Copyright © 1999 by Ken Harding
[last update: August 24, 1999]
[Other topics for beginners]
It's true that subjects like biology, geology and the like can be very technical and difficult for the beginner. Reading up on all these topics can seem time consuming and complicated. That's why I'm going to cut to the chase. In this article you'll find very little technical terminology. Most web sites and articles attempt to be brief and simple, but few are successful enough to satisfy the average reader.
How do we know that life has descended through millions of years from a common ancestor? We accept the inescapable conclusions drawn from the physical evidence. We accept evolution because that's what the evidence unambiguously tells us, and for no other reason. Some people experience difficulty in accepting evolution. That is not due to flaws in evolution, but flaws in their understanding of biology. The most common questions about evolution illustrate that few people have done any investigating for themselves. We in our modern society have gotten used to sound-byte bits of information that we can digest without having to think much. Yes, understanding evolution and science will take some effort on your part. Is it worth it? Absolutely! Of course evolution, and especially the transformation from one species into another, will seem impossible if you don't clearly understand the process, and can't see the steps in between.
To paraphrase Daniel Dennett in Darwin's Dangerous Idea, the hope that evolution will someday be refuted by some shattering breakthrough is about as reasonable as the hope that we will return to an earth-centered universe and abandon Copernicus.
Okay, how does it work?The study of the origin of life is called Abiogenesis, and that topic will be discussed elsewhere. I'm going to leave that out right now because the theory of evolution was developed to deal with things that happened after the origin of life. The study of evolution deals with existing DNA and living organisms. Abiogenesis, while important to the study of evolution, is a separate subject, dealing with pre-cellular molecular biology, and may or may not involve evolutionary processes.
Okay, so what is this evolution stuff? The scientific answer is that it is a change in a gene pool over time. And you're saying, "What's that got to do with me?" Well, here is the plain English explanation of evolution: A change in the genetic potential of a species, and how environmental forces reward or punish individual organisms because of their genes. Now you're saying "Okay, how does that turn one animal into a different kind of animal?" Well, good news! In just 15 minutes you'll have the answer!
At a minimum, three things are needed for evolution to happen. Birth (we know that happens), death (we also know that happens), and genetic variation (and we know that happens). More specifically, 1) the births of many more individuals than can survive, to give the maximum genetic potential; 2) the disproportionately high percentage of deaths of organisms who are less well suited to their environments and predatory conditions, and therefore are unable to leave as many offspring; and 3) genetic variation to produce the raw material of physical change, which is then acted upon by natural selective forces. All of this has nothing to do with the species wanting to evolve into another species. Creatures do not choose to evolve. If the environment and food supply changes, or if the species relocates to a new environment, or a new species enters the area and competes, evolution will probably occur- or the species may become extinct.
The idea that chance is the sole engine of evolution is a misunderstanding. Chance is only one factor involved in evolution. Non-random natural selection another. If evolution was random, it wouldn't work! Sometimes people say that it's too improbable that we evolved from single-celled organisms, but such calculations are only meaningful if you assume that humans are the goal of the evolutionary process, and not merely a result of that process.
See also: What is Evolution and Evolution and Chance
What is Information?One of the most common misunderstandings regards "information". The difference between living and non-living things is that living things have information embedded in them which is used to produce themselves. Rocks contain no instructions on how to be rocks; a fly contains information on how to be a fly.
Information is not a thing. It, like an idea, is dimensionless. It's simply a comparison between one thing and another, like a list of differences. Information is not a physical property. Information becomes tangible only when it is encoded in sequences of symbols: zeros and ones, letters and spaces, dots and dashes, musical notes, etc. These sequences must then be decoded in order to be useful. For information to be stored or transmitted, it must be put into some physical form- on paper, computer disk, or in DNA- all processes that take energy.
Life's information (the instructions on how it works) is encoded in genes, which are decoded by biological mechanisms. Then these mechanisms manufacture parts that work together to make a living organism. Like a computer that builds itself, the process follows a loop: information needs machinery, which needs information, which needs machinery, which needs information. This relationship can start very simply, and then over many generations build into something so complicated that some people can't imagine how it ever could have gotten started in the first place. It is important to recognize that the information encoded in DNA is not like a blueprint, which contains a scale model image of the final product, it is like a recipe-- a set of instructions to be followed in a certain order. Life's complexity arises from remarkable simplicity. DNA's message says, "Take this, add this, then add this… stop here. Take this, then add this…" These actions are carried out by a variety of proteins. The result is all the intricacy and diversity of the biological realm.
