Help re: evolution

[lostaquarium]

Hey, I have another question about evolution by natural selection. Please bear with me, as I'm really trying to understand this topic.

Natural selection:
Mutations occur randomly. Beneficial mutations occur at very low frequency. Beneficial mutations are only 'propagated' through the population when other animals (who don't have the mutation) die from selection pressures. i.e. we don't share genes like bacteria do, we actually have to come from those parents.

Let's take the example of monkeys-to-humans. I was reading this morning about long latency reflexes. When a muscle is stretched, monkeys respond by co-contracting agonist and antagonist muscles. Humans only contract their agonist muscles. These are reflexes, driven by very simple circuits of neurons (probably just 5) which are genetically coded, not learnt.

Other differences between monkeys and humans: size, upright walking, no hair, larger forebrain, speech, etc... These are in ALL humans and NO monkeys.

So, in the simple transition from monkey to human, do these mutations occur sequentially? e.g. a monkey mutates to have no hair, finds this advantageous, all other monkeys die, this monkey reproduces. Then one of his offspring mutates his long-latency reflexes, all other monkeys die, this monkey reproduces to fill the population... etc. This would suggest a series of evolutionary bottlenecks, which (in my vague impression) is not advantageous, and not the case.

Or, do the mutations occur in parallel? If so, how? Two (or more) beneficial mutations occuring in the same monkey is even unlikelier.

Please explain things using solid examples. No analogies please. I don't cope well with abstract thoughts. Details would be most useful.

Thanks

 

[Mystman]

Hey, I have another question about evolution by natural selection. Please bear with me, as I'm really trying to understand this topic.

Well, a number of things.

The most important thing to realise here is that you have chromosomes. As a woman, you have 23 pairs.

Often (not always), a beneficial mutation occurs on only 1 specific chromosome.

The second important thing (or most important, depending on who you ask ) is sex. Sex allows us to mix chromosomes, and that in a way allows for "parallel" beneficial mutations.

Say that there are 4 mutations:
Beneficial mutation B1 on chromosome 1
Beneficial mutation B2 on chromosome 2
Detrimental mutation D3 on chromosome 3
Detrimental mutation D4 on chromosome 4

I carry 1 copy of B1 and 1 copy of D3
My wife carries 1 copy of B2 and 1 copy of D3
All the other chromosomes in us both are normal.

Now, we proceed to make lots of kids. Since a child randomly chooses 1 copy of each chromosome from each of their parents, you will get children ending up with every possible combination of the aforementioned mutations or normal chromosomes.

So, you will get children having both the D3 and D4 mutations.. but you will also get children having the B1 and B2 mutations.

Kids having the B1 and B2 mutations will probably get more children of their own. Those children will again get more children, etc.

Now, lets say that in another town the same thing has been happening... only there children carrying B5/B6/B7 mutations have been produced. If those kids from another town mate with my grandchildren, they will produce B1/B2/B5/B6/B7 children. So yeah, parallel evolution.

BUT

If different mutations need to take place on the same chromosome, the story becomes a whole lot trickier. And sequential evolution also comes into play. But also 'weird', non-classical genetics start to enter the picture. Genes can be moved from one chromosome to the other, they can be copy/pasted between the two copies that you have of each gene, etc..

 

[juvenissun]

Good for you and thanks for these questions, lostaquarium.

I believe there is not an answer in science to your question. Certainly not given by people in this forum. I asked the hair question twice in the past year. I haven't got any good answer yet. When you combine the questions of genetics and fossil together, people will only stare at you with blank eyes and say that you do not understand what evolution is.

 

[Mystman]

So, in the simple transition from monkey to human

Also a thing to point out, big changes usually occur in an absurdly large number of small steps.

To take the simple transition from ape to human.. we diverged from chimpanzees some 5-7 million years ago. Taking an average "age of reproduction" of 20 years (on the high side I think), that would give us an approximate lower limit of 5.000.000 / 20 = 250.000 generations.

With each generation probably at least having on the order of a few thousand individuals, that would give us at least ~1 billion animals involved in the whole process. And probably a lot more.

