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introduction to darwin: lecture 3

This lecture asks students to think a little about Darwin. A number of questions are posed

• What is evolution? What is it that is evolving?
• What is the difference between microevolution and macroevolution
• What has natural selection got to do with evolution?
• why don't plants walk? why don't pigs have wings?
• why do whales have legs?
• Why can't humans and some primates synthesise vitamin C?
• Why do we have multiple copies of some genes?
• Why don't common ancestors reappear?
• why are there living fossils, such as coelacanths, lungfish, and tuatara?
• Given that humans/chimps take about 5,000 days to reach sexual maturity compared to 50 days or so for rats and mice, why aren't these rodents 'more evolved' than humans?
• if it is incredibly rare for the first proto-eye or wing to appear, why does that juvenile survive to breed when most juveniles die before breeding?
• How can the theory of evolution and faith in God the Creator both be true?

What is evolution? What is it that is evolving?

In The Greatest Show on Earth (it is on p33 of the "Dogs, Cows, and Cabbages" chapter in my paperback copy) Professor Dawkins writes "There is no intrinsic tendency in gene pools for particular genes to increase or decrease in frequency. But when there a systematic increase or decrease in the frequency with which we see a particular gene in a gene pool, that is precisely and exactly what is meant by evolution."

This is not what is meant by evolution in this course. Nothing of Darwin survives in the Dawkins definition

First, natural selection, absolutely central to the Darwinian account of evolution is not required. Artificial selection will do. For example, according to Professor Dawkins, Hitler's attempts to breed a master race by breeding tall, athletic blond haired blue eyed Aryan males with similar Aryan females and sterilising "inferior" breeds, counts as human evolution. Dog breeding counts as dog evolution.

Second, such an increase or decrease in gene (technically, allele) frequency may reflect natural selection in response to a temporary change in the environment (for example an ice age). It may even represent a period of increased mortality in a particular population with a patchy distribution of a certain gene. For example, it may be that blue eyed tuits tend to live near the top of a volcano. Should the volcano enter an active phase lasting a century or more, then the proportion of blue eyed tuits in the population may fall as the blue eyed sub-population has an increased mortality due to molten lava running into their burrows periodically. However, once the volcano settles down it may be that a century of flooding causes causes many of the tuits living by the lakeside, who are predminantly green eyed, to die.

None of the ice age, the volcano, or the floods are what we mean by "evolution"

Evolution is something quite different. Species evolve, not genes. Evolution is descent with modification.

Species evolve by developing new inherited features which become characteristic of the species. Using humans as an example, if one human in a million could fly, that would not represent evolution until one human in a million could not fly. The exact proportion is not important. What is important is the appearance of something new, and inherited, which comes to be present in almost all members of the species

The second thing we want from evolution is extinction and branching. Using humans as an example once again, we expect humans to become the (extinct) common ancestor of two future species, neither of which can breed with the other, and neither of which could breed with humans (if there were any left)

The approach in this course at this stage is to accept, provisionally, the Darwinian view that natural selection is necessary for evolution, but is not sufficient for evolution. So, no natural selection, no evolution. But just because natural selection is occuring does not not mean that a species is evolving. The classic example in evolutionary biology is the pepper moth. The following quote is lifted from the Wikipedia entry 'peppered moth evolution' (http://en.wikipedia.org/wiki/Peppered_moth_evolution).

The evolution of the peppered moth over the last two hundred years has been studied in detail. Originally, the vast majority of peppered moths had light colouration, which effectively camouflaged them against the light-coloured trees and lichens which they rested upon. However, because of widespread pollution during the Industrial Revolution in England, many of the lichens died out, and the trees that peppered moths rested on became blackened by soot, causing most of the light-coloured moths, or typica, to die off from predation. At the same time, the dark-coloured, or melanic, moths, carbonaria, flourished because of their ability to hide on the darkened trees.

Since then, with improved environmental standards, light-coloured peppered moths have again become common

Ultimately, you will make up your own minds as to whether this to and froing of allele frequencies counts as evolution in the sense Darwin used the term.

What is the difference between microevolution and macroevolution

Professor Coyne in Why Evolution is True (pages 32-33) defines micreovolution as "minor changes in size and shape over time" and macroevolution as "the idea that one very different kind of plant or animal can come from another"

In this course microevolution means evolution at the species level or below

Macroevolution means evolution at levels above the species. So the split of birds from the dinosaur lineage is macroevolution.

What has natural selection got to do with evolution?

The Darwinian answer is 'almost everything'. Darwinians allow genetic drift (random fluctutations of allele frequency in small populations) a role, but that is essentially it.