All of these different processes can be operating at once within the same species. In addition, more than one occurrence of each of these five processes can be going on at the same time within a single species. There are 5 mechanisms of evolution, and I'm going to group them into 2 types-- two mechanisms that decrease genetic variation (Natural Selection and Genetic Drift), and three mechanisms that increase it (Mutation, Recombination and Gene Flow). I'll provide a brief explanation of each process, but you can find out much more about each by clicking the hyperlink. These links lead to more scientific, technical explanations.
The Five Mechanisms of Evolution
1. Natural Selection
|Here is how Natural Selection works:|
|1. More organisms are born
than can survive.
2. Offspring are similar, but not identical to their parents. Every batch of offspring contains a natural range of genetic variation. Genetic variation is produced in several ways, as discussed below. Changes in the genetic code, most of the time, are either harmful to an organism or neutral to it. However, there are rare instances where such changes can be helpful to the survival of an organism. Changes in the genetics of a species can bring about physical changes which give a survival advantage to the species, allowing it to continue when other species cannot.
3. Nature "selects" the characteristics that are most effective for the conditions, and that species survives. Selective forces drive physical change. Selective forces are not "forces" like gravity, but factors that effect how many organisms live and how many die. The reason lions are so fast and powerful is that their prey is so swift and elusive. (Because any slow and weak lions would not be able to survive long enough to reproduce). The reason antelopes are so swift and elusive is because lions are so fast and powerful. (Because any slow antelopes, and any that lack the instinct to run in a zig-zag pattern, would not survive long enough to reproduce.) There are other types of selective forces: climate changes and food supply changes will eliminate any organisms which aren't well suited for survival; sexual selection is the reason male peacocks have enormous tail feathers, and why deer and moose have huge antlers-- peacocks with small feathers and moose with little antlers don't get to mate with the females. Selective pressure is any factor that makes it hard for some organisms to continue surviving, and rewards any advantage that some organisms may have been born with.
4. Over millions of years, successive generations of genetic variations, which give survival enhancements, bring about new species. Thousands of generations of small changes result in a species that can look very different from the one that it came from.
NOTE: Species evolve-- individual organisms do not. Creatures don't "change" from one thing into another... they remain as they were born. Organisms do not choose to evolve-- favorable traits are chosen by the survival of the creature; less efficient characteristics are eliminated by the deaths of organisms. Within a species, there is a predictable range of possible traits, and a guaranteed chance of random mutations. Any trait that provides a survival advantage is preserved into the next generation, but a trait that is harmful to an individual results in the death of that individual.
The process of evolution is not entirely random. Natural selective pressures are very specific. As an example, bacteria becoming resistant to antibiotic drugs isn't a random thing, is it? Certain bacteria that have developed a resistance (due to mutations) are selected for survival by a specific external pressure (the application of antibiotic drugs), which causes the death of the bacteria that do not possess the resistant trait, allowing the increased reproduction of the more resistant bacteria. Here we see a non-random, recognizable pattern. The fact that the selective pressure was caused by human made antibiotics means nothing to the theory of natural selection. The bacteria don’t know the difference.
Artificial selection is a similar process which can help you understand natural selection. Artificial selection is when humans choose certain individual organisms for their traits, for the purpose of selective breeding. Consider dog breeding. Humans select the traits (size, shape, color, temperament, etc.) that they would like, and make sure only the dogs with those traits breed. Dogs without those traits are not allowed to breed. From this process, human beings shaped dogs into all the varieties we know today, from Dachshunds to Great Danes. It makes no difference to dog genes what force is manipulating them. Artificial Selection is a great way to introduce people to the concept of selection, and to demonstrate how Natural Selection works by using the same mechanisms to shape one species into quite a different looking species. The difference between Artificial and Natural Selection is intention. In both cases, certain breeds are selected for survival, because of their characteristics. In one case, humans intentionally do the selecting, in the other, natural selective pressures do the work.
