Evolution - what YOU need to know

Courtesy: Evolution for Creationists
Over the years I have discussed evolution and creationism with a number of theists, and they often have many misconceptions about exactly what evolution is. I would like to try to set the record straight here, as well as provide a useful introduction to the theory of evolution.
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So it's a "theory" - so what?

theory - an explanation or system of anything.
Many anti-evolutionists will say "Yes, but it's only a theory, it's not real is it?"
People who say this are confused about what a theory, in the scientific sense, actually is. From my emails I know that the single most commonmisconception about evolution is to confuse the fact and the theory.

Evolution is a fact. Shocking and controversial this might sound, but bear with me. I'm not talking about Darwin's theory of evolution by natural selection. I'm talking about the changes in the gene pools of all species that occur every single day due to births and deaths. If you accept that most members of a species do not all have the exact same DNA (which is easily demonstrated), and you accept that sexual reproduction combines the DNA of two parents to form a slightly different combination of genes, and you accept that not all creatures survive long enough to be able to reproduce, then....

You have accepted that evolution is an observed, natural fact. That's all it is. A change in the genes over time. Evolution happens. Things evolve. That's what it means. There is no debate in the scientific community as to whether or not evolution is a fact. It is a fact of nature, just like gravity.

The theory of evolution, on the other hand, is an attempt to describe what is happening, how and why. The theory describes the facts and the evidence. The theory comes after observation of the facts. The theory of evolution may be hopelessly wrong (although it has stood the test of time for 150 years already), but that would not change the fact that evolution occurs - we would just have to find a new and better theory for explaining it.

A good theory can also be used to produce predictions about future observations based on the known facts and evidence. A theory should also be falsifiable - this means that it should be possible to think of an experiment that would prove the theory wrong if it is not sound. One of the big problems with creationist hypotheses is that they are not open to refutation - any possible set of evidence can be explained away with some variation on "God did it, for Mysterious Reasons".

"Theory" as used by scientists has a quite different meaning to "theory" as used by a bloke you met in the pub. A theory is an attempt to explain a observed phenomenon using evidence and experiment, not a wild guess or something that just popped into your head a moment ago.

For example, aerodynamics theory allows us to build large passenger aircraft. Tons of metal that flies because theory predicted that the wings would suck it up into the sky. Sounds unlikely, but it works. Would you refuse to get on board a 747 because it was designed by theorists?

Theories are often used to explain "laws". The Law Of Gravity is fairly obvious - drop an apple and it will fall onto the head of any scientists sitting below. (Slightly more precisely, objects are attracted to each other by the force of gravity). The theory of gravitation attempts to explain the law of gravity in detail; how it works, and what causes it. The theory of evolution, likewise, attempts to describe and explain the observed fact of evolution. Evolution happens. It can be seen, measured and experimented with. The theory of evolution describes the facts of evolution. Even if the theory of evolution turns out to be completely wrong, that won't alter the fact that evolution still actually happens - we'll just need a better explanation (one which will not only explain everything that the theory of evolution did, but it would also have to explain why the theory of evolution worked so well for so long).

Evolutionary theory is still being debated. The underlying principles are very well understood and agreed upon, but there is still disagreement over many of the fine details. This does not mean that it should be discarded, or that it is simply wrong. It just needs more work. You can test your theories of aerodynamics in a wind-tunnel in just a few hours. To properly test evolution, you really need a test-tube the size of a planet and a few billion years (but for now, we'll just have to settle for creating new species in labs).

If good, solid evidence is produced that contradicts the theory of evolution, then (as with all theories) it will have to be either radically modified to fit the new evidence, or abandoned if that is not possible. Nobody has yet managed to produce such evidence...

