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You are here: Experts > Science > Biology > Evolution > Evolutionary mutations
Evolution - Evolutionary mutations
Expert: Dana Krempels - 10/25/2009
Question
QUESTION: My understanding of evolutionary change is that it relies on mutations to occur, these more favorable mutations are more suitable to an environment and therefore become more prolific. That, however, is different than suggesting the environment itself "created" these changes or influenced the mutation in the first place. Correct? The environment creates a situation in which certain mutations turn out to be more successful but didn't increase the likely-hood of the mutation in the first place. It may seem as if environment "caused" the mutation because of how elegant the relationship between the species and the environment is. Correct? Anyway, I remember watching a program on TV that discussed how humans could evolve in the future and it suggested that if living in prolonged space conditions future humans would "evolve" stretched out Arms and Legs from living in space under zero G environments. Interesting concept but wouldn't that require a human to be born with that mutation (elongated arms and legs), not have it created by the environment? Sure maybe over a lifetime an individual living in Zero G would have their limbs stretched out, but this seemed to suggest that humans would be born with this mutation. This is false, correct? Which ultimately brings me to a main question, given our advances (crutches) of science and technology, with no real "survival of the fittest" based on our physical form can we expect to see major physical evolution in our future? It seems to me as if most evolution will take place based on mental and emotional differences, not so much on our physical form. Thank You for your time.
~Jason Haldeman
ANSWER: Dear Jason,
I think the best way to address this one is to answer your questions one by one:
"My understanding of evolutionary change is that it relies on mutations to occur, these more favorable mutations are more suitable to an environment and therefore become more prolific. That, however, is different than suggesting the environment itself "created" these changes or influenced the mutation in the first place. Correct?"
Correct.
"The environment creates a situation in which certain mutations turn out to be more successful but didn't increase the likely-hood of the mutation in the first place. It may seem as if environment "caused" the mutation because of how elegant the relationship between the species and the environment is. Correct?"
Correct, if you are speaking strictly of evolution by means of natural selection and random mutations in the form of changes in the DNA sequence.
"Anyway, I remember watching a program on TV that discussed how humans could evolve in the future and it suggested that if living in prolonged space conditions future humans would "evolve" stretched out Arms and Legs from living in space under zero G environments. Interesting concept but wouldn't that require a human to be born with that mutation (elongated arms and legs), not have it created by the environment? Sure maybe over a lifetime an individual living in Zero G would have their limbs stretched out, but this seemed to suggest that humans would be born with this mutation. This is false, correct?"
Probably. I'm not sure who made that TV program, but unless they were very sophisticated about their recent genetic knowledge, I suspect they were being Lamarckian in their evolutionary thought processes. Jean Baptiste Lamarck is the French scientist who suggested that traits acquired during an organism's lifetime could be transmitted to its offspring (e.g., giraffes stretching their necks to reach food high in the trees would develop longer necks and then pass that trait to their babies).
This idea has long been discounted, and in most cases it is clear that an organism's environment does not induce mutational change to "fit" that environment.
So the conjecture about humans becoming long and skinny because of evolution is a little bit silly, and going far beyond what we currently know about evolution.
HOWEVER, it is possible for an organism's body to develop differently under different environmental conditions. And if humans lived for many generations under zero G and the result was a change in their physical appearance (because of zero G) to be long and skinny, then babies might be born looking like terrestrial babies, but as they developed, their bodies would take on the long/skinny form (if that's what zero G would do; I have no idea, and I doubt the program creators do, either). That's not evolution. That's adaptation: change in form to the limit of one's genetic makeup.
And another big HOWEVER: Recent information is starting to appear to suggest that certain types of changes in the DNA that occur in the adult organism (especially with regards to the methylation and "packaging" of the DNA that affects which genes are expressed, and which are "turned off" *can* be transmitted to offspring. More and more examples of this eerily Lamarckian phenomenon are coming to light, and you can read a good overview here:
http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mga.section.2201
"Which ultimately brings me to a main question, given our advances (crutches) of science and technology, with no real "survival of the fittest" based on our physical form can we expect to see major physical evolution in our future? It seems to me as if most evolution will take place based on mental and emotional differences, not so much on our physical form."
You may be right, but only generations will tell. Evolutionary changes can occur extremely gradually, with strong contributions from genetic drift in small populations. Because the human population is now pretty much a global one, and humans now interbreed more freely with distantly related conspecifics than ever before, our populations are possibly on their way to becoming more homogeneous. With its members' ability to travel great distances, our population's effective size has increased tremendously. And the larger the population's effective size, the more slowly one would expect new mutational changes to become fixed in the population. They are more likely (statistically speaking) to be lost due to random chance.
But there still may be selective factors at work on Homo sapiens. As new pathogens emerge from unknown places (hint: as we cut down more and more previously inaccessible rainforest, viruses that have become commensal in other species can jump into ours and wreak havoc. Think: Ebola.), chance mutations that make certain individuals immune to emerging pathogens will make those who bear them more likely to survive and leave offspring. (Did you know that some people who are HIV positive appear to be immune to AIDS?)