So even the relatively simple transition from ape to man involves a ridiculously large number of individuals, trial and error, mixing and matching of chromosomes, etc.

 

[Bombila]

So, in the simple transition from monkey to human, do these mutations occur sequentially? e.g. a monkey mutates to have no hair, finds this advantageous, all other monkeys die, this monkey reproduces. Then one of his offspring mutates his long-latency reflexes, all other monkeys die, this monkey reproduces to fill the population... etc. This would suggest a series of evolutionary bottlenecks, which (in my vague impression) is not advantageous, and not the case.

Keep in mind, the 'other monkeys' don't necessarily die out, but may become a separate population which evolves in a variant direction of their own. Two populations of the same animal may become separated by geographical or other environmental barriers. Each population, unable to breed with the other population, has its alleles change over time until it becomes impossible for individuals from one population to breed successfully with members of the other group.

Also keep in mind the amount of time evolution takes. Given - let's move away from humans and go with some other critter - small weasely looking carnivores which hunt small mammals, and a simple one facet look at its evolution:

These are mobile creatures who hunt over a vast landscape. The critters they hunt and eat are varied themselves, in size and defense capability, in their ability to hide in holes or trees or using camouflage. In one location, the most plentiful prey may be a slow-moving burrower. The weasely carnivore most adept at digging them out may be one with a mutation that causes unusually strong thick claws. She eats better than the rest. When the burrowers are scarce, she is still able to catch enough to feed all her offspring, while others of her species are going hungry and raising fewer young. Her peers aren't dead, but her children are more successful, raise more young to reproductive age, and eventually there are more of her big-clawed descendents than of the small clawed ones. As the group goes on reproducing, the big-claw genes become more and more dominant in the population.

In another location, the same weasely carnivore's most commonly available prey can run like snot. The faster the carnivore can run, the better fed she'll be. The slower members of her species are, again, getting less food, raising fewer young. Eventually you have a very fast moving animal.

Now suppose a big-clawed, slow moving weasely carnivore meets up with a slender, long legged fast mover. Chances are good they are now so different they can't or won't mate. They are genetically different enough that one cannot successfully impregnate the other.

In this example, no species has 'died', but the original critter has evolved into two different kinds of animals, a low slung, slow moving digger with massive claws, and a gracile long legged runner with expanded lung capacity.

 

[Tomk80]

Hey, I have another question about evolution by natural selection. Please bear with me, as I'm really trying to understand this topic.

Natural selection:
Mutations occur randomly. Beneficial mutations occur at very low frequency. Beneficial mutations are only 'propagated' through the population when other animals (who don't have the mutation) die from selection pressures. i.e. we don't share genes like bacteria do, we actually have to come from those parents.

Let's take the example of monkeys-to-humans. I was reading this morning about long latency reflexes. When a muscle is stretched, monkeys respond by co-contracting agonist and antagonist muscles. Humans only contract their agonist muscles. These are reflexes, driven by very simple circuits of neurons (probably just 5) which are genetically coded, not learnt.

Other differences between monkeys and humans: size, upright walking, no hair, larger forebrain, speech, etc... These are in ALL humans and NO monkeys.

So, in the simple transition from monkey to human, do these mutations occur sequentially? e.g. a monkey mutates to have no hair, finds this advantageous, all other monkeys die, this monkey reproduces. Then one of his offspring mutates his long-latency reflexes, all other monkeys die, this monkey reproduces to fill the population... etc. This would suggest a series of evolutionary bottlenecks, which (in my vague impression) is not advantageous, and not the case.

Or, do the mutations occur in parallel? If so, how? Two (or more) beneficial mutations occuring in the same monkey is even unlikelier.

Please explain things using solid examples. No analogies please. I don't cope well with abstract thoughts. Details would be most useful.

Thanks

The mutations occur in parallel. While we don't share DNA in the way bacteria do, we do share DNA in another way, namely through sex. We have 2 copies of each of our chromosomes. Okay, not entirely correct. Women have two copies of chromosome 1 to 22 and two copies of chromosome X. Men have two copies of chromosome 1 to 22, one copy of chromosome X and one copy of chromosome Y. We produce eggs and sperm (well, women produce eggs, men produce sperm, but you get what I mean) that contain half of our DNA, one copy of each chromosome (with men, half of the sperm have an X copy of the XY-chromosomes, half the sperm have a Y copy).

