fluid.
He goes on to argue that this fluid diminishes as organisms use fluid throughout their lifetime. He thinks that species that reproduce at high rates tend to live shorter lives because the loss of the fluids involved in reproduction contributes to drying up of this fluid. Furthermore, men tend to sweat more than women, and so this contributes to their shorter lifespans than women (466b12-14). He concludes this section by saying that climate and environment affect lifespan as well.
This view clearly lacks some of the scientific information that has been discovered over the last 2000 years. Most especially the cell theory which tells us that living things are made up of cells. One textbook tells us, “[cells] are as fundamental to the living systems of biology as the atom is to chemistry.” So, put in Aristotle’s own language, he is missing a lot of detail about the material cause of living things, that he simply was not in a position to know about. I personally find it interesting that he emphasizes the liquid nature of this fundamental substance, since cells are mostly a liquid substance.
Contemporary Biology on Aging
Contemporary biology views aging as the result of “cell death and dysfunction.” Throughout an organism's life they replace their cells thousands of times through cell division, or mitosis. As children, we do this for growth. As adults, we do this for health and maintenance. As we get older, this process becomes less and less efficient. This causes two problems. First, we replace our cells slower and slower. Second, cells begin to lose their ability to function at a high level.
How does this account for the range of lifespans though? After all, all things are made of cells, so why are some able to live longer than others? Joao Pedro de Magalhães thinks there are two factors: environment and size. Environment seems to dictate lifespan because it correlates with metabolic rate. Organisms that live in frigid climates seem to have longer lifespans because their bodily processes (cell division, respiration, circulation, etc.) operate much more slowly than temperate animals. Animals in more temperate climates have quicker metabolisms, which lower their lifespans.
Size is also a factor here because it usually determines the ecological role that that organism will have. For example, large animals tend to have less predators. Since this is the case, their life cycle can take longer. These species will tend to reproduce multiple times in a life cycle, raise offspring for longer, and live longer lives. Smaller organisms, on the other hand, tend to be prey. This causes them to need to develop and reproduce quickly in life, leading to a shorter life cycle.
There are exceptions to these factors. Some temperate climate animals live longer than frigid climate animals. Some smaller animals live longer than large animals. Magalhaes argues that this is due to behavioral adaptations though. Bats, for example, are a small organism, but live longer because they have behaviors like flocking that help their survival and reproduction.
While this is the mainstream narrative for how aging occurs, there are two strands of new research that are pertinent here. First,in studying the process of DNA replications, scientists have found that the strands of DNA get a little bit shorter every time they are replicated. Since every cell division relies on this process, it makes sense that this would lead to the degradation of these cells over a lifetime. Every cell division makes our cells a little bit weaker.
A second strand of new research comes from Dr. Tom Myers. Myers specializes in anatomical tissue training. He describes the human body in terms of a structure called fascia that connects all muscles and tissues throughout the body. He describes how throughout life we get less and less liquid, though. As a zygote, humans are roughly 98% water. As a newborn, roughly 90% water. Throughout life though, this percentage continues to decrease all the way down to below 70%. This lack of hydration leads to a drying of the tissues that connect the tissues of the body.
And so, from a modern perspective, aging is due to the deterioration of cells over a lifetime. There is a range in animal lifespan dependent on the size, environment, and given behavioral adaptations for that type of organism. New research seems to indicate that there are also genetic and anatomical components to aging. It seems that through the process of cell division, our DNA gets shorter and shorter, which progressively can accumulate to the aging process. Also, that tissue gets dehydrated over time, which leads to deterioration.
Compare
It seems to me that Aristotle is similar to modern conceptions of aging in at least four ways. First, that there is a material cause that is responsible for the aging process. Second, the environment and size of the organism are important factors that correlate to their lifespan. And third, he has some interesting biological details that seem to be upheld today.
The first comparison is in strategy. Both Aristotle and Modern depictions of life spans think that there is a material cause in the thing that causes the aging process. The fact that modern science posits material causes only is unsurprising. Aristotle, who is famous for positing four causes of things, takes a surprising turn by emphasizing the material cause here. His reasoning is sound though. Plants and animals are made up of material things, and so their lifespans will be dependent on the material processes that make up that organism.
The second comparison is that both conceptions of lifespan see size and climate as factors at play here. While the modern perspective thinks this is exhaustive, Aristotle thinks there are more factors. But, it is interesting that these are the two factors that Aristotle spends the most time on. Clearly then, he thinks these are very important factors to clear up to get a solid answer on this issue. A further comparison can be embedded in this one: both perspectives hold that there are odd exceptions to these factors. Aristotle gives the example that horses are larger than men, but don’t live as long. Magalhaes describes how behavioral adaptations explain these quirks. Regardless, though, both perspectives argue that while the factors are helpful guidelines, they are not absolute.
