Question for scientist type people.. Evolution

[3113]

okay i will give a primer on natural selection, and the balance of it with mutation and random genetic drift. feel free to skip this post as it may bore some of you to tears but outside of lit, this is possibly one of my favorite topics.

A science geek! Swoooon

Boring? Where I come from that kind of lecture is foreplay.

You'll stick around, right? flirt, flirt

 

[3113]

So it's in the group's interest to preserve as many of its members as it can, whether they're fast or slow or weak or strong. Maybe it was some skinny weakling who first thought up the bow and arrow, or some helpless schizophrenic who first tried eating an oyster. We care for our elderly because their wisdom and experience have tremendous survival value to the group.

So love and affection have very high survival value. They're built into us for a reason.

It's more than just group survival on that level, it's group survival at the most primal level, survival of the young. Thanks to our intelligence, which requires not only big heads but slow growth (i.e., unlike most animals our young cannot stand or cling to their parents within hours of birth), we have very vulnerable babies.

We aren't like animals who have a litter and within a few months the young can survive on their own, hunt down their own food, etc., and the adults can wander off. We have one child (on average) per mother and it needs to be protected, feed, etc. for several years. Love, affection, attatchment to one another, as well as grouping, is the only way to protect pregnant and nursing mothers as well as babies and young children and so get the next generation into adulthood.

 

[phdbio]

A science geek! Swoooon

Well with an invitation like that what's a guy to do but stick around. Perhaps i am just easily swayed. when i learn how to quote things properly this will be easier but as to your comments about human reproduction (i am a nerd wow it just hit me sorry) we are slow but it is worse in some animals. the theory behind this is that or rather was that some individuals mate fast and make lots of babies to put into the world but lose a large majority of them and the other half makes one good one and hopes for the best. we fit into the latter. not that one is better than the other. the other thing you have to realize is that human evolution isn't very similar at all to what happens in the wild. we have no competition for resources really (yes you could argue but why we really aren't limited) and then the idea of isolated populations doesn't really apply to us either. i think most people in my field leave the human population stuff to the biological anthropologists because human populations don't behave similarly to others.

now if that wasn't nerdy enough for you i will have to amp it up a bit

 

[3113]

you have to realize is that human evolution isn't very similar at all to what happens in the wild. we have no competition for resources really

But didn't most of human evolution (i.e. all the important components we're living with today, including walking upright, language and brain size) happen while humans WERE living in the wild? Competing for resources and fighting off predators like every other beast? Not to mention the problems the come with an ice age (i.e. the one that started 2 million years ago) which included limited resources even in temperate zones and, therefore, would have created an enviornment where there's more rapid selection? That is, where favorable differences (like locking knees) could mean life and death? As compared to an enviornment where everything is warm and fruitful and so locking knees don't make much of a difference to survival?

Amp up that brain, baby, show us what you got!

 

[phdbio]

yes the majority of the big things are already in place and would have happened just like with the more evolved animals. i am not debating that but again it happened over millions of years

a bit of a correction not a problem but environments dont influence selection in that if it gets warm i evolve to deal with warm weather. rather it causes differential reproduction and traits that were deletarious or less benefical in previous conditions are now beneficial. also i think you mean a more heterogenous environment can increase the rate of extinction not selection and if you didn't mean that then let me suggest it


i think the biggest problem is that we see this on an individual level. you have to let go and step back to the population level and see that i will do no better but perhaps my offspring might.

so locked knees if hypothetically didn't make a fitness difference in normal weather but in the ice age was lethal then if i crawled around like some of you i would die but if i was standing then only my genes and not yours would get passed on. but those types of lethal alleles aren't the norm. the norm is small differences that are slightly acted on by selection.

 

[R. Richard]

But didn't most of human evolution (i.e. all the important components we're living with today, including walking upright, language and brain size) happen while humans WERE living in the wild? Competing for resources and fighting off predators like every other beast?

Actually, not all early pre-human/human populations competed for resources and fought off predators. No, some early pre-human/human populations used sanctions against the predators. However none of the populations that used sanctions survived.

 

[3113]

a bit of a correction not a problem but environments dont influence selection in that if it gets warm i evolve to deal with warm weather. rather it causes differential reproduction and traits that were deletarious or less benefical in previous conditions are now beneficial.