So if you get a child, this child will have half of your chromosomes and half of your partner's chromosomes. This way, your child will get a part of the mutations that have occurred in you and a part of the mutations that will occur in your partner. And this way, DNA is shared.

Now, this is not all, because during the formation of your sex cells another process will occur. This is called recombination and means that the your own chromosomes will exchange material when they form sex cells. So in stead of a sperm or egg cell getting chromosome 1A or 1B, it will get part of 1A and part of 1B and so on.

This way, mutations that have occurred in your partner and in you will all have a chance to find their way into your children.

Here is a diagram of the process of formation of sex cells, which may help you understand further.

The biology project of the university of Arizona has a nice tutorial on this:
Meiosis Tutorial

 

[FedererFan]

Good for you and thanks for these questions, lostaquarium.

I believe there is not an answer in science to your question. Certainly not given by people in this forum. I asked the hair question twice in the past year. I haven't got any good answer yet. When you combine the questions of genetics and fossil together, people will only stare at you with blank eyes and say that you do not understand what evolution is.

Way to be open-minded and wait to see if anyone answers!

 

[Tomk80]

Way to be open-minded and wait to see if anyone answers!

Juvenissun has been provided with answer often enough. He just mistakes being obtuse with asking intelligent questions.

 

[Bombila]

Tomk80, nice post with pictures. I've often noticed that many people asking about evolution or rejecting evolution are very unclear on basic biological facts, right down to not knowing the anatomy of a cell or how cells divide and multiply. Often they lose track of the meaning of any argument because they really don't understand the mechanics of what is being discussed.

http://www.christianforums.com/t7365267/#post51604076

 

[Mystman]

Now, this is not all, because during the formation of your sex cells another process will occur. This is called recombination and means that the your own chromosomes will exchange material when they form sex cells. So in stead of a sperm or egg cell getting chromosome 1A or 1B, it will get part of 1A and part of 1B and so on.
http://www.biology.arizona.edu/CELL_BIO/tutorials/meiosis/main.html

I knew that said process was possible, and takes place whenever there is a double stranded break..

..but I didn't know that it actually happens on purpose during meiosis. Kinda makes sense though.

You learn something new every day.

 

[Wiccan_Child]

Natural selection:
Mutations occur randomly. Beneficial mutations occur at very low frequency. Beneficial mutations are only 'propagated' through the population when other animals (who don't have the mutation) die from selection pressures. i.e. we don't share genes like bacteria do, we actually have to come from those parents.

Not exactly. Beneficial traits are propagated by reproduction: it doesn't matter if your competitors die, just that you don't die. Natural selection selects for those who are better, but not necessarily against those who are worse. Natural selection can choose between those who survive and those who die, but only because those who die can no longer reproduce, and sometimes death benefits you (inasmuch as your inheritable traits might be spread more if you die, or otherwise don't reproduce).

Let's take the example of monkeys-to-humans. I was reading this morning about long latency reflexes. When a muscle is stretched, monkeys respond by co-contracting agonist and antagonist muscles. Humans only contract their agonist muscles. These are reflexes, driven by very simple circuits of neurons (probably just 5) which are genetically coded, not learnt.

Other differences between monkeys and humans: size, upright walking, no hair, larger forebrain, speech, etc... These are in ALL humans and NO monkeys.

So, in the simple transition from monkey to human, do these mutations occur sequentially? e.g. a monkey mutates to have no hair, finds this advantageous, all other monkeys die, this monkey reproduces. Then one of his offspring mutates his long-latency reflexes, all other monkeys die, this monkey reproduces to fill the population... etc. This would suggest a series of evolutionary bottlenecks, which (in my vague impression) is not advantageous, and not the case.

It's more gradual than you make out: mutations arise all the time, when (and only when) conception occurs. Every now and then, a mutation makes an offspring slightly more likely than its kin at having descendants. Nothing has to die .

