Bill Nye the Science Guy debated Ken Ham, a young earth creationist who runs Answers in Genesis and the Creation Museum, Tuesday at the Creation Museum in Kentucky. The question they debated was “Is creation a viable model of origins in today’s modern, scientific era?” I won’t get into the debate itself, you can watch the debate in many places, such as here and here and decide for yourself who won or lost and whether or not they presented convincing arguments. What I do want to get into here is an article I saw called “22 messages from creationists to people who believe in evolution.” It illustrates why paleoaerie was created in the first place. When I read these statements from creationists, the lack of comprehension of really basic science concepts was highly discouraging. This isn’t even just about evolution, it’s about basic science understanding and logical thought processes. If one doesn’t even understand what a theory is, how can that person be expected to make a rational decision about anything? Life becomes nothing more than random guesses. We are blind men in a watch tower. “Blinken! What are you doing up there?” “Guessing? I guess there’s no one coming.” That’s no way to run your life, much less the whole of society.
So I thought I would provide at least some sort of answer to these questions. Many of them are questions that are quite commonly raised, so it is worth at least attempting to answer them. The first thing to address, though, is the title of the article itself. Scientists do not “believe” in evolution. It is not a religion or ethical/moral code. Scientists accept evolution because of the staggeringly huge amounts of evidence that supports the theory, not because some scientific leader told them they must believe it or go to science hell.
1. Bill Nye, are you influencing the minds of children in a positive way?
I’m not Bill Nye, but for me, I would say yes. Any attempt to teach children how to think rationally, to question how the world works and to use evidence to attempt to answer those questions, is a positive influence. Teaching children to obey and believe simply because they are told to without question is a bad influence. That is how horrific atrocities are committed and accepted by a blind populace. Every great discovery, invention, or acheivement came about because someone asked a question (more likely several questions) and trying to figure out the answer beyond just accepting what they were told. The bow and arrow, agriculture, medicine, computers, basic housing, nothing man-made would exist if we never asked questions and strived for answers. Creationism the way Ken Ham and others formulate it, is telling people to NOT ask questions, the only answer you need is “God did it.” That sort of thinking not only denies the reality of our shared experiences, but dooms civilization to failure and would have kept us in the trees. We would never even have made it to the caves. That is why this is important.
2. Are you scared of a Divine Creator?
There are two (more than that actually, but two is what I am sticking with here) ways to answer that question. If one starts with an atheist point of view, one cannot truly be afraid of something you don’t believe exists. But this question falsely assumes that evolution and religion are mutually incompatible, that one cannot believe in evolution and a Divine Creator at the same time. This is wrong. Pope Benedict stated that evolution is true, even calling the idea they are incompatible an absurdity. Pope Pius XII endorsed evolution, as did Pope Paul II, and Pope John Paul II called evolution “an effectively proven fact.” Surely no one could call these leaders godless or lacking in Christian religion. Billy Graham, an influential Baptist Evangelical leader, was not opposed to evolution. Pat Robertson, leader of the 700 Club, has called Creationism a joke and that a 6,000 year old earth is ridiculous. He has no problems with theistic evolution, only nontheistic evolution. In other words, he accepts in God-guided evolution. Truth be told, there is NOTHING in evolutionary theory that denies God. God is not a necessary part of the theory, but it does not claim God did not guide it. Francis Collins, Director of the National Institute for Health, is well known to be a devout religious man, yet also firmly accepts evolution.
3. Is it completely illogical that the earth was created mature, i.e. trees created with rings…Adam created as an adult…?
Yes. I think it is illogical. For that to be true, you have to admit that God is intentionally lying to you. Why would God create an earth that gave all appearances of being much older if God did not expect you to accept the evidence God provided? Is it logical to assume God lies to you? If so, why would you worship a God that is a liar?