One of the problems with developing evolutionary theory is that large changes happen over a very long period of time. Small-scale evolutionary changes can be done today - dog-breeding, myxamatosis-resistant rabbits in Australia, the Goatsbeard flower in America, fruit-flies in laboratories, antibiotic resistant bacteria. Evolution is happening, and to deny that is foolish. To say "It's only a theory, so it doesn't mean anything." is also foolish. It is a theory supported by overwhelming, freely available evidence, with just a few details to iron out. I think many creationists realise this, which is why they are trying to demolish the theory by ridicule and misinformation (if you came here thinking it's "just a theory, just a wild guess" then you have fallen victim to their campaign) or prevent it from being taught in schools. If they are so sure it is wrong, all they have to do is disprove it by normal, rational, scientific means. They're not having much luck so far, which is why they rely on misrepresentation of the facts.

Think about the theories that keep your plane in the air, next time you go to the airport. Would you refuse to board it because it was designed using "just" the theories of aerodynamicists and engineers?

(For more about what is and is not a theory, check the Infidels library. )

This section is expanded upon further in Fact AND Theory.

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Human beings are not the ultimate result of evolution

Some people think that eventually all species will evolve into human beings - that we are somehow the ultimate creature, that we are the best there can be, that the evolution of all organisms is striving to converge on the human being. The analogy is that evolution is a sort of ladder, with each rung representing a higher level of "perfectness". Naturally, we humans are right at the top of this ladder.

This is a complete fallacy.

Crocodiles, for instance, will never evolve into humans. Crocodiles haven't really changed much at all over the last hundred millions years or so. They are extremely well adapted to their environment, and there is little (if any) "evolutionary pressure" being exerted on them. What that means is that their environment is not changing in any drastic manner, and they have no predators preying on them. In order for them to change it would require some sort of external influence that affected their chances of living long enough to reproduce and pass on their genes to their children.

Humans may eventually evolve into something measurably different, though it takes a vast amount of time to do so. For the moment, we fit into the ecological niche that we suit best. Humans are not the most complex creatures ever to have lived. The only thing that sets us apart from other animals is our intelligence. Our bodies work in pretty much the same way as the bodies of other mammals. Our bones aren't tougher, our muscles aren't stronger, and our blood isn't better at carrying oxygen. Apart from our brains, we are quite unremarkable.

Where certain conditions exist, creatures most suited to those conditions will live and thrive there, slowly becoming extremely well adapted to those conditions. If the conditions change, the creatures less able to adapt will die out, being replaced by the offspring of the members of the population who were slightly more suitable. Those genes that helped the creatures survive to reproduce are passed on, increasing in number in the gene pool - those that prevented it from managing to reproduce are not passed on, decreasing in number in the gene pool. This is basically how evolution works.

If you imagine nature producing an environment which requires certain characteristics for survival (such as deep-ocean vents, or rainforest canopy, or hot deserts), it is likely that creatures will gradually evolve with those characteristics, to "fit the hole" that nature provides.

As a simple example, imagine a world that has deep oceans and warm, sunny beaches (much like ours). In the sea live some crabs. To begin with, these crabs can only survive in water a few feet deep. Their world ends where the tide washes up and down the shoreline - they can eat, live and breed only in the warm shallows. As there is more food in the warmer, sunnier waters near the beach, the crabs are driven there to feed. As the waves crash in and out, some will be washed up onto dry land, or stranded on a sand-bank as the tide goes out, and perish. Others might be able to survive just long enough to scuttle back into the sea. This creates what is called a "selective pressure" on the crabs - natural selection weeds out those individuals unable to tolerate being out of water for prolonged periods. Those who can will be able to spend much more time on the shoreline - they will get the richer pickings, and they will have a greater probability of breeding and passing on their genes. Some of their offspring might not be able to last as long out of water as the parents, but others might be able to tolerate it a little more. Again, these will have a slight advantage in terms of feeding, mating and survival (they might be able to escape marine predators by climbing onto a dry rock). It becomes a positive feedback loop. The genes of those who survived longest and generated the most offspring will become more abundant in the population as a whole. After many generations, the crabs will be scuttling around on the beach, foraging for food, no longer restricted to a purely marine lifestyle.