Or, do the mutations occur in parallel? If so, how? Two (or more) beneficial mutations occuring in the same monkey is even unlikelier.

Which is why large morphological changes take many generations to occur. Most beneficial mutations are small things, like changing how a protein folds to slightly increase the efficiency of a particular metabolic pathway.

But yes, mutations occur in parallel: as time goes by, mutations arise in all individuals at the moment of conception. Each mutation has a certain chance of being beneficial, and this very much depends on whether previous mutations have taken place.

For example, when reviewing the famous E. coli experiment, scientists found that ancestors 10000 generations back would also evolve the unique ability to ingest and metabolise citric acid, but ancestors even further back would not.

 

[Nathan45]

Hey, I have another question about evolution by natural selection. Please bear with me, as I'm really trying to understand this topic.

Natural selection:
Mutations occur randomly. Beneficial mutations occur at very low frequency. Beneficial mutations are only 'propagated' through the population when other animals (who don't have the mutation) die from selection pressures. i.e. we don't share genes like bacteria do, we actually have to come from those parents.

not true, beneficial mutations can be passed diagonally through sex. If you have a beneficial mutation and you reproduce sexually with someone who doesn't have the mutation, your kids might inherit the mutation.

Let's take the example of monkeys-to-humans. I was reading this morning about long latency reflexes. When a muscle is stretched, monkeys respond by co-contracting agonist and antagonist muscles. Humans only contract their agonist muscles. These are reflexes, driven by very simple circuits of neurons (probably just 5) which are genetically coded, not learnt.

Other differences between monkeys and humans: size, upright walking, no hair, larger forebrain, speech, etc... These are in ALL humans and NO monkeys.

First off, the "monkeys" that humans evolved from are not like the monkeys you see today. The monkeys you see today are our distant distant distant cousins. Humans and monkeys share a common ancestor. depending on your definition of "monkey" the common ancestor of humans could be considered a monkey (that would be a loose non-scientific definition).

So, in the simple transition from monkey to human, do these mutations occur sequentially? e.g. a monkey mutates to have no hair, finds this advantageous, all other monkeys die, this monkey reproduces. Then one of his offspring mutates his long-latency reflexes, all other monkeys die, this monkey reproduces to fill the population... etc. This would suggest a series of evolutionary bottlenecks, which (in my vague impression) is not advantageous, and not the case.

No.

It has to do with sexual selection. Do men find hairy legs in women attractive? No? So i'd say, non-hairy legged women have a slight adaptive advantage when it comes to reproduction. This doesn't involve anyone dying necessarily just involves people with less hairyness being more likely to reproduce.

it all happens gradually among a population... they're selected for various factors... less hairyness, larger brains, and better ability to run (FYI: monkeys can be bipedal when they want to be, humans are just better at it. ). So if you take all of that + more into account, put it in the environment, the fitter animals are more likely to successfully find mates. so over the generations, you end up with animals that are less hairy, have larger brains and can run better.

Or, do the mutations occur in parallel? If so, how? Two (or more) beneficial mutations occuring in the same monkey is even unlikelier.

as i said, whenever you have children with someone else you share genes. If you have one beneficial mutation and your partner has another, your child might get both beneficial mutations.

 

[Nathan45]

To explain further, here's the rough process of speciation among a sexually reproducing species:

1) Before speciation

You have a bunch of animals who are the same species (call them monkeys) all living in roughly the same geographical area.

2) Separation

For speciation to occur, two populations of the same species have to stop reproducing with eachother (this doesn't have to be absolute, there can still be a little bit of gene transfer in the beginning at least). If two groups of animals are sexually reproducing with eachother they can't really split off from eachother because they're always sharing their genes.

So what you have is, for whatever reason, one group of monkeys doesn't reproduce with the other group. Maybe they're separated by a river. Maybe they're marooned on an island. maybe they just don't like eachother. for whatever reason the monkeys split up into two groups. In this example, one goes off and lives in the open savannahs and one group of monkeys lives in the forest.

