On page 61, Shubin makes a claim that teeth can tell a lot about an organism's lifestyle. This is true for the fossils found now-a-days because back hundreds of years ago, the main goal was solely to eat and survive. Now that humans are advanced enough to go through life without worrying about finding food (for the most part), is an evaluation of our teeth enough to be able to piece together our lifestyles? If not, is there any other part of our skeletons that could tell more? Consider in your response our abilities to make our own lifestyle choices without endangering our lives, like being vegetarian or vegan for example.
Jackie James
(jackie.james@comcast.net)
The structure of an animal’s mouth and teeth are indicative of that specific animal’s diet. As such, examining the teeth of humans would shed light only onto the diet of humans, but further conclusions may be drawn. Humans are omnivores, with neither carnivore nor herbivore specializations for digesting food. Humans are “opportunistic feeders,” meaning that they will survive by eating whatever food is available (http://www.vrg.org/nutshell/omni.htm). Earlier in evolutionary history, there would be a significant disparity between organisms that were herbivores versus those organisms that were carnivores. For example, many herbivores lack upper incisors and canines, cutting the plants with their lips instead. However, all herbivores need their molars for grinding the mouthfuls of food, because the herbivore's molars are big and ridged for better grinding (Sydenham, S. & Thomas, R. Animal Digestion www.kidcyber.com.au (2004)).
ReplyDeleteCarnivorous creatures would have sharper teeth to allow for mechanical digestion of the specific animal prey. Here we see the role between structure and function. As teeth are structured and shaped differently, the can mechanically digest various foods. So omnivorous creatures like humans would possess teeth capable of consuming both plants and animals. We see this feature in human teeth, as explained by John McArdle, Ph.D. “The short canines in humans are a functional consequence of the enlarged cranium and associated reduction of the size of the jaws. In primates, canines function as both defense weapons and visual threat devices. Interestingly, the primates with the largest canines (gorillas and gelada baboons) both have basically vegetarian
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ReplyDeletediets." (http://www.vrg.org/nutshell/omni.htm). What he points out is a number of skeletal features that point to an omnivorous diet, even if that wasn't the intended purpose. These traits include the size and shape of the jaws and the enlarged cranium. The structure of the human skeleton provides the capacity for an omnivorous diet. One might consider, then, that vegetarians would possess similar teeth to those herbivores in nature. However, this assumption does not take into account the process of evolution. As the theme of evolution concludes, a variation is not seen in a single individual. Rather, random mutation occurs in the genetic code which creates variation in characteristics in different individuals. Those new characteristics could establish a selective advantage over other characteristics in the presence of some environmental pressure. Thus, those individuals with the characteristic, in this case omnivorous teeth for example, would be more able to survive and reproduce. Because humans possess the ability to digest meat and plants, the structure of the teeth continues to provide the capacity to ingest these foods. Overall, consider the circumstance that a vegetarian may not be able to consume plants. They would have to have the ability to consume meat, or else face starvation and die.
While observations of a carnivorous diet may lead scientists to conclude that the animal being observed has an active lifestyle, in the case of humans, that conclusion would be incorrect. Other skeletal features can suggest the lifestyle of an organism, such as the structure of the actual skeleton. Skeleton structure is an indication of an animal’s movement, because the skeleton helps transmit movement with the help of muscles (http://www.emc.maricopa.edu/faculty/farabee/biobk/biobookmusskel.html#Types of Skeletal Systems). By examining an animal’s skeleton, one can determine the type of lifestyle the animal lives. If in the future there continues to be a lack of natural pressure on the human species, and humans continue to develop their sedentary lifestyles, it is possible that mutations in the DNA that cause a variation in skeletal structure, one that impedes an active lifestyle and one that in the presence of a natural pressure would have been eliminated, could come into existence.
Vickram Pradhan 1/2A
vickram.pradhan@yahoo.com
I agree with Vickram, I also think that teeth play a very significant role in determining the lifestyle differences between different organisms. While it is true that most humans do not have to actively search and hunt for food anymore, I think that it will take a very long time evolution-wise for our teeth to actually change their shape and function to fit our diet, since we are still eating the same plants and meat that we did for centuries. To elaborate on Vickram’s points about the effect of teeth on humans’ lifestyles, the size and layout of teeth definitely account for many consequent differences between humans and other animals in terms of consumer/producer roles in the food chain and diet preferences; while mammalian bipeds like humans segregate teeth into types (incisors for tearing, canines for piercing, and multi-pointed molars/premolars for grinding), most tetrapods have a much simpler, undifferentiated tooth layout that does not fit as well as the upper/lower structure of human teeth (Campbell 512). The complex layout of human teeth proves a selective advantage because individuals with well-formed teeth that could masticate easily and digest energy/nutrients more quickly and efficiently were chosen through natural selection to continue reproduction and survival. It can be argued that complex tooth structure contributes to the reason why humans are more abundant in population than some other animal species. In addition to tooth structure, the growth patterns of humans is vastly different to more primitive animals like reptiles; mammals generally only have two sets of teeth (infant and adult) throughout their lives, while nonmammals continuously grow and replace their teeth over time (Shubin 61). Even though the constant replacement of teeth may seem like an evolutionary advantage in that reptiles can replenish stronger teeth and avoid breakdown due to age, the truth is that mammals DON'T have to frequently replace teeth because the precise interlocking between the crests/troughs of upper and lower teeth allows humans to chew and digest far more efficiently than reptiles, while other animals are forced to replace weak, worn-out teeth by necessity (Source 1).
ReplyDelete(continued from previous comment)...While teeth do play a very important role in evaluating lifestyles of organisms, the overall jaw structure is also tell-tale of animal differences. Reptiles and birds cannot chew at all: since their jaws open and close in a simple hinge motion, they typically gulp down their food before it is fully chewed and broken down by salivary amylase and other digestive enzymes in the mouth, losing some nutrients that humans can acquire from chewing. Humans, on the other hand, can change distances of chewing over minute details because of their complex rotatory and sliding jaw joints in the jaw, which is huge selective advantage in the digestion of food and broad range of diet that humans can enjoy (Source 1).
ReplyDeleteIn addition, it would be far fetched to consider veganism and vegetarianism as endangering lifestyle choices, but these dietary changes may change an individual's tooth shape and structure gradually over time to suit the function of not eating meat/dairy products. The shape of teeth depends heavily on the an animal's diet; for example, while cats have blade-like sharp teeth for meat-eating and herbivores have flatter teeth to digest plants, humans have evolved to have all-purpose teeth with sections that specialize in breaking down both (Shubin 61). If an individual chooses to only eat plant products throughout his or her life and successfully becomes a herbivore, he or she may find their teeth to have a flatter shape and more smoothness at an elderly age in comparison to an individual who has been eating meat their entire lives. Vickram is correct in pointing out that this does not warrant evolution because it does not cause genetic variation in multiple individuals. Vegetarianism, unless it becomes universally popular and practiced, may not prove to have much evolutionary significance over long periods of human history, since most civilizations of the world still regularly eat meat (disregarding certain religions that practice vegetarianism; flatter teeth are probably more evident in these populations).
Sources:
1. http://science.jrank.org/pages/47829/mammals.html
2. Campbell (Chapter 25)
3. Neil Shubin
Christine Lin
choco_cat11@comcast.net