However, natural selection does not account for speciation.

Nor does natural selection explain changes to ontogeny (the embryological development of a species).

The central role accorded to natural selection in Darwinian theory has never had universal support. It was not accepted by Darwin's peers. An alternative view is that organisms "co-construct and coeveolve with their environments" ( Click here for a link)

why don't plants walk? why don't pigs have wings?

It does seem that some evolutionary futures are closed to a species. In particular it seems that evolution can't run backwards to a common ancestor, much less back to a common ancestor and then forward from that common ancestor. For example, it seems that no mammal will ever develop the ability to photosynthesize.

why do whales have legs?

Professor Coyne in Why Evolution is True (pages 47-52) discusses this question at some length. He adopts the standard line that the ancestors of whales left the sea with other tetrapods, and then returned to the sea at which time legs were no longer useful. He adopts what is essentially a Darwinian reworking of the Lamarckian use-disuse idea in suggesting that natural selection promoted movement towards vestigial legs as this was a more efficient use of the whale's metabolic resources. i.e forming legs was a waste of effort so mutations that produced shorter legs had a selective advantage.

Why can't humans and some primates synthesise vitamin C?

Professor Coyne in Why Evolution is True (pages 67-69) writes that the production of vitamin C from glucose requires four genes, each coding for a different protein. Humans and some primates share a specific mutation in the fourth gene of the series. He says that mutation occurred about 40 million years ago.

It is important to be clear as to exactly what Professor Coyne is asserting here. He is saying that there is a single individual animal (the one in whom the mutation occured) that is the direct ancestor of all living gorillas, orang-utan, chimpanzees, and humans today. He is also saying that the mutated copy of that gene (and not the 'good' copy on the individual's other chromosome of that pair) was passed to all offspring with surviving descendants. This is a strong claim which tests the limits of plausibility, especially as it is unclear what reproductive advantage accrues from a reliance on dietary sources of vitamin C.

Why do we have multiple copies of some genes?

Professor Coyne in Why Evolution is True (page 211) points out that chimps have only copy of the gene that codes for the salivary enzyme amylase (which breaks down dietary starch into digestible sugar) while humans have between 2 and 16, average 6 copies. He suggests that the ancestral human diet must have been much richer in starch than that of other great apes.

why don't common ancestors reappear?

In his chapter 'The Ark of the Continents' in The Greatest Show on Earth Professor Dawkins provides a well written standard account of how various species, having made the highly unlikely trip from the mainland to the Galapagos Islands, then made the shorter but non-trivial journeys to the various islands in that group. These various island populations remained (for practical purposes) reproductively isolated from each other, and the result has been a proliferation of new species.

For example, each island has its own species of giant tortise.

Each of these species is a progression away from the ancestors of the mainland tortise which first made it to one of the Galapagos Islands.

Why is none of these species a regression from the land tortise towards its ancestors?

The standard Darwinian answers are pretty much forced.

My underlying question is this. Can the Darwinian response be tested? Is it falsifiable? If not, is it scientific or mere speculation?

why are there living fossils, such as coelacanths, lungfish, and tuatara?

It seems that there are evolutionary dead ends. This is inconsistent with the Darwinian theory.

Given that humans/chimps take about 5,000 days to reach sexual maturity compared to 50 days or so for rats and mice, why aren't these rodents 'more evolved' than humans?

This depends on what one means by 'more evolved'.If mutations are still appearing in the genomes of rats and mice and if natural selection is still operating on those mutations then 'more evolved' may be a meaningless phrase.

if it is incredibly rare for the first proto-eye or wing to appear, why does that juvenile survive to breed when most juveniles die before breeding?

That juvenile has a comparable risk of juvenile mortality to his or her birth cohort.

This is a significant problem for Darwin's theory

How can the theory of evolution and faith in God the Creator both be true?

Darwin didn’t see any conflict between the “fact” of Biblical truth and the “fact” of evolution by descent from a common ancestor.

Revelatory truth is an internal thing. If it could be tested and falsified in a scientific way it would change its nature, becoming a matter of reason rather than one of faith.

Revealed truth will still be revealed truth in two hundred years.

Scientific truth is a relative thing. It is not absolute. It is provisional, always just one (confirmed) experiment away from being overturned. Our understanding of the theory of evolution by natural selection is quite different to the theory as outlined by Charles Darwin. In 200 years time the “fact” of evolution by common descent will be understood quite differently from the way it is today. That is the nature of science.

I believe that creationists make what philosophers call a category error when they claim that the literal truth of Genesis can be scientifically proven. That truth is a revelatory truth and it would cease to be so were it proven scientifically.