3) They drift apart.

Now, each separate group of monkeys will get separate mutations and will evolve differently. Different random mutations will arise in one group and not the other. Usually within a species the genes and different mutations will be pretty well mixed around every few generations due to sexual reproduction. But if the species spits into two or multiple groups, this doesn't happen and they go their separate ways.

4) Selection pressures may be different. (note that the order of 3 and 4 could be reversed)

If you introduce a predator into an environment, or the climate is different, or the food source is different, then one of the groups of monkeys may find that whatever made them good at picking fruit in the forest is now obsolete, and they need to be able to survive in a hot open savvanah where they have a different climate, different dangers and different food sources. It's not that a monkey can't survive in the savvanah, but humans are better at, and the common ancestor of the human and chimp will be selected differently in the open plains than it would be in a forest.

5) The two groups get farther and farther apart such that they eventually become totally different.

let's say one group of monkey lived in the forest by picking nuts and berries. They'd evolve to be better climbers.. maybe they'd have four dexterous hands for better climbing/grasping. They'd be good climbers but they wouldn't need to be good runners cause there arn't a lot of straitaways in the forest and there are lots of things to trip over.

the second group, found itself living in the open plains. Suddenly, standing upright is an advantage because it's more efficient for running (it's been proven that humans are much more efficient runners than chimps). Since all their feet are used for is running now, not grasping, the feet become sturdier and less agile, less suited for grasping and more suited for running. I guess they lost their hair cause it was hot in the savannah but that's up for debate. Also instead of mostly picking berries/nuts, they have to catch prey.. or at least the ones that can catch prey are going to have a wider variety of food sources cause there isn't a lot else to eat in the savannah. So humans evolved to be smarter and good runners so we could chase down big animals with spearheads so we'd have something to eat. at least that's as good a hypothesis as any. Also evolving to be smarter can't be a bad thing, in any case?

6) after millions of years of separately evolving with different random mutations and completely different selection pressures, the species are just totally different and can't reproduce anymore. IIRC, chimps and humans parted ways 4-7 million years ago (they're not sure on the exact date). But humans were basically apes that lived in the open, doing a lot of hunting, and chimps were apes that lived in the forest subsisting on picking berries, nuts, etc.

 

[29apples]

I attended a seminar last semester regarding laughter in chimps in humans. It was very interesting and he shared a few interesting observations.
1. We can't make ourselves laugh, but other people laughing does make us laugh
2. Males are funnier. They make females laugh at a higher rate, and is one quality that many women listed as desirable in his pole. Also males tend to laugh less than females.
3. We are the only species that "laughs out loud."

Chimpanzees also have the ability to laugh, however they can not do it "out loud" since they do not have a well developed larynx (voice box). He showed a video of someone tickling a young chimp and it was making a sound like a panting dog, but it was more exaggerated.

We are also the only biped species. The ability to walk upright has reduced the pressure on our diaphragm. As a result we are only only species that does not breath in unison with our running stride. This reduced pressure has allowed for the selection to be more permissive on our voice box, because our diaphragm is no longer forced to breath at a certain rate when we run. As a result, humans with more developed voice boxes we able to be selected for.

So I make the assertion that our ancestors probably learned to walk upright first, and then they developed the ability to communicate with speech.

 

[Nathan45]

interesting post, apples.

We are also the only biped species. The ability to walk upright has reduced the pressure on our diaphragm.

it's worth noting though that chimps can walk upright. They just don't do it most of the time and arn't as good at it as people.

here's a video of a chimp that was basically raised as a human, walking upright (you only have to watch the first ~15 seconds of this video to see it):

http://www.youtube.com/watch?v=-C6NkRUbI38

(This is oliver the famous chimp. Note that he isn't really a "humanzee" they did DNA tests and it's just a chimp that acts human. there was some speculation... All chimps can walk upright but they don't usually do it unless they're carrying something or trying to get to something above them. )

 

[Bombila]

...

