Now evolving in biology classes: a testier climate

Some science teachers say they're encountering fresh resistance to the topic of evolution - and it's coming from their students.

Nearly 30 years of teaching evolution in Kansas has taught Brad Williamson to expect resistance, but even this veteran of the trenches now has his work cut out for him when students raise their hands.

That's because critics of Charles Darwin's theory of natural selection are equipping families with books, DVDs, and a list of "10 questions to ask your biology teacher."

The intent is to plant seeds of doubt in the minds of students as to the veracity of Darwin's theory of evolution.

The result is a climate that makes biology class tougher to teach. Some teachers say class time is now wasted on questions that are not science-based. Others say the increasingly charged atmosphere has simply forced them to work harder to find ways to skirt controversy.

On Thursday, the Science Hearings Committee of the Kansas State Board of Education begins hearings to reopen questions on the teaching of evolution in state schools.

The Kansas board has a famously zigzag record with respect to evolution. In 1999, it acted to remove most references to evolution from the state's science standards. The next year, a new - and less conservative - board reaffirmed evolution as a key concept that Kansas students must learn.

Now, however, conservatives are in the majority on the board again and have raised the question of whether science classes in Kansas schools need to include more information about alternatives to Darwin's theory.

But those alternatives, some science teachers report, are already making their way into the classroom - by way of their students.

In a certain sense, stiff resistance on the part of some US students to the theory of evolution should come as no surprise.

Even after decades of debate, Americans remain deeply ambivalent about the notion that the theory of natural selection can explain creation and its genesis.

A Gallup poll late last year showed that only 28 percent of Americans accept the theory of evolution, while 48 percent adhere to creationism - the belief that an intelligent being is responsible for the creation of the earth and its inhabitants.

But if reluctance to accept evolution is not new, the ways in which students are resisting its teachings are changing.

"The argument was always in the past the monkey-ancestor deal," says Mr. Williamson, who teaches at Olathe East High School. "Today there are many more arguments that kids bring to class, a whole fleet of arguments, and they're all drawn out of the efforts by different groups, like the intelligent design [proponents]."

It creates an uncomfortable atmosphere in the classroom, Williamson says - one that he doesn't like. "I don't want to ever be in a confrontational mode with those kids ... I find it disheartening as a teacher."

Williamson and his Kansas colleagues aren't alone. An informal survey released in April from the National Science Teachers Association found that 31 percent of the 1,050 respondents said they feel pressure to include "creationism, intelligent design, or other nonscientific alternatives to evolution in their science classroom."

These findings confirm the experience of Gerry Wheeler, the group's executive director, who says that about half the teachers he talks to tell him they feel ideological pressure when they teach evolution.

And according to the survey, while 20 percent of the teachers say the pressure comes from parents, 22 percent say it comes primarily from students.

In this climate, science teachers say they must find new methods to defuse what has become a politically and emotionally charged atmosphere in the classroom. But in some cases doing so also means learning to handle well-organized efforts to raise doubts about Darwin's theory.

Darwin's detractors say their goal is more science, not less, in evolution discussions.

The Seattle-based Discovery Institute distributes a DVD, "Icons of Evolution," that encourages viewers to doubt Darwinian theory.

One example from related promotional literature: "Why don't textbooks discuss the 'Cambrian explosion,' in which all major animal groups appear together in the fossil record fully formed instead of branching from a common ancestor - thus contradicting the evolutionary tree of life?"

Such questions too often get routinely dismissed from the classroom, says senior fellow John West, adding that teachers who advance such questions can be rebuked - or worse.

"Teachers should not be pressured or intimidated," says Mr. West, "but what about all the teachers who are being intimidated and in some cases losing their jobs because they simply want to present a few scientific criticisms of Darwin's theory?"

But Mr. Wheeler says the criticisms West raises lack empirical evidence and don't belong in the science classroom.

"The questions scientists are wrestling with are not the same ones these people are claiming to be wrestling with," Wheeler says. "It's an effort to sabotage quality science education. There is a well-funded effort to get religion into the science classroom [through strategic questioning], and that's not fair to our students."