2. Genetic Drift
In a population of limited size and if a given pair of parents have only a small number of offspring, then even in the absence of all selective forces, the frequency of a gene will not be exactly reproduced in the next generation because of sampling error. With a large number of offspring (or in a large population) this will not have much effect in each generation because the random nature of the process will tend to average out. But in a small number of offspring (or in a small population) the effect could be rapid and significant. Genetic Drift is one of the major forces of evolution, along with Natural Selection.
Click here for a more detailed explanation of Genetic Drift.
The idea that all living things intentionally change their own DNA is a serious misunderstanding.
At the conception of some living organisms, mistakes occur in the copying process of DNA. (Most people know these as birth defects.) "Bad" errors result in the death of the organism. But not all mutations are harmful-- a small percentage of these "mistakes" can actually benefit the organism by making it more efficient in its survival- either in finding food, avoiding predators or finding a mate. These "good" errors are then transmitted to the next generation, and those organisms head off in a different direction from the original species—resulting in a different looking organism. The idea of which mutations are "good" and which are "bad" depends on the current situation and selective pressures.
Each chromosome in our sperm or egg cells is a mixture of genes from our mother and our father. Recombination can be thought of as gene shuffling. In most sexually reproducing organisms, there are two of each chromosome type in every cell. For instance in humans, every chromosome is paired, one inherited from the mother, the other inherited from the father. Because of recombination, both of the chromosomes are a mix from the mother and father. On average, we have 50% of our genes from each parent. This means we also inherit - on average - half of all their variant genes. This means that children are not exactly like either of their parents, giving selection something to work on.
5. Gene Flow
New organisms may enter a population by migration from another population. If they mate within the population, they can bring new genes to the local gene pool. This is called Gene Flow. In some closely related species, fertile hybrids can result from inter-species matings. These hybrids can carry genes from species to species. Gene flow between more distantly related species occurs infrequently. This is called horizontal transfer. Gene flow introduces new DNA information into a species' gene pool.
Click here for the Synthesis of Modern Genetics and Evolution
But does all this bring about new species, or just variation within the same species?A common non-scientific objection to evolution is that evolution can produce new varieties within a species, but the stage-by-stage transformation of one species into another is not possible. No reasons are ever given for this limitation, just that it can't happen. Well, I'd like a reason, please. All we ever get is the incorrect statement that macro-evolution has never been observed. (Yes, it has: Observed Instances of Speciation ) Enough with that. What, specifically, makes the evolution of new species impossible? What is this elusive limitation of which they speak?
The emergence of a new species takes many generations to happen. In most cases, the life span of species, especially large animals, is too long for us to observe changes directly. For very short-lived species such as insects and plants, the emergence of new species has been observed. (More Observed Instances of Speciation)
There are variations within different types of dogs- but they are still dogs. But that is not saying a lot. There are more differences between a poodle and a German shepherd than in a German shepherd and a wolf-- but the wolf is categorized as a separate species. All such categorizations are done by humans... it is our decision what constitutes a separate species. The differences in all the breeds of dogs are produced by humans, through selective breeding, from a single, original type of wild dog. If humans can do that in so short a time (several thousand years) by encouraging favorable traits to be passed on to the next generation, and discouraging unfavorable characteristics, Natural Selection must be far more efficient and effective at creating new types. When you add other evolutionary processes that humans aren't able to use, such as Genetic Drift and Gene Flow, it becomes even more obvious how powerful these natural forces are. Couldn't a fox and a wolf have evolved from the same common ancestor? If nature can create new varieties within a species, what limits the process to stopping before it changes the species, until it looks altogether different? The same process that accounts for the differences in all breeds of dogs also produces new species-- it is just a matter of degree.
A transition from 'A' to 'Z' would be too big of a jump for us to observe. But a transition from 'A' to 'B', would not be, nor would a transition from 'B' to 'C'. In this way, you can have a gradual transition from 'A' to 'Z'. The fact that small changes can be observed in short-lived species is EVIDENCE of 'A' to 'B', 'B' to 'C', etc.