We are also the only biped species. The ability to walk upright has reduced the pressure on our diaphragm. As a result we are only only species that does not breath in unison with our running stride. This reduced pressure has allowed for the selection to be more permissive on our voice box, because our diaphragm is no longer forced to breath at a certain rate when we run. As a result, humans with more developed voice boxes we able to be selected for.

So I make the assertion that our ancestors probably learned to walk upright first, and then they developed the ability to communicate with speech.

This reminded me...

Birds are also bipedal, and they possess a more efficient breathing system than mammals do. Many of them also make a lot of intricate sounds, and some are very, very loud.

This article is talking about the elongated trachea many birds have, particularly the very loud ones. In fact, bird voices are complicated, and involve more structures than human voices do. Better to read Darren's article, though, instead of me mangling it in synopsis.

Ridiculous super-elongate, coiled windpipes allow some birds to function like trombones - - or is it violins? : Tetrapod Zoology

 

[plindboe]

Hey, I have another question about evolution by natural selection. Please bear with me, as I'm really trying to understand this topic.

I think you would benefit hugely from reading a real textbook on evolution. There are just too many things in your post I want to address, but I'm not even sure where to start.

I recommend this one-> Evolution Home Page

Peter

 

[plindboe]

Chimpanzees also have the ability to laugh, however they can not do it "out loud" since they do not have a well developed larynx (voice box). He showed a video of someone tickling a young chimp and it was making a sound like a panting dog, but it was more exaggerated.

YouTube - Giggling Chimps

Makes me laugh too when I see it.

Peter

 

[29apples]

This reminded me...

Good call on the birds, they had completely eluded me.

 

[lostaquarium]

To all those bringing up meiosis and different chromosome arrangements - still missing the point. Recombination is fine, but ONE of your parents still MUST have the gene. To have a new mutation, you MUST be born from someone who has it. Bacteria can absorb DNA from their environment or transfect each other with it. Eukaryotes can't. If a new mutation "spreads" to fill a whole population, it must EVERYONE in the population has come from the ONE individual (albeit combined with many others). My problem with that is that it seems very unlikely, and creates genetic bottlenecks... (Alternatively, I just can't get my head around it )

Bombila - the point about speciation is interesting, but doesn't really help. My problem is, 6 billion humans must have come from one ancestor. Not once, but many times - in fact, almost as many times as the number of mutations, from the long journey from chimps to humans.

Also a thing to point out, big changes usually occur in an absurdly large number of small steps.

(Also Wiccan_Child said something similar.)
Doesn't that make the situation even more unlikely? If hairlessness occured due to a single mutation (let's call it A) that would create one bottleneck, i.e. everyone would have to be descended from the person who first got A. But if hairlessness was due to many gradual mutations (A, B, C, D, E ...), then every hairless person would have to accumulate almost every one of those mutations, i.e. everyone who didn't have "A" dies out, "A" fills the population, "B" mutates, everyone who doesn't have "B" dies out, "B" fills the population, "C" mutates, ... etc... etc...

Not exactly. Beneficial traits are propagated by reproduction: it doesn't matter if your competitors die, just that you don't die.

But to address my question, if one mutation fills the entire population, those who don't have the mutation must not have successfully reproduced. i.e. died without reproducing (I should have clarified).

not true, beneficial mutations can be passed diagonally through sex. If you have a beneficial mutation and you reproduce sexually with someone who doesn't have the mutation, your kids might inherit the mutation.

They're still your kids. What do you mean "diagonally"?

as i said, whenever you have children with someone else you share genes. If you have one beneficial mutation and your partner has another, your child might get both beneficial mutations.

But 3/4 of your children (if it's Mendelian) will not have those beneficial mutations. And since those mutations eventually fill the population, those other children must have died before they reproduced. That's still a lot of deaths. Hence bottleneck.

Nathan45 - re your post #13. You've explained speciation very well, and thanks, that clarifies a lot. But it wasn't my question at all. You've outlined a whole new load of mutations, which is precisely what I'm concerned about.

I think you would benefit hugely from reading a real textbook on evolution. There are just too many things in your post I want to address, but I'm not even sure where to start.

I recommend this one-> Evolution Home Page

Peter

Thanks, I'll certainly peruse that at some point