The Evidence for Evolution

 

          Let us begin this discussion with a definition(s) of the word and concepts of evolution.  But also, review the following website, which gives a very comprehensive narrative on the evidence for evolution: http://www.teachthemscience.org/evidence .

Dictionary.com’s definition of “evolution.”:

 change in the gene pool of a population from generation to generation by such processes as mutation, natural selection, and genetic drift.

Medical Dictionary:

 a: the historical development of a biological group (as a race or species) : PHYLOGENY b : a theory that the various types of animals and plants have their origin in other preexisting types and that the distinguishable differences are due to modifications in successive generations

Science Dictionary:

The process by which species of organisms arise from earlier life forms and undergo change over time through natural selection. The modern understanding of the origins of species is based on the theories of Charles Darwin combined with a modern knowledge of genetics based on the work of Gregor Mendel. Darwin observed there is a certain amount of variation of traits or characteristics among the different individuals belonging to a population. Some of these traits confer fitness—they allow the individual organism that possesses them to survive in their environment better than other individuals who do not possess them and to leave more offspring. The offspring then inherit the beneficial traits, and over time the adaptive trait spreads through the population. In twentieth century, the development of the the science of genetics helped explain the origin of the variation of the traits between individual organisms and the way in which they are passed from generation to generation. This basic model of evolution has since been further refined, and the role of genetic drift and sexual selection in the evolution of populations has been recognized. See also natural selection, sexual selection.

Our Living Language : Darwin’s theory of evolution by natural selection assumed that tiny adaptations occur in organisms constantly over millions of years. Gradually, a new species develops that is distinct from its ancestors. In the 1970s, however, biologists Niles Eldridge and Stephen Jay Gould proposed that evolution by natural selection may not have been such a smooth and consistent process. Based on fossils from around the world that showed the abrupt appearance of new species, Eldridge and Gould suggested that evolution is better described through punctuated equilibrium. That is, for long periods of time species remain virtually unchanged, not even gradually adapting. They are in equilibrium, in balance with the environment. But when confronted with environmental challenges—sudden climate change, for example—organisms adapt quite quickly, perhaps in only a few thousand years. These active periods are punctuations, after which a new equilibrium exists and species remain stable until the next punctuation.

Summary

These definitions agree that new species derive naturally from the modification of older species.  They differ as to the rates, e.g. gradual versus quite quickly.  Some definitions emphasize Darwin’s theory, e.g. over time the natural selection of those  gradually acquired variations that were the most reproductively fit.  One definition notes the role of genetics in variation.  But nobody has seen one species become another.  Two questions arise.  What is the evidence that a species has descended from an older species? The other question asks if the new species has been designed.  The first question might be posed by a creationist, the second by a proponent of Intelligent Design.

The Fossil Record

To provide evidence for speciation from older life forms, I turn to Kenneth Miller’s Only a Theory: Evolution and the Battle for America’s Soul.[1]In it, Miller, a Professor of Biology at Brown University, discusses the fossil record’s record of Life’s dramatic changes over millions of years.  He notes the sequential  character of the appearances of Life forms, a pattern beginning with bacteria and single celled algae and lasting two billion years.  With the Ediacaran period 570 million years ago, the first complex organisms appeared.  The closely following Cambrian explosion, lasting 30 million years, brought forth a plethora of ancestors to many of today’s phyla.  It is this paleontological record that Eldridge and Gould refer to as they write about Punctuated Equilibrium.  But the fossil record has plenty of examples of Darwin’s gradual change in speciation.

Miller turns to the evolution of the horse to illustrate more closely the gradual and sequential movement from older to more modern forms.  The earliest horses appeared 55 million years ago in the rich fossil sediments of North America.  The family tree includes some 3 dozen extinct genera and narrows down to a single genus, Equus, which include the modern horse, donkey, and zebra.  There is no question here that older forms morphed into new ones. 

Genetic Evidence for Evolution

Perhaps the most compelling evidence for evolution, the descent of life forms from previous forms, lies in the gene records.  Miller provides a most graphic and definite finding to support the idea that humankind and primates share a common ancestor, e.g. are descendant cousins.[2]  He writes that scientists have long known that Primates have 48 chromosomes, and humans 46.  Hypothesizing that there had been a fusion of two  primate chromosomes, they discovered that human chromosome 2  indeed demonstrated 2 telomeric DNA sequences joined together in the middle of the chromosome, and two centromeres in the opposite outer quarters of the chromosome.  The specific DNA sequences in each centromere closely match those of primate chromosomes 12 and 13.  This finding confirms without doubt the common ancestry of primates and humans, certainly indicating the unmistakable presence of evolution. 

 

 

 

 

Fig 2. The fusion of primate chromosomes 12 and 13 to form human chromosome 2.  Courtesy the following website, which is also an excellent reference for the evidence of evolution:  http://www.teachthemscience.org/evidence

Molecular Tinkering

                The second question we are considering is whether or not a new species, descended from an older species, has indeed been designed for its new role.  Intelligent Design declares that living systems are irreducibly complex, e.g. a particular system could not function if it were assembled piecemeal.  The idea is that absent any component part, an eye, or an organism’s blood clotting system, or the cilia of a bacteria, would be rendered powerless to do its job.  Hence, then, such an irreducibly complex organ system must have been designed.

  However, the evidence indicates that organisms are continually co-opting other systems to do new and novel jobs.  For example, there is abundant evidence that bacteria have been able to duplicate genes for the poison injection system, then modify the duplicate gene to create a functional cilium.  The is termed tinkering, e.g. the rearrangement of Lego-like components of a system to create a new system. This capacity of organisms to modify themselves is evidence that the organism indeed possesses agency.  Stuart Kauffman terms the creation by the organism of a new structure a “Darwinian pre-adaptation.”  Organisms’ ability to do this are emergent features of creatures.  This molecular tinkering is unpredictable. 

The diversity of structures and functions of G-Protein-Coupled Receptors (GPCRs) is a perfect illustration of F. Jacob’s famous idea: ‘evolution is molecular tinkering.’[3]   The receptor is a folded protein that is imbedded in cell surface membranes.  It traverses the cell membrane 7 times, and when activated by one of a large number of stimuli, it sets off a molecular cascade that enables the cell to make a response.   Stimuli include light rays, odorants, hormones, and an array of regulatory ions and molecules.  Life has apparently tweaked these receptors innumerable times to achieve improved perception, self regulation, and adaptation.  Did these changes come about randomly, or is God the tweaker, ID style, or does Life have some active capacity to modify or mold itself?  I subscribe to a group of scientists, termed MetaDarwinists, who posit the latter.

Fig. 3. GPCR. The protein structure making up the GPCR has been altered numerous times to create receptors for the array of stimuli shown in the diagram. 

 

 

 

 

 

 

 

 

 

 

 

 



[1] Miller KR, Only a Theory: Evolution and the Battle for America’s Soul (Viking, New York, 2008).P. 46-50.

[2] Miller p. 105-109.

[3] The EMBO Journal vol . 18 No. 7 pp. 1723-1729. 1999.

 

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3 thoughts on “The Evidence for Evolution”

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