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.
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.
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. Haeckels indiscretion
takes nothing away from the fact that embryonic development provides a great deal of information about the evolution of
More about Ernst Haeckel
Correcting Haeckels 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.
More on the peppered moth controversy