Over time, different evironmental conditions will shape different aspects of their bodies. They may come to rely on a particular type of food, or they shell may change in size and shape (to provide protection against the environment or predators). They will come to be radically different from their ancestors - a new species. They are, of course, still crabs - but they are a new type of crab, unable to breed with (or even meet) the species that they originated from. After a million years of separation and differing environmental conditions, these new crabs may have split further into a number of different, new species, or may have been changed into a type of creature that can no longer be called a crab.

Evolution is not a ladder - it's an enormous bush with millions of branches. We humans (and the chimps, gorillas and other apes) are just the current crop of leaves on part of the vertebrate/mammal/primate branch. As long as life exists on this planet, the bush will keep on spreading, and humans will be just one more branching-point with several new twigs growing from it.

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Human beings are not descended from gorillas or chimpanzees

This is a rather foolish idea that creationists like to use to discredit the theory of evolution. They say "Evolution teaches us that our great-great-great-grandparents were monkeys. How ridiculous. Ho hoho". We are not descendants of apes - we are apes. If alien collectors came to Earth and beamed up a bunch of animals, they would put humans in the same collections as chimps and gorillas. In terms of taxonomy, we are just a strange type of big-brained, bald ape. Gorillas, chimps, orang-utans and humans are all part of the same section of the evolutionary hierarchy, just on different branches. We are not "higher" than gorillas; we have not evolved from them, but alongside them. We share a common ape-like ancestor with them (in the same way that we share a common ancestor with all primates, and then all mammals, and then all verterbrates and so on). That is the difference.

Again, creationists would still be unhappy at this idea. But hey, if we are not apes, then what are we? We are

  1. Kingdom - Animal
  2. Phylum - Chordata - have backbone
  3. Class - Mammalia - females have mammary glands
  4. Order - Primates - single pair of mammary glands
  5. Family - Hominidae - erect, two-footed walk
  6. Genus - Homo
  7. Species - sapiens ( Homo sapiens - You and me, friend).
and our DNA differs from that of the other Great Apes by only a fraction. Our skeletons, internal organs, nervous system and so on are almost identical to that of the other apes. We differ only in that we are less hairy and more intelligent ( usually :)

Some people still don't get it :
"We are Homo sapiens, you can consider yourself a primate, however I don't." - zoner, alt.atheism

If we are not apes, what are we? Fish? Fungi? How do we differ so much that we cannot be included in the same family as chimps and gorillas? How can we be distinct from chimps if we share 99% (approximately - some sources say it's about 98%, others go as high as 99.6%) of the same DNA, including pseudogenes ( "junk" DNA - see Further Reading section at the end).

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Doesn't "Survival of the fittest" mean it's good for the strong to destroy the weak?

The idea that the theory of evolution advocates racism is dealt with on my Evolution And Racism page.

Apart from that, it is a common misunderstanding that "survival of the fittest" means (in humans terms) survival of the biggest, strongest and most technologically advanced. Historically, this attitude has been used to justify the domination and destruction of technologically less advanced cultures ("Look, these people don't have locomotives! They are obviously sub-human beasts. We'd better slaughter them for the good of the species!").

"Fitness", in terms of evolution, simply means "best adapted to the environment". For example, if your environment contained a pack of hungry lions, yourself and a tortoise, the tortoise is a lot more likely to survive lion-attack than you are. You might be bigger, stronger, faster and brainier than the tortoise, but he's the one with retractable limbs and a hard, thick shell. Fitness does not refer to speed and strength, but the ability to live long enough to reproduce and pass on your genes to the next generation. ( Further clarification on this )

As the environment changes, so to do the attributes that contribute to the fitness of a species. If the climate changes, or a food supply is lost, or a new predator comes along, then the fitness of the individual will be judged on how well it can cope with the new situation. It may be that fleetness of foot matters less, and thickness of fur matters more. Natural selection will either destroy the species or cause it to be changed over subsequent generations until it is "fit" once more.