4. Does not the Second Law of Thermodynamics disprove evolution?
No. The Second Law of Thermodynamics states that 1. Heat will not flow from a cold object to a hot object. 2. Any system which is free of external influences becomes more disordered with time, which can be expressed as entropy. 3. You cannot create a heat engine which is 100% efficient in converting heat to useful work. For example, a (working) refrigerator is clearly colder on the inside than on the outside. It maintains this temperature by pulling heat from the inside and dumping it outside. One might say that this violates the 2nd law, but it doesn’t because it uses the fact that pressure and temperature are intertwined. It pumps a coolant that absorbs heat from the interior, thereby becoming less dense. It then takes that coolant and compresses it, releasing the heat so the coolant than then start the cycle over again. This requires energy to do this. The refrigerator uses electricity to add energy into the system, which is lost through this process. Overall, the entropy goes up, despite the refrigerator becoming less entropic on the inside, that disorder is simply moved outside. In the same way, the earth is collects a vast amount of energy from the sun. That energy is absorbed by plants, which then gets (very inefficiently) converted to work energy by themselves and everything that eats them. Overall, the process is extremely inefficient. Without the sun, no life could exist on earth, entropy could not be fought. But the sun supplies so much energy, it is simplicity itself to create order in some areas even while disorder of the whole increases.
5. How do you explain a sunset if there is no God?
Disregarding the spelling mistake (English teachers, where are you?), this question doesn’t even make sense. Sunsets happen because the earth rotates on its axis. Stand in front of a light with a little Lego person on your forehead and turn around. That Lego person on your forehead will experience a “sunset” for every revolution you make. Now imagine that process as you standing on the earth and the light being the sun.
6. If the Big Band is true and as taught as science along with evolution, why do the laws of thermodynamics debunk said theories?
They don’t. See above. Both evolution and the Big Bang Theory are formulated with the laws of thermodynamics in mind and are fully compatible with them. If they weren’t, no scientist would take them seriously. They are, so we do.
7. What about Noetics?
To be honest, I’ve never heard of Noetics. One minute while I perform Google-fu…According to Wikipedia, “noetics is a branch of metaphysical philosophy concerned with the study of mind and intellect. Noetic topics include the doctrine of the agent/patient intellect (Aristotle, Averroes) and the doctrine of the Divine Intellect.” What about it? This has nothing to do with evolution. If you are asking where consciousness comes from, one first has to define what you mean, as there is no universally accepted definition. However you define (presuming one is using a rational definition), humans are hardly unique in being “conscious”. The idea that we are the only animal that is conscious is simply a conceit to make us feel special. There are gradients of consciousness exhibited by a wide range of animals that are not human. Therefore, it seems to have evolved. If one is talking about the idea that you can know the universe simply via self-examination, there is abundant evidence that shows just how fallible human perception is. There are entire fields of study devoted to the topic. It is how magicians perform their craft, why marketers are so successful. As helpful, beneficial, and worthwhile it is, self-examination without reference to the outside world cannot even accurately teach you about yourself, much less the universe.
8. Where do you derive objective meaning in life?
Again, this has nothing to do with evolution. Meaning in life is a personal decision, not an objective part of the universe. The meaning of life is what you make of it. Thus, an objective meaning of life is a non sequitor as it is subjective by definition.
9. If God did not create everything, how did the first single-celled organism originate? By chance?
Yes. There are a lot of hypotheses about how that happened, but we don’t honestly know. At any rate, the question has nothing to do with evolution. Evolution does not deal with the origin of life, only what happened to it after it was here. If you want to understand the physical processes that led to the origin of life, I suggest you talk to a biochemist and biophysicist. That is in their bailiwick, not in evolutionary theory. But let’s ask that question in a different way. If God created everything, how did God get created? Did He create himself? And sorry, but the answer of “He always existed” is simply a copout. The other problem with this question is the assumption that there are only two possible mutually exclusive answers, that it is either evolution or God. What if it were aliens? No, I’m not seriously suggesting that, if for no other reason than it only pushes the question back to where the aliens come from and so answers nothing. I am simply saying that other possibilities exist. They are also not mutually exclusive. You can accept evolution AND God if you wish. You may as well ask how can a pilot fly if he didn’t invent airplanes. One is not dependent on the other, nor does one being true rule out the other.