Granted. A black skinned population transplated from Africa to ice age Europe aren't going to produce caucasions just because the enviornment is better suited to lighter skin and eyes. But paler skinned off-spring over millions of years will do better in such an enviornment and develop whereas they would not if the group were still in Africa were more melanin in the skin is better protection against the hot sun, etc.

Yes?

also i think you mean a more heterogenous environment can increase the rate of extinction not selection and if you didn't mean that then let me suggest it

Leaning in. Yep, that's what I meant, I just didn't have the correct terms to hand. But you do Any other suggestions?

but those types of lethal alleles aren't the norm. the norm is small differences that are slightly acted on by selection.

Okay. But wouldn't the lethal ones make a bigger and quicker change on the species? Back to the locked knees: the ice age causes a drought in the temperate zones, resulting in grass lands rather than forests. This makes it easier for preditors to run down any of our ancestors who are crawling through the grass. but those that stand up right, seeing danger over the grass and, with those knees, can outrun those predators to safety, survive.

What I'm asking is: even though these lethal alleles aren't the norm, do they have equal power in evolutionary change? Or are they so rare that even if they do pack a punch, the norm outweighs them?

 

[3113]

Actually, not all early pre-human/human populations competed for resources and fought off predators. No, some early pre-human/human populations used sanctions against the predators. However none of the populations that used sanctions survived.

From what I understand, sanctions were only used on against creatures that were not predatory, which is why they never worked. If, say, you use sanctions against a blow-fish (we will call that fish "Iraq" for the hell of it) that just puffs up and looks scary rather than a shark (let's call that one "Iran") then all you do is starve the false predator rather than the real one and, thus, provide false evendence that sanctions don't work.

Few prehuman/human populations were wise enough to realize that this false evidence was provided by leaders who enjoyed feeding warriors to predators even if it depleated the tribe of all fighters and resources.

 

[R. Richard]

so locked knees if hypothetically didn't make a fitness difference in normal weather but in the ice age was lethal then if i crawled around like some of you i would die but if i was standing then only my genes and not yours would get passed on. but those types of lethal alleles aren't the norm. the norm is small differences that are slightly acted on by selection.

The difference that locked knees make was quite probably not a direct one. The locked knee lets the possessor roam at will, carrying the tools that the bipedal posture makes it possible to use.

An orangutan is limited to a forest area. When the forest area disappears, so does the orangutan. We are seeing that today. A grazing animal is limited to grasslands. Of course, the grazing animal can move but probably does not except as a desperate last resort; there nay not be water or proper graze in a new environment. Predators must follow the prey. However, a bipedal proto-human can move from environment to environment. A bipedal proto-human can carry water across desert land and food across barren land, something that other animals can't do. Of course, it is an enormous advantage for the bipedal proto-human to develop intelligence. A bipedal proto-human will be part of a very successful group. Eventually the group will outgrow the resources in any area. Then, the weakest of the bipedal proto-humans will be driven out into new lands where they must learn to survive or die. Of course the brain and the tools of the bipedal proto-humans allow them to adapt the environment to them, rather than just adapting to the environment.

An extreme example of the situation is the ancient Chukchi/Inuit peoples. They lived in an impossibly harsh environment and survived only by designing and using specialized tools that allowed them to survive. The Northman culture of the late 10th century was an advanced European civilization. However, the Northmen tried to adapt Greenland to their use instead of adapting themselves to Greenland. The Inuit were still there when the last of the Northmen gave up.

 

[Huckleman2000]

...An extreme example of the situation is the ancient Chukchi/Inuit peoples. They lived in an impossibly harsh environment and survived only by designing and using specialized tools that allowed them to survive. The Northman culture of the late 10th century was an advanced European civilization. However, the Northmen tried to adapt Greenland to their use instead of adapting themselves to Greenland. The Inuit were still there when the last of the Northmen gave up.

I'm reading a book that explores that Greenland situation, among many others. I haven't gotten to that part yet, but if I had I would have some very interesting things to say, if the first part of the book is any indication. It's called "Collapse - How societies Choose to Fail or Succeed" by Jared Diamond. He won a Pullitzer for "Guns, Germs, and Steel", which I've heard is excellent, but haven't read yet.

