After repeatedly being chastened for logical fallacies, some scientists have gotten a little bit smarter. Rather than committing the same old logical errors, they have branched out into new and subtler forms. Lets look at the following example:
Chimp and human DNA are more than 98 percent similar. While this does not prove that chimps and humans share a common ancestor, it is unlikely that this level of similarity could have happened by chance alone. Since humans have approximately 24,000 genes, finding greater than 98 percent correlation is like flipping a coin 10,000 times and having it come up heads every time. Therefore, no reasonable person can seriously doubt that humans and chimps share a common ancestor.
The logical flaw in this argument is what we call the false dichotomy. The argument presupposes that there are only two explanations exist for chimp and DNA similarity. As the argument goes, either chimp and human DNA similarity is due to chance or the similarity is due to common descent. Since chance can be (mostly) ruled out, we must accept the theory of common descent.
Ask yourself this: Are those the only possibilities? Do the major opponents of the theory of common descent claim that the DNA similarity is due to chance? Well, no. The major opponents of common descent are either intelligent design advocates or Christian creationists (or maybe there is no difference between the two groups), and they certainly do not claim that DNA similarities came about by chance alone. Typically they claim that a hyper-intelligent being and/or God created both chimps and humans. If that is true, DNA similarity will be due to design and not to chance.
Another tactic, which is not a logical flaw strictly speaking, is the claim that its acceptable for science to commit logical fallacies because science does not use deductive logic but rather inductive logic. Even though this argument is like a Christian saying that 2+2 can equal 5 because Christianity doesn't rely on math to make its claims, I will take a few lines to destroy the argument that inductive reasoning is valid.
What is inductive reasoning? It is the claim that people can look at a few examples and derive a general rule that explains them all. For example, we can go out into the wild and see some white swans, go to the zoo and see some white swans, and watch a swan documentary and see some white swans. From this we can conclude that all swans are white. The problem with this is that black swans exist but are only in Australia. Accordingly, we can see that inductive reasoning can result in false conclusions even when all inputs are true.
More sophisticated scientists will say that although this is true, Bayesian statistics can overcome the problem of induction. Thomas Bayes was a Presbyterian minister who calculated that he could determine whether a line down his billiards table was exactly in the middle by throwing a large number of billiard balls onto the table in such a manner that they could land anywhere on the table. This method does not result in certainty, but it is believed to result in a certain statistical likelihood.
The reason why this argument generally doesn't work for science is because most scientific investigations are not comparable to throwing billiard balls on a table in such a way that they could land anywhere. Lets look at the following argument to illustrate this point:
The radioactive half-life of uranium-238 is 4.5 billion years, plus or minus 10 percent. Multiple labs all across the United States and in other countries have conducted countless experiments and they have all confirmed that number. Accordingly, although the above argument is logically flawed (affirming the consequent), we can calculate the half-life at around 4.5 billion years with great statistical certainty.
The problem with this argument is that just as the billiard balls in Bayes example needed to be thrown out on the table in such a way that they would land anywhere, so too the U-238 half-life experiment needs to be conducted in such a way that the data points collected could come from anywhere during the 4.5 billion year half-life. Rather than doing so, all the data points have been collected in the past 100 years. As such the argument is comparable to saying that we could calculate whether a Democrat will win the next US presidential election by asking a large number of people who live in one small city block of New York who they plan to vote for.
Another logical fallacy we will look at is called begging the question. This formal fallacy involves assuming that what you set out to prove is true right from the start and then reasoning around in a circle to prove the initial premise true. This chain of circular logic is invalid. Heres a common example:
We scientists have seen examples of evolution in Escherichia coli bacteria (E.coli) in our laboratories. We can, therefore, conclude that E.coli is also evolving out in the wild and has been doing so for millions of years. We know this because the past is a good guide to the future and so we know that future experiments will continue to show that E.coli is and has been evolving since the first E.coli bacterium existed. We know that the past is a good guide to the future because we have used it in the past, and it has always worked well. Accordingly, it will continue to do so in the future.
As you may have seen, the key to the argument is that the past is a good guide to the future because it has worked in the past and will (they assume) work well in the future. This is a prime example of begging the question. Heres an example in practice:
The universe must be many billions of years old because we can see light from stars that are billions of light years away. Light travels at a constant speed of about 300,000 km/s. We know that the speed of light is constant because we have conducted tests in the past and we know that future tests will confirm this number (because the past is a good guide to the future) and so it is not possible that the speed of light was higher in the past.
This is a classic example of begging the question. The conclusion should be rejected.
The final argument is that although the logic is abysmally bad, the conclusion might still be true. After all, if we say: All men are mortal. Carlos is mortal. Therefore, Carlos is a man then our final conclusion is true even though the logic was bad. This argument misses the point. Although its true that bad logic can sometimes lead to correct answers, said answers cannot be considered proven. As such, the claim that genetic diversity can be explained by the process of evolution is on equal footing with the claim that Vishnu created and maintains the universe. A reasonable person, such as I, would be agnostic about both claims.
