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Evolution - Evolutionary mutations
Expert: Dana Krempels - 10/23/2009
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
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