The terms dealt with i nthe book are not long enough to demonstrate evolutionary processes. I does deal with rise and fall of both isolated civilizations, such as Easter Island, as well as more well-connected civilizations. The choices people made, regarding division of resources, exploiting different regions and so forth, make for deep but fascinating reading.

In terms of influencing your story, I think it would be more of an education in how different cultures evolved through interaction with their environment, but not how different species evolved. Still, I suppose the ideas could be extrapolated, given enough isolation and a culture that has survived longer than any other due to some enlightened worldview.

 

[past_perfect]

I'm reading a book that explores that Greenland situation, among many others. I haven't gotten to that part yet, but if I had I would have some very interesting things to say, if the first part of the book is any indication. It's called "Collapse - How societies Choose to Fail or Succeed" by Jared Diamond. He won a Pullitzer for "Guns, Germs, and Steel", which I've heard is excellent, but haven't read yet.

The terms dealt with i nthe book are not long enough to demonstrate evolutionary processes. I does deal with rise and fall of both isolated civilizations, such as Easter Island, as well as more well-connected civilizations. The choices people made, regarding division of resources, exploiting different regions and so forth, make for deep but fascinating reading.

In terms of influencing your story, I think it would be more of an education in how different cultures evolved through interaction with their environment, but not how different species evolved. Still, I suppose the ideas could be extrapolated, given enough isolation and a culture that has survived longer than any other due to some enlightened worldview.

I have read "The rise and fall of the third chimpanzee", which raises some interesting points as well - definitely worth reading. At least before I'd never imagined that the length of a prospective partner's earlobes might be a decisive factor for feeling attracted to them.

 

[Huckleman2000]

I have read "The rise and fall of the third chimpanzee", which raises some interesting points as well - definitely worth reading. At least before I'd never imagined that the length of a prospective partner's earlobes might be a decisive factor for feeling attracted to them.

I have big earlobes.
No brag. Just fact.

 

[elsol]

I have big earlobes.
No brag. Just fact.

Don't ears keep growing for a human's entire life... or something.

Thus if we live long enough everyone would have big earlobes.

 

[past_perfect]

The point he is raising is that we choose people who have roughly the same length as we have... as well as people of similar hair colour and so forth (just a statistical value - which happens to be 100% accurate in my personal life - although I did not manage to verify the earlobe thing with hindsight).

 

[Huckleman2000]

Don't ears keep growing for a human's entire life... or something.

Thus if we live long enough everyone would have big earlobes.

I don't think so, but I know they do get hairy as you get older. This just draws attention to the earlobes, of which you'd been blissfully unaware until they became a source of revulsion.

It's like the moon looks bigger when it's close to the horizon.

 

[elsol]

The point he is raising is that we choose people who have roughly the same length as we have... as well as people of similar hair colour and so forth (just a statistical value - which happens to be 100% accurate in my personal life - although I did not manage to verify the earlobe thing with hindsight).

Not true for me... but as mentioned above I'm Latin.

I think culturally we're color collectors... blondes, brunettes, redheads, short little chinitas (ooh...la..la...nothing like a cute asian girl speaking with a latin accent... hmm, except maybe redheads with green-eyes getting offended because someone calls her white 'cause she's more Latin than I am).

 

[past_perfect]

Not true for me... but as mentioned above I'm Latin.

I think culturally we're color collectors... blondes, brunettes, redheads, short little chinitas (ooh...la..la...nothing like a cute asian girl speaking with a latin accent... hmm, except maybe redheads with green-eyes getting offended because someone calls her white 'cause she's more Latin than I am).

As I said - a statistical value - sure there are exceptions. I seem to have chosen exclusively within these parameters - I have brownish hair and all of my long-term partners had a similar colour. The one blonde that crept in turned out to be not quite so blonde after ...uhm... further inspection (that was much easier to verify in the past... ).

 

[Weird Harold]

i think the biggest problem is that we see this on an individual level. you have to let go and step back to the population level and see that i will do no better but perhaps my offspring might.