10. I believe in the Big Bang Theory…God said it and BANG it happened.
That’s not a question, just a statement of opinion. It also has the serious flaw in that it indicates the person refused to even consider the question, going on nothing more than blind faith. That’s ok in a religion, but is a horrendous failure in science. That sort of thinking also fails the reality test, in that reality does not care what you believe. You may believe you can fly and jump off a tall building, but unless you have brought along a parachute or hang glider or some such object, the ground will still kill you. Personally, I would rather someone tested the parachute before I staked my life on it.
11. Why do evolutionists/secularists/huminists/non-God believing people reject the idea of their being a creator God but embrace the concept of intelligent design from aliens or other extra-terrestrial sources?
First off, English teachers, help this man. Second, almost no one does, so this question makes no sense. It lumps a whole lot of people into a very strange category. Most people who “embrace the concept of intelligent design from aliens” are generally considered whackjobs and not taken seriously, so it both has nothing to do with evolution and everything to do with a very incorrect view of people who accept evolution. The accepted scientific thinking on life originating from aliens is that there is no proof or any real evidence for that idea, so it is not considered at all scientific and is therefore unaccepted. There are a few people that support the idea, but as far as I know, no one, not even them, really consider it a scientifically supported hypothesis.
12. There is no inbetween…the only one found has been Lucy and there are only a few pieces ot the hundreds necessary for an “official proof.”
First off, there is no “official proof” of anything in science. There is either evidence supporting it or not supporting it. Secondly, there are far more fossils than of just Lucy. There are multiple species of Australipithecus, as well as Ardipithicus, Sahelopithicus, Paranthropus, Homo habilis, Homo erectus, Homo neanderthalensis, etc. May I suggest you spend some time perusing the Smithsonian site on human origins? They have quite a nice discussion of human origins and present far more than just Lucy.
13. Does metamorphosis help support evolution?
Yes, it does. Careful study of how different animals undergo metamorphosis has helped to elucidate the relationships between a large number of different animals. The study of amphibian and insect relationships requires a detailed examination of how those processes play out and they have been exceedingly helpful in understanding the evolutionary pathways in these groups. There are still plenty of unanswered questions, but that is why we do research, to try to answer those questions. Moreover, research on those topics is an important part of medical research on regeneration, in the hope that if we can fully understand it in other animals, we may be able to bring that knowledge to bear on helping humans do it to, so that we may one day grow back lost limbs and organs and not have to depend on prosthetics.
14.If evolution is a theory (like creationism or the Bible) why then is evolution taught as fact?
If evolution were indeed a theory like creationism, it would not be taught as fact, it wouldn’t be taught at all because it would be only fit for a religion class. But it is a theory in the same way that gravity is a theory. There is no law of gravity, there is a Theory of Gravity that explains the mathematical relationships and how it works in the universe. A scientific theory is not simply a guess. It is a scientific concept that explains a large array of observable facts, a concept that has been tested and retested and tested again by lots and lots of people. Scientific theories are constantly being revisited to see if new observations still support it. The simple fact of the matter is that no one has been able to provide any better hypothesis that explains the observable data. Sorry, but “God did it” is not a verifiable hypothesis. One cannot even proof or disprove God exists, God is a concept that falls outside of science. If someone can come up with a way to either proof God exists that can be objectively tested or can come up with a better hypothesis that disproves evolution, again, with objective, verifiable facts, they would become famous and would win the Nobel Prize. That hasn’t happened, so until it does, we will stick with evolution.
