Saturday, December 20, 2008

Evolution and me: a personal story (part 8)

Part 8: Observing is believing?

In 1870, a shipment of nursery stock from China arrived in San Jose, California, carrying an unsuspecting menace that would cause devastation for farmers across Northern America. The small fruit-eating insect, now known as the San Jose scale, soon spread rapidly across United States and Canada, destroying orchid trees as it went. Carl Zimmer, in his book, Evolution, recounts the fascinating story behind this small pest (pages 241-243).

At first, farmers could totally eradicate outbreaks of the San Jose scale by spraying their crops with a mixture of sulphur and lime. However, by the turn of the century, a number of farmers began to realise that this pesticide was beginning to loose its potency; a few scales would survive the spraying and then breed rapidly. Farmers in Washington state were convinced that manufacturers were supplying poor quality pesticide, so they built their own factory to produce a 'pure' form of sulphur-lime. But even their home-made concoction failed to curb the spread of scales. The question was: why did such an effective pesticide became totally useless in just a few years?

Enter the entomologist A.L Melander. In 1912, after studying the San Jose scale problem, he realised that the scales were developing a resistance to the pesticide. How? His short answer was that evolution was happening.

The long answer is as follows:

  1. In the scale population, there were a few individuals that possessed a mutation that made them resistant to the sulphur-lime pesticide.
  2. Under normal circumstances, the mutation would remain in only a few individuals. However, when farmers started applying the pesticide, most of the non-resistant scales – initially comprising a majority of the population – were killed off. But the resistant scales carrying the mutation survived.
  3. The surviving individuals would then breed with each other and other non-resistant scales to produce resistant offspring. Over time, with consistent application of the pesticide killing off non-resistant scales, the mutation would spread throughout the entire population, eventually making the pesticide ineffective against a growing number of resistant scales.

This is a classic example of Darwin's theory of natural selection, beautifully expressed in an example that was experienced by many people. And this scenario has occurred many times in humankind's struggle against germs and insects. One only has to think about the constant need to change medications in order to combat Malaria, to recent scares over drug resistant strains of Tuberculosis. These and many other cases show that biological evolution does happen.

But there is one very valid objection in response to this. One can argue that all I'm describing here is microevolution, the small changes that occur within species, and what I've argued above does not support macroevolution, the large changes that result in new species.

My response to this? Watch this space . . .

Next post: The unbelievability of change
Return to the table of contents for 'Evolution and Me'

Wednesday, December 17, 2008

Evolution and me: a personal story (part 7)

Part 7: So . . . is evolution scientific?

Creationists are right: experimentation and observation are important aspects of science, but this is not the whole story. The process of developing ideas (known as hypotheses), making risky predications based on those hypotheses, and then testing these against physical observations, is what forms the foundation of science. This process, called hypothesis testing, is an integral part of the scientific method (see here, here and here). I find it quite strange that in all the creationist and apologetic books I have in my collection, not one of them mention hypothesis testing when discussing science.

Biological evolution, or the idea of common decent, is scientific because we can test it by making risky predictions about what patterns we should expect to observe in the natural world (i.e., in DNA, in the fossil record, in the anatomy of living animals, etc) if evolution were true. We can also, in principle, falsify evolution by thinking about what observations we would not expect to make if evolution was true.

Although an idea can be scientifically valid, this does not mean that it is a scientific fact. Many scientific ideas have failed testing by continuously disagreeing with physical observations. I have argued that evolution is scientific, but I will also argue in the following posts that evolution has been positively confirmed by such a wealth of data that it can be safely regarded as a scientific fact as per Stephen Jay Gould's definition.

But before I move on, I want to first list my sources. Most of the information that will inform these posts originates from the website TalkOrigins, in particular Douglas Theobald's 29 Evidences for Macroevolution. This paper is quite extensive, running to almost 270 pages, so if you are keen to read it in full you can download the PDF version here. Alternatively, for something less complex, you can visit the excellent site Understanding Evolution (thanks to Lui for bringing this to my attention). I will also draw on various books I've read over the years and will reference these in specific posts.

For those of you who want to read argument against my position, take a look at Answers in Genesis and TrueOrigins. In particular you can download a critique of 29 Evidences for Macroevolution here.

Finally, I want to stress the following: I’m not a philosopher, scientist, or biologist, so if you are an academic working in science, creationism, or evolution and you feel I've misrepresented your field of study, please let me know in the comments section, at least for the benefit of other readers. Everything I write on this blog is open to correction, and I really appreciate those who bring my mistakes to my attention. And I also welcome, and hope for, healthy and respectful debate in the next couple of posts.

Now that I have outlined my story of how I came to believe in biological evolution, and provided a brief outline of what science is, I will now jump straight into the specific evidences that convinced me.

And the first revolves around the question of why we struggle to keep insects off our crops . . .

