Darwin and the Sloth
Apr 19, 2013
13 minutes read

Be warned: The work here, written for a philsophy class from the past, has little to do with the thoughts/feelings/beliefs of the author. Much was written with an intentional bias or viewpoint which was given as part of the assignment. Tread lightly, and try not to take it too seriously.

Darwin’s theory of natural selection has proven to be reliable in its explanation of the origin of variation in species around the world. Biological development throughout the entire world can be observed behaving according to the models that Darwin proposed, from the smallest bacterium to the development of the largest ocean dwellers. Time and time again, when we explore the strangest and most obscure of extreme environments, where we think no organisms may exist, we find something which has adapted in the most ingenious way, according to the struggles of it’s life, and it’s predecessors. For Darwin, the ideas that he applied in life to investment and economics matters were found to also apply to the natural world. A similar ebb and flow emerges in the sea of choices that encompass selection, such as the fluctuation in the number of hatchlings of a specific spider subspecies, to the availability of a certain plant that an animal may use as food or shelter. Like in economics, all factors that have any say in the success of an organism (or in economics, an investment) must be understood in order to fully grasp the reasons for the demise or success of said systems, for such organisms are simply an investment of energy and time rather than time and money like that of an investment or company. The sloth is a species of mammal that is somewhat similar to an anteater, it’s known for it’s extremely slow movement. Darwin’s idea was that many different components feed into the engine of selection, that it cannot be attributed to one specific alone; rather to a compound of influences.. Sexual selection, the climate, social behaviors, the multi-natured aspect of trait gain, and the small ‘trifling’ differences between organisms can create a new species – this can be seen when observing such a unique creature as the sloth.

Darwin wrote about what he referred to as ‘sexual selection’. Sexual selection is sometimes a difficult element to identify. Traits that are classified as being influenced by the aspects of sexual selection are often times useless for the productivity of the species as a whole, but serve as a way to increase the chances of procreation nonetheless. The element of sexual selection is common among species that show a marked difference between the sexes, and are dependent on these differences in the sexes to achieve a higher rate of effectiveness in regards to proliferation and individual procreation.

This depends, not on a struggle for existence, but on a struggle between the males for possession of the females; the result is not death to the unsuccessful competitor, but few or no offspring. Sexual selection is, therefore, less rigorous than natural selection. Generally, the most vigorous males, those which are best fitted for their places in nature, will leave most progeny. But in many cases, victory will depend not on general vigor, but on having special weapons, confined to the male sex. …for the shield may be as important for victory, as the sword or spear.

Examples of such aspects are the courting rituals of various wild bird species, and the showmanship of male battling sea-lions. These behaviors serve only to hinder the progress of that individual group (dancing is a waste of energy, and battling often injures or cripples otherwise healthy male sea-lions), but serve as a way to secure rights to a female, and in so help the species as a whole by spreading favorable traits. Mammals, as a whole, often times show distinct differences from sex to sex, and sloths are no different. Like most other mammal, female sloths undergo live birth, begin lactating, and nurture and protect their young which cling onto their back and breasts with an instinctive grip (akin to the suckle reflex) until adolescence when they gain independence. Unlike other mammals, however, female sloths in heat who have yet had the chance to mate scream at the top of their lungs , wasting precious energy and making themselves a target for the rest of the area until they mate, are killed by predators, or fall out of season. This is significant , as the main defense for a sloth in the wild is subterfuge. They have a significant disadvantage towards all of their known predators, and as a main defensive mechanism stay hidden. Mating, once initiated, is extremely fast in respect to the time scale that a sloth normally works within. This fact, too, is significant when thinking of how Darwin’s ideas apply. Sexual selection is two fold in this given example. The male is motivated to mate for the sake of fathering progeny, however the male sloth is also motivated to squelch the screams of a nearby female, as she is actively attracting predators to a location that he must expend energy to escape from. This pressure causes a decision process to happen for the male. Does he escape a female he may possibly have no interest in, in order to avoid danger, or does he simply silence her with sex? The second part that shows this trait is inherited is the length of time per copulation. A sloth takes seven to twelve hours to fully explore any given tree, an hour and a half to climb a tree it’s familiar with. Why then is such a species able to finish copulation within five minutes, when it can do no other action with such haste? It is because of a pairing of sexual traits within the male and female to aid with procreation. The male can act with haste when need be, and the female sloth has the power of psychology and the fear of a predator under her control to force the hand of the male, for fear and lust are equally motivating, and when used together have proven to be useful for the sloth as a species.

