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Importance of Misconceptions
Importance of Misconceptions
Evolution and natural selection are fraught with misconceptions, unfortunately. Even the phrase "survival of the fittest" is problematic and overly simplistic. Misconceptions regarding evolution have, in part, caused many controversies amongst society. It is important that we tackle some of these misunderstandings not only to avoid mistakes, but also to allow you to become a more scientifically literate citizen.
Evolution is Aimless
Evolution is Aimless
One of the most common misconceptions regarding evolution is regarding its goal. Evolution does not have a goal. It does not care if a species goes extinct or speciates
You should think of evolution more like applied probability. If an individual has a beneficial trait, they will be more likely to survive and reproduce. There are no guarantees. Tons of beneficial traits die out when the individuals with them die of disease or predation, for example.
In other words, not all beneficial traits will spread within a species. In fact, not all traits that do spread will be beneficial. This is particularly important when thinking of small populations due to the random effects of genetic drift.
Sexual Selection - It's Not All About Survival
Sexual Selection - It's Not All About Survival
Recall that biological fitness has two components: survival and reproduction. Adaptations increase an organism's fitness by increasing either their survival or their reproduction (or both!).
Interestingly, adaptations can even actively decrease an organism's survival, but still be positive for their fitness if it increases their reproduction significantly. Some classic examples of these are intricate courtship rituals that are extremely time and energy-intensive (see the peacock spider mid-display here).
Sometimes an organism's adaptation actually leads to their death, but increases their chances of successful reproduction. The prime example of this that comes to mind for most people is that of the praying mantis. The male praying mantis allows a female to consume his body during copulation in order to elongate the duration of the act and allow him to deposit more sperm into the female.
The male Australian redback spider does this as well, and actually somersaults into the female's mandible himself! Some of these strategies will be explored more in ecology.
Evolution's (Usually) Glacial Pace
Evolution's (Usually) Glacial Pace
While it is true that evolution is typically a long-term process that takes place over many generations, not all evolution is as slow as you may be tempted to think.
Ultimately, the speed at which evolution occurs is influenced by the following factors: mutation rate, length of generations, severity of selection pressures, and how alleles are passed on.
If mutation rate is high, there will be more genetic variation on which natural selection can act. If generation times are short, evolution can be rapid. If selection pressures are intensive (i.e. it is life-and-death), the beneficial traits may spread more quickly. Finally, sexually reproducing organisms often have more genetic diversity in their offspring, but it can be slower. Sometimes alleles can even be passed to individuals outside of reproduction...
Antibiotic Resistance - Evolution at a Terrifying Pace
Antibiotic Resistance - Evolution at a Terrifying Pace
One of the scariest attributes of bacteria (most of which are harmless, of course) is their ability to rapidly evolve.
Bacteria can do lateral gene transfer (conjugation) to increase the rate at which traits may spread, reproduce rapidly, and have frequent mutations. They are incredibly quick evolvers.
Again, most bacteria are perfectly harmless (and sometimes essential) to human life. However, some do, of course, cause disease in humans and other organisms. Luckily, we have been using antibiotics to keep infections at bay since the accidental discovery of penicillin in 1928 by Alexander Fleming.
Antibiotics work by killing bacteria, but not all bacteria are equally susceptible to any given antibiotic. A large population of bacteria will have some individuals that are very resistant to a given antibiotic, some with mild resistance, and some with little to no resistance. The antibiotic will, therefore, be more effective at killing some bacteria than killing others.
National Nosocomial Infections Surveillance (NNIS) System. National Nosocomial Infections Surveillance (NNIS) System Report, Data Summary from January 1990 – May 1999, Issued June 1999. Am J Infect Control. 1999; 27(6): 520-32. http://www.ajicjournal.org/article/S0196-6553%2899%2970031-3/fulltext
When you introduce an antibiotic to a population of bacteria, you are essentially creating artificial selection. You are selecting for individuals with high resistance by killing everyone else.
If you stop taking your antibiotic at this point because you're starting to feel better, the bacteria will now rapidly reproduce. And that means that the bacteria with high resistance will be reproducing and creating copies of those alleles.
The only reliable way to combat this would be to follow through with the prescribed antibiotic treatment in its entirety (even if you are starting to feel better).
Improper prescription and use of antibiotics has led this to be a global issue, with resistant strains of major illnesses that should be treatable such as tuberculosis to have outbreaks. The graph shows some strains over the course of only 20 years, but keep in mind that these data are from about 20 years ago, so it has gotten worse and more widespread since.
Individuals Don't Evolve - Populations Do
Individuals Don't Evolve - Populations Do
Evolution does not affect individuals directly. Evolution affects populations. Natural selection affects individuals, of course - that is what determines whether you survive and reproduce or not.
But an individual will not evolve. A human could live on the water and spend 14 hours a day swimming, but they will never develop gills or fins.
Along these same lines, entire species do not necessarily evolve into new ones. he classic example of this misconception comes from skeptics asking, "If we came from monkeys, why are there still monkeys?"
Humans did not evolve from any still-living monkeys. Rather, we share a (relatively) recent common ancestor. We will clarify this further when we discuss phylogenies and evolutionary trees.
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