Common Misconceptions about Evolution

Evolution can occur without morphological change; and morphological change can occur without evolution. Humans are larger now than in the recent past, a result of better diet and medicine. Phenotypic changes, like this, induced solely by changes in environment do not count as evolution because they are not heritable; in other words the change is not passed on to the organism's offspring. Phenotype is the morphological, physiological, biochemical, behavioral and other properties exhibited by a living organism. An organism's phenotype is determined by its genes and its environment. Most changes due to environment are fairly subtle, for example size differences. Large scale phenotypic changes are obviously due to genetic changes, and therefore are evolution.

Evolution is not progress. Populations simply adapt to their current surroundings. They do not necessarily become better in any absolute sense over time. A trait or strategy that is successful at one time may be unsuccessful at another. Paquin and Adams demonstrated this experimentally. They founded a yeast culture and maintained it for many generations. Occasionally, a mutation would arise that allowed its bearer to reproduce better than its contemporaries. These mutant strains would crowd out the formerly dominant strains. Samples of the most successful strains from the culture were taken at a variety of times. In later competition experiments, each strain would outcompete the immediately previously dominant type in a culture. However, some earlier isolates could outcompete strains that arose late in the experiment. Competitive ability of a strain was always better than its previous type, but competitiveness in a general sense was not increasing. Any organism's success depends on the behavior of its contemporaries. For most traits or behaviors there is likely no optimal design or strategy, only contingent ones. Evolution can be like a game of paper/scissors/rock.

Organisms are not passive targets of their environment. Each species modifies its own environment. At the least, organisms remove nutrients from and add waste to their surroundings. Often, waste products benefit other species. Animal dung is fertilizer for plants. Conversely, the oxygen we breathe is a waste product of plants. Species do not simply change to fit their environment; they modify their environment to suit them as well. Beavers build a dam to create a pond suitable to sustain them and raise young. Alternately, when the environment changes, species can migrate to suitable climes or seek out microenvironments to which they are adapted.

What is Evolution?

Evolution is a change in the gene pool of a population over time. A gene is a hereditary unit that can be passed on unaltered for many generations. The gene pool is the set of all genes in a species or population.

The English moth, Biston betularia, is a frequently cited example of observed evolution. [evolution: a change in the gene pool] In this moth there are two color morphs, light and dark. H. B. D. Kettlewell found that dark moths constituted less than 2% of the population prior to 1848. The frequency of the dark morph increased in the years following. By 1898, the 95% of the moths in Manchester and other highly industrialized areas were of the dark type. Their frequency was less in rural areas. The moth population changed from mostly light colored moths to mostly dark colored moths. The moths' color was primarily determined by a single gene. [gene: a hereditary unit] So, the change in frequency of dark colored moths represented a change in the gene pool. [gene pool: the set all of genes in a population] This change was, by definition, evolution.

The increase in relative abundance of the dark type was due to natural selection. The late eighteen hundreds was the time of England's industrial revolution. Soot from factories darkened the birch trees the moths landed on. Against a sooty background, birds could see the lighter colored moths better and ate more of them. As a result, more dark moths survived until reproductive age and left offspring. The greater number of offspring left by dark moths is what caused their increase in frequency. This is an example of natural selection.

Populations evolve. [evolution: a change in the gene pool] In order to understand evolution, it is necessary to view populations as a collection of individuals, each harboring a different set of traits. A single organism is never typical of an entire population unless there is no variation within that population. Individual organisms do not evolve, they retain the same genes throughout their life. When a population is evolving, the ratio of different genetic types is changing -- each individual organism within a population does not change. For example, in the previous example, the frequency of black moths increased; the moths did not turn from light to gray to dark in concert. The process of evolution can be summarized in three sentences: Genes mutate. [gene: a hereditary unit] Individuals are selected. Populations evolve.

Evolution can be divided into microevolution and macroevolution. The kind of evolution documented above is microevolution. Larger changes, such as when a new species is formed, are called macroevolution. Some biologists feel the mechanisms of macroevolution are different from those of microevolutionary change. Others think the distinction between the two is arbitrary -- macroevolution is cumulative microevolution.

The word evolution has a variety of meanings. The fact that all organisms are linked via descent to a common ancestor is often called evolution. The theory of how the first living organisms appeared is often called evolution. This should be called abiogenesis. And frequently, people use the word evolution when they really mean natural selection -- one of the many mechanisms of evolution.

Suggested Further Reading

An excellent, detailed exposition of the means by which the Earth's age is known, as well as the history of attempts to estimate that value, is given in Dalrymple (1991) . This book is a must-read for anyone who wishes to critique mainstream methods for dating the Earth. A review of this book in the young-Earth creationist journal Origins ( Brown 1992 ) includes the following text:

"Dalrymple makes a good case for an age of about 4.5 billion years for the material of which the Earth, Moon, and meteorites are composed. [...] His treatment in The Age of the Earth has made it much more difficult to plausibly explain radiometric data on the basis of a creation of the entire Solar System, or the physical matter in planet Earth, within the last few thousand years. In my opinion, the defense of such a position is a losing battle."

(Note: R.H. Brown believes life on Earth and the geological column to be young, but argues that a proper reading of Genesis allows the Earth itself to be much older.)

For those who wish to develop more than a layman's understanding of radiometric dating, Faure (1986) is the prime textbook/handbook on the topic.

There are several shorter works which describe creationist "dating" methods and/or creationist challenges to mainstream dating methods. The best in my opinion is Dalrymple (1986) . Brush (1982) and Dalrymple (1984) are also very good.