The climate is one of the most powerful attributes that Darwin mention, when speaking about the effect it has on the entirety of the Earth. From the inferences made from what we can observe of our historic geology to the lineages and ancestries that we can now more easily track with more advanced sciences in regards to the biological tree of life, we can see that the climate plays and has played a huge role in developing life and all of it’s variations here on Earth. Climate change has often contributed to the rise and fall of certain species, presently and in the past. Darwin observed the impact that it had during his personal experiences as a naturalist.

In looking at many small points of difference between species, which, as far as our ignorance permits us to judge, seem to be quite unimportant, we must not forget that climate, food, &c., probably produce some slight and direct effect. It is, however, far more necessary to bear in mind that there are many unknown laws of correlation of growth, which, when one part of the organization is modified through variation, and the modifications are accumulated by natural selection for the good of the being, will cause other modifications, often of the most unexpected nature.

Darwin here shows the importance of realizing that an organism is dependent on it’s habitat along with the other factors of selection. These all play into their success as a species, and the chances they have to procreate. A sloth is limited in the paths of selection available to it, as the main staple available to them for consumption is a low calorie leaf diet, as they dwell near or on top of the canopies of rain forests. This creature’s traits – to remain high in the canopies and survive on a low calorie diet as a large mammal, come at a price. As this mammal must survive on such small energy numbers, it has only a third of the muscle tissue that a normal mammal its’ size has, and moves extraordinarily slow. The animal may, if provoked, move quickly in short bursts, but it’s very damaging and energy intensive to the sloth, and they may not be able to recover with the diet that they are capable of maintaining. This relates to Darwin’s ideas of the ‘correlations of growth’, or more simply stated, some traits come innately with other traits, and may or may not be able to be separated any more finely. For example , the sloth is a large mammal, but the calories that they intake on a daily basis are similar to an average mammal a third the size, and they have little in fat reserves, as they live on the margin of survivability for their size. Both ideas can be applied to this context; the correlation of growth between speed and strength and caloric intake, and the diet and climate factors that impose limits on the environment that the sloth is a native of.

Social aspects, Darwin noted, are often times needed in the animal world to foster a better chance at survival for yourself or your family. A social link between mother and child, father and mother, and parents with the rest of their species and the world are all fostered within the lifespan of certain animals within the animal kingdom. The industriousness of a colony or the warning call of pack animals in order to alert their neighbors to the presence of a predator can all be boiled down to the social aspect of natural selection. Communication fosters intelligence and group decision making, often times an improvement when compared to an individual’s decisions, and this also has proven to be true for all forms of organisms.

Natural selection will modify the structure of the young in relation to the parent, and of the parent in relation to the young. In social animals it will adapt the structure of each individual for the benefit of the community; if each in consequence profits by the selected change. What natural selection cannot do, is to modify the structure of one species, without giving it any advantage, for the good of another species;