I think I'd say that the problem is most "laymen" see evolution in terms of visible or detectable changes. Darwin didn't understand the underlying minutia of genetic drift and DNA when he came up with the theory of natural selection and neither do most people today.

in order for natural selection to occur you must have 3 things. differences in the phenotype of individuals (physical manifestation of thier genes could be how they look or strength of thier immune system), 2 these differences must be heiritable (able to be passed on to the next generation), and 3 that this trait or phenotype must have some effect on fitness (overall success of the individual over a lifetime).

...Selection can happen very rapidly but in fact it rarely does without human interaction in the process.

I disagree with your third requirement. There are a lot of selectable traits that do nothing for the survival of the individual but do increase the individual's chance of producing offspring. Things like bigger and brighter feathers to attract a mate do nothing to enhance the individual's survival -- being more noticeable to predators might actually decrease the chance of survival -- but they do result in mating earlier and more often so bigger and brighter feathers get "selected" as quickly as some other difference that is beneficial to survival.

So with selection being weak it takes evolution quite some time. now mutation in the truest sense is a change in the genetic code or the A's T's G's and C's of your genome. this rate is slower than you can imagine something like 1 x 10^-6 or -7. so very slow. and selection can only act on those mutations that show up in the phenotype of individuals so if there is a very small change or even a silent mutation (one that doesn't change the protien made) then selection doesn't act on it.

I think that in terms of what most people think of as "evolution" the process relies more on those "silent mutations" spreading throughout a population because they aren't "selectable" at the time they appear. A change in the way a protein or enzyme is made might not make an immediate difference to survival or sexual prowess but turn out to be the key to survival when "evolutionary pressures" change.

Also, "silent mutations" don't really happen in "isolation;" they get distributed through a population by occuring in an individual that has some other "selectable" trait and become "linked" to that "selectable" trait -- like the "link" between Sickle Cell and resistance to Malaria I mentioned earlier.

Finally random genetic drift is the removal of genetic information from a population due to sampleing error. example....flipping a coin - flip it 100 time it will aproximate 50/50 but if you only sample a small poplulation of flips say 5, it wouldn't be suprizing to get all heads or 4 heads and a tail. that doesn't mean that the coin isn't balanced. it just means you didn't sample enough.

Couldn't "Evolution" be considered as "beating the odds?" It does sort of depend on some individual, or group of individuals, having the right combination of previously "silent mutations" and "copy errors" to cope with changing evolutionary pressures.

The odds of any one individual inheriting all of the factors that make something like bipedalism possible -- locking knees, changes to the pelvis and inner ear, straighter and stronger bones, etc -- has to be a Probability something similar to winning a Lottery three days in a row. In other words, "evolution" doesn't begin at the middle of a bell curve, it begins on the outer slopes of a bell curve.

 

[phdbio]

here goes nothing....

What I'm asking is: even though these lethal alleles aren't the norm, do they have equal power in evolutionary change? Or are they so rare that even if they do pack a punch, the norm outweighs them?

yes lethals cause changes faster just as strongly selected on traits change frequency in a population faster. So yes you see a large change quickly. but the majority of your genome is made up of these recessive slightly deleterious alleles.

It's called "Collapse - How societies Choose to Fail or Succeed" by Jared Diamond. He won a Pullitzer for "Guns, Germs, and Steel", which I've heard is excellent, but haven't read yet.

Both are must read's. they are really well written. there are a couple of others you might like called: Cod and a second called Salt and i think maybe a third called Water by Mark Kurslansky (spelling?) all very good.

If you like the earlobe thing there was an experiment done in the early 90's i think that i refer to as the sweaty shirt experiment. the MHC locus is a huge complex with lots of genes that have to do with your immune response and theoretically you should want to mate with someone that has a different allele at all of these genes to give you the broadest immune system. It was thought that humans should be able to detect the difference because this trait is tied so closely to fitness. so they had a group of men put on white t shirts and wear them for a week without taking them off or washing them. they then had a group of women come in and smell all the shirts and then genotyped both the men and women. they proved their point and the shirts the women found the least offensive were the ones that had the complimentry or opposite rather MHC loci.

Now to harold....

