Is this a likely explanation for the reason that evolutionary limits have not done more to reduce the occurrence of cancer, a potentially deadly condition? Does evolution only impact traits of organisms that will have effects before and during the age of reproduction? Are there any other common conditions generally occurring after the age of reproduction that show evidence of this theory? Is there good evidence that disproves the theory? How, if at all, does this theory relate to any themes of biology other than evolution?
Please provide a thorough, informed, well-organized response supported by specific examples and evidence that addresses the multiple aspects of the prompt.
I believe that evolution still affects an organism even after reproduction, because the component of survival is still intact. For example, as we learned in class, women will eventually reach an age when they can no longer reproduce which is known as menopause. This transition not only ensures that the female does not try to reproduce without sufficient resources, but also promotes altruistic behavior in which the elders assist with the raising of family offspring. Though Jerry Coyne does say on page 251 that altruistic behaviors is a matter of choice, we promote such behaviors in our society in hopes that these behaviors will continue on for generations.
ReplyDeleteIn regards to the cancer issue, I believe evolution has not done much to combat cancer is because our lifestyle choices leads to a higher or lower probability of cancer. I think that even if one is diagnosed with cancer after pregnancy, the problem is that maybe the genes that the female passes onto the offspring are also mutated. I think one of the main problems is that evolution takes a very long period of time for humans because we have a long interval between generations, and cancer mutates genes at a quicker rate than evolution, making evolutionary adaptations difficult to develop. Also, people with cancer have a much lower rate of survival and chances of survival of offspring, so the idea of cancer still being an issue even after thousands of years is a problem of how one chooses to live.
I believe that evolution would not effect organisms after they pass reproductive age. This assuming that the disadvantageous trait only effects the organism once it passes reproductive age and has no effect on the organism before it passes reproductive age. This is because the disadvantageous trait would not affect the organism before they reproduce and therefore will not affect the organisms chances of reproducing. Therefore the trait can be passed from generation to generation and is never erased.
ReplyDeleteHowever, this would not hold true in human cases of cancer. Cancer is generally the product of lifestyle choices rather than genetic weakness, as described by Ji. Also, human technology would interfere with the erasure of cancer weaknesses in humans, as modern medical practices would allow some humans to overcome cancer (as based on the theme of technology) based on accessibility to treatment and accuracy of diagnosis.
The increased likeliness of cancer in people past reproductive age is likely caused by other influences. As stated in an article of Nature magazine (http://www.nature.com/nature/journal/v448/n7155/full/nature05985.html), aging lowers a cells ability to maintain DNA integrity, among other functions. The cells do not trigger cancer, but are more vulnerable to cancer because they weaken overall. This would indicate that survivalship becomes less important to organisms after they pass reproductive age therefore validating my first argument that disadvantageous traits after reproductive age are often not fixed and validating my second argument that genes that make one more vulnerable to cancer are a relatively minor influence.
To clarify, the mutation of genes not being suppressed by cancer is not necessarily based on genetic heritage. It presents later in life because of the multiple mutations that are necessary. Lifestyle affects the risk of cancer, but the actual genetic mutations are still the real problem. If cancer was occurring more often in humans before reproduction, then would evolution result in more mechanisms that prevent mutations in genes that code for the regulatory proteins of the cell cycle?
ReplyDeleteWould it be possible for evolution to result in another checkpoint say, between S1 and G2? S1 is when DNA is replicated and G2 is when the cell finishes growth to prepare for mitosis (Campbell 231). If there was a checkpoint right after synthesis, wouldn't that decrease the chance of reproducing damaged genes?
Do you think that specific change is a possibility?
The three previous have brought up very good points about the evolution of cancer. Genes coding for cancers that appear after reproductive age are not a significant disadvantage for the entire reproductive chain of the family. (I am referencing cancers that are purely or significantly caused by genetics.) By the principles of altruism, it is helpful to have older relatives around to help raise the young offspring (in the case of humans, kids). While true, in today’s society of humans, altruism is far less necessary for survival. If a kid loses a grandparent to cancer, of course (s)he will be sad and may go through some emotional trauma, but this is effect is not strong enough to effect survival rates. A kid who loses grandparents to cancer is not more likely to die than a kid with all four grandparents; therefore natural selection does NOT favor the child with four grandparents and no cancer genes. Therefore it is unlikely that cancer will evolve into obsoleteness. This may not be the case in wild animals where parental and grandparental care is necessary for the physical survival of the offspring.
ReplyDeleteTo reference the original prompt, another example of a disease that may or may not reach evolutionary limits is Huntington ’s disease (we studied this disease during the genetics unit). According to Campbell “a lethal dominant allele can escape elimination if it causes death only after an individual who carries the allele has reached a relatively advanced age.” The dominant allele for Huntington’s disease is a prime example; Huntington’s disease causes irreversible deterioration of the nervous system around age 40 (Campbell 279). At this point, most people with the disease have dominant have already reproduced, and thus had a 50% chance of passing on the dominant allele. Since a person doesn’t know whether or not he has Huntington’s until it becomes apparent at age 40, this gene has continually been passed on and affects 1 in 10,000 people in the US. Now, with advances in science, doctors can perform tests to see if the Huntington allele is in the individual’s genome, thus whether or not the individual will suffer neurological deterioration at age 40. Taking the test to find out and furthermore what to do with this information (in reference to family planning) are extremely personal decisions and do not ensure the gene’s eradication.