A troubled history Teaching that humans evolved by a process of natural selection has long stirred passionate debate, captured most famously in the Tennessee v. John Scopes trial of 1925.

Today, even as Kansas braces for another review of the question, parents in Dover, Pa., are suing their local school board for requiring last year that evolution be taught alongside the theory that humankind owes its origins to an "intelligent designer."

In this charged atmosphere, teachers who have experienced pressure are sometimes hesitant to discuss it for fear of stirring a local hornets' nest. One Oklahoma teacher, for instance, canceled his plans to be interviewed for this story, saying, "The school would like to avoid any media, good or bad, on such an emotionally charged subject."

In the mountain town of Bancroft, Idaho (pop. 460), Ralph Peterson teaches all the science classes at North Gem High School. Most of his students are Mormons, as is he.

When teaching evolution at school, he says, he sticks to a clear but simple divide between religion and science. "I teach the limits of science," Mr. Peterson says. "Science does not discuss the existence of God because that's outside the realm of science." He says he gets virtually no resistance from his students when he approaches the topic this way.

In Skokie, Ill., Lisa Nimz faces a more religiously diverse classroom and a different kind of challenge. A teaching colleague, whom she respects and doesn't want to offend, is an evolution critic and is often in her classroom when the subject is taught.

In deference to her colleague's beliefs, she says she now introduces the topic of evolution with a disclaimer.

"I preface it with this idea, that I am not a spiritual provider and would never try to be," Ms. Nimz says. "And so I am trying not ... to feel any disrespect for their religion. And I think she feels that she can live with that."

A job that gets harder The path has been a rougher one for John Wachholz, a biology teacher at Salina (Kansas) High School Central. When evolution comes up, students tune out: "They'll put their heads on their desks and pretend they don't hear a word you say."

To show he's not an enemy of faith, he sometimes tells them he's a choir member and the son of a Lutheran pastor. But resistance is nevertheless getting stronger as he prepares to retire this spring.

"I see the same thing I saw five years ago, except now students think they're informed without having ever really read anything" on evolution or intelligent design, Mr. Wachholz says. "Because it's been discussed in the home and other places, they think they know, [and] they're more outspoken.... They'll say, 'I don't believe a word you're saying.' "

As teachers struggle to fend off strategic questions - which some believe are intended to cloak evolution in a cloud of doubt - critics of Darwin's theory sense an irony of history. In their view, those who once championed teacher John Scopes's right to question religious dogma are now unwilling to let a new set of established ideas be challenged.

"What you have is the Scopes trial turned on its head because you have school boards saying you can't say anything critical about Darwin," says Discovery Institute president Bruce Chapman on the "Icons of Evolution" DVD.

But to many teachers, "teaching the controversy" means letting ideologues manufacture controversy where there is none. And that, they say, could set a disastrous precedent in education.

"In some ways I think civilization is at stake because it's about how we view our world," Nimz says. The Salem Witch Trials of 1692, for example, were possible, she says, because evidence wasn't necessary to guide a course of action.

"When there's no empirical evidence, some very serious things can happen," she says. "If we can't look around at what is really there and try to put something logical and intelligent together from that without our fears getting in the way, then I think that we're doomed."

What some students are asking their biology teachers Critics of evolution are supplying students with prepared questions on such topics as:

• The origins of life. Why do textbooks claim that the 1953 Miller-Urey experiment shows how life's building blocks may have formed on Earth - when conditions on the early Earth were probably nothing like those used in the experiment, and the origin of life remains a mystery?

• Darwin's tree of life. Why don't textbooks discuss the "Cambrian explosion," in which all major animal groups appear together in the fossil record fully formed instead of branching from a common ancestor - thus contradicting the evolutionary tree of life?

• Vertebrate embryos. Why do textbooks use drawings of similarities in vertebrate embryos as evidence for common ancestry - even though biologists have known for over a century that vertebrate embryos are not most similar in their early stages, and the drawings are faked?

• The archaeopteryx. Why do textbooks portray this fossil as the missing link between dinosaurs and modern birds - even though modern birds are probably not descended from it, and its supposed ancestors do not appear until millions of years after it?