This question not only misunderstands what a scientific theory is, but it misunderstand what the theory of evolution is. Here then is the essence of evolutionary theory: everything changes. Specifically, living organisms change. Even more specifically, we can observe those changes in the genetic distributions within populations. If we see genetic changes in populations, we have proven evolution happens. Basically, if you can agree that you are not a clone of your parents, you accept evolution. That is why we teach evolution as a fact, because it is.
15. Because science by definition is a “theory” – not testable, observable, nor repeatable, why do you object to creationism or intelligent design being taught in school?
Because science by definition is none of those things. To be considered science, it must be testable, observable, and repeatable (at least in some aspect). Thus, a dinosaur bone is not science. It is a fact. It exists. That it is a dinosaur and that a dinosaur means a specific thing is science because it is a testable concept. Other people can take that definition of what a dinosaur is and make their own observations to test it. They can make predictions and then see if those predictions hold up. If it can’t do this, it’s not science. Something that is not testable, observable, nor repeatable is called speculation or religion, but most emphatically NOT science. That is why we resist creationism or intelligent design being taught. They have no evidence to support them, they have no testable predictions that would support the ideas and what few predictions they have made have been proven wrong. Therefore, they have nothing to do with science and should not be taught as science. If they are going to be taught in school, it should be limited to a religion class. Even then, that religion class, to be allowable in a public school, would also have to teach equally other religions. So unless you are willing to have Islam, Judaism, Shintoism, Buddhism, Satanism, and any other religion taught on an equal footing, you can’t have them in a public school that is bound by law to not advocate any single religion over another. To do so violates our most fundamental right, freedom of religion.
16.What mechanism has science discovered that evidences an increase of genetic information seen in any genetic mutation or evolutionary process.
There are actually several processes. It would take several books to adequately answer that question, so I will just mention a few in brief. Genes get accidentally duplicated all the time, our genomes are filled with duplicated genes. Most genes we have are in fact part of gene “families” which originated from the duplication of an earlier gene. When this happens, the duplicated gene is then free to evolve into something else. The original gene is still constrained by its original function, so it has a limited ability to change without breaking. However, that spare gene can change independently and it doesn’t matter if it can no longer perform its original function. It then has the ability to over time pick up a new function. Another way to increase genetic information is through viral infections. Our genome is about 8% viral origins. Viruses function by inserting themselves into the genome of their host and using the host cell to make the viral proteins. When the virus copies itself and spreads to other cells, it very often takes a small part of the host genome with it. Also, quite often, a virus gets inserted into a host genome, but loses its ability to replicate itself, thereby getting trapped in the host cell. If that cell happens to be a reproductive cell, which happens, it will get passes on to offspring as a permanent part of the genome. This is in fact virtually the entire basis of the field of gene therapy. Another way is good old fashioned sex. Hybridizations occur between closely related species all the time. Most of the time, those hybrids are sports, they can’t reproduce, but sometimes they can. Red wolves and Gray oaks are great examples of species that have been created through hybridizations. Plants are the ultimate masters of hybridization. They hybridize and create new species at the drop of a hat. They also readily duplicate their entire genomes. Of course, bacteria and many prokaryotes regularly swap genes among each other in a process called conjugation. There are many other ways, this is just the tip of the ice berg, but I hope I have demonstrated that increasing genetic information is really quite easy and happens all the time.
17. What purpose do you think you are here for if you do not believe in salvation?
Again, another question that has nothing to do with evolution. How does this even relate to the topic? The other flaw in this question is that it assumes we all have a purpose at all. What evidence can you give me that anyone has a purpose? What evidence can you give me that you can know the mind of God well enough to know what that purpose is? What is the purpose of a baby that dies at birth? What is the purpose of a person that never has children? Why do we need a purpose? Each of us are here because our parents had unprotected sex. There is no requirement that it be any deeper than that. It is fine to ask that question, but honestly, what does that have to do with science or evolution? For me, I think our purpose is what we choose to make it. Only you can answer what your purpose is and only if you decide to create one for yourself. As far as Salvation goes, why do we need to believe in Salvation? Why do we need Salvation? For us to need Salvation, that requires that God made us imperfectly so that we need to be saved. Why would God create something that needed God to rescue it? What need did God have to create something who’s only purpose was to worship God and ask to be rescued? These are not scientific questions. They are religious, philosophical questions. They are by their very nature outside the realm of science, at least, until someone comes up with a way to objectively test them. But they most certainly do not have anything to do with whether or not evolution occurs.
