Notes from a first Evolution Lecture

Whilst pouring through old files (and trying to re-organize them) the other day, I came across a manila folder labeled 'Evolution Lecture Notes'. Curious, I opened it up to find sheets that I had used to prepare my first ever lecture on evolution - when I was teaching O-level Biology, in 1974. This was as part of my (then) Peace Corps assignment, at a secondary school in the north of Barbados

The notes were interesting and intriguing, not only for being the first used for a teaching assignment, but because I had used them to answer student questions - then, and in later years in other venues. They were also interesting in that word of my evolution teaching had spread round the school and reached the ears of two Scripture teachers. They then challenged me to a debate, which I happily agreed to. Provided they allow me double the presentation and rebuttal time - to equalize their numbers!

Anyway, the part of the notes that is likely most apropos here, for a short space, has to do with the questions that were asked and the answers I gave. I still find these answers as good then as now, but agree if I were to redo them I'd had many more details to do with the genetics and micro-biology. (The prospective redone parts are given in italics)

So let's start the ball rolling. In each case a student question is numbered and given in black, and then my response to follow.


1. Evolution states that advanced life came from non-life - how can this be?

Actually, the theory of evolution says no such thing, but this is a common error. The concept of life possibly arising from non-life is the theory (actually more hypothesis) of noogensis.

What evolution says is that incremental changes to proteins, and genetic structures are made over time which then become passed on by a process of natural selection to successive generations of an organism. The attributes passed on generally confer a survival advantage.

2. Can you give an example?

Sure! The success of natural selection is measured by the fitness (w) and the selective value (s): E.g. w = 1 – s

As an illustration, consider a German cockroach species with allele D, where D denotes resistance to the pesticide dieldrin, and d denotes non-resistance.

In the population after some defined time, let three genotypes be exhibited in the population: DD, Dd and dd. Now, on average over time let each dd and Dd individual produce one offspring, and each DD produce two. These average numbers can be used to indicate the genotype’s absolute fitness and to project the changes in gene frequency over succeeding generations.

The relative fitness (w) is meanwhile given by:

w = 1 for DD

w = 0.5 for Dd

w = 0.5 for dd

The selection values, relative measures of the reduction of fitness for each genotype, are given respectively by:

s = 1 – 1 = 0 for DD

s = 1 – 0.5 = 0.5 for Dd

s = 1 – 0.5 = 0.5 for dd

As we expect, the dieldrin-resistant genotype displays zero reduction in fitness, and hence maximum survival rate. By contrast the d- allele can be regarded as ‘deleterious’. Evolution in this case favors the replication of all those German roaches with genotype DD. Those others (dD, dd) will die out at disproportionate rates. As they die out, therefore, only the hardiest DD genotypes will remain.

Indeed, it can be shown that over successive generations of these roaches the gene frequency (of d) will decrease by:

delta q = -s p q^2 / (1 - sq^2)

where p denotes the frequency of the favored allele, and q the frequency of the "disadvantaged" or "deleterious" allele. Fixing ideas, let's say at a particular time that a gene frequency "snap shot" of the (German) cockroach population under study yields: p(D) = 0.60, q(D) = 0.40. i.e. the favored allele is reproducing at the ratio 3:2 relative to the deleterious one, d.

Assume as before that s = 0.50. A simple table can be constructed (via successive iterations of the previous formula) showing the declining gene frequency of d relative to D:

The Table has headers:

p ---- q -----q^2 -------delta q

Where the 2nd quantity is the one to keep an eye on. The first couple entries - row by row are:

0.60 ----- 0.40-----0.16----- (-0.13)

0.73-------0.27 -----(0.073)----(-0.10)

Each new (delta q) of course feeds back to reduce q in the next iteration. Thereby the loss of 'd' genes through selection is balanced by the gain of the 'D' genes that confer reproductive advantage. This example is based on a starting mutation, but others can be invoked to show how a sipmle minor adaptive change in structure and function - can directly lead to a permanent structure, e.g. the bacterial flagellum - as Watson noted.

Similar evolutionary advantage can be see with the mutations of the influenza virus, which is also why flu vaccines have to be changed each year. The influenza virus change is a perfect example of evolution in action.

3. Don't you assert a tiny probability for any given step happening?

Not at all. another misgiving and misunderstanding. As you can see using the preceding example of the German cockroach, all that is needed is for the gene frequency associated with the favored allele (in this case, DD) to constantly increase relative to the disfavored ones. This happens automatically as the less-favored die out over time, and following the table above shows this. Hence, probabilities are not fixed, say like that to achieve a royal flush in poker, but can be enhanced by the dynamics of the fitness-change.