• Peppered moths. Why do textbooks use pictures of peppered moths camouflaged on tree trunks as evidence for natural selection - when biologists have known since the 1980s that the moths don't normally rest on tree trunks, and all the pictures have been staged?

• Darwin's finches. Why do textbooks claim that beak changes in Galapagos finches during a severe drought can explain the origin of species by natural selection - even though the changes were reversed after the drought ended, and no net evolution occurred?

• Mutant fruit flies. Why do textbooks use fruit flies with an extra pair of wings as evidence that DNA mutations can supply raw materials for evolution - even though the extra wings have no muscles and these disabled mutants cannot survive outside the laboratory?

• Human origins. Why are artists' drawings of apelike humans used to justify materialistic claims that we are just animals and our existence is a mere accident - when fossil experts cannot even agree on who our supposed ancestors were or what they looked like?

• Evolution as a fact. Why are students told that Darwin's theory of evolution is a scientific fact - even though many of its claims are based on misrepresentations of the facts?

["Mostly, mutation is just a consequence of the inexactness of large scale chemical processes."]

Does it become less exact on a larger scale than a smaller scale? Or less exact in more complex life forms or does that make a difference? Would you expect more variation in humans than say, fruit flys? I know - fruit flys have a lot of similar DNA to humans (or so I've heard). Thanks.

If you're asking about the "raw" mutation rate -- the rate at which changes occur within the genome -- it does vary among different species, but not in the way you presume.

In general (but with many exceptions), the more "complex" organisms have *lower* mutation rates, not higher. The reason is that with more complex cellular machinery, it opens the door for more complex, more varied, and more effective mutation prevention strategies, and more effective repair mechanisms.

Also, complex organisms had to evolve such "anti-mutation" protections for the simple fact that for a given mutation rate, a longer (i.e. "more complex") genome will suffer proportionally more total mutations than a shorter one (e.g. twice the genome length, twice the total mutations at a given mutation rate).

So as genomes grew in order to contain more genes, it became more important to find ways to lower the mutation rate (per basepair per year) in order to keep the total number of new mutations per generation from growing dangerously large. On the other hand, simple organisms (those with small genomes) with short generation times (and/or which produce large numbers of offspring) can tolerate much higher mutation rates and still have a good statistical chance of producing workable copies of themselves.

I wanted to include a table of the different mutation rates for various organisms, but it's actually rather hard to draw together information from various sources into one table in a way that they can be directly compared. The reason is that the mutation rate can be measured in several different ways, and the way in which a given study will choose to measure it for the organism being studied will vary depending upon what exactly the researchers were wanting to measure. For example, I've run across mutation rates measured in most of the following ways (each of which is useful for different purposes):

"Mutations per X per Y",
Where X can be any of:
per basepair
per total genome
per effective genome (i.e. that portion of the genome which "matters")
per generation
And Y can be any of:
per year
per year since last common ancestor (measured as the number of silent mutations actually accumulated via genetic drift in a given lineage)
per replication (i.e. cell division)
per generation

This makes at least 16 different measures of mutation rate...

To complicate matters, some particular types of mutations occur at a steady rate over chronological time (for example mutations induced by background radiation or chemical free radicals), whereas others occur as a result of DNA replication itself (for example copy errors), so each of the different ways of measuring "mutation rate" may not be comparable to the others, depending upon the generation time or number of cell replications for a given species (since the different measures will include differetn mixes of the "per time" and "per division" mutation types).

But with that caveat in mind, here are some various mutation rate measures:

Coronaviruses (a type of RNA-based virus, which includes the virus causing Hepatitis) have a high mutation rate, resulting in an average of three mutations per genome per generation.

The copy error rate (*only*) for E. coli is 1/10^8 basepairs per replication.

The human mutation rate is around (1 or 2)x10^-8 per basepair per generation. Given the human genome size, this means that each human contains around 100 novel mutations in their genome. However, it is unknown what portion of those occur in "junk DNA", result in silent basepair substitutions, homologous amino acid substitutions, etc. -- likely well over 90% of them are neutral in various ways.

