Can someone explain the logical validity of the statement: "Evolution is the foundation of modern biology"?

Question

I want to understand better the logical steps leading from the theory of evolution to modern biology. Would we not be able to have modern medicine without first having the theory of evolution? What would the impact on biological sciences be without the theory of evolution?

Answer 1

"Nothing in biology makes sense except in the light of evolution." -Theodosius Dobzhansky (a great biologist)
(The full essay is attached as a source).

Your question about the series of "steps" from evolutionary theory to modern biology is hard to answer simply because the phrase "modern biology" isn't a single thing, but a *huge* collection of diverse fields (from zoology, botany, bacteriology, virology, genetics, embryology, anatomy, cladistics, paleontology, biochemistry, medicine, etc. etc.). The point is that evolution is the UNIFYING THEORY that brings all of these things together ... i.e. gives them all a common explanation and a framework that connects them all. Evolution explains *so much* of what we see in biology, that nothing seems to make sense without it. Examples:

Relationships between species: All the classification of species (phylum, class, order, family, genus, species) makes sense in evolutionary terms. The relationships between apes is closer than their relationship with monkeys and other primates, which is closer than their relationship with other mammals, etc.

Distribution and diversity of species: E.g. the distribution of old world primates (including apes) in Africa, vs. the new world primates (tailed monkeys) in C. and S. America shows a geographic isolation that corresponds well with plate tectonic evidence of the split of the African and South American continents. E.g. the genes for color vision are primarily isolated to old world primates, while new world primates are as "colorblind" as other mammals. This makes sense only in the light of evolution from ancestors that branched at certain geological times, and this timing corresponds to what we find in the fossil data, and to the molecular (DNA) clock.

Genetics: The percentage of genes shared between closely related species (e.g. primates) is higher than with more distantly related species (e.g. mammals) and with much more distant species (non-mammalian vertebrates), etc.

Molecular (DNA) similarities: This is independent of genes, and has to do with just how much our DNA *molecules* show differences that correspond exactly to the rate of random mutations of nucleotide-pairs.

Vestigial structures: E.g. leg bones in whales and dolphins make no sense except in the light of evolution from land-dwelling mammals. Or the plantaris muscle in the human calf ... a muscle so thin and useless in humans it is mistaken for a nerve by medical students ... it makes no sense except in the light of evolution from a common ancestor with other primates, in which this muscle is used for *grasping with the feet*!

Homologous organs: E.g., the ear-bones in mammals have an equivalent structure to the hinged jaws of reptiles, which only makes sense as a structure repurposed from a reptilian ancestor. Or the structure of the forelimbs of primates, bats, birds, and reptiles all only make sense in the light of a common ancestor. There are dozens of other examples in embryos and proteins and genes (e.g. the specific genes coding for the hemoglobin molecule in humans and the myoglobin molecule in chimps are homologs (third source below).

Embryology: The development of embryos shows the existence of genes inherited from common ancestors with other organisms.

Biochemistry: The metabolism of different organisms use the same mechanisms. It's not just that the specific structure of some insulin or cytochrome molecule is used by different organisms ... but that it is used *only* by organisms that can be traced to a common ancestry.

You asked specifically about medicine ... there are dozens of examples. For example, the way that bacteria can literally evolve over time to create new strains that are resistent to certain antibiotics is a perfect illustration of natural selection ("survival of the fittest") at work ... the antibiotics provide environmental pressures and the bacteria respond to them. Medical researchers also use these principles to understand the appearance and spread of viruses, the genetic properties of cancer, the inheritance of genetic diseases and conditions, etc. etc.

Evolution provides the backbone that unites all of these things.

Answer 2

I find it interesting how you posed the question. Not simply “explain the statement” or even “explain the validity of the statement” but “logical validity.” It is as though you find the proposition to be obviously absurd that one needs to question how a valid conclusion can be drawn from a false premise.

Here are a few things to consider that will put things in perspective. Science is not in the business of finding truth. Truth is the realm of mathematicians and the religious. A proof in mathematics will always be true in a given system forever. The divinely inspired also claim to know the truth, whatever that may be. However, science is a way of figuring things out. What the practitioners of science do is to take observations, create a model that explains those observations, figure out the consequences (predictions) of the model and then design experiments that test the predictions. If the experiment is consistent with the predictions, that does not mean the model is true. For example, take the Standard Model of physics. It has withstood every experiment ever designed to find some flaw in its predictions. Even though it can correctly predict how subatomic particles will behave down to the limits of our ability to measure, we know that this theory is not complete and is not true because it does not include gravity. What scientists want are experiments that show where the model fails because that forces us to confront the new observations and revise or create a new model that is more complete and more accurate. A theory is what scientists call the most complete and accurate model of a subject. This is in stark contrast to creationism or intelligent design dogma. Under that scenario, the truth is already known, it makes to predictions and it cannot be falsified.