Dangerous environments drive evolution (as mentioned above, crocodiles aren't in much danger from anything, which is why they haven't evolved greatly for a long time). Strong selective pressures cause a species to evolve rapidly. This is one of the reasons why hospitals are having trouble with anti-biotic resistant bacteria - if the drugs kill 99% of the bugs, that leaves the last 1% who are resistant to the drug. These are the ones that will create the next generation, naturally much more resistant to the same drugs. Some bacteria have even been found that actually feed on anti-biotics! From an evolutionary point of view, this is to be expected - it is inevitable.

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Creatures do not decide how to evolve

I spoke with someone once who thought that things evolved by deciding to, like this:
lungfish : Oh, I need to get further up the beach for food. I'd better grow stronger legs.
amphibian : What a nice beach, but now I'd like to climb that tree, I'd better evolve into a monkey.
monkey : If only I had a better brain...
Tinman : If I only had a heart... (sorry, couldn't resist that)
And so on.

This is obviously nonsense. Try it yourself. Tonight, will yourself to be able to see infra-red and see what your eyes are like in the morning.

This is the way it works:
In a population, there will be minor differences in all the creatures (unless they are all identical twins). These differences will give each creature minor advantages or disadvantages over other members of the population. When the environment around them changes (trees growing taller, introduction of predators, disease, whatever) some of the creatures will be better suited to those circumstances than others, increasing their own chances of survival and likelihood to successfullymate. (If this doesn't make sense, please let me know why not.)

Their offspring will inherit some of the characteristics of their parents, giving them a slight advantage over their peers. This is called evolution through natural selection. Survival of the fittest. It is a remarkably simple concept. (See the crab story, above)

Indivudal organisms DO NOT EVOLVE. I am not evolving, you are not evolving, your pet goldfish is not evolving. Your genetic makeup will remain as it was when you were born. However, the frequency of different genes in all members of species does change over time, with every single birth and death. Evolution applies to an entire species over many generations, but not to individual members. To use a rough analogy, think of the design of our vehicles. They have changed from horse-drawn carts, through the Ford "Model T", to our modern cars. Vehicle design has changed over time, but the individual vehicles themselves do not alter. A "Model T" will not slowly become a Pontiac Firebird if you leave it in the garage long enough, but as time goes by, the "species" of motor vehicles does change.

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Species do not spontaneously change into new species

Another method used to attempt to discredit evolution is the following:
"So, according to evolutionary theory, species keep changing from one to another? Whoever heard of a fish giving birth to a frog? Whoever heard of an frog giving birth to a monkey? How ridiculous! What nonsense it is!"

Well, that certainly is nonsense, and that idea is only ever used by creationists who either don't understand what they're talking about, or just want to heap ridicule on it by misrepresenting it. No evolutionist would even think about suggesting such a stupid idea. To say that one species suddenly starts giving birth to new animals is to demonstrate ignorance about the theory of evolution (or worse, misrepresentation of easily-understood science).

However, it is true to say that a creature may give birth to something that is 0.0001% closer to being a truly different species. After a few million years, and thousands and thousands of generations, a new species may well have evolved (ie. one that is measurably different to it's ancestors, and could not breed with members of the original species).

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Complex organs such as eyes can evolve gradually

Many creationists use the example of the human eye to debunk evolution. The argument goes like this:
The human eye is an extremely complex organ, with many parts working in unison for it to function - the lens, retina, iris, optic nerve, muscles etc. It would be impossible for such a thing to spontaneously pop into existence, and each of the individual parts are uselesswithout the rest.

Well, I agree. That is a perfectly valid argument. However, no evolutionist would even consider suggesting that the eye simply appeared on some new-born primate a million years ago.

The eye evolved very slowly, over a long span of time, starting with a simple patch of light-sensitive cells, and evolving into it's present state. The following rough diagram illustrates the development:

eyeball evolution

The green represents the creature that is evolving, the pink represents light-sensitive cells. Imagine these changes happening over a period of two million years (which is a microscopic fraction of the history of the Earth), each generation of creatures only changing by afraction of a percent).
A: The creature is blind. This has obvious disadvantages as it cannot see predators approaching, and has to relyon sound, smell etc.

