Genetics as it applies to evolution, molecular biology, and medical aspects.
Hello, please bear with me as I am not a biology student, nor am I savy to biological terms. But, in my quest to understand adaptation with regards to evolution there is a question I have that I can't really find the answer for. I understand how organisms adapt to their environment and survive because of this, what hasn't really been explained in my readings is how this specifically happens.
Here is a hypothetical example. Say in South America a forest develops black tree trunks over a long period of time. Now a normally brown butterfly or moth that lived on the bark of these trees was in peril and most died off. But some of these butterflies developed black features to match these trees because they could survive and not be pecked off by birds. How does the butterfly know to change its coat color? Is this a freak mutation? Even if it is a mutation it would be a great coincidence to go this color. I don't understand how this comes about. All I hear is, "It adapted to its environment" but that doesnt' explain how the genes changed. The butterfly doesn't tell its genes to change. And futhermore what about species of animals that can change their features instantly like some lizards. Or butterflies that developed eyespots on the outer edges of their wings so to scare off predators? How does the butterfly know eventually to make genes to do this? How does it know what an eye looks like in the first place? I know it takes thousands of years for this to happen. But even over time how do the genes change to produce these features? I haven't found in any book so far that explains this. Sorry for the long letter but this is bugging me.
Characteristics and variations are produced more or less randomly(mutations, horizontal gene transfers etc). It's less of an organism adapting rather having organisms of a species having specific traits being the only ones who survive.
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Individual organisms, of course, don't evolve much. It's the populations and ultimately the species that change over evolutionary time. The answer to your question lies in the concept of variation. Random mutations occur all the time in individuals, which are members of populations. These mutations lead to variation in the population. Look at our own species. There are tall people and short people, and people of every height in between. This is natural variation. Let's take your brown butterflies as an example. Individual butterflies can only be one colour - for life. But within the population of butterflies in the forest, individuals can range in colour from light brown to dark brown. ON AVERAGE, the darker butterflies will survive better than the lighter-coloured ones when resting on black tree trunks since they are harder to see by predators. So, the darker butterflies will ON AVERAGE produce more offspring. Over time, the average colour of individuals in the population will become darker (dark parents - dark offspring). Maybe some day a few thousand years later, a mutation occurs that produces not only a dark brown butterfly, but a black butterfly. This mutation is even better for survival and quickly spreads through the population over the years. The evolution of eyespots is a bit more involved but essentially occurs by the same mechanism, though something as complex as this would take far longer to evolve. Hopes this helps a bit. Summary: evolution = variation + selection
wbla3335 has essentially got it right. Variation in indiviuals leads to some individuals surviving and reproducing better than others. Those that survive pass on those traits to their offspring. Over time the traits that allow for better survival or reproduction will occur with greater frequency in the population. Variation in individuals doesn't neccesarily occur just thorugh random mutation; there are other mechanisms. It is important to note that in this process the organism doesn't have to be aware of the process. That is, it doesn't have to "know" that changing color or developing spots that mimic eyes is beneficial. But if a butterfly developed a rudimentry eyespot as part of normal variation, that happened to scare birds off more than it's neighbor that didn't have the eyespot, it might be more likely to leave more offspring that inherit the eyespot trait. Overtime more butterflies with the eyespot will be around.
More complex adaptiations develop by the same mechanisim but in small steps, and the intervening steps don't necessarily have anything to do with the final adaptation as we see it. For example, bird feathers may have originally come about as something to insulate an ancestor of birds, to keep it warm, and was later modified to be be useful for flight.
One final note of caution about the word adaptation. The word is unfortunately used in two distinct ways. One way is the way we have been using it here, to describe the evolutionary change in populations of organisims through natural selection. The other way adaptation is used is to describe how an individual changes to cope with short-term environmental change. For example, some mammals grow longer fur in the winter to deal with the cold season; humans might put on more clothing. So this short-term adaptaion can be physiological or behavioral. It should be pointed out that the ability to grow longer fur in response to seasonal changes or respond through behavioral changes is itself the long-term evolutinary type of adaptation.
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