What Evolution does is model how and why populations change. Darwin took a set of observations and proposed Natural Selection as the mechanism behind the changes. He did this before knowing anything about DNA, genes or mutations yet his ideas fit with these later discoveries. Evolution had nothing to do directly with the discoveries of the past century but it puts those discoveries together into a coherent story. Others have pointed out some resources if you are truly curious.

Answer 3

SecretSauce and Haysoos have both provided an exceptionally accurate and thorough answer to your question. I would have said the same...

One example that I can add, as a biologist researching cancer, is the 'micro-evolutionary' process that occurs as cancerous cells develop from normal cells in the body:

Cells are a small-scale example of how living things can undergo small genetic mutations (spontaneous or not) that manifest themselves as an entirely different phenotype. A normal cell divides and gives rise to one normal cell just like itself and a cell where one nucleotide was missing- This produces a physical mutation that causes the cell to function differently. And when it divides, it gives rise to more cells just like itself. There are many genetic changes that occur in a cell population that brings some/all of the cells from early to advanced malignancy. In general, certain genes are turned on or off that allow a group of cells to a) form its own vascular network (by over-expressing EGFR; thus supplying itself with nutrients), b) metastasize (ie: the gene 'c-met' which allows a cell to break away from the tumor and invade the blood supply), c) have the ability to leave the circulatory system, d) land, and e) develop where it lands. Different mutations control each of these processes, and the mutation that is responsible for step (c) is dependent on that of step (a). Cancer cells mutate so readily and quickly due to their fast rate of mitosis that not only can they easily change phenotype and function, but they also easily become resistant to drugs fashioned against them (ie: chemotherapies). Chemoresistance, therefore, is one example of evolution (at least on a cellular scale) and how it is relevant to modern medicine/biology.

Answer 4

There is an incredible diversity of living organisms on this planet. From microscopic virii that require other cells in order to reproduce to gigantic blue whales that cruise the depths of the oceans. Some are incredibly specialized: the fungus Laboulbenia grows exclusively on the rear portion of the elytra of one species of beetle, Aphenops cronei, which is only found in a handful of limestone caves in southern France. Other organisms are incredibly adaptable and can survive nearly anywhere. One species has even managed to use bits of its environment to modify its surroundings such that it can even survive temporarily well outside the Earth's atmosphere, and has even reached the surface of our lunar satellite.

At the same time, there is a continuity of general morphology. As different as the organisms of the Earth are, they also share a number of similarities. The basis of heredity in all Earth organisms is a few similar strands of nucleic acid. There is not one six-limbed vertebrate, even though there are other groups of organisms with multiple limbs. All of the vast variety of insects share a basic body plan of three body parts, six legs, and four wings. Even their mouthparts are amazingly similar, even with the wide array of different structures they have been modified into.

The theory of evolution, that simple idea that natural selection of variation within a population leads to changes in that population over time provides an explanation for both this extraordinary diversity, as well as this remarkable unity of morphologies.

Evidence supporting the theory comes not just from genetic and morphological comparison between the vast array of living species, but also comparison of fossil forms. The diversity, array and morphology of all of the fossils known have completely supported the theory of evolution.

In addition, the chronological ages determined for the fossils also fit into the pattern that would be predicted by the modern diversity of living organisms. The biogeographic distribution also fits this pattern, explaining things like why there are porcupines in Canada but not Russia, and why kangaroos are only found only in Australia. These pieces of evidence could be predicted by the theory of evolution and the evidence from geology of the ages and movement of the continents, and the actual facts again support the theory of evolution.

Other observed phenomena, such as drug resistance in bacteria, or pesticide resistance in mosquitoes can also be predicted by the theory of evolution. Indeed, we see these things happening, and evolution explains why.

No other theory in the entire field of biology has both the predictive and explanatory powers that the theory of evolution holds. Without the theory of evolution, the best explanation anyone could give about almost any observed behaviour, adaptation or morphological variation in the biological world would be "ummm... I dunno... that's just the way it is."

No other theory has as much physical evidence supporting it either, including well known principles as the theory of gravity, or the theory of heliocentrism.

The only opposition to the theory of evolution comes from a few camps who are upset that the particulars of how it reveals that life came about and adapted to the conditions of the Earth disagree with the creation myths set forth in their holy scripts, and a handful of people who seem to be mortified with the idea that we might be related to chimpanzees (as if being formed from dirt was somehow superior).