The third comparison is not related directly to the topic of aging, but more reflective of the peripheral biology of both perspectives. I think there are some fascinating similarities worth articulating here. One is the idea of R-selected species. In modern biology, species can be split based on their reproductive patterns. Some species live longer lives, parent more, and reproduce multiple times over their lifetime. These are classified as K-selected species. R-selected species, then, are species that reproduce lots of offspring all at once, live shorter lives, and more than likely only reproduce once in their lifetime. Magalhaes describes how since r-selected species are likely to be prey, they are evolved to have this reproductive strategy. Aristotle recognizes that animals can be classified by reproductive strategy. His cause for their shorter lifespan is different: that their frequent copulation leads to quicker dryness of the fluid he posited. Although he doesn’t apply an evolutionary cause, it is interesting that he recognizes a difference in reproductive strategies and that it seems to have an impact on lifespan.
Another area that fits under this point is Aristotle’s description of whether cold climate animals live as long as warm climate animals. Aristotle says, “it happens that animals with little or no blood are in northerly regions either entirely absent (both land and water animals) or, when they do occur, they have a smaller and shorter life.” Although there is disagreement here between Aristotle and Magalhaes on which organisms live longer, the fact that Aristotle thinks that the unique operation of the biological systems of these organisms contributes to their lifespan is eerily similar to Magalhaes’s description of the metabolic rates of these organisms affecting their lifespan.
The fourth comparison is between Aristotle and Dr. Tom Myers. The perspectives of these two are alarmingly similar. Both hold that the deterioration of the liquid that makes up organisms causes the aging process. The older an organism gets, the more they dry up. While Aristotle is hesitant to prescribe a name to this liquid, Myers is comfortable just sticking with water and its relations to the tissues of the body. Regardless of this terminological difference though, they are very similar here.
In conclusion, we’ve seen a lot that is similar between Aristotle and modern conceptions of aging. First, there seems to be a material cause. Second, size and environment are important factors. Third, there is some similar use of distinctions in biology between Aristotle and the moderns. Fourth, Aristotle seems to be very closely aligned with modern research on fascia tissue and its relationship to dehydration and the aging process. Now, let’s look at how Aristotle differs from today’s perspective.
Contrast
I think that Aristotle can be contrasted from modern conceptions of aging in three ways. First, his material cause is different. Second, his list of factors is longer. Third, his peripheral biology has some differences from modern viewpoints.
I made a comparison in the previous section between Aristotle and modern biology on the point of a material cause being at play in the process of aging. I am putting this as a contrast here because the material cause given is different. Modern biology posits cells as the basic unit of structure and function for living things. Aristotle did not have access to microscopes, and so could not use cell theory as his material cause. I think an argument can be made that Aristotle’s description of “a humid element” that is “neither easily congealed nor easily dried up” could be applied to cells. Cells, after all, are mostly liquid, and can be found in abundance in every part of any living thing. I will not try to make that point, though. Rather, we will leave it that both parties posit a material cause, but do not have the same conception of what that material cause is.
The second contrast is that Aristotle thinks that there are more factors at play than just size, environment and behavioral adaptation. In addition to these factors, Aristotle thinks that it is helpful to analyze whether the animal is aquatic or terrestrial along with bloodless or sanguineous. This demonstrates Aristotle’s knowledge of the animal kingdom, as the difference between open and closed circulatory systems is still fundamental to classifying organisms. For our purposes though, we only need to note that there is a difference here.
Third, is that Aristotle has some peripheral biological reflections that are off the mark. Aristotle argues that warm climate animals live longer than cold climate animals. Magalhaes gives examples of organisms in these areas that live extraordinarily long lives, and credits this to their slower metabolic rates. So, while they both appeal to some similar biology here, they differ in their conclusion on which organisms live longer.
Conclusion
In this paper, I have compared and contrasted Aristotle’s perspective with the modern perspective of what causes organisms to have set lifespans. Aristotle is similar to modern perspectives in holding that material causes are fundamental here, that size and environment are major factors in determining how long a species will live, and in some of his periphery biology. He seems to compare very nicely to research on the relationship of fascia tissue and dehydration in the aging process as well. Aristotle differs from modern biology in describing what the material cause is, in his listing of relevant factors, and in some of his periphery biology. If you can look through terminological differences that Aristotle has with us, he is an incredibly clear and valuable voice for biological science.
Bibliography
Aristotle. On Length and Shortness of Life found in The Complete Works of Aristotle: Volume 1.
Translated by G.R.T Ross, Edited by Jonathan Barnes. Princeton, NJ: Princeton University Press, 1984. Print. 740-744.
Kumar, Abbas, Fausto, and Mitchell. Robbins Basic Pathology 8th Edition. Philadelphia, PA:
Saunders Elsevier, 2007. Print. 28-29
Joao Pedro de Magalhaes. Why do Animals Have Different Life Spans? Found at
https://ed.ted.com/lessons/why-do-animals-have-such-different-lifespans-joao-pedro-de-magalhaes
Dr. Tom Myers. Are You Aging or Just Drying Out? Wellcast Academy. Found at
Reece, Urry, Cain, Wasserman, Minorsky, and Jackson. Campbell Biology 9th Edition. San
Francisco, CA: Pearson Education. 2005. 319.
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