Evolution - A Primer of Sorts (Evolution)

Member Name: Redhead23

Product:	Evolution
Date:	18/08/01 (124 review reads)
Rating:

Advantages: Makes sense, Solves many mysteries, Interesting topic to discuss

Disadvantages: Public knowledge is watered down to a simplified version of evolution, leading to misunderstandings

Okay, when I saw this category I was at first a bit confused - while I don't have blind faith in science, evolution has so far appeared to me as the only credible explanation for the complexity and diversity of life on Earth and possible elsewhere in the Universe, be it in the past, present or future.

So how can they put this up for discussion - and in particular against WHAT? Is this a discussion about evolution vs. creation or a discussion about what being man *really* descends from - or is this about something else entirely and I have simply missed the point?

While I am aware that we don't descend from *apes* as such, I do know that genetically, apes are our closest relatives. We share a large amount of our genetic material with apes (in particular chimpanzees - 99% - and other primates), and to me it makes sense that at some point in the past there must have been a common ancestor. But I don't know ENOUGH about our exact genetic makeup nor do I have access to a fossil back catalogue that would allow me to compare our physical appearance to that of early primates, so I shall leave this part well alone.

But why else am I writing this opinion then? I guess it is mainly because I have just browsed through the previously written opinions in this category, and have realised that most people who disagree with good old Darwin don't seem to have understood his ideas properly (if at all).

I'm no expert on this subject, but I've read quite a few books (see "Recommended Reading" at the bottom) on evolution and genetics in addition to what I learned at Uni, so while I might not know all the proper terms and statistics, I still do have an understanding of evolution beyond the watered-down versions that are dished out in schools.


##### What is Evolution - The Basics #####

The first pillar for the theory of evolution is that over time, natural mutations* occur in the genetic makeup of
all living things due to copying mistakes and exposure to natural mutagens (i.e. substances that cause DNA to mutate, or change, through chemical and physical interference) and that - while many mutations either have no direct effect or result in decreased survival ability - such mutations can sometimes be of advantage to the specimen who carries it. That much is fact - mutations do occur, and they can either be indifferent, beneficial or detrimental to the life form they affect.

The second part of the theory is called 'Natural Selection', also known as 'Survival of the Fittest'.
A common misconception here is that 'Survival of the Fittest' only relates to how *big* and *strong* an individual is, but that is not really true for most cases. Adaptation is the key, i.e. the ability to cope with changes in the environment or to spread outside their own niche.

The idea behind natural selection is that, if there are different varieties of the same species, those individuals who - due to minute mutations - have a slight advantage over the other individuals who do not have that mutation, are on average a bit better off than the 'main group'. As a result, the individual with an advantageous mutation has a slightly higher chance of surviving, and is thus more likely to reproduce successfully and pass on that particular trait to its descendants.

Over time, beneficial mutations thus allow a species to adapt better to their environment. This increases their chances of survival, and the surviving mutants interbreed and fortify the mutation. Given sufficient time (we're talking many, many generations here), the smallest change can accumulate and become more complex.


Take for example a colony of birds that live on a secluded island. They're all pretty happy, have no predators threatening them and have plenty of food to feed the whole colony and produce offspring. These birds have for generations li
ved on the fruits of a certain plant, and the shape and size of their beaks is just right for the kind of food they normally eat.

Due to natural mutations, there are one or two birds that have a slightly different-shaped or sized beak, for example it is a bit straighter than the bent beaks of its colleagues. Under normal circumstances, this kind of bird wouldn't really stand a chance of setting a new trend - all his colleagues are happily munching away on their fruits, while a mutated bird either eats the fruits with more difficulty or has to make do with other kinds of food that are more suitable for its mutated beak to reach.

The mutation can either die out completely (either because the bird ladies don't fancy the slightly different shape of beak, or because the bird doesn't get enough food to become strong enough to impress potential mates - in both cases, the mutation doesn't get passed on because the bird has no offspring) or it will be watered down because the mutated bird still has the same chances as the other birds when it comes to surviving and reproducing, and thus the mutation doesn't get passed on to a larger amount of offspring than the 'normal beak' genes.

Now imagine that there is a reason why the amount of fruits isn't sufficient to feed the whole colony any more - for example the population rises abruptly or there is a change in climate and the plants the birds have been living on don't produce sufficient amounts of fruit anymore to feed the whole colony - the birds have a problem! Some of them will probably die of starvation because only the stronger birds in the group can get enough food - they might be able to fight better in order to defend their food sources.

But here, a bird with a slightly different beak has a nice advantage over all the others, even over the stronger birds - while they are stuck with fighting for the only food source they are able to reach, a bird with
a smalller, longer or straighter beak might also be able to reach food sources that the others can't get to, for example fruits that are hidden away deeper, say in the ground, inside the plant and so on. In the same way, a bird with a slightly stronger than average beak might be able to crack nuts and fruits that the other birds' beaks aren't able to open.

