First page – Explanation: what evolution is and how it works
Previous page – Evidence for evolution

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    The theory of evolution is opposed by a number of groups outside the scientific community. Here, we'll look at their most popular arguments, and then see if they stand up to inspection.

Evolution is just a theory.
    In casual conversation, the word "theory" means a hunch, or an idea that's not supported by much evidence. In science, though, the word means something very different. To the scientist, the word "theory" means an idea supported by countless experiments and countless pieces of data. Calling something "a theory" is as close as a scientist can get to calling something "truth." Scientists continue to refine and test the theory of gravity, the theory of relativity, atomic theory, and the theory of evolution. Over the centuries, scientists disproved countless theories and created others to improve their understanding of the nature of life, the world and the universe.
      Could the theory of evolution be disproven? Certainly, but only by the same system of undisputed facts, rigorous methodologies and structured experiments scientists use to expand our understanding.

Evolution doesn't explain where life or the universe came from.
    That's entirely correct, and also entirely beside the point. Evolution explains what happens to life when you already have life and a universe, much like how gravity describes what happens to mass when you already have it. Saying that evolution doesn't explain where the universe came from is like saying that gravity doesn't explain where matter comes from – it's entirely true, but entirely beside the point.

Evolution is purposeless.
    Just because something is purposeless doesn't mean that it does not exist. Water doesn't have a purpose when it flows across a table, but that doesn't mean that it doesn't flow. Evolution is undeniably purposeless, but it still exists.

Evolution is godless.
    Evolution does not require a god in order to work. Neither does a kitchen stove. Being godless doesn't mean that stoves don't work, nor does it mean that evolution doesn't work.

Scientists don't know everything.
    No, scientists do not know everything. It's the fact that scientists do not claim to know everything that lets them refine their ideas based on new observations. It's science's flexibility that makes it strong.

Evolution isn't necessary.
    Some people say that whether or not evolution is true, it doesn't really change anything for us right now. Since evolutionary theory creates so much strife and division, why not set it down for the sake of harmony? However, evolution is very relevant. Evolution is the only tool we have to predict how nature will react to our actions. When your doctor prescribes an antibiotic, if you don't take all of it, you'll only kill the bacteria vulnerable to it, while the tougher ones survive and reproduce. Only by taking all your antibiotics will you kill all the bacteria, and not create a selection pressure towards the tougher ones. Without evolution, we would never know that people not taking their antibiotics is one of most important things creating drug-resistant infections. We need to understand evolution: if we don't understand it, we'd never know how nature could change to possibly harm us.

Achilles' heel
     Some challengers of evolution will point to one piece of information that they say definitively proves that evolution cannot be true, like a supposed fossilized human footprint next to a fossilized dinosaur print. Usually, these pieces of information wind up being misunderstandings, but even those that haven't been invalidated yet are not going to disprove evolution. Evolution is supported by a mountain of evidence. To disprove it, you will need a mountain of contrary evidence. If you have a mountain of evidence for something, and a handful of data against, odds are that data is a fluke. The only way to show that it isn't a fluke is to get a huge amount of evidence showing that evolution isn't true. Contrary to what some (not all) challengers of evolution may tell you, a huge amount of contrary evidence does not exist. So trying to find an "Achilles' heel" in evolutionary evidence cannot work, because you'll need far, far more than just a handful of information.

Gaps in evolutionary history
    Some challengers of evolution point to gaps in the fossil record as evidence that evolution is poorly supported, as there are dark periods where we don't know what happened. First, this doesn't say anything about how evolution works; all it says is that we don't know all the evolutionary changes that have taken place over history. Second, more gaps does not mean less knowledge. If you suspect that species A evolved into species D, you have one gap. If you find a fossil from species B which looks like it is a transitional fossil between A and D, you now have two gaps. When you find a fossil from species C, between B and D, you now have three gaps. Yes, you have more gaps. But that's because you actually know more now.

If we evolved from monkeys, why are there still monkeys?
    First things first: we didn't evolve from monkeys. We have a common ancestor with monkeys – our ancestors branched off from the same small, ape-like organism millions of years ago. Second, even if we did evolve from monkeys, evolution works on the level of the population, not the species. There are still bird-biting pipiens mosquitoes flying around London. Only part of the population went underground and evolved. Just because a new species evolved from one population of an old species doesn't mean that all the populations of the old species went extinct.

