Science News: Victory for Peppered Moth

Image by Виталий Гуменюк

For decades science teachers have used the Peppered Moth (Biston betularia) as a prime example of natural selection. Prior to the Industrial Revolution in Europe, the Peppered Moth population in England consisted of a high percentage of light-colored salt and pepper moths (known as typica) and a low percentage of dark moths (known as carbonaria). At that time, the majority of trees were also light-colored due to the growth of lichens on their bark, providing typicas camouflage. Dark moths, it was presumed, were disproportionately spotted by birds and eaten, thus keeping their population low.

As the Industrial Revolution progressed, the lichens began to die and the tree trunks became darker as they collected soot from the growing number of factories. At the same time, the percentage of light moths began to decline, while carbonarias increased and became the majority. The assumption of scientists was that now the darker moths had better camouflage and the best adaptation to avoid predation, while the lighter moths were now easy prey.

This is classic Natural Selection: A given population (members of the same species living in the same place and time) always contains a variety of phenotypes (traits), some of which are better than others at helping an organism survive long enough to reproduce and pass the adaptation to their offspring. However, environmental changes (like pollution) can alter the balance, shifting greater fecundity to organisms with a different phenotype, causing their proportion in the population to increase.  

The example was so classic, so cut and dry, so obvious, that few scientists and even fewer science teachers ever questioned its validity. The hypothesis was proposed as early as 1896, according to The Scientist (May, 2012) and validated in the 1950s by Bernard Kettlewell, who collected compelling evidence that bird predation was in fact the selective force at work and that moth camouflage was affected by pollution, by placing light and dark moths directly on trees in polluted and unpolluted tracts.

However, in the 1980s, Peppered Moth experts started to identify flaws in Kettlewell’s experiments. Perhaps most compelling was their finding that tree trunks might not be the moths’ preferred resting place, thus calling into question the whole camouflage/bird predation hypothesis. It also threatened to make fools of the thousands of science teachers who were still using the Peppered Moth as a prime example of Natural Selection. Worse than this, however, was the field day it created for creationists, who called the Peppered Moth story a fraud and an example of scientists’ fallibility.

Enter Michael Majerus, an evolutionary biologist from the University of Cambridge, and a 50-year expert on Biston betularia. Starting in 2001, according to The Scientist, he set out to confirm Kettlewell’s findings using a more robust and convincing protocol. First, through years of direct observation, he discovered that the moths’ preferred resting site was the lateral branches of trees (not their trunks). Then, rather than artificially placing moths in a desired setting as Kettlewell did, he released thousands into an unpolluted tract covered with nets (so they couldn’t escape and confuse migration with predation).

Over the course of seven years he found a 9% lower survival rate for carbonaria moths, indicating that they indeed had a lower fecundity in an unpolluted setting and suggesting that they were in fact being consumed at a higher rate.

Majerus died in 2009 from an aggressive mesothelioma before his results could be published. However, a detailed account of his work was published this year in Biology Letters (February 2012) by some of his peers.

The lesson for K-12 science teachers is that they need to stay up to date on scientific discoveries and debates. In my experience, this does not happen often enough. Many (if not the majority) of those who teach science have little, if any, practical experience doing science in a real-world setting and few read scientific journals with any regularity. Furthermore, it is very rare that they have time to meet with colleagues to discuss new discoveries, review journal articles, analyze methodologies, or debate controversies, something that is an important cornerstone of university research.

Scientists Induce Evolution of Multicellular Yeast

(Image by AZAdam)

(From the Discover Magazine blog)

Natural selection is the process by which organisms well-suited to a particular environment reproduce at a faster rate than their competitors.  In this experiment, the scientists engaged in artificial selection by creating an environment which made it very difficult for lone yeast cells to survive, thus encouraging the proliferation of cells with adaptations conducive to colonial life. They did this by suspending the cells in tubes of liquid and then centrifuging them, which forced clumped cells down to the bottom of the tube, while lighter single cells floated. They discarded the supernatant (liquid with single cells), and repeated the experiment with the clumped cells until they had high concentrations of cells that had an affinity for clumping.

By this process, they were able to isolate 10 different strains of yeast cells with adaptations conducive to colonial life. They grew these cells in Petri dishes where they grew as snowflake-shaped colonies that resembled and behaved like multicellular organisms. When a snowflake got too large, part of it broke off and formed new snowflakes. There were also signs of division of labor, with some cells committing suicide (apoptosis) to create weak points for the snowflakes to break when they were ready to reproduce.

While it may seem surprising that yeast could evolve multicellularity so rapidly, there is evidence that yeast evolved from multicellular fungi. Thus, they may have retained genes necessarily for multicellular life and reactivated them under the selective pressure of this experiment.

Few High School Biology Teachers Accurately Teach Evolution

I hate to bag on my own colleagues, but the evidence is overwhelming: most high school biology teachers either do not teach evolution or undermine their own teaching by giving nods and winks to creationist ideas. (See Most high school biology teachers don’t endorse evolution, by Valerie Strauss.)

