Saturday, 31 August 2013

Are Humans Devolving?

I occasionally come across people arguing that advances in modern science and technology have halted human evolution and that we are now devolving as a species. The basic argument goes something like this: millions of people who would've died because of allergy, disease, birth defect, injury, etc. now survive and reproduce. Therefore, their weaker genes are contaminating the human gene pool and we've defeated natural selection. Sounds reasonable, right? Everyone's familiar with the phrase "survival of the fittest". The survival of weaker people must be a bad thing. 
And this will probably happen. It's "science". 
This argument bears striking resemblance to the reasoning used to justify various compulsory sterilization and euthanasia programs of the early 20th century. However, eugenics has largely disappeared and is now widely considered to be immoral. The Charter of Fundamental Rights of the European Union prohibits eugenics-based practices explicitly. Though the immorality of eugenics doesn't refute the argument that humans are devolving, perhaps it is a clue that the reasoning behind eugenics is flawed. 

I haven't actually taken any biology courses, so I'm probably unqualified to address the devolution argument, but it seems to me that it indicates an oversimplified view of what evolution really is. Suggesting that we no longer evolve is basically saying that humans are a special class of life that breaks all the rules when it comes evolutionary biology. In which case, the theory of evolution requires some significant revision to account for the anomaly that is humanity. 
Aside: I hope that no creationist cherry-picks this blog post for anti-evolution causes.
The phrase "survival of the fittest" is an elegant way to describe natural selection, but perhaps it does so too succinctly and is too easily misinterpreted. The argument that because we co-operate to cheat death we've somehow halted our evolution inherently assumes that "fitness" refers only to physical strength and robustness. When Darwin used the phrase, "fittest" was intended to mean "best adapted for life in their local environment". 

Physically weaker members of a species often still reproduce. In fact, this probably contributes to the species' overall viability by increasing genetic diversity. There is a misconception that in species living in hierarchical groups controlled by alpha males, the alphas do all the mating and all the other guys die bachelors. While alpha males typically mate far more frequently, other males still manage to sneak in a few trysts to pass on their genes. You might say that having the cunning to pass on genes despite inferior strength indicates greater intellectual fitness. Brain overcoming brawn. Clearly, physical fitness is not the only way for a species to survive and reproduce in its environment. 

To elaborate on the importance of intellectual fitness, let's look at tool use. We've mastered the use of tools, but we are not uniquely endowed with this ability. Sea otters use rocks both for prying abalone and to break open their hard-shelled prey. Chimpanzees use sticks to fish for termites, sharpened sticks to spear Senegal bushbabies (which are nocturnal primates, not Senegalese infants), and stone hammer and anvil to break open nuts. Capuchin monkeys also use stone hammer and anvil to break open nuts and seeds. Elephants use sticks to swat flies and chewed up tree bark to plug holes dug for groundwater (preventing evaporation). 
In addition to bashing shellfish with rocks, sea otters do adorable things like hugging their offspring.
Animals capable of tool use have evidently benefited from intellectual fitness during their evolutionary history. Some of these animals would probably not survive if tools were suddenly unavailable today. Yet believers in human devolution don't seem to think that sea otters are also devolving because a lot of them would starve to death if appropriate oyster-smashing rocks became unavailable for some reason. Antibiotics and epi-pens similarly don't reverse human evolution simply because some of us couldn't survive without these tools. 

Creatures can evolve traits to better equip them for survival in their environment, but they can also evolve the intelligence to manipulate their own environment to make it more survivable. Tool use is just an example of manipulation of one's environment, something that many living things do to various extents. Gorilla traps are something humans have added to the gorilla environment. The gorillas need not evolve traits to make them more difficult to ensnare because they already possess the intellectual fitness necessary to dismantle the traps and teach this skill to the younger generations. In other words, the gorillas manipulate their environment to remove a threat to the survival of their species. Fundamentally, this is hardly different from the human campaign to eradicate polio
With humans devolving and apes spearing bushbabies and dismantling snares, this scenario is inevitable.
While our ability to manipulate our environment has progressed far beyond the basic tool use seen in the animal kingdom, our quest for survival is fundamentally the same as any other creature's. The fact that we cannot survive outside the artificial environment of our making doesn't mean our evolution has halted. It is the environment humans actually live in that matters, not the fantastical universe where intelligence is eschewed and human survival is decided by physical fitness alone. In the developed world, the reality is we've created an environment where nutrition is optimal, children are (usually) vaccinated against preventable diseases, and antibiotics and epi-pens are readily available. Under such survivable conditions, it is to be expected that physical fitness becomes less important and what might have been "weaker" genes in the past start to make their way back into the gene pool. The belief that the increase in reported cases of asthma and allergies in children in the industrialized world signifies a devolution of the species is misguided. A rise in the prevalence in peanut allergy is simply to be expected wherever peanut allergy becomes more survivable, because the genes responsible for the condition are no longer a significant threat to fitness. 