Now that the 'normal' birds are suffering a slight disadvantage, the 'outsiders' with ever so slightly different beaks will on average be slightly better-nourished than the majority of the colony, simply because they are not dependent on the same food source that the starving majority depends on. No matter how small that advantage is, it still means that the mutants stand a better chance at surviving, they are more likely to find a mate (because their ability to eat different foods makes them slightly stronger than the 'normal' specimens, and thus more eligible as potential mates) and will thus pass on the new trait to younger generations.

Over a long time, the trend for straighter or otherwise better adapted beaks will accumulate and other mutations can either increase the trend or push it in a different direction. Given hundreds or thousands of generations, the mutated strain of birds could have developed much longer and straighter beaks than the original population and established a new niche for themselves, while the original form has either died out (because the food source has dried out completely) or re-established itself after the food crisis - Voilà, there you have a new species of bird!


In the same way, it is quite obvious that in a snowy landscape, a white rabbit is much less likely to be spotted by a predator than a brown or grey rabbit - they can easily blend in with their environment, while a grey rabbit could be spotted from far away.

Now it would be ridiculous to claim that such changes from grey rabbit to white rabbit ta
ke place 'overnight' - and that is why I think many people have problems accepting Darwin's ideas.
But evolution doesn't happen overnight - it happens in tiny little steps that, if they are of advantage to the mutated individual, increase the individual's chances of survival and reproduction and over time, the trend accumulates and strengthens itself.

In the case of the rabbits, even the slightest trend towards a lighter-coloured coat will, on average, give a rabbit slightly higher chances of surviving because it is ever so slightly less visible to predators than the darker specimens. No matter how small a lighter-coloured rabbit's advantage is, over time there is a trend for rabbits in such a region to have ever lighter-coloured coats because these individuals are more likely to be overseen by predators and reproduce to pass on the trait.


*For example, modern humans have an average error rate of roughly 1 in 3.3*10^8, i.e. out of our 6.6*10^9 DNA 'letters', roughly 200 change in every generation. Quoted from Mark Ridley, "Mendel's Demon", see book list at the bottom.


##### When did this Evolution Malarkey start then? #####

While the origin of life itself is still a bit of a mystery (I'm open for various ideas, such as the boring old primordial soup, Divine or alien intervention or the newer theory that primitive life originated in rocks near vaults in the deep sea), it has been shown that even primitive molecules can 'evolve' and will compete for resources against other variations. One particular experiment showed that a strand of amino acids (the basic building blocks of life) put into one glass of nourishing solution after the other evolved into a different, faster-reproducing (the building blocks basically attach themselves to the existing strands) and more stable strand and eventually dominated the pool of strands in the glasses.

In the same way
, single-celled organisms can compete against each other - take for example an organism that has a gene for producing a protein coat around the cell. If the organism's genes mutate to produce a slightly different, more stable, protein, then the organism resulting from it will have a stronger coated cell and is less likely to die. A single-celled organism that divides faster than its rivals on the other hand will multiply at a much faster rate and soon dominate the pool of single-celled organisms, although limited resources (if the population lives in a secluded area cut off from other enviroments and resources) will soon put an end to the spread.


If you define life (I'm not talking about complex or even sentient life here) as a conservation and spreading of information - and that's basically what DNA is, a way of spreading and archiving information - then anything that allows the information to be spread more efficiently and into different niches will benefit the progress of life as such.

But in order for evolutionary progress to happen, you also need change - take for example a very isolated colony of single-celled organisms that live deep underground.
Let's assume there isn't really a limit on the resources - say because the area of soil they live in is very large - as a result, the population can grow without decreasing the available resources, so as long as the environmental conditions stay the same, most mutations would put the organism at a disadvantage.

This is simply because the area they live in stays the same, and resources are plentiful - being able to metabolise different chemicals than the rest of the organisms do wouldn't really be an advantage, as these chemicals might not be as plentiful as the original food source, and the mutated organisms wouldn't thrive any more than the rest, possibly even die out because they don't have as much resources as the 'normal' strains.
r>It is only when circumstances press a species to move into another niche (for example a warmer, drier, colder, wetter etc. environment or one where different chemicals are available to metabolise) in order to survive, that natural selection can come into the game and encourage different attributes rather than reinforce the 'traditional' ones.

There are still single-celled life forms populating secluded areas of Earth that are not much different from the early forms of life, and one ends up wondering why the heck they didn't move on to something 'higher' up the evolutionary ladder. The only satisfying answer so far seems to be that there is no NEED to - as long as a species has its established living space and has enough resources to continue doing what it's good at, then any trend away from that adapted norm will have a negative effect and will not become stronger.

It is quite possible that life did indeed start out near the bottom of our oceans, where organic molecules got trapped in the porous stones. If that is the case, then the intense volcanic activity of Earth's beginnings might actually have contributed to the development of complex - and later sentient - life forms. This is simply because volcanic activity can disrupt and change the environment, for example by propelling rocks from the bottom of the sea to higher regions, maybe even onto dry land. In such a situation, mutations that were previously useless can lead to adaptation to the new circumstances, and thus allow life to spread into new areas and become more complex.