Macroevolution is the cumulative effect of many small changes in a species… there can be so many changes that at some point, the new species doesn't even look like the old one. The different traits that cause these changes don't have to occur concurrently all in one generation. For example, the traits that allow a fish to leave the water and colonize the land (bony, muscular fins, neural patterns, lungs, instincts, etc.) wouldn't all suddenly appear in a single fish through a bunch of separate, coincidental mutations. These genetic changes occur over hundreds of thousands, even millions, of years. Any one of these physical changes does not have to occur fully functional and complete in order to be useful-- any slight advantage that a partial trait can bestow is beneficial to the continuation of the species, and could be passed on to the next generation.
Did lungs just 'pop up' in an individual fish? The mechanism for new genetic information is mutations. Imagine that a freshwater fish had a mutation which allowed the lining inside its esophagus to absorb oxygen directly. None of the other fish would have had this trait. Maybe for hundreds of generations this trait was passed on without any real benefit, but as a neutral trait. Then the oxygen became depleted in the lake in which this fish lived. The fish discovered that it could swim up to the surface of the water and get a gulp of air, exactly like the lungfish does today. Now there is selective pressure to evolve a 'proper' lung. With the fish spending time near the surface, it skimmed the shallows for food. To assist this, bony fins that can be used for propulsion on the bottom of the shallow water would be extremely useful, and individuals who had this trait would be more successful at exploiting this environment for food, and leave more descendants. When bony, muscular fins evolved, it was inevitable that the fish would use this ability to eventually go up onto dry land to exploit that untapped food resource. A million years might have passed with this species making only brief, occasional excursions onto land. Then came amphibians, with moist skins who still had to lay their eggs in water, then reptiles who could further colonize the land with watertight skins and watertight eggs-- what an important step that was. Then mammals and birds both arose from reptiles, able to produce heat internally, but the birds (and two species of mammals) continued to lay eggs. All this would be impossible to witness within the whole history of human life. But it's not impossible for this to happen in, say, hundreds of millions of years.
Remember that organs do not have to arise fully functional to be useful. Organs certainly do not 'pop up' in one or two generations. In the case of the eye, you can realize that a partial eye will offer some benefit to a species. Consider early on, before the emergence of land animals, that it would be beneficial for sea-going creatures to be able to distinguish where the surface of the water is. Therefore, light sensitive cells on the head would be very useful, wouldn't they? Would a predatory fish that had light-sensitive cells benefit if those cells were able to distinguish movement and shapes? Would prey fish have a better survival rate if they could see the predators? Every improvement on a light sensitive cell would serve a purpose. You do not need to see perfectly for eyes to serve a purpose. Even people with 10% vision can make out objects and avoid colliding with them. They certainly would not want to lose whatever vision they have. If you had a choice between one eye or no eye, you would of course choose one. Color vision is better than color blindness, which is better than nothing. According to Richard Dawkins, the eye evolved independently about 40 times during the history of life on earth, and a 'camera eye' could evolve "rapidly" from a light sensitive cell.
Remember that organs may assume different functions over time, and each organ did not necessarily 'start from scratch'. Also, different enzymes assume different functions as well. Certain digestive enzymes are related to certain blood-clotting enzymes, for example.
Microevolution is the small changes within a species, and macroevolution is the long term, cumulative effect of many small changes.Seeing the evolutionary progress is like walking through a forest of giant redwood trees. You might look at the giant trees, and also see a few tiny saplings, and say "I wonder if these little two foot high saplings have anything to do with these 300 foot giant trees?" But no one has witnessed the growth process from seed to full grown giant redwood! It takes time. But that doesn't mean that we can't figure out what happens.
If you accept microevolution, but not macroevolution, you should ask yourself: what limits the process to making only small changes within a species? (i.e. Why can't hundreds of such small changes, say over 10 million years, result in a different species?) Can you come up with a reason?
There are no 'end products' of evolution because evolution has not stopped. The whole idea of "end products" and a rising hierarchy of "higher" life forms is incorrect. Species adapt to current environmental pressures, and also from pressures from predators and/or competing species. With this is mind, one cannot speak about "end products", unless all such pressures reach an unchanging state. Extinct species are not necessarily "unsuccessful" just because they became superseded by a new variant. They might have been extremely successful for 99% of their duration. Were the dinosaurs an unsuccessful species? They dominated the earth for 160 million years, far longer than humans. But things change- environments, competition, available resources, etc. What was successful yesterday might be unsuccessful tomorrow. Evolution is like a game of rock, paper, scissors... which one is best?
