Keeping Up with the Times

Scientific ideas change with new evidence and increased technology. What was (and unfortunately in some cases still is) in the textbooks when some of us were in school is now considered passť. Here we include some particular cases in which keeping up to date with the science is essential in order to avoid causing student misconceptions by conveying our own.


Missing links
The incompleteness of the fossil record is a given. Neither every individual living thing nor every species of life is contained in the fossil record, let alone discovered for analysis. Evolutionary theory is concerned with seeing the patterns and understanding transitional forms, not with determining a pedigree for every living thing. Thus, the term, “missing link,” has no meaning when it comes to understanding the history of life.

Defining a reptile
Reptiles are commonly thought of as cold-blooded land-dwelling vertebrates with scales. However, a look at the tree displaying all animals we think of as reptiles includes a branch from the dinosaur line that we refer to as “birds.” So, the grouping we think of as reptiles is only valid if birds are included and that requires a considerable adjustment to our usual idea of what a reptile is.

Warm-blooded and cold-blooded classifications
Many textbooks group animals in terms of the temperature of their blood relative to their surroundings. “Birds and mammals” is a common example. This has problems. If we were to actually group animals that can control their internal temperature physiologically we would lump some tuna, some sharks, some moths, bees, and aardvarks into a nonsensical mess. While it is fine to refer to living things’ ability to regulate internal temperature, it is very misleading to classify on this basis.

Presenting Linnaean classification as phylogenetic
In many cases, Linnaean classification reflects actual phylogenetic lineages. However, Linnaeus had no clue about evolution and he had little information to work with other than gross anatomy. In the past century, scientists have learned much about the relationships of living things through lines of evidence that were unimaginable to scientists of the 18th century. So, many of the original groupings posed by Linnaeus are now known to be incorrect, based more on convergent evolution than on common ancestry. However, scientists still use the Linnaean system because of its convenience and there is no reason at this time to entirely toss it from the science curriculum.

Two or five kingdoms
Fifty years ago all living things were either plants or animals. This required shoehorning fungi into the plant kingdom and classifying ciliated protists as animals. A couple of decades later some scientists felt that a five-kingdom scheme would be more appropriate. The five-kingdom system solved some problems, but suffered from an inability to account for all living things. The most current attempt to draw a map of all of life abandons kingdoms in favor of flexible domains.

explore further View, and review, the three domains

Dogs and bears are related because they share similar features
The phrasing of this statement is misleading. It confuses evidence with cause. A better way to put this is to say, “Physical similarities between dogs and bears tell us that they are related.” Having similar features does not cause relatedness. Relatedness is due to having common ancestors and nothing more.

Haeckel’s embryos
Ernst Haeckel, a 19th century German biologist, noticed remarkable similarities in vertebrate embryos during their developmental stages. This is now known to be an important observation because these similarities reflect the common ancestry of vertebrates.

Unfortunately, Haeckel, apparently in his enthusiasm to make his point, modified the drawings of these embryos to make them appear more alike than they actually were. These fudged sketches (or versions derived from them) have appeared in many biology textbooks since then and have recently provided much fodder for antievolutionists. Haeckel’s indiscretion takes nothing away from the fact that embryonic development provides a great deal of information about the evolution of vertebrates.

explore further More about Ernst Haeckel

explore further Correcting Haeckel’s drawings in textbooks

The peppered moth
Many biology and life science textbooks use industrial melanism as an example of natural selection, displaying an illustration of the peppered moth undergoing evolution. Unfortunately, many of the textbook photographs of the moths consist of preserved specimens stuck to tree bark (If your textbook contains these photos, note that the wings of the moths may be in unnatural mounted positions.). This “faking” of moth distribution was used to test the likelihood of predation based on visibility of prey. However, this has also been set upon by antievolutionists as proof that evolution never happened. Industrial melanism, however, is a genuine phenomenon and the case of the peppered moth holds up well to scientific scrutiny. The population of dark moths did rise and fall in response to industrial pollution, and this was most striking in regions of the countryside with high rates of pollution.

explore further More on the peppered moth controversy

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