B: A random mutation has given this creature a patch of light-sensitive cells (not a problem - see below). It can detect light and dark. A sudden change of light to dark could indicate a predator approaching, allowing the creature to defend itself (by fleeing, fighting etc.) and dramatically increase it's chances of surviving and reproducing. Which is more likely to survive long enough to reproduce - a creature that runs when a shadow passes over it, or one that stands still? Your skin is covered in cells/nerves that detect heat, pressure, taste, smell and so on. Light is not that much different (see below).

C: Two patches, one either side of the head have developed (no surprise, as symettrical mutations are very common). The creatures can now determine which side the shadow is approaching from, and run in the opposite direction (or it may distinguish open spaces from dark shelter, for instance). Again, a huge improvement in their chances of survival from a fairly small change in their body. Slugs and snails see like this (admittedly, they can't run very well, but who wants to eat a slug anyway?).

D: If the patch of cells becomes hollow, cup-shaped, it gives the ability to better determine the direction of light (a dome would work just as well, but would be easier to damage. Also, a hollow would help create greater contrast with well-defined shadows). One side of the cup will be better-lit than the other. This creature can therefore better determine the direction that a shadow is approaching from (or, again, find a dark shelter more easily).

E: The hollow deepens over time and starts to close in on itself. A photographer would recognise this a pin-hole camera. It will form a reasonable image on the cells (retina), allowing the creature to see shapes, not just differentiate between light and dark. The Nautilus (a marine mollusc) has eyes exactly like this.

F: A transparent membrane covers the pin-hole, forming a crude lens (alternatively, the eye may be filled with a transparent jelly). This will make the images formed on the retina much sharper as well as protecting the delicate surface from dirt and infections. The creature can see predators/prey much more clearly now.

G: Muscles around the lens develop, allowing the creature to alter the shape of the lens and change focus. Now it can clearly see objects close by or far away. This is how the eyes of most mammals (such as humans) function. The Chameleon's eyes are quite different - instead of changing the shape of the lens, muscles move the lens backwards and forwards to focus the image, in the same way that an auto-focus camera works.

Further incremental refinements include the iris (to restrict the amount of light), eyelids (to protect and clean the surface of the eye) and muscles to rotate the eyes.

This is not the way all eyes develop - there are thousands of different styles of eye in the world, all doing a similar job in different ways. Eyes do not develop quickly, but over thousands of generations (on the geological timescale, this is still just the blink of an eye. Ho ho!). To say that "half an eye is no use" is wrong. Half an eye (eg. example D) is much better than no eye at all.

Many creationists would say "But how did those first light-sensitive cells appear?". Well, your entire body is covered with light-sensitive cells. Your skin can detect heat radiation, can it not? What is this radiation? Infra-red light! It is easy to see how small mutations could lead infra-red sensitive cells to become more sensitive to shorter wavelengths of light, ie. "visible" light. Also, photons of certain wavelengths are absorbed by certain pigments/chemicals, affecting the chemistry of the cell in a manner that the brain may detect.

Remember, the creatures do not consciously attempt to grow eyes, and evolution does not drive them towards having any particular type of eye. Each new, tiny, random change will either increase or decrease that individual's chances of surviving to reproduce. Obviously, the ones that do manage to reproduce will pass on those characteristics that enabled them to do so.

Our eyes are allright, and serve us well, but there are creatures with far more complex optical systems than the human eye. Ours may evolve a bit more, but they do their job well enough for survival, which is what it's all about.

As an aside, it should be noted that the human eye is still quite badly "designed":

(Personally, I'd like a good zoom-lens and the ability to choose the wavelengths I can perceive. A God could have done a better job of it, but we're stuck with crappy old natural evolution. Oh well...)

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Creatures are not colourful just to please God

One of the more bizarre discussions I had on alt.atheism was about camouflage and dramatic colouration on various animals - stripes, spot, bright and shiny colours on animals, birds and fish.

The theist I was talking to believed that animals such as the Zebra could not possibly have arisen through evolution, and that their markings were decisive proof that God exists. He thought that the distinctive black and white stripes of the Zebra can have no other possible purpose than to be aesthetically pleasing to God.

