Modern Theory of Evolution

There is a modern theory of evolution. There are some things we have learned over the last 150 years since Charles Darwin first proposed his theory of "descent with modification."

Darwin's theory was amazingly accurate considering the state of scientific knowledge in 1859.

Darwin knew nothing of DNA or genes, backbones of the modern theory of evolution. He even leaned toward Lamarckism, the belief that traits developed during our lifetime would pass on to our children.

Nonetheless, The basics of Darwin's theory of evolution were exactly right and have passed every test with flying colors for 150 years:

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  • Nature's imperfect reproductive methods regularly produce mutations, so that there are always unique individuals.
  • Individuals which, as a result of those mutations, are better adapted to their environment will have more offspring, either because they survive more often or are better able to attract mates.
  • Those more suitable adaptations will be prone to spreading through an entire population.
  • Over time, as those adaptations accumulate, populations are modified into new species.
  • Given the immense amount of geologic time on this earth, this process, known as "natural selection," has produced all life on the earth from one or a few parents.

This basic idea of descent with modification has been backed up on every front. Here, however, are some of the new things that we've learned over the last 150 years.

DNA: The Book of Life

The modern theory of evolution is able to speak much more clearly about how evolution happens due to the discovery of DNA, the genetic code that controls all natural life.

Charles Darwin was able to say:

Therefore I should infer from analogy that probably all the organic beings which have ever lived on this earth have descended from some one primordial form, into which life was first breathed. (On the Origin of Species, ch. 14)

Darwin had to base that on the following similarities between all living things:

  • Common chemical composition
  • Common germinal vesicle (this is a nucleus that is formed when a cell begins to split in two)
  • Common cellular structure
  • Common laws of growth and reproduction

As an example of these commonalities, he cited a common reaction to poisons, so that a gall-fly's secretions creates the same growth on a wild rose as it does on an oak tree (ibid.).

From the modern theory of evolution we know that the similarities are far more than he could have imagined.

Every living cell has a common code, the simple 4-letter code of DNA, that controls its growth and reproduction. Every human, every insect, every plant, and every bacteria consists of cells made of proteins that are coded for by DNA.

All DNA is transferable. Some viruses, which are not even cells but mere snippets of DNA, have even been assimilated into human DNA during our evolutionary history (see Wikipedia, "Human Endogenous Retrovirus").

Even more interestingly, today insulin for diabetics is produced by taking human DNA and putting it in bacteria or yeast cells so that they produce the exact insulin that our bodies produce. Here's how the National Institutes of Health describes it:

Recombinant DNA is a technology scientists developed that made it possible to insert a human gene into the genetic material of a common bacterium. this "recombinant" micro-organism could now produce the protein encoded by the human gene. (From National Institutes of Health)

Whether you object to evolution or not, you have to admit that this method of insulin production is amazing.

The modern theory of evolution takes into account the genetic code, which Darwin could have known nothing about.

Punctuated Equilibrium

We'll cover punctuated equilibrium as the next aspect of the modern theory of evolution because it's so well known among anti-evolutionists.

Punctuated equilibrium is a theory developed in the 1970's by Stephen Jay Gould and Niles Eldridge. They publicized their theory as a drastic reformation of Darwinistic evolution, and young earth creationists loved it. They loved the description of high-speed evolution, and they loved the attack on traditional "gradualistic" Darwinism.

Unfortunately, it was not as drastic a reformation as Gould and Eldridge made it out to be.

Simply put, in the modern theory of evolution punctuated equilibrium (or "punk eek," as its opponents like to call it) says that species will tend to be stable for long periods, having adapted to their environment and their competition. Only when some change in the environment arises will the species begin to evolve again, and they will do so rapidly in response to new selection pressure (created by the change in environment).

Thus, Gould and Eldridge named it "punctuated" (periodic points of evolution) "equilibrium" (a general stability most other times).

The problem is, there's nothing really new about the idea except how far they took it. Even back in 1859, Darwin talked about evolution happening in a punctuated manner ("at long intervals"):

I do believe that natural selection will always act very slowly, often only at long intervals of time, and generally on only a very few of the inhabitants of the same region at the same time. I further believe, that this very slow, intermittent action of natural selection accords perfectly well with what geology tells us of the rate and manner at which the inhabitants of this world have changed.(ibid., ch. 4, emphasis mine)

Darwin "very slow" evolution is actually at least somewhat similar to Gould and Eldridge's very fast evolution. Both are talking about change occurring over thousands of years interrupted by even longer periods of stasis. Darwin calls the intermittent spurts slow, and Gould calls them fast. This has more to do with their reference points than a difference in idea. Ten thousand years to effect a change at the species level would have been a "long interval of time" to Darwin, but it was rapid to Gould, a modern scientist whose conception of geologic time scales would have been much larger (and much more accurate) than Charles Darwin's.

Gould and Eldridge did propose that evolution occurs faster than had been previously suggested, and they did suggest longer periods of stasis (stability without change). Nonetheless, punctuated equilibrium, while an addition to the modern theory of evolution, was no threat to Darwin's original theory.

Gene Expression

One very recent aspect of the modern theory of evolution actually gives a little credit to long-discredited Lamarckism.

It is not just our genes that control our development, but also how those genes are expressed. A recent issue of National Geographic explains:

Just as you don't need different words to write different books, so you don't need new genes to make new species: You just change the order and pattern of their use. (Matt Ridley, "Modern Darwins": February, 2009; p. 70)

The author provides several examples, one of which is:

The pattern of gene expression that builds the bones in [a paddlefish's] fins is much the same as the one that assembles the limb in the embryo of a bird, a mammal, or any other land-living animal. The difference is only that it is switched on for a shorter time in fish. (ibid., p. 71)

Matt Ridley's article is talking about DNA sequences that control the expression of specific genes; therefore, he is still talking about actual genetic changes. The modern theory of evolution is considering something still more unusual, however:

Recently, however, Lamarck's name has been creeping back into the scientific literature. The reason: an explosion in the field of epigenetics, the study of changes in genetic expression that are not linked to alterations in DNA sequences. Some of these epigenetic changes can be passed on to offspring in ways that appear to violate Mendelian genetics. (Robert Koenig, "Uphill Battle to Honor Monk Who Demystified Heredity"; Science, April 7, 2000, Vol. 288, Number 5463, p. 38)

This isn't quite Lamarckism, but the article is suggesting that changes to a parent's hormones can affect gene expression in offspring. In other words, changes in your health and fitness may affect the way your child's body uses the DNA you give it.

Summation of the Modern Theory of Evolution

Darwin's original theory is still intact. The modern theory of evolution just happens to give a lot more information on <strong><em>how </em></strong>evolution occurs.

  • We know now that <strong>every living cell of every living creature is programmed by the genetic code contained in the DNA of the cell</strong>. All life as we know it uses DNA, and DNA of one species can be moved to the cell of any other species. We are even using this truth to get bacteria and yeast to produce insulin for humans.
  • We know that evolution is not as constant as Darwin might have thought it was. Evolution tends to progress in surges as the environment changes, and those surges can be quite rapid from an evolutionary standpoint.
  • We are also learning that while DNA contains genes that programs the growth and development of all living things, there are other factors that influence gene expression. Even today we do not understand this fully, and the new science of epigenetics has taken on the task of learning about these factors.

Overall, though, the modern theory of evolution has only established and confirm Darwin's basic idea of descent with modification and left us marveling at his incredible insight into the progress and development of life on earth.

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