Next post: Observing is believing?
Return to the table of contents for 'Evolution and Me'

Sunday, December 14, 2008

Evolution and me: a personal story (part 6)

Part 6: 1.7 seconds of arc

On the 29 May 1919, the world witnessed a total eclipse of the sun. The path of totality passed from northern Brazil, across the Atlantic Ocean and finally to Africa. The best place to view that eclipse was the island of Principe, off the West Coast of Africa. On that day, a small team of scientists sat huddled on the island around a bunch of telescopes, waiting to take photographs of the eclipse. The leader of the team was the astronomer Arthur Eddington, and the photograph he eventually took revolutionised our understanding of the universe.

When Albert Einstein published his general theory of relativity in 1915, he realised that, if his theory was a valid description of reality, we would expect to make particular and specific observations. His theory stated, for example, that gravity curves space. If this were true, Einstein thought, we would expect the sun's gravity to curve light from distant stars. In other words, if the sun moved in front of a specific star, that star would still be visible to us because its light would curve around the sun. Not only did Einstein's theory make this prediction, but he also used the theory to calculate the exact amount by which the sun's gravity would bend light. The answer: light would be deflected by 1.7 seconds of arc, less than one thousandth of a degree.

The 1919 eclipse (read this article for a full account) was the perfect opportunity to test this prediction, and although there is some doubt over Arthur Eddington's original calculations, the photograph he took proved that light from distant stars was deflected by the sun's gravity, by almost the exact amount which Einstein predicted. This result has been consistently confirmed many times over by many astronomers since 1919, and it stands as one of the many examples in science where a theory was tested and confirmed by empirical evidence.

In 1963, Karl Popper, probably the most well known contributor to the philosophy of science, published an article titled Science as Falsification. Drawing on the confirmation of Einstein's theory by the 1919 eclipse, Popper outlined, within just a few pages, his own view on what separates scientific ideas from non-scientific ideas. I suggest you read the entire paper here, but his main points are as follows:

  • It is easy to find confirmations for any kind of theory. So to determine the validity of a theory, we have find some way to test it.
  • Scientists test ideas by making risky predictions (i.e., examples of what evidence we would expect, and not expect, to observe in the world around us if a specific theory is correct). In the example above, Einstein's prediction was that the sun's gravity would bend light, but he made it a risky prediction by calculating by how much it would bend: by 1.7 seconds of arc.
  • By testing a theory in this way, we make it possible to refute (i.e., to falsify) the theory. For example, if we observed that light was not deflected by the sun, then Einstein's theory would be invalidated. According to Popper, a theory which is not refutable, at least in principle, by any conceivable event is non-scientific (solipsism is an example of a 'theory' that is irrefutable and thus non-scientific).

In other words, a theory is scientific if it makes risky predictions that can be tested against physical observations, and is thus liable to falsification.

This is just a basic outline of what makes a theory scientific. For a much more overall and comprehensive description of science as a method, read here.

Next post: So . . . is evolution scientific?
Return to the table of contents for 'Evolution and Me'

Sunday, December 07, 2008

Evolution and me: a personal story (part 5)

Part 5: Two initial observations

What is science? I know this question cannot be satisfactorily summarised in one or two blog posts. But I will try my best to provide a brief, and thus probably inadequate, response. And my answer will draw upon the story of a young man who, in 1919, was incredibly intrigued by a solar eclipse.

But before I explore his story, I just want to highlight two things I initially observed when I started reading up on the whole evolution/creationism debate:

  • At first, I was struck by a seemingly unsolvable dilemma: both sides of the debate claim to have 'scientific evidence' for their respective views. TalkOrigins has pages and pages of claimed evidence for evolution, so does Answers in Genesis for creationism. So how could I decide between the two?
  • Creationists often argue that biological evolution is not scientific. This article, for example, argues that macroevolution cannot be scientific because it does not adequately meet the criteria of science (i.e., the criteria of experimentation and observation). Macroevolution cannot be observed, the argument goes; thus evolution is not science.

When I started reading up on the philosophy of science, I slowly realised two important things related to the points above: (1) that not all evidence is of equal quality, and (2) there is a lot more to science that creationists let on.

There is some debate, especially amongst philosophers of science, over what actually constitutes science. I will not cover all differing views (read here to find out more), but in the context of this series I will adopt a pragmatic view of science that most scientists are probably familiar with.

And one of the chief founders of this view was the young man I alluded to in the beginning of this post, a man whose answer – to the question of how one can determine if an idea is scientific or not – was inspired by astronomer Arthur Eddington's observations of the 1919 eclipse; observations that resulted in a confirmation of Einstein's general theory of relativity.

This man was Karl Popper, and I will cover his story in the next post . . .

Next post: 1.7 seconds of arc
Return to the table of contents for 'Evolution and Me'