I disagree with your third requirement. There are a lot of selectable traits that do nothing for the survival of the individual but do increase the individual's chance of producing offspring. Things like bigger and brighter feathers to attract a mate do nothing to enhance the individual's survival -- being more noticeable to predators might actually decrease the chance of survival -- but they do result in mating earlier and more often so bigger and brighter feathers get "selected" as quickly as some other difference that is beneficial to survival.

Traits under selection have nothing to do with the survival of the organism. My goal in life isn't to survive and the goal of selection isn't to survive. It is to increase fitness, that is to pass on my genes as often as possible. i never said survivial because that isnt' important. How often i pass on my genome is. So bright feathers are a great way to increase fitness. When i say success i mean reproductivly (don't we all mean that really though)

Also, "silent mutations" don't really happen in "isolation;" they get distributed through a population by occuring in an individual that has some other "selectable" trait and become "linked" to that "selectable" trait -- like the "link" between Sickle Cell and resistance to Malaria I mentioned earlier.

when you talk about mutations, silent just mean that they do not change the protien but rather only the codon. And most mutations accrue in regions of the genome turned off and thus not expressed and not under the influence of selection. so the way in which these grow in a population is purely stochastic. As for linkage...that is a whole other bag...i know that you don't mean linkage in the genes linked way so i will just skip it. and the reason for sickle cell remaining in the population is heterozygote advantage where you have AA Aa and aa. well the Aa gives you resistance to Malaria but inorder to maintain that in a population you will always have to have a few aa and AA. This is one way genetic diversity is maintained in a population.

Couldn't "Evolution" be considered as "beating the odds?" It does sort of depend on some individual, or group of individuals, having the right combination of previously "silent mutations" and "copy errors" to cope with changing evolutionary pressures.

Most of genetics is about probabilities and especially population genetics. the reason statistics was developed was because of the sophisticated math required to answer these types of questions. So, Sir Ronald Fischer and Sewall Wright made up statistics as they went and are the fathers of population genetics as well as statistics.

As far as evolution being "beating odds." i would have to say no because of selection. if it were due to drift and mutation alone then yes it is purely stochastic but because of directional selection the model is more probalistic.

 

[3113]

The point he is raising is that we choose people who have roughly the same length as we have... as well as people of similar hair colour and so forth (just a statistical value - which happens to be 100% accurate in my personal life - although I did not manage to verify the earlobe thing with hindsight).

Interesting point on this--but only from pure observation on my part. I have noted that some gay couples go for near mirror images of themselves. I remember a pair of men who had been together a long time; not only were they about the same height, etc., but they'd both shaved their heads, grown large mustashes and, as with so many couples, they dressed alike. (Although, to be fair on this point, couples often buy clothes at the same store if possible. That is, a man and woman might buy their clothes at the Gap, creating a wardrobe with similar colors and cuts--or the woman might buy clothes for the man that, again, have similar colors to her own. If we have a gay couple, then it might well be economial sense to buy clothes at the same store. And if they are similar in height and weight, wear each others clothes). I'm sure these two were often mistaken for twins or just brothers.

Hmmmm. Maybe this explains the popularity of the incest category....?

But this actually makes sense. Humans group together with others who share their interestes and beliefs, one might say that the choir likes to be preached to, be in a church with others who share their values on every level from morality to aesthetics to interests. And people tend to want to kill or be rid of those who aren't on the same page. This, of course, goes along with being uncomfortable around those who look different--and the unease we feel if we may feel at a social gathering if we look different, even if we're just wearing the wrong clothing (or would we argue that this is nurture not nature? Hard to distinguish if it is).

Which raises the question...

Yooo-hoo! Phdbio! ....wouldn't such a propensity for narcissism undermine fitness by making humans lean too much toward inbreeding?

(P.S. Could you say "stochastic" again? Sloooowly and in a sentence? )

 

[phdbio]

what you are describing is two things actually...#1 humans don't follow the rules perfectly and we don't work towards our highest fitness which, may be sad but whatever, it makes us happy so we deal with it. case in point homosexuality...this has zero evolutionary support. why would you choose to give up your fitness entirely. your gene line ends with you. nothing against homosexuals and geez i know i am going to get beat up but that is the truth as far as the answer goes. as far as my beliefs well i think if you are gay/bi/hetero as long as you are happy then don't worry about genetic theory.