 

Tom Schmal

The result is that few U.S. high school students are really being taught evolution in an accurate or comprehensible way. Not only is this unfair to students who graduate believing they have mastered biology, when many have not, but it is a violation of teachers’ responsibility to accurately teach the content standards, including the scientific process (how scientists obtain data, analyze it and determine the validity of their hypotheses).  

Here are some of the details from Strauss’ article:

• Only 28% of biology teachers consistently teach the National Science Teachers Association (NSTA) recommended evolution curriculum,
• Around 13% of biology teachers explicitly include creationism or intelligent design for at least part of their curriculum
• The remaining 60% either fail to explain the scientific process sufficiently, undermine the authority of evolution experts, or legitimize creationist arguments
• Many teach evolutionary biology as if it is only applicable to molecular processes, but not to populations or the process of speciation.
• Many tell students that they don’t have to “believe in evolution, but they have to know it for tests, which, for many students, implies that it is just one of many explanations that may or may not be true.
• Others tell students to decide for themselves what to believe, even though scientists are as certain of the validity of evolution as they are about any other scientific fact. We would not tell students to decide for themselves if the Holocaust or slavery occurred (although I wonder, based on the evolution data, if there are many biology teachers who are also climate deniers).

This is Not Simply a Problem of Religious Teachers Refusing to Do Their Jobs

Just like a Christian pharmacist should be required to sell all legal drugs, including birth control, a Christian biology teacher should be required to teach the content standards, including evolution. However, the problem is not just an issue of religious activists deliberately refusing to do their jobs. For some teachers, the last two examples above (e.g., “you don’t have to believe; just know it for tests” and “you decide what to believe”) may result more from a desire to respect their students’ cultural and religious beliefs and not insult or alienate them, than from their own religious biases or activism. I regularly have students tell me that they don’t have to learn evolution because it’s against their religion. My response is, “Well, actually you do. It is an important part of biology and it is in the content standards. Furthermore, it is impossible to understand other parts of biology without a foundation in evolution. Evolution helps scientists to develop new medicines, understand certain diseases and even make predictions about climate change.”

My response is not insulting or demeaning, nor does it undermine the science by implying that evolution is just one of many explanations that one can choose to believe, or not. On the contrary, it emphasizes that evolution is a lynchpin of biology, not just a stand-alone branch of the discipline. It is important to emphasize that evolution can be taught and misconceptions about it can be corrected, without engaging in the kind of hostile and insulting discourse expressed by people like Richard Dawkins. This sort of behavior probably does more to shut down students’ curiosity and openness to new ideas than to dispel their faith-based misconceptions.

In order to correct misconceptions is important to clarify the scientific process, particularly the meaning of the word “theory,” which many people misuse to mean “belief” or “opinion,” rather than its actual scientific meaning: “fact, based on a collection of related hypotheses that have been repeatedly verified.” Also, before I even get into the nuts and bolts of evolution, I emphasize the distinction between the scientific process, which is evidence-based, and faith-based thinking, where one believes without (or despite) evidence. I even go so far as to tell students that in certain circumstances faith-based thought is sometimes the most effective way to think (for example, having faith in oneself can help one remain motivated and focused during sports or academic challenges), but that in science, evidence is required, lots of it, and it must be verifiable by independent researchers using controlled experiments. Faith that a scientific hypothesis is right (without evidence) can lead to deadly consequences.

Another problem is that many science teachers have little or no experience doing “bench” science, having earned a degree in biology and then a teaching credential without having worked in a lab. As a result, they sometimes do not fully understand the scientific process themselves. For example, many cannot explain why a randomized, double blind, controlled study is more compelling than anecdotal evidence. Even doctors sometimes have this problem. Consider all the times you have heard doctors give advice based on their anecdotal experience with other patients.

Many Americans (including some biology teachers) do not truly understand evolution, making it difficult to believe and even harder to teach. This is due in part to the considerable misunderstandings and oversimplifications that are perpetuated in our culture (e.g., “we came from monkeys,” which implies that monkeys gave birth to humans or had sex with humans; in contrast to the idea that we share a common ancestor).

Even without the misconceptions, evolution is not an easy theory to understand. For example, the idea that an organ as complex as the human eye could be the result of random mutations and natural selection seems really far-fetched, until one realizes that the rudiments of vision, proteins that sense and respond to light, have existed for millions of years and have been utilized in sensory organs of animals that existed long before the evolution of the modern eye. It is also difficult to really get a handle on the slow rate of random mutations and how they can accrue in organisms without some background in biochemistry. For example, I don’t think that most biology teachers understand or teach that human DNA polymerase, the enzyme that builds new DNA molecules during replication, has a natural mutation rate of about 10^-8.

Of course none of this is to say that there aren’t creationist biology teachers who deliberately try to undermine the teaching of evolution. A recent Gallop poll shows that 40% of Americans believe in young Earth creationism (i.e., the Earth and all its life were created by God 10,000 years ago), while another 38% believe in a form of evolution with God playing a role in it. No doubt some of these folks have made it into biology classrooms as teachers.