WELCOME TO THE DISCUSSION GROUP FOR THE BOOK "YOUR INNER FISH" BY NEIL SHUBIN. PROMPTS AND POSTS ARE STUDENT GENERATED. THIS IS A COLLECTIVE EFFORT TO ENGAGE IN DISCUSSIONS THAT CONNECT THE THEORY OF EVOLUTION WITH THE BIOLOGICAL CONCEPTS AND THEMES DISCUSSED IN OUR COURSE THROUGHOUT THE YEAR.
Wednesday, March 30, 2011
Those Darn Hernias
Shubin states that the reason that humans have hernias is because humans were morphed from fish bodies into mammalian bodies (193). Describe why this occurs in terms of evolution and how this evolution relates to reproduction in mammals.
The reason that humans have hernias is a fishy one; it results from "taking a fish body and morphing it into a mammal" (Shubin 193). Fish have gonads that extend toward their chest, while mammals don't. This is a good thing because mammals that are males produce sperm that need the exact right range of temperatures to develop correctly. The scrotum is the device that males use to monitor and control the temperature while the sperm are developing. It is also advantageous for males to have a dangling scrotum because it is a sexual signal that would help them reproduce. The problem with this arrangement, according to Shubin, is that the route that the sperm travels to exit through the penis is circuitous, traveling up toward the waist, looping over the pelvis, through the pelvis, and then out. This seemingly absurd route came from our shark ancestors; our gonads begin devlopment in the same place as sharks because we have evolved from them. As they grow and develop, the gonads descend, which creates a weak spot in the body wall. This weakness in the body wall means that "guts can escape the body cavity and be squeezed to lie next to the spermatic cord," which creates a hernia (Shubin 195). Although human males do have this propensity for hernias (females do not because they do not have a giant tube running through this section of the body), it is better for reproduction because of the controlled temperatures of the scrotum and the closer proximity for more efficient fertilization and reproduction.
Shubin discusses hernias while explaining our evolutionary relationship with fish and other early organisms from whom we have evolved to develop advanced structures and functions within our body, and our changed lifestyle that has brought about the development of diseases such as obesity, stroke, hiccups, and hernias. “Our propensity for hernias”, as Shubin states, was developed due to the position of our reproductive structures, gonads, in our bodies. Sharks or fish have gonads that are positioned at the front of their bodies near their hearts in the chest area (Shubin, 193). However, as advanced species such as humans developed and reproduction became more complex, this structure would become less plausible. This is because of temperature. Male sperm, especially, need to be maintained at a certain temperature in order to remain healthy. Just as we had learned earlier in the year, in terms of proteins, structures can denature in extreme conditions (Campbell, 84). These sperm, in hot temperatures, especially near the heart, would “malformed”, and in cold temperatures, they would die (Shubin, 193). It was a selective advantage to change the position of the gonads in the bodies of organisms as they evolved in order to better ensures reproduction. What we have now is the scrotum that acts as a temperature-controlling sac that the sperm “reside in” (Shubin, 193). However, the pathway of the sperm “travels through the deferent duct through up the spermatic cord into the pelvic cavity, over the ureter to the prostate behind the bladder…through the prostate and empties into the urethra” (“Pathway of Sperm”, University of Maryland Medical Center). The reason for this complex pathway, as Shubin explains, is because the development of human gonads begins up near the liver, similar to sharks (Shubin, 195). This complex pathway allows the sperm to descend and meet the egg at a closer point of fertilization (Shubin, 195). This increases our chances of fertilization making this complex pathway another selective advantage as an adaptation.
(con't) However, these selective advantages come with their own consequences. In this case, the consequence is hernias. Hernias develop, as a result of the gonads’ descend, by creating a weak spot in the body wall (Shubin, 195). Hernias develop when a hole in the body wall causes abdominal content to pour out of the wall, moving in when laying down and moving out when standing up creating great pain and discomfort (“Hernia”, National Digestive Diseases Information Clearinghouse). If the amount of flow out of the hole is too great, then the abdominal contents may not be able to fall back into to the cavity, which could cause a disruption of blood flow. Inguinal hernias occur in the groin and are specific in that fat or part of the intestine “slide through a weak part at the inguinal ring” (“Inguinal Hernia”, National Digestive Diseases Information Clearinghouse). Because the majority of the reproductive cycle takes place in the female, their body walls are stronger and more “enforced” to withstand most stress on the body walls. Labor, the process by which childbirth occurs, requires the strong contractions to “force the fetus out of the uterus and through the vagina” (Campbell, 1015). These contractions require the female body walls to have adapted to be strong, because otherwise they would rupture while giving birth, and humans would not be able to effectively give birth, which could possibly bring about the extinction of our species. The stress of the descend of gonads can cause these sorts of ruptures in the body walls, but their selective advantage is too great and is crucial for the continuation of our species and the functioning abilities of our own bodies.