18. Why have we found only 1 of “Lucy”, when we have found more than 1 of everything else?
See question 12 for “Lucy”. To add to that, most fossil species consist of at most a few specimens. So it is not true that we have found more than one of everything. But more to the point, we have found seveal specimens of Austalopithicus, several different species in fact. So it is not true that we have only found one. There are numerous examples.
19. Can you believe in “the big bang” without faith?
First off, “the big bang” has nothing to do with evolution. It doesn’t even have anything to do with life on earth. You can accept evolution and reject the Big Bang Theory, they are completely independent. Second, yes, you can. Do you seriously think the physicists who came up with the theory just pulled it out of their butts? Or do you think they started with observations of the known universe. They did in fact start with observations and deduced the big bang theory based on physical and mathematical principles. It had nothing to do with faith, it had everything to do with observations of the known universe. It would also never have been accepted by other physicists if they couldn’t defend the math. It will also be unceremoniously dumped if anyone provides a better explanation. I don’t have the mathematical background to understand the evidence for the theory. Thus, I accept the Big Bang Theory because there are lots of people that do have the background and have examined it in detail and have not been able to demolish it yet. But by all means, if you want to learn the math well enough to take a crack at it, go for it. There are plenty of physicists that will be happy to help you out and study whatever you come up with. The Big Bang Theory actually got its named as a derogatory comment from Dr. Fred Hoyle, a physicist that did NOT accept the theory initially. But eventually, the math and observable facts won people over. No faith involved.
20. How can you look at the world and not believe someone created/thought of it? It’s amazing!!!!
I agree, the universe is amazing. I don’t think you can explore the world as much as biologists do without thinking the universe is amazing. But because I know something of how it works, I find it endlessly more amazing than if I didn’t.people become scientists precisely because they think the universe is amazing and awe-inspiring. So awe-inspiring in fact, they want to know more about it. They are not content to just sit back and ignore it. But the question has nothing to do with evolution. It again assumes that evolution and a Creator are mutually exclusive. As I stated above, and as so many religious leaders and religiously devout scientists have stated ad nauseum, it is OK to believe in God and still accept evolution as being true. Let me ask you, which is more amazing, God did it, or we are the descendants of stars that exploded billions of years ago, spreading their elements across the universe, which eventually coalesced into our planet and finally at long last became us? Is the story of our connection to the universe in a very real, physical way as living descendants of the stars any less awe-inspiring than God waved his appendage and poof we are here? Does one story mean the other didn’t happen? No, I don’t think so.
21. Relating to the big bang theory…where did the exploding star come from.
Again, nothing to do with evolution. Also, it wasn’t a star, stars didn’t exist yet. Finally, heck if I know, ask an astrophysicist. No way is an evolutionary biologist ever going to be able to adequately answer that question. You are asking the wrong people and associating things that have no connection to each other. This sort of question is like asking an Olympic swimmer to compete in the heavy weightlifting competition and then assuming he can’t swim because he lost the weightlifting competition.
22. If we come from monkeys, then why are there still monkeys?
First, we did not come from monkeys. Monkeys and humans both came from a common ancestor. Second, when you were born, did your parents die? What makes you think that just because one species evolved that the ancestral species has to go extinct? Life is not a perfectly linear ladder of existence. If it did work that way, there could only be one species on the planet at a time and that obviously isn’t true. I assume everyone can agree that new phones use the technology of pre-existing phones and improve upon them. When the new phones are created, do all older phones magically disappear? I don’t think so. Or perhaps, do the older phones gradually start going by the wayside as they get replaced over time. Taking this even farther, did kids stop drawing their names in sand because the internet was invented? Did hieroglyphs on Egyptian obelisks vanish because of TV? No, they stuck around. The evolution of a species does not require the ancestors to die out. In fact, that rarely happens.