If this were to happen with a very virulent, fast-spreading pathogen, it's conceivable that a large percentage of the human population could die off, leaving only those immune individuals to repopulate. And whatever their physical features might be, they would probably not be representative of the human population that we have today, and so genetic drift might occur rather dramatically with respect to appearance, as well as genetic immunity to AIDS.
So, hypothetically, humans *could* change drastically in appearance, given the right set of circumstances. But until something really surprising like that happens, I think you're right and that any evolutionary changes that take place in our species will be subtle, and very slow to become fixed (if ever) in the global population at large.
Whew! :)
Dana
---------- FOLLOW-UP ----------
QUESTION: very interesting...I am not a student of science so I admit some of this is going to be quite confusing so I thank you for your patience, I guess my question now becomes: does this mean that the DNA(including ?epigenetic markers?) that gets passed on to offspring can be different at two different stages in life? I understand that my core DNA is the same my entire life but it appears as though epigenetics can change during my life. Forgive my crude analogy I realize this is probably very elementary and perhaps incorrect but on a basic level If DNA is like hardware epigenetic material is like software that manipulates, turns on or off certain parts of DNA. Could this mean that depending on how I live my life or depending on my environment that If I have a child at a young age and if I have a child late in life there could be differences based on epigenetics? While My DNA that is passed on(I understand only part of the offspring's DNA is mine the rest from the mother) is the same, certain Methyl(?) indicators or other epigenetic materials will have changed over time? This seems to suggest Lamarck may have been on the right path...It would also suggest evolution would be quicker with epigenetics than without...Final question, to your knowledge if you could hypothesize about humans, does our current understanding suggest that the DNA passed on later in life with more epigenetic changes is more likely to pass on higher detrimental risks like cancers or other negative traits of positive influences like better memory or metabolism? In other words is there evidence to suggest that epigentetic change is largely poitive or negative? Thank you so much for your time...
~Jason
Answer
Dear Jason,
"Does this mean that the DNA(including ?epigenetic markers?) that gets passed on to offspring can be different at two different stages in life? I understand that my core DNA is the same my entire life but it appears as though epigenetics can change during my life."
There are two different types of mutations: somatic and germline. Somatic cell mutations are those that occur in an animal's body, and do not have direct evolutionary consequences because those mutations are not passed on to offspring. Germline mutations, which take place in the cells that give rise to sperm or eggs (depending on your sex), can be passed on to offspring. And it is *here* that any epigenetic changes can be passed on to your offspring.
As any animal (including you or I) develops, different genes turn "on" and "off" as cells divide, differentiate and mature into a specific cell type. This means that the "packaging" of those genes can change, since the level at which a particular gene is transcribed and translated into protein (which pretty much forms the identity of the cell) can be strongly affected by the way the genes are packaged in any given cell cycle. Such changes are not exactly epigenetic, since they are somatic.
Only DNA packaging changes in your germline that are passed on to your offspring can be considered true epigenetic inheritance.
"If DNA is like hardware epigenetic material is like software that manipulates, turns on or off certain parts of DNA."
Epigenetic changes might be considered a little bit like software, yes. Difficult to make a really good analogy, but that one works pretty well.
"Could this mean that depending on how I live my life or depending on my environment that If I have a child at a young age and if I have a child late in life there could be differences based on epigenetics?"
Epigenetic changes in your DNA that occur in the germline could, hypothetically, happen at any time in your life. So a change that happens early in your life could be passed on to an earlier offspring, and additional changes could be passed on to later offspring. But also note that it's not confirmed that all germline cells might change. There is a massive amount we don't yet know about how epigenetic changes are passed on.
"While My DNA that is passed on(I understand only part of the offspring's DNA is mine the rest from the mother) is the same, certain Methyl(?) indicators or other epigenetic materials will have changed over time?"
It's possible, but not necessarily the case. Again, we don't really understand. But there are a few really intriguing phenomena that beg explanation. For example, there is a statistically real increase it the likelihood that a later son will be homosexual if his mother has borne many sons before him. Do hormones play a role in turning on or off mom's own genes that affect the uterine environment? How does that happen? We don't know. We see only the end result and a trend, but don't know how it happens.
Check out some of these fascinating articles:
http://www.springerlink.com/content/p6637137p0n10857/
Even being right- or left-handed might be affected by epigenetic factors. So cool.
"This seems to suggest Lamarck may have been on the right path...It would also suggest evolution would be quicker with epigenetics than without..."
Yes, you could certainly say that. With caution.
"if you could hypothesize about humans, does our current understanding suggest that the DNA passed on later in life with more epigenetic changes is more likely to pass on higher detrimental risks like cancers or other negative traits of positive influences like better memory or metabolism? In other words is there evidence to suggest that epigentetic change is largely poitive or negative?"
To my knowledge, no such link has yet been established. But it's an interesting question, indeed.
It's known that women who took certain drugs to reduce the risk of miscarriage in the 1950s have offspring with a much higher risk of certain types of reproductive system cancers than the general population. Whether this risk is due to true germline mutations or epigenetic changes has yet to be established. But I would not be surprised if in the near future we find a real trove of amazing things that are due to changes that happen in an individual's life and passed on to offspring in surprising ways.
Thanks for the interesting questions that make me ponder even more! :)
Dana
http://www.futurepundit.com/archives/002449.html
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