#2 - as far as the idea of us choosing people more like ourselves....that is the whole we don't fit the mold thing but some things we do...shoving others out while protecting people who are more like ourselves is just protecting people who share more of their genome with us than with the invading group. so we are still passing on our genes if just through our comrades.

oh another point...nature nurture thing...thats a pet peeve. you can't tell the difference ever, okay well almost never. you are affected by your environment period. sorry thats a different soap box when the quatitative genetics thread starts i will start inserting formulas and models to deal with this.

as for using stochastic in a sentence.... lets see.... my research deals with stocastic catestrophic events (hurricanes) and thier effects on populations living along the northern gulf coast?

 

[3113]

what you are describing is two things actually...#1 humans don't follow the rules perfectly and we don't work towards our highest fitness which, may be sad but whatever, it makes us happy so we deal with it.

Yeah, you're right. These kinds of discussions get tricky because one moment you're discussing fitness and evolution and locked knees, but then you pull back the tight-focus camera and suddenly you remember that everything in the big picture is...stochastic meaning that while the majority of the bell curve may lead to fitness, there's still going to be a random percentage at either end that doesn't or doesn't seem to support fitness. It may be a mutation that goes along with the fitness genes and just pops up now and then (sterility, for example), it may be something that was useful and isn't now, or that goes along for the ride and does nothing (being able to curl one's tongue?).

Or may be something that's going to occur given the complexity of the reproductive system.

For example, homosexuality. There was a long thread on this way back when, and we won't get into it, but there are theories that argue homosexuality as evolutionary viable (good for the fitness of the human race) as well as others that argue that it's inevitable in a small percentage given the delicate cocktail of hormones required by the womb in order to create a human baby. A cocktail that's mixture can easily change--naturally as well as artifically (like smoking while preggers) and affect the child's development.

As you pointed out, it's one of those thing that hasn't hurt our survival, especially since homosexuals CAN reproduce even if they don't enjoy the sex when they do.

oh another point...nature nurture thing...thats a pet peeve. you can't tell the difference ever, okay well almost never. you are affected by your environment period.

Agreed--and no need to get up on the soapbox. But it is an interesting point given the original reason for this thread. Elsol's idea seems less evolution and more a matter of nurturing--i.e., short-term enviornmental demands as compared to a millions years of elements developing, genetic drift, etc.

Elsol's idea is more in line with a bunch of shipwreck survivors stuck on an island. There's only so much food, so people kill off the sick babies, children and old folk (let's say), in order to maintain a sustainable population. And those that don't eat much get to stick around longer. So, within fifty years or so, the grandkids maybe skinny and small, but they're not pigmies.

To get an island of pigmies will require a lot more time and may or may not happen, depending on all kinds of factors....

Or am I going in a completely wrong direction again?

as for using stochastic in a sentence.... lets see.... my research deals with stochastic catestrophic events (hurricanes) and thier effects on populations living along the northern gulf coast?

*Faint*

 

[phdbio]

3113 you are pretty much right on with everything you said. so good job

 

[dr_mabeuse]

Evolution Without Mutation

Just came across this article and I should probably wait till I wake up and can think about it more clearly, but it excited me because it suggests a way that genetic change can occur without actual mutation - by a kind of patching of DNA from one organism to another.

This article describes how scientists searching for the organism with the smallest genome - the fewest number of genes - have found some bacteria who are have so few genes that they can only exist under very special condition inside other cells, almost as organelles, possibly a step away from fusing their own DNA with their hosts to form a new species.

I'm a complete believer of the scientific theory of evolution, but random mutation as the sole driving force always bothered me. For one thing, some of the "compexity" issues the intelligent design people raise aren't easily answered by the mechanism of random mutation. Genetic patching offers another mechanism which would allow a faster transfer of complex biological information, it seems to me.

Secondly, it just seems the more I learn about biology, the more symbiosis and general "messiness" I see. I remember how shocked I was when I learned that the mitochondria in our cells were nce free-living organisms who established a symbiotic relationship with our own cells. I think we'll probably be learning pretty soon how viruses play a role in evolution too, and I wouldn't be surprised to find out about inter-species exchange of DNA fragments.

Anyhow, it's an interesting little article. If nothing else, it has the seeds for a cool Halloween story.