I explained the purpose of such markings, and how they could quite easily arise through simple natural selection:
Individually, Zebra stripes make the animal stand out dramatically against any background, except for that of a herd of Zebra. When the herd is together, the stripes serve to break up the outline of individuals, making it harder for predators to select any individual.Even though Zebras that become seperated from the herd are much more likely to be killed and eaten, the ones in the herd will be safer.
The purpose of camouflage is to hide the creature using it, by breaking up it's outline and blending it in with it's background. Inthe case of the Zebra, the herd creates it's own background.

He didn't see it that way, though. The conversation changed from land animals to fish, as I have a couple of tropical fish tanks (I don't have any Zebras in the house) and could use them as examples. Small colourful fish, like the Neon Tetra, which swim in large shoals and have bright, colourful shiny scales are a good example.

Neon Tetra
A single Neon Tetra. Pretty, isn't it?

In the wild, the Neon Tetras in a shoal move together, presenting a mass of quickly changing, brightly coloured shapes to a potential predator. Each member of the shoal hides within the shoal itself. The chances of any one individual being killed are quite small, and the shoal itself will certainly survive. Again, fish that become seperated from the shoal have a slim chance of survival, as they are easy to spot, but within the ever-changing mass of the shoal, they should be much safer.

Neon Tetra
A whole bunch of them. But... Oh no! Where's the first one gone?!?

Again, my "adversary" could not see it that way. He did not think that any form of camouflage had any beneficial effects for any creature, predator (eg. tiger) or prey (eg. zebra). He had been pretty much backed into a corner by his own beliefs by now, under the relentless attack of logic and reason and factual example. So, as is too often the case when debating against theists, he opted for a pitiful cop-out.
I asked him what theory he had to explain why some creatures are killed and others are not, and what did he say?

"Guardian Angels"

- he thought that each fish in the river, each zebra in Africa, has it's own personal guardian angel to protect it from predators (they don't seem to be doing a very good job, otherwise there would be no lions), and that camouflage and colouration had absolutely no other purpose than to please God.

It is very difficult to argue against this sort of mind-set, but you can get some remarkable results if you persevere.

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Don't I have to give up belief in God if I accept evolution?

Some people feel that evolution pretty much does away with the need for a God. Others feel that evolution is one of the mechanisms that God uses to make things work. This response to a similar question from the talk.origins archive feedback section sums it up quite well :

from June 1998 feedback

"As a Christian who does accept evolution as a fact I also want to point out that as a Christian I am also a creationist, in that I believe that "In the Beginning God created the Heavens and the Earth." Far from being a religious belief thatbegins with "there is no God", evolution is simply one of the tools that God created to run His creation. Other tools include gravity, electromagnetism and the strong nuclear force. The Bible says that God holds all things together. Yet modern science tells us that the three forces I just mentioned are what hold all of matter together, from protons and neutrons all the way up collosal galactic clusters. In other words, God is not needed. Does this mean that those three forces are really religious beliefs that begin with "there is no God"? The Bible also says that God is the cause of all disease and the cure for all disease. Does this mean that thegerm theory of disease and the immunological theory of disease resistance are beliefs that begin with "there is no God" because God isno longer needed to explain epidemeology?

It is certainly true that God transcends the natural universe and could have made it any way He wanted to. However, His creation -- the universe -- isby definition a natural phenomenon. It is controlled by naturalistic, mechanistic forces and what we can see of it appears to evolve over time. Unless God is trying to fool us, it would appear quite obvious that God indeed has used evolution to createand develop the modern universe.

For more information see the archive God and Evolution.

It is not necessary to abandon your beliefs because of evolution. Many theists find that it actually strengthens their faith as they can see and understand the processes used by their God.

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© Adrian Barnett 1998,1999
Last updated: 14th March 1999

Constructive criticism of this is always welcome. I'm a programmer, not a biologist. If I've screwed up somewhere, let me know.

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