It’s been observed countless times in nature that when the shape of an animal diverges at the behest of the young such as the kangaroo, or that certain young animals have a much greater chance of living through infancy and achieving procreation as an adult if they possess the ability to understand social cues given to them by other animals in their species. Sloths show both tendencies; that of partial group-think, and that of innate, untaught behaviors of child and mother. A sloth gives birth upside down, hanging by foot from a branch. When born, the infant (who is sometimes forty to sixty feet in the air suspended by his mother’s’ efforts) has the innate tendency to grasp and grab and it’s mother for support, as well as the suckle reflex that is prevalent in most other mammals to initiate breast feeding, which of course was initiated first during gestation of the young in the course of the mothers’ pregnancy. In the likely event of the mother dropping the infant, the fall rarely kills the animal, however the mother must begin a rigorous bargaining process mentally : does she risk endangering herself to go to the bed of the rain forest to gather her fallen ilk, or does she leave the infant to die of exposure and eventual predation? Other females give the panicked mother their opinion on the state of things through subtle social gestures. If the group decides it’s a bad idea, which they most often do for the sake of individual safety, the sloth infant will eventually freeze to death or be eaten by a predator. This instinct arose from a necessity to limit the losses of victimized sloth mothers by predatory creatures during the recovery of their young ones, and is an example of social group aligned thinking in a mammalian animal ‘society’.

Darwin understood the realities of the human perspective. The human, being an entity that continues for a finite amount of time, is a finite size and finite weight judge things with their finite perspective, and not with regards to the realities of real nature. Darwin knew that humans lacked modesty, and as such he spoke about there being possibly great importance within matters that humans considered to be ‘trifling’. An animal may appear to just be a certain color for happenstance reasons, but the real power behind the reason for that color that the animal displays is probably hidden in wisdom that humans lack the perspective to fully understand, or even observe.

Although natural selection can act only through and for the good of each being, yet characters and structures, which we are apt to consider as of very trifling importance, may thus be acted on. When we see leaf-eating insects green, and bark-feeders mottled-gray; the alpine ptarmigan white in winter, the red-grouse the color of heather, and the black-grouse that of peaty earth, we must believe that these tints are of service to these birds and insects in preserving them from danger.

All aspects of the origin of an organism, regardless of how minute they appear to the observer, must be equally analyzed and thought of as simply a way to bolster that organisms ability to live life or be productive in their own individual way (measured by an organisms fit to a habitat, not simply by numbers of production and proliferation). A key, but subtle, factor in the success of the sloth is one of those things often overlooked as minute, as it is not accompanied by any drastic behavior such as a loud scream or the personal tragedy of a fallen child. The fur of a sloth is home to millions of green algae, and their accompanying bacterium cohorts. This attracts many insects and predators of such things to the solitude of the nearly still fur coat of the host sloth, and aids in their diet by adding to their caloric intake via skin absorption of compounds expelled by the bacteria and algae, and the occasional eating of insects found seeking the algae as nourishment for themselves. Not only does this aid in the sloth’s terribly poor diet, but it affords them some of the same protections that their closest companions, the trees, employ themselves. The green algae waterproofs the sloth, aids them in times of great heat to preserve water, and as a natural insect attractant, acts as a great form of camouflage – doubly important as it is the sloth’s soul defense.

Sexual selection, the climate, social behaviors, the multi-natured aspect of trait gain, and the small ‘trifling’ differences between organisms can create a new species – this can be seen when observing such a unique creature as the sloth. The sloth, being particularly unique in comparison to most animals that we as people have exposure to, is a prime example of the specialization that may occur over millions of years with only the pressures demonstrated by Darwin to be acting upon it. That isn’t to say that the pressures are small or easily surmountable, the opposite is true. It does, however, so easily demonstrate that the same is true for all of science. A small force over a period of time that would be seen as ludicrous to man is always the strongest demonstration of force itself. The greatest excavations of land that man has ever seen was not done overnight by explosion and drastic action, but rather the engine for grand-scale change in the world is constant forces over long periods of time, constantly driving change by taking the platform that the species has stepped off from away and offering little to return to should that species’ fail with the toolset they are born with. And thus, more and better specialized offspring shall always be newly created, for nature never runs out of clever tricks to demonstrate to man.


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