The replication accuracy of HIV (the virus which causes AIDS) is so sloppy that even though the HIV genome is only 9000 basepairs long (compare to humans with a genome 3,000,000,000 basepairs long), its error-prone replication results in one or two new mutations every time it replicates, for a mutation rate of a whopping 1.7x10^-4 mutations per basepair per generation. This is actually the secret of HIV's success -- it mutates and evolves so rapidly that by the time an infected person's immunue system develops antibodies to the virus, many of the HIV viruses in their body have already changed enough that the antibodies don't recognize them. And by the time the body has produced antibodies to match the newer forms of the virus, the virus has changed yet again. In this way HIV stays one step ahead of the body's immune system, and maintains the infection for decades without being wiped out, as would have been the case for most ordinary viral infections. Eventually the body's overworked immune system collapses entirely, bringing on full-blown AIDS. Similarly, the HIV virus has proven adept at evolving defenses against the drug cocktails that have been formulated in an attempt to slow or halt its growth in the body. Like insect pests evolving immunities to commonly used pesticides, the HIV populations in even a single person's body rapidly evolves immunity to the drugs designed to block its growth, sometimes within mere weeks.

The rate of *accumulation* of neutral mutations in a population across generations in a lineage (i.e. the "molecular clock") is statistically constant for all tested mammal species at 2.2x10^-9 mutations per basepair per year. See Mutation rates in mammalian genomes. This paper also has some fascinating results concerning the times of divergence for various mammalian lineages. For example, humans and chimps last shared a common ancestor 5.5 million years ago.

One of the most cited papers on mutation rates is Rates of Spontaneous Mutation. It contains a wealth of information about how mutations occur in general, as well as specific data on actual mutation rates in various species. Also check out the links at the bottom for the dozens of papers it cites, and the dozens of papers which have cited this one -- many are available online.

This paper also contains specific information which can help answer one of the questions you ask: The mutation rate in fruit flies is 3.4 x 10^-10 mutations per basepair per replication (e.g. cell division), whereas the corresponding rate for humans is 5.0 x 10^-11 (see Table 5). So fruit flies have a mutation rate almost ten times that of humans. As I mentioned earlier, they can "afford" to thanks to their more rapid generation times and more prolific reproduction rates. Also note that while this means only 0.16 mutations on average per total genome per single human cell division, the process of developing an adult human from one original fertilized egg cell, and then producing the next generation of sperm/ovum, results in a chain of about 400 cell divisions (and 20 years of time on average) between each generation, genome-wise, so a rate of 0.16 mutations per genome per cell division corresponds to a rate of about 64 mutations per genome per human generation (as already mentioned above).

When discussing mutations, the natural follow-up question is, what proportion of mutations are likely to actually be harmful, neutral, or beneficial? Here's a paper which seeks to find hard numbers to answer that question: Direct Estimate of the Mutation Rate and the Distribution of Fitness Effects in the Yeast Saccharomyces cerevisiae . Yeast may seem a poor study subject in order to learn about mutations in humans and so forth, but despite their superficial similarity to other unicellular organisms like bacteria, yeast are actually eukaryotic organisms and have more in common, metabolically and genetically, with other eukaryotes (including humans) than they do with bacteria and other prokaryotes. This study found that in the Yeast being studied, the rate of *harmful* mutations was 1.1 x 10^-3 per genome per diploid cell division. Extrapolated to humans, the per generation rate of harmful mutations would be 0.92 (i.e. roughly one per human). The study also found that of the harmful mutations, 30-40% were lethal, whereas the other 60-70% were harmful in some way but did not completely prevent the cell which inherited it from developing or functioning.

Finally, although you ask about the mutation rate, and I've addressed that specific question, mutation rates alone are only one component of the rate of *evolution*, which might be what you're really asking about. Even with the same mutation rate, the rate of evolutionary change in various species depends heavily upon population sizes, survival pressures, reproductive rate, and a large number of other factors, and on the whole these factors make a much larger contribution towards rates of evolutionary change than does just the raw mutation rate.

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