Our abilities to co-operate and to manipulate our environment, i.e. our intellectual fitness, serve us far better than our physical fitness today. I think the expectation should be that humans will gradually become smarter as a species while simultaneously making the human environment increasingly survivable. It's what we've been doing for all of documented history (and for a long time prior, too). That hardly seems like devolution to me.

Saturday, 24 August 2013

Natural: Not a Synonym for Healthy

More and more I hear and see the word natural used to market products under the premise that natural things are good for you. Why should people equate natural with healthy? There are a plethora of things that occur naturally and are harmful to us. Asbestos; harmful elements like mercuryleadarsenic, and radon; plus poisons like amatoxinbotulinum toxintetrodotoxinricintetanospasmintaicatoxin, and PhTx3 can all be found in nature. Furthermore, how much of our food is truly natural? Even the most basic foods we eat are unnatural. We've hybridized nature's wild fruits, vegetables, and grasses to create nearly all modern crops, artificially increasing yields, edibility, and nutritional value. We've taken nature's wild animals and bred them selectively to artificially make them dumber, more docile, more productive, and meatier. When wild animals see the bountiful feasts we've created for ourselves, they are enticed to take it for themselves. After all, what creature wouldn't want to exploit a new food source which is both plentiful and nutritious? So we have to fight back against birds, rodents, insects, and other natural invaders to preserve our artificially enhanced food sources. Without our intervention, all of the crops and domesticated animals of our creation would disappear. 
Given the opportunity, this robin and his pals will gorge themselves on orchard cherries.
It's difficult to make the argument that we were better off before we started artificially enhancing the human environment. We are smarter, larger, healthier, more comfortable, and have greater longevity than ever before. I doubt that very many of the people buying into the "all-natural" trend would agree that we'd all be better off if we stopped adding Vitamins A & D to milk, iodine to salt, and folic acid to flour. 
Flour fortified with folic acid helps prevent Spina Bifida, much to the chagrin of today's all-naturally fed mothers.
Perhaps instead of letting the latest trend decide for us what is and isn't healthy, we should trust scientific evidence and the people qualified to interpret that evidence. Certified organic food isn't healthier than the regular stuff. There's no significant difference between milk produced by dairy cows and milk produced by dairy cows on the growth hormone rBST. High-fructose corn syrup doesn't hinder weight loss or cause weight gain (consuming too many calories does). 

Even worse than the use of the word natural to market overpriced foods is its use to market herbal supplements. Sure, we've been using some herbal remedies for thousands of years. The efficacy of some natural remedies, like willow bark, is well established and led to improvements in modern medicine.
Powdered willow bark might work, but I'm not convinced it's better for me than Aspirin.
Many other remedies, however, haven't been subjected to the same scientific scrutiny. Herbal supplements don't need to be effective and they don't need to be approved by a regulating body before hitting the market. Health Canada basically only requires that the ingredients of an herbal supplement be labelled correctly and that the stuff doesn't pose a significant health risk if taken as directed. The U.S. FDA has essentially the same relaxed rules. While many supplements are probably harmless, there are a few that could be dangerous. St. John's Wort might help with mild depression, but there isn't enough evidence to use it to treat major depression and it isn't more effective or significantly better tolerated than other antidepressants. Plus, it interacts with a number of different drugs, including oral contraceptives. Comfrey helps heal damaged skin and bone, but its toxic effects on the liver resulted in the FDA banning comfrey preparations intended for ingestion. Kava might help with your anxiety, but it often takes several weeks to start working, and some possible adverse effects include liver damage and dangerous interactions with alcohol and other drugs. Those are just three examples of supplements that have received enough attention to identify some of the risks. There are hundreds of untested, barely regulated supplements out there being marketed with unsubstantiated claims of significant health benefits, and new ones are coming out all the time. Without the clinical testing required of real medicine, the harmful effects of herbal supplements can go undetected longer and affect a much larger number of people. Remember, just because something's been around for a long time doesn't mean that it's right. 

In conclusion, the next time you see the word natural associated with a food or supplement, keep in mind that natural does not equal healthy, many artificial enhancements have made our lives better, and that the word natural has probably been placed there just to sucker you out of some money. 

Friday, 2 August 2013

Guessing on Multiple Choice Tests

You've probably heard someone give advice along the lines of "when in doubt, guess 'C'" when taking multiple choice tests. The alleged reasoning behind it is that there's a statistical advantage in guessing 'C' consistently rather than randomizing your answers.