Writings by old-Earth creationists demonstrate that argument for an old Earth is quite possible without "assumption of evolution." The best few are Stoner (1992) , Wonderly (1987) , and Young (1982) . In addition, Wonderly (1981) , Newman & Eckelmann (1977) , and Wonderly (1977) are also good.

And, of course Strahler (1987) covers the entire creation/evolution controversy (including all of the topics discussed here) in a reasonable level of detail and with lots of references.

Accumulation of metals into the oceans

In 1965, Chemical Oceanography published a list of some metals' "residency times" in the ocean. This calculation was performed by dividing the amount of various metals in the oceans by the rate at which rivers bring the metals into the oceans.

Several creationists have reproduced this table of numbers, claiming that these numbers gave "upper limits" for the age of the oceans (therefore the Earth) because the numbers represented the amount of time that it would take for the oceans to "fill up" to their present level of these various metals from zero.

First, let us examine the results of this "dating method." Most creationist works do not produce all of the numbers, only the ones whose values are "convenient." The following list is more complete:

Accumulation of meteoritic dust on the Moon

The most common form of this young-Earth argument is based on a single measurement of the rate of meteoritic dust influx to the Earth gave a value in the millions of tons per year. While this is negligible compared to the processes of erosion on the Earth (about a shoebox-full of dust per acre per year), there are no such processes on the Moon. Young-Earthers claim that the Moon must receive a similar amount of dust (perhaps 25% as much per unit surface area due to its lesser gravity), and there should be a very large dust layer (about a hundred feet thick) if the Moon is several billion years old.

Decay of the Earth's magnetic field

The young-Earth argument: the dipole component of the magnetic field has decreased slightly over the time that it has been measured. Assuming the generally accepted "dynamo theory" for the existence of the Earth's magnetic field is wrong, the mechanism might instead be an initially created field which has been losing strength ever since the creation event. An exponential fit (assuming a half-life of 1400 years on 130 years' worth of measurements) yields an impossibly high magnetic field even 8000 years ago, therefore the Earth must be young. The main proponent of this argument was Thomas Barnes.

There are several things wrong with this "dating" mechanism. It's hard to just list them all. The primary four are:

1.While there is no complete model to the geodynamo (certain key properties of the core are unknown), there are reasonable starts and there are no good reasons for rejecting such an entity out of hand. If it is possible for energy to be added to the field, then the extrapolation is useless.


2.There is overwhelming evidence that the magnetic field has reversed itself, rendering any unidirectional extrapolation on total energy useless. Even some young-Earthers admit to that these days -- e.g., Humphreys (1988).


3.Much of the energy in the field is almost certainly not even visible external to the core. This means that the extrapolation rests on the assumption that fluctuations in the observable portion of the field accurately represent fluctuations in its total energy.

4.Barnes' extrapolation completely ignores the nondipole component of the field. Even if we grant that it is permissible to ignore portions of the field that are internal to the core, Barnes' extrapolation also ignores portions of the field which are visible and instead rests on extrapolation of a theoretical entity.
That last part is more important than it may sound. The Earth's magnetic field is often split in two components when measured. The "dipole" component is the part which approximates a theoretically perfect field around a single magnet, and the "nondipole" components are the ("messy") remainder. A study in the 1960s showed that the decrease in the dipole component since the turn of the century had been nearly completely compensated by an increase in the strength of the nondipole components of the field. (In other words, the measurements show that the field has been diverging from the shape that would be expected of a theoretical ideal magnet, more than the amount of energy has actually been changing.) Barnes' extrapolation therefore does not really rest on the change in energy of the field.

How Old Is The Earth, And How Do We Know?

he generally accepted age for the Earth and the rest of the solar system is about 4.55 billion years (plus or minus about 1%). This value is derived from several different lines of evidence.

Unfortunately, the age cannot be computed directly from material that is solely from the Earth. There is evidence that energy from the Earth's accumulation caused the surface to be molten. Further, the processes of erosion and crustal recycling have apparently destroyed all of the earliest surface.

The oldest rocks which have been found so far (on the Earth) date to about 3.8 to 3.9 billion years ago (by several radiometric dating methods). Some of these rocks are sedimentary, and include minerals which are themselves as old as 4.1 to 4.2 billion years. Rocks of this age are relatively rare, however rocks that are at least 3.5 billion years in age have been found on North America, Greenland, Australia, Africa, and Asia.

While these values do not compute an age for the Earth, they do establish a lower limit (the Earth must be at least as old as any formation on it). This lower limit is at least concordant with the independently derived figure of 4.55 billion years for the Earth's actual age.

The most direct means for calculating the Earth's age is a Pb/Pb isochron age, derived from samples of the Earth and meteorites. This involves measurement of three isotopes of lead (Pb-206, Pb-207, and either Pb-208 or Pb-204). A plot is constructed of Pb-206/Pb-204 versus Pb-207/Pb-204.

If the solar system formed from a common pool of matter, which was uniformly distributed in terms of Pb isotope ratios, then the initial plots for all objects from that pool of matter would fall on a single point.

Over time, the amounts of Pb-206 and Pb-207 will change in some samples, as these isotopes are decay end-products of uranium decay (U-238 decays to Pb-206, and U-235 decays to Pb-207). This causes the data points to separate from each other. The higher the uranium-to-lead ratio of a rock, the more the Pb-206/Pb-204 and Pb-207/Pb-204 values will change with time.