The reason that humans have hernias is a fishy one; it results from "taking a fish body and morphing it into a mammal" (Shubin 193). Fish have gonads that extend toward their chest, while mammals don't. This is a good thing because mammals that are males produce sperm that need the exact right range of temperatures to develop correctly. The scrotum is the device that males use to monitor and control the temperature while the sperm are developing. It is also advantageous for males to have a dangling scrotum because it is a sexual signal that would help them reproduce. The problem with this arrangement, according to Shubin, is that the route that the sperm travels to exit through the penis is circuitous, traveling up toward the waist, looping over the pelvis, through the pelvis, and then out.
ReplyDeleteThis seemingly absurd route came from our shark ancestors; our gonads begin devlopment in the same place as sharks because we have evolved from them. As they grow and develop, the gonads descend, which creates a weak spot in the body wall. This weakness in the body wall means that "guts can escape the body cavity and be squeezed to lie next to the spermatic cord," which creates a hernia (Shubin 195). Although human males do have this propensity for hernias (females do not because they do not have a giant tube running through this section of the body), it is better for reproduction because of the controlled temperatures of the scrotum and the closer proximity for more efficient fertilization and reproduction.
Also used Wikipedia: Hernias.
Hannah Kay (hgkay@aol.com)
Shubin discusses hernias while explaining our evolutionary relationship with fish and other early organisms from whom we have evolved to develop advanced structures and functions within our body, and our changed lifestyle that has brought about the development of diseases such as obesity, stroke, hiccups, and hernias. “Our propensity for hernias”, as Shubin states, was developed due to the position of our reproductive structures, gonads, in our bodies. Sharks or fish have gonads that are positioned at the front of their bodies near their hearts in the chest area (Shubin, 193). However, as advanced species such as humans developed and reproduction became more complex, this structure would become less plausible. This is because of temperature. Male sperm, especially, need to be maintained at a certain temperature in order to remain healthy. Just as we had learned earlier in the year, in terms of proteins, structures can denature in extreme conditions (Campbell, 84). These sperm, in hot temperatures, especially near the heart, would “malformed”, and in cold temperatures, they would die (Shubin, 193). It was a selective advantage to change the position of the gonads in the bodies of organisms as they evolved in order to better ensures reproduction. What we have now is the scrotum that acts as a temperature-controlling sac that the sperm “reside in” (Shubin, 193). However, the pathway of the sperm “travels through the deferent duct through up the spermatic cord into the pelvic cavity, over the ureter to the prostate behind the bladder…through the prostate and empties into the urethra” (“Pathway of Sperm”, University of Maryland Medical Center). The reason for this complex pathway, as Shubin explains, is because the development of human gonads begins up near the liver, similar to sharks (Shubin, 195). This complex pathway allows the sperm to descend and meet the egg at a closer point of fertilization (Shubin, 195). This increases our chances of fertilization making this complex pathway another selective advantage as an adaptation.
ReplyDeleteSonia Doshi (soniadoshi7@gmail.com)
(con't)
ReplyDeleteHowever, these selective advantages come with their own consequences. In this case, the consequence is hernias. Hernias develop, as a result of the gonads’ descend, by creating a weak spot in the body wall (Shubin, 195). Hernias develop when a hole in the body wall causes abdominal content to pour out of the wall, moving in when laying down and moving out when standing up creating great pain and discomfort (“Hernia”, National Digestive Diseases Information Clearinghouse). If the amount of flow out of the hole is too great, then the abdominal contents may not be able to fall back into to the cavity, which could cause a disruption of blood flow. Inguinal hernias occur in the groin and are specific in that fat or part of the intestine “slide through a weak part at the inguinal ring” (“Inguinal Hernia”, National Digestive Diseases Information Clearinghouse). Because the majority of the reproductive cycle takes place in the female, their body walls are stronger and more “enforced” to withstand most stress on the body walls. Labor, the process by which childbirth occurs, requires the strong contractions to “force the fetus out of the uterus and through the vagina” (Campbell, 1015). These contractions require the female body walls to have adapted to be strong, because otherwise they would rupture while giving birth, and humans would not be able to effectively give birth, which could possibly bring about the extinction of our species. The stress of the descend of gonads can cause these sorts of ruptures in the body walls, but their selective advantage is too great and is crucial for the continuation of our species and the functioning abilities of our own bodies.
Sonia Doshi (soniadoshi7@gmail.com)