Practice Question for Evolution

[luvharps292]

Hey Everyone! 

Excited for physiology?? YESS :) 

Here's an old exam question that pertains to evolution to get you guys thinking! I'll also be posting up the answer by the end of the week, so give it a shot! 

"If the left ventricle is weakened by disease, it may be difficult for it to pump out the blood it receives from the right ventricle, resulting in chronic distension (over-inflation) of the left ventricle.  The resulting stretching of the walls of the left ventricle make it even weaker, creating a downward spiral that ends in death caused from massive failures in the circulatory system.  If natural selection operates to maximize survival and reproductive fitness, how could evolution have produced a system that is so prone to heart failure of this sort?"

~Kristen Chen 

[Kristen Chen]

Any takers on evolution? Email me! 

[Kristen Chen]

Hey Kristen! 

I'm not too sure about how the heart could have evolved to be the way it is, but part of the answer to the question could be that the heart was always susceptible to diseases like heart failure. In the past, humans lived to an average of 33 years so old age diseases such as heart failure wasn't a problem for the population. Now with our advances in technology and medicine, the average age of a human being is a lot higher than it was in the past. Now the genetic susceptibility of humans to these diseases are more apparent than they were in the past. 

In terms of evolution, natural selection doesn't care about the health of the organism. It only cares about giving the organism a better chance of reproducing and passing on its genes to the next generation. I remember Dr. Herrera mentioning that there are some flies in California that only live for a day, but during that one day they are able to mate and lay eggs for the next generation. 

So in a nut shell, evolution does not look to extend the life span of a species, it only looks to increase the reproductive fitness of the species. Humans could have always had the genetic disadvantage/susceptibility to diseases such as heart failure, but it hasn't become a problem until now because in the past we pretty much only lived to around 33 years old. Now, with our level of medicine we are living a lot longer than in the past so we are facing these problems that we never had to face before.

That was a long confusing answer haha!

Helen

On Sunday, January 27, 2013 11:22:26 PM UTC-8, Kristen Chen wrote:

[Kristen Chen]

Hey Kristen,

I agree with what Helen said about evolution having nothing to do with lifespan or general health and only being concerned with reproductive fitness. In that vein, heart issues do normally arise after 30 years or so, indicating that evolutionary processes would be unconcerned with them.

Another aspect I was thinking about was that the walls of the ventricle must be elastic in order to expand and contract and pump blood throughout the body. If the walls were more rigid, blood would be unable to appropriately circulate since the LV walls wouldn't be able to pump the blood out with as much force. Increased rigidity would be bad for humans, even if it did result in less of a downward spiral. 

Basically, I agree with the first response, but I think there are other reasons why the heart is the way it is!

Thank you for the question :)

Maya

On Sunday, January 27, 2013 11:22:26 PM UTC-8, Kristen Chen wrote:

[Kristen Chen]

Disease in the left ventricle is something that comes with old age. Survival in old age is not important for reproductive success because by the time you're old enough to have heart disease, you should have already reproduced, so from evolution's perspective, it's fine if you die. Evolution selects for systems that enhance reproductive success, not lifespan, so the quality of the system is good enough to get you through the reproductive years and that's why it's been left that way.-Sheena

On Sunday, January 27, 2013 11:22:26 PM UTC-8, Kristen Chen wrote:

[Kristen Chen]

Perfect! 

The "official Herrera answer" to this question is as follows: "Heart failure of the type described most commonly occurs in middle and advanced age, well past the 

reproductive phase of life. Over most of the time we have existed as species, lifespan was much shorter than in modern times. Thus, it is like that the mechanisms that cause heart failure would not have a negative effect on fitness during human evolution."

And Maya, I think that your other ideas about why the heart is the way it is, is very valid and a great point! 

I picked this question for you guys primarily to show you all that even in a semi-long question that is filled with details, the main point that Dr. Herrera is trying to test is actually a pretty simple explanation/concept and one that he discussed extensively in lecture.  So anyways, just don't get freaked out by how many words there are, because you probably know the answer, and it's probably more simple than the question suggests! BUT make sure you have the concepts down, because they will be tested over and over again! Good luck! :)

 

  
On Sunday, January 27, 2013 11:22:26 PM UTC-8, Kristen Chen wrote: