Some questions from a newbie

[Djalapeno86]

Hi everyone,

 

I'm an engineer who enjoys philosophy and science but nevertheless forgot a lot of things about evolution. Recently I had a long discussion with my friends and came up with questions of which I can't answers on the internet and textbooks.

 

1. Are we still evolving (obviously it should be so)? But what is the evidence that we have been evolving in the last...say 500 years and what are these changes? Any legit reference?

2. Can external conditions cause genes to change? If yes, why parents with unaligned teeth who wear braces will still have kids with unaligned teeth? If no, then how do species evolve in the first place?

3. People have different skin color, height, hair etc and therefore have slightly DNAs, right? We call this variation, I believe. Chimpanzees' DNA is 97% similar to ours (or some number along the line). What is the cutoff that distinguish variation and different species, then? 99.99%?

 

Thanks in advance!

[rktpro]

1 I think in the past 500 hundred years no evolution has been observed.

2 External conditions or the conditions of environment results in evolution of species not their physical conditions.

 

By the way, I am myself confused at this.

If we assume that evolution is true then why not we still get a...er...fish from an elephant?

And if you ask them how boneless amoeba attained bones-they say it is due to Mental Encouragement!

But there is no relation between bone and brain. Prick your teeth with pin and you get no pain!

CONFUSED-everyone is.

[JorgeLobo]

to:

#1. Evolution is presumed to be continuing - and slowly as before.

 

#2 - the mantra is "acquired changes are not inherited." Why would you expect them to be? To your example, how would braces affect the genetic information of sperm and ova?

#3. Not aware of a cutoff of the "similarity" % that distinguishes species. Understand that metric speaks more to technique than taxonomy.

[SMF]

Jalapeno86 and JorgeLobo. The species concept can be difficult and there are several definitions. One version involves the metrics of physical traits and is mostly important to paleontologists. Another definition is based on reproductive isolation. So, if there are groups of animals that cannot interbreed because they are on distant islands, they could be considered to be separate species even if they appear identical and can breed successfully in the laboratory. I think the least confusing definition is the biological one that says that species consist of groups of animals that are able to interbreed with complete interfertility (e.g. produce viable young) whether they do or not. This definition would say that horses and donkeys are separate species because mules are not naturally fertile. In actual practice, all three of these descriptions, along with the new genetic understanding, are blended into an operational definition for research purposes.

 

Rktpro, it would take hundreds of millions of years for an elephant to evolve into a fish. I can't even think of the series of selection pressures that might have this result and all the ecological niches in this pathway are currently already occupied. As for comparing amoebas and you with your internal bones, it would be better to make the comparison between amoebas and your osteoblasts that make and maintain your bones. An osteoblast crawls about in the same manner as an amoeba and has a similar appearance, although smaller, and secretes the components of bone into the extracellular environment. Secretion is common to all single cell organisms. In fact, every cell in your body was a freely roaming cell during its development and you are just a colony of these cells, so you had better keep them happy because they might decide to all split at once and you will dissolve like the wicked witch of the west. Your confusion regarding evolutionary mechanisms is easily cured with a little study.

 

SM

Edited March 23, 2011 by SMF

[Ringer]

1. Are we still evolving (obviously it should be so)? But what is the evidence that we have been evolving in the last...say 500 years and what are these changes? Any legit reference?

 

Yes. . .

http://www.sciencemag.org/content/309/5741/1720.short

http://www.sciencemag.org/content/309/5741/1717.short

 

That's from a single issue of Science, there are more floating around

2. Can external conditions cause genes to change? If yes, why parents with unaligned teeth who wear braces will still have kids with unaligned teeth? If no, then how do species evolve in the first place?

External conditions and acquired traits are different. Your example is acquired trait; also if external condition does cause mutation in a gamete it will not affect the genome of the parent. There are also many other ways genes can mutate without external influence, such as mistakes being made during transcription.

 

3. People have different skin color, height, hair etc and therefore have slightly DNAs, right? We call this variation, I believe. Chimpanzees' DNA is 97% similar to ours (or some number along the line). What is the cutoff that distinguish variation and different species, then? 99.99%?

 

This is a fairly difficult question to answer. You have to realize our definition of species is rather arbitrary. Usually we refer to a species as a population that is capable of interbreeding in nature and can produce viable offspring. Obviously this definition has some problems but it works for this. And remember the way we define species was in place long before genome sequences were coming out.

 

Saying the our genes and Chimp genes our 99% similar can be misleading to some for just the reason you said. Our DNA has a certain amount of DNA that actually codes for certain amino acids and portions that are non-coding DNA. We all have, for the most part, the same coding and non-coding segments. We all have 23 homologous pairs. Chimps have a different number of coding and non-coding segments, a different number of homologous pairs, etc. An example is our chromosome 2, which is evolved from 2 separate chromosome that our on a chimpanzee. There are a lot of other things one could get into but hopefully this gives the gist.

 

 

 

[Djalapeno86]

For #2: Aren't wearing braces and, let's say an environmental condition that forces a duck to hunt underwater (just making this example up), are both physical alteration? I know that wearing braces won't change your genetic information, but how does the later example do in such a way that it evolved to....emmmmm....platypus? Sorry I couldn't find a better example, but you got the premise.

 

to:

#1. Evolution is presumed to be continuing - and slowly as before.

 

#2 - the mantra is "acquired changes are not inherited." Why would you expect them to be? To your example, how would braces affect the genetic information of sperm and ova?

#3. Not aware of a cutoff of the "similarity" % that distinguishes species. Understand that metric speaks more to technique than taxonomy.

 

Focusing #2 (I think I got the ideas for my questions #1 and #3):

 

Let's take a population of giraffe for example. Let's say in the beginning there are 50% short necked ones and 50% long necked giraffes. Pulling your own neck over 30 years won't change any of your DNA information, correct?

 

What constitutes evolution are:

1. Mutation

2. Gene crossovers

 

The question is how do we end up with all long-necked giraffes today? Is it because of:

1. Many of the short ones died without having the chance to breed?

2. Or is it because nature has determined that the dominating trait (if a long-necked giraffe and a short-necked giraffe mate) is "long-neck"? Or is it a combination of both?

3. Pulling their neck actually does change their genetic information...very very slightly. And if your offsprings keep doing the same thing, and their offsrpings etc, then it'll build up and you'll have a slightly taller giraffes and so on.

 

If the first one is true, then in our society evolution is not required because:

1. People support each other to a certain extend. People won't die easily as inferior giraffes.

2. Technology improves survival

 

And therefore the human population won't converge to a single definable population with "ideal" traits. The diversity will be maintained at least to a certain extend.

 

If the second is true, then it is a scary thought that nature actually "selects" what traits are good or bad for you. But I know this is unlikely based on direct observation of human population.

 

The third sounds appealing to me. But I don't know how valid that is lol....

 

 

 

External conditions and acquired traits are different. Your example is acquired trait; also if external condition does cause mutation in a gamete it will not affect the genome of the parent. There are also many other ways genes can mutate without external influence, such as mistakes being made during transcription.

 

 

 

 

 

Thanks for all the responses guys! I am pretty satisfied with issue 1 and 3, but I'd like to explore more on issue 2.

 

Let me just copy my reply to Ringer:

 

==========

Focusing #2 (I think I got the ideas for my questions #1 and #3):

 

Let's take a population of giraffe for example. Let's say in the beginning there are 50% short necked ones and 50% long necked giraffes. Pulling your own neck over 30 years won't change any of your DNA information, correct?

 

What constitutes evolution are:

1. Mutation

2. Gene crossovers

 

The question is how do we end up with all long-necked giraffes today? Is it because of:

1. Many of the short ones died without having the chance to breed?

2. Or is it because nature has determined that the dominating trait (if a long-necked giraffe and a short-necked giraffe mate) is "long-neck"? Or is it a combination of both?

3. Pulling their neck actually does change their genetic information...very very slightly. And if your offsprings keep doing the same thing, and their offsrpings etc, then it'll build up and you'll have a slightly taller giraffes and so on.

 

If the first one is true, then in our society evolution is not required because:

1. People support each other to a certain extend. People won't die easily as inferior giraffes.

2. Technology improves survival

 

And therefore the human population won't converge to a single definable population with "ideal" traits. The diversity will be maintained at least to a certain extend.

 

If the second is true, then it is a scary thought that nature actually "selects" what traits are good or bad for you. But I know this is unlikely based on direct observation of human population.

 

The third sounds appealing to me. But I don't know how valid that is lol....

========

Any idea?

[CharonY]

1) Evolution is basically the change of allele frequency in a given population. Only under certain conditions (e.g. under the so-called Hardy-Weinberg equilibrium) evolution will stop. Hence, it is ongoing also for humans. What some of the posters may mean is that certain selective forces may be diminished or change. Others (as e.g. sexual selection) may be of higher importance than others.