I decided to investigate this claim. Let's first check the case when the professor distributes the correct answers evenly and randomly, not favouring any one letter. Take for example a test with 30 questions, where each answer is independent of the others and there are four choices per question (A, B,C, or D). Assuming that you really have no clue which is the correct answer, any guess has a 25% probability of being correct. This is true regardless of whether you choose randomly (let's ignore for the moment that humans are notoriously bad at generating random values on their own) or if you decide to choose the same letter consistently. Here's why:

The instructor randomly chooses which letter is correct, without bias, so the probability of any letter happening to be the correct answer on a particular question is 25%. If you also guess randomly without favouring any letter (i.e. each letter is guessed, on average, 25% of the time), you should then expect that 25% of the correct answers are 'A', 25% of your guesses are 'A', thus 6.25% of your guesses (25% of 25%) are correct. The same is true of 'B', 'C', and 'D', so that overall you expect 4*6.25% = 25% of your guesses to be correct. Now if you consistently choose 'C' for the same random test, the probability that 'A' is correct is 25% but the probability that you guess 'A' is 0%. This is also true of 'B' and 'D'. When you choose 'C' 100% of the time, overall you should expect that 3*0.25*0 + 1*0.25*1 = 25% of your guesses are correct.

Since the guess is either right or wrong, this is a problem for the binomial distribution. The mean is n*p and the variance is sqrt[n*p*(1-p)], where n is the number of trials and p is the probability of the desired outcome. In our example multiple-choice test, whether you guess randomly or choose 'C' every time, you would expect, on average, to get 30*0.25 = 7.5 correct answers. To reinforce the point that both approaches to guessing are equal here, I simulated 50,000 of these tests in Excel and generated the following plot.
Probability distribution for correct guesses on tests with random answers to four-choice questions.
The average was 7.49 correct answers with a standard deviation of 2.37 when all guesses were random. When 'C' was guessed consistently, the average was 7.50 with a standard deviation of 2.38. The binomial distribution with n = 30 and p = 0.25 predicts an average of 7.50 and a standard deviation of 2.37. It's pretty clear that both guessing schemes give the same results when the correct answers are random and evenly distributed among the possible choices. 

Now that it's clear that there's no advantage if answers are randomly and evenly distributed, let's investigate the case where the instructor favours one letter over the others. It turns out that no matter how biased the instructor's distribution of correct answers might be, if you randomly guess each letter 25% of the time, your probability of choosing the right answer is still 25%. Let's assign unknown probabilities for each letter being assigned as correct by the instructor: pA, pB, pC, and pD. The sum of these unknown probabilities must be unity. So when the probability of guessing A, B, C, or D is 25% each, the probability of being correct is then 0.25pA+0.25pB+0.25pC+0.25pD = 0.25(pA+pB+pC+pD) = 0.25*1 = 25%. That all changes if you consistently choose 'C' though. In this case, your probability of getting the right answer is 0pA+0pB+1*pC+0pD = pC. I varied pC between the most unfavourable case (where 'C' is never the correct answer) to the most favourable (where 'C' is always the correct answer) to generate the following plot:

Probability distribution for correct answers when 'C' guessed consistently for different values of pC.
Obviously, there's some benefit to choosing 'C' if you know that the instructor favours 'C' over the other letters. But you also get screwed if the instructor doesn't like to use 'C' or simply chooses to favour another letter because he wants to penalize the people who always guess 'C'. While it looks pretty nice that more of the curves I plotted are shifted to the right rather than left of the curve for random guessing, if the choice of which letter gets favoured is random, the chance that 'C' is never the right answer is higher than the chance that it is always correct. To illustrate, I ran a simulation which I think is slightly more realistic than the examples above.

I assumed that pB + pC is 54% on average, which is just a guess on my part but I feel it is reasonable because answers aren't randomly assigned a letter. Numerical answers are often ordered from smallest to largest and statements like "All of the above" are reserved only for 'D' because they'd be confusing if they weren't. I used the normal distribution to generate the random variations in individual tests, so that pB + pC can vary from 0 to 1, but is usually close to the average. I similarly used normally distributed random numbers to split up pB and pC, so that on average pC is half of (pB + pC), but can vary from 0 to 100%. Same idea with pA and pD. Random guesses by the test taker are still equally distributed on average between the four choices. Plotted below are the results of 250,000 simulated tests.
Probability distribution for correct answers based on "realistic" multiple choice tests.
With random guessing we expected to be right 25% of the time on average and to see a binomial distribution after many tests. When 'C' is guessed consistently, things get more complicated, but a simple approximation can be found using the normal distribution. As you can see in the plot, the approximation works fairly well. It is clear that random guessing gives you more consistent results than guessing 'C' all the time. Always guessing 'C' increases your chances of getting 1 in 3 guesses right, but it also increases your chances of doing worse than 1 in 6, simply because your results are influenced by how the distribution of answers was biased by the instructor for the particular test. Overall, consistently guessing 'C' resulted in 2% more correct answers. But of the 250,000 simulated tests, random guessing beat consistently guessing 'C' on a total of 125,568 tests (i.e 50.23% of the time).

To summarize, if you happen to know that the creators of the test favour 'C' for correct answers, guessing 'C' consistently gives you an edge. In the long run, sticking with 'C' probably gives you a very slim advantage over random guessing, though guessing randomly gives you better consistency in the results of your guesses.