See also: Macroevolution,
Click Here for detailed explanations of Horse Evolution, and Archaeopteryx- the evolution of birds
If we evolved from apes, why are the apes still here?Well, one reason that apes still exist is that we did not evolve from them. Modern apes and humans share a common ancestor. We did not evolve from any group of modern apes-- therefore apes are unaffected by human evolution. All of human evolution occurred after the split.
The belief that when a new species evolves, it must replace the original species is a misunderstanding of the evolutionary process. It's just like you and your brother... you both do not necessarily share the same fate, do you? If your brother moves to another country, do his actions and descendants have any affect on you and yours? And just because you descended from your father does not mean that your father is dead. Dogs surely evolved from wolves, and there are still wolves.
If the new species gives the original species too much competition, the original species could be driven into extinction and be replaced by the new one. But there are many reasons why the new species might not replace the old one... such as relocating away from the old species, a change in the type of diet, an abundance of food. The original species can still continue to exist as long as it can make a living. Sometimes the new species replaces the old one; sometimes the old and new species both continue to exist. Another way to think about it is that a species is like a river. If that river branches off, there is no reason that both streams should go in the same direction.
Click here for a more detailed explanation of this topic
The rocks don't lieThe fossil record demonstrates unambiguously the continuous evolution of life. In the oldest and deepest levels of rock there are found no fossils at all. Above that are found the simplest forms of life-- bacterial fossils and invertebrates. Then above that are found vertebrate fish, and above that more complex creatures. Within the strata that contain the most primitive reptiles, you find no mammal or bird fossils- only reptiles, fish and invertebrates. In the strata that you first find mammals, they are found to be small, rodent-sized carnivores, unlike any living mammal... no large modern mammal types can be found. In the strata that contain Archaeopteryx, no types of modern birds are fossilized. In the level of the Australopithecine hominids, like Lucy, you can't find any Neandertal fossils. At the level where you uncover homo erectus fossils, there are no modern human remains. You never find people with dinosaurs, or dinosaurs with trilobites. It is very clear. There are no fossils found out of order. There are no paleontology discoveries that conflict with our understanding of how life evolved over the ages. Sure, we could have more examples of transitions, and I'm all for putting more paleontologists in the field to discover them. But consider this- in the big picture, nearly every species is a transition to another. Crocodiles haven't evolved much in the last 200 million years, but that's rare to find a species so well-fitted that it does not change over time. In this sense, nearly every fossil ever uncovered represents a transition to another species (except those species which resulted in extinction).
The fossil record mirrors the genetic record. The appearence of major groups in the fossil record is substantiated by relationships later shown by DNA comparison testing. There is no other explanation for this relationship between DNA and fossils besides evolution. (see also: Evidence for Evolution)
For evolution to take place, hundreds of millions of years must pass. Radiometric Dating methods ("Carbon 14 Dating") - are the means by which we know that the earth is incredibly old. The claims that these methods are unreliable is untrue. See also: Radiometric Dating for Beginners.
But evolution is "just a theory"!Go here for my answer to that.
What about God?The theory of evolution does not address the issue of God, either positively or negatively. The theory of evolution, like any scientific theory, certainly does not need the intervention of a deity, and there are many evolutionists who choose not to speculate about the involvement of God, for a number of reasons-- chiefly among them that there is no evidence to support such a notion, and scientific theories by definition need to be constructed on purely mechanistic, physical processes. On the other hand, there are evolutionists who choose to view the theory as the method by which God placed life on this planet. As this is America, they have the right to believe such. The decision whether or not to incorporate God into evolution is a personal one, based on prior beliefs.
See also: Evolution and Philosophy, and God and Evolution.
Other topics for beginners:
So, What's With this Second Law of Thermodynamics Thing?
In the Beginning...(the Origin of Life)
Carbon 14 and other Radiometric Dating Methods- good or bad?
But It's JUST a Theory!
What's Wrong with Creationism Anyway? (coming soon)
What about "Intelligent Design"? (coming soon)
Introduction to Evolutionary Biology, and The Five Major Misconceptions about Evolution