 

2) Generally not. What you describe is basically Lamarckian inheritance and for the most part it does not happen. However, there is a limited area which may allow certain acquired traits to be inherited. But this is certainly more of an exception rather than the rule.

 

3) Nature operates in a continuum. There is no real cut-off in nature and while categorizations can make sense for certain aspects, it is always to a certain extent arbitrary. Some categories are better reflected, some worse, but none is perfect.

[Ringer]

For #2: Aren't wearing braces and, let's say an environmental condition that forces a duck to hunt underwater (just making this example up), are both physical alteration? I know that wearing braces won't change your genetic information, but how does the later example do in such a way that it evolved to....emmmmm....platypus? Sorry I couldn't find a better example, but you got the premise.

 

An environmental force that forces a duck to hunt underwater will not cause a duck to hunt underwater if said duck is incapable of hunting underwater. Therefore that duck would no longer be able to hunt and would die out, while the ducks that could go underwater, although may have not hunted there before, out survive/reproduce the other kind. A behavioral change may then take place predisposing the ducks who have survived to eat underwater animals, etc etc.

 

 

 

Focusing #2 (I think I got the ideas for my questions #1 and #3):

 

Let's take a population of giraffe for example. Let's say in the beginning there are 50% short necked ones and 50% long necked giraffes. Pulling your own neck over 30 years won't change any of your DNA information, correct?

 

What constitutes evolution are:

1. Mutation

2. Gene crossovers

 

Crossover and mutation are just a couple of many ways that evolution to occur

 

 

The question is how do we end up with all long-necked giraffes today? Is it because of:

1. Many of the short ones died without having the chance to breed?

If they can't reach the leaves then they would not be able to survive. They would probably not be able to produce offspring if they can't eat

 

2. Or is it because nature has determined that the dominating trait (if a long-necked giraffe and a short-necked giraffe mate) is "long-neck"? Or is it a combination of both?

Somewhat, but long neck isn't necessarily a simple Mendelian dominate/recessive trait and even if it were nature doesn't really 'decide' which is which. The became the majority phenotype, most likely, because of the method above. As long as the neck is 'long enough' for the giraffe to survive and reproduce it will be kept.

 

3. Pulling their neck actually does change their genetic information...very very slightly. And if your offsprings keep doing the same thing, and their offsrpings etc, then it'll build up and you'll have a slightly taller giraffes and so on.

No. If this were true, as shown in an early experiment on evolution, you could cut off the tails of mice and their offspring would not have tails. Or if you say they would have shorter tails then if you continued to cut off the tails they would end up disappearing after a long enough time. This obviously doesn't happen.

 

If the first one is true, then in our society evolution is not required because:

1. People support each other to a certain extend. People won't die easily as inferior giraffes.

Giraffes support each other too. So do ants, so should they not evolve. I don't know what ways you assume giraffes are inferior.

2. Technology improves survival

Again this has little effect on evolution overall.

 

And therefore the human population won't converge to a single definable population with "ideal" traits. The diversity will be maintained at least to a certain extend.

 

There are no ideal traits. Traits that work in one condition may not in another. Early philosophers' ideas that there were 'ideal' forms to made and animals change towards those forms are wrong.

 

If the second is true, then it is a scary thought that nature actually "selects" what traits are good or bad for you. But I know this is unlikely based on direct observation of human population.

 

Nature doesn't select for what is good for 'you' but what allows offspring. Take peacocks, their tails are not really what one would consider 'good for you'. It doesn't give an advantage for survival, but it does attract peahens so they can reproduce. Nature doesn't care if they get eaten by a predator so long as they survived long enough to reproduce.

 

 

 

 

[Djalapeno86]

An environmental force that forces a duck to hunt underwater will not cause a duck to hunt underwater if said duck is incapable of hunting underwater. Therefore that duck would no longer be able to hunt and would die out, while the ducks that could go underwater, although may have not hunted there before, out survive/reproduce the other kind. A behavioral change may then take place predisposing the ducks who have survived to eat underwater animals, etc etc.

 

~~~So based on your first paragraph, evolution for the duck example is a combination of natural selection and change of behavior? That makes quite some sense. But does this apply in general? ~~~

 

 

 

Crossover and mutation are just a couple of many ways that evolution to occur

 

 

 

If they can't reach the leaves then they would not be able to survive. They would probably not be able to produce offspring if they can't eat

 

 

Somewhat, but long neck isn't necessarily a simple Mendelian dominate/recessive trait and even if it were nature doesn't really 'decide' which is which. The became the majority phenotype, most likely, because of the method above. As long as the neck is 'long enough' for the giraffe to survive and reproduce it will be kept.

 

 

 