In the same way, the 'mysterious' (well it was very likely a meteorite impact or a similar natural catastrophe) extinction of the dinosaurs is another example of how change and adaptation lead to evolution and thus more complex life. Back in that time, there weren't that many other species around - primitive insects, fish, mammals and smaller reptiles were pretty much t
he only non-plant life that competed with the dinosaurs. The dinosaurs were mostly big, mighty and powerful - and the other life forms often ended up living hidden away from the surface in order to avoid being eaten by the nasty predators - underground, under rocks, in the deep seas and so on, where the big predators couldn't reach them.

A major catastrophe that affects the surface of the Earth - for example by blocking out sunlight after a massive meteorite impact - can end up diminishing the plant life, reducing the population of herbivore dinosaurs and in the end killing the predatory dinosaurs because there are is not enough prey to hunt. The plants will survive over time, as their spores can survive for a long time and will bud once the conditions have improved again - but the larger surface-dwelling dinosaurs weren't so lucky. While they were quickly running out of food, the smaller (proto-) mammals, insects, reptiles and fish had already adapted to living 'out of the way', i.e. underground, in caves, the deep sea and so on, so such a catastrophe affecting the surface life isn't all that much of a change to them.

Once the dinosaurs were wiped from the face of the Earth, the other species finally got the chance to spread and explore new niches. Personally, I doubt that mankind would even be here if the dinosaurs hadn't been wiped out, but that's just my opinion. Then again, maybe dinosaurs had stagnated in their evolution and would have died out anyway, just a bit later...


##### Why I believe in Evolution #####

Rather than blindly believing in evolution 'just like that', I tried to understand it and follow the ideas with my own thoughts - so far, it makes a lot of sense, much more so than simply stamping it off as 'It's God's work, y'know'. After all, isn't using an even more complex, much harder to understand being like God to explain US being here a bit too e
asy a way out? Explaining away something you don't understand by blaming it on Divine intervention doesn't make the real question go away, it's just easier than trying to understand the subject and drawing your own conclusions from it.

The problem is of course that it is difficult to 'prove' an evolutionary step - after all, the life forms that roamed Earth before us didn't purposely drop dead in places where they could be fossilised and preserved for us to analyse millennia down the line!

The few fossil records we have are sheer coincidence, and the fact that we have no fossil records of some in-between stages does not necessarily mean that these life forms never existed - they just happened to live and die in an area where either the geological circumstances didn't allow fossilisation, or where seismic activity destroyed any existing fossils. In addition, we can't just dig up every inch of the planet to look for fossils, so quite a large amount of fossils may never be uncovered.

In many cases, large fossil excavations are often the result of an accident in the past, i.e. a large group of a species was surprised by flood and drowned, allowing the sediments to fossilise their bones. It's not all that easy to find such places, and it's even harder to track down one for a particular species you are looking for.

One other point about the 'missing link' is this: evolutionary progress very often coincides with a change in circumstances, be it because the environmental conditions changed or because groups of a species were geographically separated. This also means that, unless the precise conditions that lead to a migration or environmental change are known, it is nigh-on impossible to find out where exactly they went.


But while the fossil records may not be able to prove anything, I still believe that Darwin's theory of evolution makes a hell of a lot of sense, especial
ly since the discovery and exploration of genes later backed up Darwin's speculations. While Darwin still believed that the traits of a life form are 'blended' in the offspring (this gave Darwin doubts about his own theory, as a blending would always weaken genetic traits rather than preserve them during reproduction), we now know that in complex life genetic material is passed on in the form of chromosomes, and that whole genes and gene complexes can be passed on to the next generation in one piece, although they might not always get expressed.

Had Darwin and Mendel (who lived around roughly the same time) been able to exchange their ideas, I am quite sure that they would both have been much more confident in their work. But hey, that's life in all its complexity and weirdness! ;-)


I hope I made the concept of evolution a little clearer now. If not, please let me know.
Alternatively, below is a list of books that cover the subject rather well.
Thanks for reading this if you've made it this far :-P

Redhead23


##### Recommended Reads #####


"The Blind Watchmaker", Richard Dawkins, Oxford University Press

This book explains the workings of natural selection extremely well, and even without any prior knowledge of genetics you should be able to get a wonderful insight into how complex life could evolve from simple life. Contains many interesting examples from zoology.


"The Selfish Gene", Richard Dawkins, Oxford University Press

This goes more into the genetic aspects of evolution, but is a very interesting read that explains many of the curiosities of life as well as providing interesting examples of adaptation to specialised niches.


"Mendel's Demon", Mark Ridley, Phoenix/Orion Books Ltd

Discusses the problems that arise from the mutations necessary for evolution to happen and deals with the quest
ion of how complex life could arise in spite of the danger of a 'mutational meltdown', the danger of losing information through random changes.


"The Fifth Miracle", Paul Davies, Penguin Science

This deals with the origin of life, possible theories and the question of whether or not we're alone in the universe.


"Darwin's Radio", Greg Bear, Harper Collins Publishers

A Sci-Fi novel that comes up with an imaginative and plausible 'missing link' theory and also features an extensive glossary to brush up the readers' knowledge of genetics.