The error of many creationists is to assume all evolutionary probabilities are fixed, and all are remote. An example often given (misplaced) is the likelihood of taking a Jet apart and having it come back together by itself. This is erroneous since the Jet is already a manufactured item. Hence if one disassembles it there is zero probability of its reconstruction unless extraneous factors are inserted. Like a team of Jet builders!

Natural selection works differently, in that certain features of living things are already selected for then their repetition is enhanced via reproduction. It is not the same at all. In fact, the increased probability is usually already set once a single simple change occurs. This usually starts with micro-evolution. Micro-evolution implies an incremental change in a small proportion of DNA.

Examples of micro-evolution include the re-arrangement of amino acids in proteins such as haemoglobin, or the altered genes for a specific genetic character in successive generations of the fruit fly. For example:

Generation I (AMINO ACID SEQUENCE): FF BBB EE DDD KK
Generation XXIII (AMINO ACID SEQUENCE): KK BBB DD DDE FF EE

(N.B. Each capital letter denotes a particular complex of ~ 10,000 arrangements of A( adenine), G(guanine) , T (thymine) and , C(cytosine)

The preceding illustration discloses re-arrangement of the amino acid sequence, by base substitution, in a succeeding generation of for fruit flies. Such re-arrangement is prima facie evidence for species micro-evolution, i.e. at the microscopic level of observation characterizing genes and amino acids.

4. Why are there no missing links?

"Missing link" is a common erroneous term. It implies there is one and only one transitional species leading from a common ape-human ancestor to humans. This is the wrong end of the stick. In fact, what we are dealing with is a series or sequence of transitional links that have occurred over the past 6-8 million years. The most recent of these finds (and most distant ancestor) was "ardis" described in an earlier blog entry. There are doubtless dozens of others in the fossil record before him -her.

Why so hard to find? Not because evolution is "wrong" but because the Earth's crust is dynamic. It is not one solid mass but composed of over 15 tectonic plates which continually shift, move and crush up against each other. It is a wonder, given that, we have managed to find any fossils. Bear in mind here: evidence of absence is not absence of evidence!

For this reason, the prima facie evidence of evolution doesn't rest on fossils alone but on genetics.

For example: ·

We know humans and chimpanzees have the exact same cytochrome- c protein sequence. In the absence of common (evolutionary) descent, the chance of this occurrence is conservatively less than 10^-93 (1 out of 10^93). Thus, the high degree of similarity in these proteins is a spectacular corroboration of the theory of common descent.

Furthermore, human and chimpanzee cytochrome- c proteins differ by ~10 amino acids from all other mammals. The chance of this occurring in the absence of a hereditary mechanism is less than 10^29. The yeast Candida krusei is one of the most distantly related eukaryotic organisms from humans. Candida has 51 amino acid differences from the human sequence. A conservative estimate of this probability is less than 10^-25.

In terms of the genetic aspect, we know from the chimp-human chromosome studies (first published in Science; Vol. 215, p. 1525, 1982 by O. Prakash and J; Yunis. ) that a remarkable homology exists between chimp and human chromosomes when heterochromatin is excluded. They found no less than thirteen IDENTICAL chromosome pairs, that included chromosomes: 3, 6-8, 10, 11, 13, 14, 19-22, and XY.


The next question was not in the original set but is added here, since it appears to have become a huge issue with the creationist crowd:

5. Doesn't the 2nd law of thermodynamics prohibit evolution? If the second law asserts everything is winding down and getting more disorderly, how can you have more orderly and advanced biological organisms?


This is directly a result of misinterpretation of the 2nd law. Strictly speaking the law states:

Entropy (the state of disorder) will tend to increase over time in any closed system.

The last part is very crucial but it is exactly the part that the creationist crowd omits, which renders their question a non-starter.

The reason is that neither the Earth nor its biological systems are "closed" systems, hence do not exhibit constantly increasing disorder.

The Earth, for example, is open to the radiant energy of the Sun and receives some 1360 watts per square meter. Plants on the Earth are likewise OPEN to solar energy, and receive it and then use it in the process of photo-synthesis. Other oganisms eat the plants and thereby incorporate that energy into themselves.

Thus, the path is cleared for higher organizational development and speciation.

We do not see a constant wind-down because all these systems are OPEN, not closed.

Hopefully, readers will find the above answers intriguing and thought -provoking.