~~~~So natural selection plays a major role here? In this example, I don't see how evolution takes place then... It is just a reformation of the population towards a certain direction (=long necked population), if you wish...~~~~~~

 

 

No. If this were true, as shown in an early experiment on evolution, you could cut off the tails of mice and their offspring would not have tails. Or if you say they would have shorter tails then if you continued to cut off the tails they would end up disappearing after a long enough time. This obviously doesn't happen.

 

~~~Got it. ~~~

 

 

Giraffes support each other too. So do ants, so should they not evolve. I don't know what ways you assume giraffes are inferior.

 

 

~~~When I said inferior giraffes, I'm referring to short-necked giraffes who are inferior to long-necked giraffes. But anyways, according to you the short necked giraffes won't be able to survive so definitely there's a limitation of support in the population. ~~~~

 

Again this has little effect on evolution overall.

 

~~~OK. I thought if there's no pressure to survival, evolution will be halted. ~~~

 

 

 

There are no ideal traits. Traits that work in one condition may not in another. Early philosophers' ideas that there were 'ideal' forms to made and animals change towards those forms are wrong.

 

 

 

Nature doesn't select for what is good for 'you' but what allows offspring. Take peacocks, their tails are not really what one would consider 'good for you'. It doesn't give an advantage for survival, but it does attract peahens so they can reproduce. Nature doesn't care if they get eaten by a predator so long as they survived long enough to reproduce.

 

 

 

 

 

 

 

 

So in general what I'm getting is that evolution is caused by gene crossover & mutation, natural selection, and change of behavior. But I still don't get how natural selection & change of behavior result in physical changes (or any other factors that I might've missed). Note that I'm focusing on physical evolution, not behavioral or any other type of evolution. E.g. I'm interested in how horses get bigger overtime and elephants get smaller over time. If external pressure cannot change gene (or the gene of the offsprings), then what can?

 

Can you give me a specific example of what causes physical changes of a species, then? Maybe that'll be clearer for me.

 

Nature doesn't select for what is good for 'you' but what allows offspring. Take peacocks, their tails are not really what one would consider 'good for you'. It doesn't give an advantage for survival, but it does attract peahens so they can reproduce. Nature doesn't care if they get eaten by a predator so long as they survived long enough to reproduce.

 

 

 

 

 

 

 

BTW peacock's tail is actually 'good for them' since it supports one of the two basic instincts of living being, right? Survival of self and survival of the population (reproduction). Again, this is natural selection, I'm guessing. I'm still wondering what causes physical changes of the population and more importantly how.

[Ringer]

Evolution of, say, size can happen because there is always variation within a population. The variation is allows different animals to reproduce and have offspring that may or may not, depending on the environment and variation type, be better adapted to the environment.

 

Say that there is a population of trees called S1. Now obviously there will be trees the that are shorter and some that are taller, but overall most have an average height. Now say that another species of tree is introduced,S2, into this population that has a slightly taller average. Since the sun is needed for these trees to produce energy the small trees will not be able to get sunlight and die off. The S2 population, being taller, is easily surviving and getting enough sun at the expense of the shorter trees. Now since there was variation in height in the S1 species there will be some that are surviving and reproducing and having offspring with that height. So long as this goes on for many generations the S1 allele for height can be dramatically changed and the overall height will be higher than previous generations. Perhaps the S1 and S2 species cross-bred (I don't remember if trees asexually reproduce or not but you get the idea) and now there are no S1 or S2 species at all, just a tall S3 species. In any case, whether S1 and S2 stay separate or interbreed, the allele frequency of the height of trees has changed so evolution has happened.

[SMF]

Ringer. You may wish to modify your, otherwise, helpful description a little. For example two species, redwood and Douglas fir, occupy the same region and compete but they would never merge into a single (S3) species because they are unable to interbreed. If two distinct groups interbreed naturally, they would usually be called variants of a single species. SM

[Ringer]

I'm assuming that the S2 species doesn't naturally occur in the same area as S1 and was introduced to that area by some means. A further assumption is that these two species are rather closely related and are able to interbreed but were considered different species because barriers made them unable to do so (i.e. allopatric speciation). I know it is a stretch but this is really just a thinking exercise to try to help him.

[SMF]

Ringer, you added assumptions are quite reasonable and not a stretch at all. I was just concerned that someone coming here to learn about evolutionary mechanisms might take away the idea that distinctly different species could merge if they were competing in the same ecology. SM

[Djalapeno86]

Oh, I got it now. Thanks for your help~!