Chimp and human DNA are more than 98 percent similar. While this does not prove that chimps and humans share a common ancestor, it is unlikely that this level of similarity could have happened by chance alone. Since humans have approximately 24,000 genes, finding greater than 98 percent correlation is like flipping a coin 10,000 times and having it come up heads every time. Therefore, no reasonable person can seriously doubt that humans and chimps share a common ancestor.
The logical flaw in this argument is what we call the false dichotomy. The argument presupposes that there are only two explanations exist for chimp and DNA similarity. As the argument goes, either chimp and human DNA similarity is due to chance or the similarity is due to common descent. Since chance can be (mostly) ruled out, we must accept the theory of common descent.
Ask yourself this: Are those the only possibilities? Do the major opponents of the theory of common descent claim that the DNA similarity is due to chance? Well, no. The major opponents of common descent are either intelligent design advocates or Christian creationists (or maybe there is no difference between the two groups), and they certainly do not claim that DNA similarities came about by chance alone. Typically they claim that a hyper-intelligent being and/or God created both chimps and humans. If that is true, DNA similarity will be due to design and not to chance.
Another tactic, which is not a logical flaw strictly speaking, is the claim that its acceptable for science to commit logical fallacies because science does not use deductive logic but rather inductive logic. Even though this argument is like a Christian saying that 2+2 can equal 5 because Christianity doesn't rely on math to make its claims, I will take a few lines to destroy the argument that inductive reasoning is valid.
What is inductive reasoning? It is the claim that people can look at a few examples and derive a general rule that explains them all. For example, we can go out into the wild and see some white swans, go to the zoo and see some white swans, and watch a swan documentary and see some white swans. From this we can conclude that all swans are white. The problem with this is that black swans exist but are only in Australia. Accordingly, we can see that inductive reasoning can result in false conclusions even when all inputs are true.
More sophisticated scientists will say that although this is true, Bayesian statistics can overcome the problem of induction. Thomas Bayes was a Presbyterian minister who calculated that he could determine whether a line down his billiards table was exactly in the middle by throwing a large number of billiard balls onto the table in such a manner that they could land anywhere on the table. This method does not result in certainty, but it is believed to result in a certain statistical likelihood.
The reason why this argument generally doesn't work for science is because most scientific investigations are not comparable to throwing billiard balls on a table in such a way that they could land anywhere. Lets look at the following argument to illustrate this point:
The radioactive half-life of uranium-238 is 4.5 billion years, plus or minus 10 percent. Multiple labs all across the United States and in other countries have conducted countless experiments and they have all confirmed that number. Accordingly, although the above argument is logically flawed (affirming the consequent), we can calculate the half-life at around 4.5 billion years with great statistical certainty.
The problem with this argument is that just as the billiard balls in Bayes example needed to be thrown out on the table in such a way that they would land anywhere, so too the U-238 half-life experiment needs to be conducted in such a way that the data points collected could come from anywhere during the 4.5 billion year half-life. Rather than doing so, all the data points have been collected in the past 100 years. As such the argument is comparable to saying that we could calculate whether a Democrat will win the next US presidential election by asking a large number of people who live in one small city block of New York who they plan to vote for.
Another logical fallacy we will look at is called begging the question. This formal fallacy involves assuming that what you set out to prove is true right from the start and then reasoning around in a circle to prove the initial premise true. This chain of circular logic is invalid. Heres a common example:
We scientists have seen examples of evolution in Escherichia coli bacteria (E.coli) in our laboratories. We can, therefore, conclude that E.coli is also evolving out in the wild and has been doing so for millions of years. We know this because the past is a good guide to the future and so we know that future experiments will continue to show that E.coli is and has been evolving since the first E.coli bacterium existed. We know that the past is a good guide to the future because we have used it in the past, and it has always worked well. Accordingly, it will continue to do so in the future.
As you may have seen, the key to the argument is that the past is a good guide to the future because it has worked in the past and will (they assume) work well in the future. This is a prime example of begging the question. Heres an example in practice:
The universe must be many billions of years old because we can see light from stars that are billions of light years away. Light travels at a constant speed of about 300,000 km/s. We know that the speed of light is constant because we have conducted tests in the past and we know that future tests will confirm this number (because the past is a good guide to the future) and so it is not possible that the speed of light was higher in the past.
This is a classic example of begging the question. The conclusion should be rejected.
The final argument is that although the logic is abysmally bad, the conclusion might still be true. After all, if we say: All men are mortal. Carlos is mortal. Therefore, Carlos is a man then our final conclusion is true even though the logic was bad. This argument misses the point. Although its true that bad logic can sometimes lead to correct answers, said answers cannot be considered proven. As such, the claim that genetic diversity can be explained by the process of evolution is on equal footing with the claim that Vishnu created and maintains the universe. A reasonable person, such as I, would be agnostic about both claims.