There are no transitional fossils.
    There are transitional fossils. One example of this is the Tiktaalik, the half-fish, half-amphibian fossil that we looked at earlier. Other classic transitional fossils include the dinosaur-to-bird Archaeopteryx, the doglike-mammal-to-whale Ambulocetus, and the apelike-mammal-to-human Australopithecus, though there are countless others.

There is controversy over whether evolution is true.
    Something along the lines of 99.9% of working biologists accept evolution. The Discovery Institute, an evolution-challenging organization, sometimes collects the names of PhDs who oppose evolutionary theory. The number of actual, working biologists on their lists is minimal at most. Most people on those lists don't even have jobs in the scientific community, let alone biology degrees. Among biologists, there simply isn't any controversy.

Evolution cannot be tested.
    This idea is quite popular, but as we saw with the lizard experiment and the E. coli bacteria experiment, evolution can be tested.

Evolution is Darwinism.
    Many challengers of evolution call evolution "Darwinism," after Charles Darwin, the man who first thought of the idea of natural selection. It makes biologists look like they accept everything Darwin wrote at face value. Nothing could be further from the truth. Much of what Darwin had to say has been disproven. Biologists only care about what the evidence shows, not what people had to say. Evolution is just that: evolution, not Darwinism.

Irreducible complexity.
    Irreducible complexity is the idea that some traits couldn't have evolved naturally, because if they're missing just one mutation, they don't work, and so selection pressures couldn't push toward the development of those traits. It's an interesting idea, but it doesn't stand up to the facts. Remember the experiment where E. coli bacteria evolved to eat citrate? That took 3 different mutations. If the bacteria were missing just one of those mutations, it wouldn't be able to eat citrate. If irreducible complexity is true, then those bacteria could never have evolved the way they did. However, they did evolve, (and thanks to the freezing of samples every 500 generations, you can actually track the evolution) so it can't be true. Irreducible complexity simply doesn't hold up to testing.

Intelligent Design
    Some challengers of evolution advocate an idea called "Intelligent Design." Intelligent Design states that, because of irreducible complexity, an Intelligent Designer must be responsible for changes in organisms over time. This idea has three problems: it relies on irreducible complexity, it's a "science stopper," and it's not testable.

    First, irreducible complexity isn't true. We saw this in the E. coli citrate experiment. So, Intelligent Design has no basis. Second, the idea of Intelligent Design blocks scientific progress. As soon as you ascribe a natural phenomenon to supernatural causes, you stop investigating it. The supernatural cannot, by definition, be studied (if it could, it would just be natural), and so science just stops.

    Third, science relies on experiments. You can't run an experiment to test Intelligent Design. It's simply not possible. Before conducting an experiment, the researcher has to decide what the different possible outcomes of the experiment would suggest about what he's studying.  So, if you're going to run an experiment on Intelligent Design by, say, putting bacteria in a flask and watching them, you would first have to decide, "OK, if the bacteria do any of these four things, then there isn't an Intelligent Designer, but if they do any of these five things, then there is one." You can't do that. You cannot identify what features you'd expect an intelligently designed universe to have. You can't test for God. Because of these three flaws, Intelligent Design not only isn't valid, it's not even science.

    These are all the most common arguments used against evolution. The thing is, though, that none of them hold up particularly well under scrutiny. If you continue learning more about evolution (and I encourage you to!), you'll probably run across some new arguments. Most of these arguments will be based on misunderstandings of the evidence or how evolution works, so if you do encounter an argument against evolution, do a little research. It's virtually certain someone has explained why the argument doesn't stand.

    This text covered a staggering amount of material. You learned about the five observations on which evolution is based. You learned how mutations add new genes to the gene pool, how selection pressures change the gene pool through nonrandom reproduction, and so how change in the gene pool over time changes populations and produces new species. In other words, you learned that mutations at random cause nonrandom reproduction.  You learned about descent with modification. You learned about some of the evidence supporting evolution, about fossils, rock layers, the Tiktaalik, amino acid sequences, the Caribbean island lizard experiment, the E. coli citrate experiment, and about London mosquito evolution. Finally, you learned why the arguments against evolution don't hold up.

    Evolution is fantastically important – one of the most important ideas ever thought of by mankind. Despite evolution's certain truth, much of the public clings to other ideas, ideas supported by neither logic nor evidence. With the information you've read today, you are equipped to understand what both sides of the evolution debate are saying.