There you go, 22 answers to 22 questions. I hope it has become obvious that the objections people raise against evolution, for the most part, have nothing to do with evolution. Those that do have something to do with evolution are based on a serious lack of understanding about how the world and science works. The history of life truly is the greatest story ever told. Let’s focus on learning that story and spend less time on arguments about the existence of the publisher.
When I worked at the Denver Museum of Nature and Science as a volunteer in the educations collection (if you ever get the chance to volunteer at a museum, do it, it was a lot of fun and very educational), I happened upon a man with a young boy by his side, whom I presume was his son, looking at an impressive skeleton. I thought how great it was the man took time to bring his son to the museum. But when the boy asked what the skeleton was and the man answered, “Allosaurus rex,” my opinion of the experience dropped. I’m still glad he brought the boy to the museum, but it could have been so much better.
So what was wrong with what he said? There is no such creature as an “Allosaurus rex.” There is an Allosaurus and there is a Tyrannosaurus rex, but not the two together. It also did not help that the man was standing directly in front of the plaque that read, “Fin whale.”
Much has been written on what a dinosaur is and what is not, but considering the extreme levels of confusion in the general populace, I thought it worth discussing it here. Not everything that is a big skeleton and/or extinct is a dinosaur. In addition to the above whale, I have heard dimetrodons, pterosaurs, saber-toothed cats, mammoths, giant rhinos, mosasaurs, modern elephant skeletons and many other things called dinosaurs, when in reality, NONE of the previous creatures qualify as dinosaurs.
So, if none of those are dinosaurs, what is? What are some of the things people think about when they try to define dinosaurs? The first thing that most people think about is a giant, scaly reptile. However, some dinosaurs were the size of chickens, so not all of them were big. Many also had feathers, so the scaly motif is not altogether correct either. They are reptiles, but unlike anything most people would consider a reptile today.
Other traits people often use to distinguish dinosaurs are that none of them were aquatic and none of them flew. These aren’t really true either. Some will say they only lived in the Mesozoic Era and died out at the end of the Cretaceous Period 65 million years ago. Again, false. It is true that most animals considered dinosaurs did indeed live only in the Mesozoic Era, but not all died out at the famous K-T extinction event. Some of you may be thinking to yourselves the author has no idea what he is talking about. Nevertheless, as we will see, some dinosaurs are quite at home in both air and water, especially the ones that lived past the Mesozoic.
Even if all these things were true about dinosaurs, none of it really matters. These traits are all distinguishing characteristics that are generally true about most dinosaurs, but not necessarily true about all. What defines an organism is not the same as the diagnosis. Definitions are done by evolutionary relationships. Diagnoses tell us how we can recognize them, what distinguishing characteristics can be used. However, distinguishing characteristics do not necessarily describe all the members of the group. For instance, one might distinguish all members of a family by their last name, but if people get married and change their last name, they do not suddenly stop being a member of the family. A daughter, for example, is defined by who her parents are, not by what name she has. Likewise, her distinguishing characteristics tell us who she is as an individual and can give us clues to her family relationships, but her definition as a daughter depends solely on her relationship to her parents.
I should note here that it wasn’t always this way. Back in the old days, organisms were grouped by similarity, who looked like whom, so at that time, there was really no difference between definition and diagnosis. But as people studied organisms more closely, they found that a lot of times, superficial similarities masked deeper differences, which indicated they weren’t really related at all. So for most of the last century, scientists have tried to find real, evolutionarily related groupings to build something akin to a geneology of life. To do so, it became evident that definitions and diagnoses of groups had to be different, so for the last couple of decades, definitions have been based on relationships and diagnoses based on characteristics. This system of classification by defining groups according to their relationships is called phylogenetic systematics.
So, how then do we define a dinosaur? The standard modern definition of a dinosaur has been stated as the most recent common ancestor of Triceratops and modern birds and all of its descendants (Padian, 1997). Note this means that all birds are, by definition, dinosaurs. So it is obvious that some dinosaurs are quite small (e.g. hummingbirds), flew (most birds), and could reasonably be called aquatic (e.g. penguins). The reason for this is because the earliest birds are clearly closely related to animals, such as Velociraptor and its close relatives, which are indisputably dinosaurs. If one took a picture of Archaeopteryx which had no feathers to a bunch of elementary school kids and asked them to identify it, the general answer is that it is obviously a dinosaur, but put feathers on it and they call it a bird. They are thus both correct answers. Dr. Thomas Holtz has proposed a slightly different definition: the most recent common ancestor of Megalosaurus and Iguanodon and all of its descendants. Both definitions encompass the same groups of animals as far as our understanding goes, but Holtz’s definition includes the dinosaurs that were first discovered, so is considered by many to be a superior definition.
Unfortunately, scientists don’t always talk about these terms correctly either, making the whole process confusing. Michael Benton, a leading paleontology researcher with numerous well-respected publications, got it wrong when he defined dinosaurs according to synapomorphies in The Complete Dinosaur. While synapomorphies are used in developing modern classifications, they are used for diagnoses, not definitions of groups, which Dr. Benton assuredly knows (as evidenced by the fact he normally states it correctly in his other works), but when someone is as prolific as Dr. Benton, the occasional error is bound to slip in now and then.
Synapomorphies are very important in figuring out relationships. Unlike any old similarity, synapomorphies are shared, derived characteristics, meaning that the character is the same in the organisms being compared because they share a common ancestor, i.e. they are derived from the same source. Of course, because it requires knowledge of the common ancestor, synapomorphies can only be identified AFTER one has a hypothetical relationship. Thus, to discover strong relationships, scientists will create (mathematically, using a computer because it is way too complex to try doing by hand for anything beyond a few species), all the possible relationships between all the organisms under consideration and then map all the characteristics they can onto every possibility. The relationships requiring the fewest inconsistencies and providing the simplest explanation is considered the most likely. Inconsistencies can occur due to convergent evolution (organisms not closely related developing similar characteristics due to similarities in environmental constraints) or homoplasies (characteristics changing back to a previous form), but with examination of enough characteristics, good relationships usually appear. Of course, the more data you can put into the analysis, the better the results normally get, which is why we continue to study and try to find new fossils and collect more data (and who wouldn’t want more fossils?).
This is all well and good, but how then do we recognize a dinosaur when we see one? Dr. Benton provided a good list of skeletal characteristics, which really won’t mean a lot to people who are not very familiar with skeletons and scientific terminology (but a basic description can be found here and Wikipedia has a surprisingly in depth description). Nevertheless, there are some generalities we can make. If we exclude birds, we can say the non-avian dinosaurs (that we know of) died out at the end of the Cretaceous Period. They all carried their legs underneath their bodies like mammals (and birds of course) and were decidedly unlike other reptiles. None were fliers, although the most bird-like ones got close, and none were aquatic, although some did indeed at least go wading. But remember, these are generalities and if we find a dinosaur with flippers, as long as it otherwise appears related to other known dinosaurs, it will still be a dinosaur. But if it does not fall within the relationships defined above, it will not be a dinosaur, no matter how much it may look like one.
I don’t have an online source for the Padian article, so here is the reference.
Padian, K. 1997. Dinosauria: Definition. pp. 175-179. In Currie, P.J. and K. Padian (eds.) Encyclopedia of Dinosaurs. Academic Press.