Gaining Insight into Evolution and Natural Selection

[DaveC426913]

I have read some amount of literature on evolution and natural selection over the years and, while I certainly learn a lot, it never seems to quite help me grok the breadth of change over deep time.

So I have some rather naive thoughts that I'll phrase in the form of incredulity. They are simplified, for the sake of brevity; I understand that it's a nuanced topic.

I don't for a second doubt that it's the case, I just have to ... trust in the science.

1] Dogs are bred for different things. (Not the best starter topic, since this involves artificial selection) Terriers are bred for digging. If we assume that this is an instinctive trait (not learned from a parent), then there is something in the wiring of the brain that tells all these dogs to dig. Their DNA, the only thing a breed has in-common with its kin, must encode the genes to build the neural pathways that cause it to want to dig. That, and ten thousand other subtle behaviors must be encoded in the genes, which cause proteins to make pathways, which survive the embryonic process to birth, which cause it to ... what? dig? That subtlety of encoding is virtually inconceivable to me.

2] Complex mammals dream; cats do; dogs do. I suppose rodents do too. I'm not sure about non-mammals. That means that the process for dreaming must have come from their common ancestor - that shrew that lived alongside the Tyrannosaur 80 million years ago. If more distant animals - such as any of the mammals' classificationary cousins - also dream, that means dreaming was well-established even before mammals split off. Unless we are going for convergent evolution here...

3] Cows have tufted tails, the better to swat flies away with, and over-large eyelashes that help keep flies out of their eyes (pick any other subtle traits). They evolved these things as an evolutionary advantage (granted, this is oversimplified). Does this mean that of the one gajillion cowoids that went before it, a statistically significant number of them died or were unable to breed effectively because they had short eyelashes and broom-like tails? I should find a better example but, in essence, does it not hold true that a critter has some subtle trait because .9999 gajillion of its ancestors dies whereas of those that di not have that trait a whole gajillion died? I am aware that many traits evolved alongside other traits, without any apparent advantage. Still, the net outcome is that advantageous traits - even ridiculously subtle ones - were selected for.

4] I imagine an idealized critter, with only two traits, say, a blob that has a skin-texture and a leg-length.
The smooth-skinned has a slight advantage over pebbly-skin, but long legs has an advantage over short legs. (Let's say they live on the surface of fast-running water or some such). Smooth skin prevails over pebbly-skin, but in doing-so, wipes out a bunch of long-legged, pebbly-skinned varieties. Ultimately, the two traits evolve independent of each other. Skin gets smoother, legs get longer, even though many of both kinds of being wiped out.

I guess I can see it at the scale of just a few traits, but the number of individual traits of any complex critter is virtually uncountable. This critter has wider tubes for its lymph nodes, that critter has striations in its liver, another critter has eyes nearer the top of its head, yet another has smaller blood corpuscles. It is virtually unfathomable that these traits can evolve essentially independent of each other in a population, when the traits are essentially competing with each other to "help" the critters survive.

Some day I want to write a program like this. An idealized critter, with a hundred traits, all with some sort of (unknown!) advantage or disadvantage, or both - (traits that, in the real world, might to allow it to - or prevent it from - breeding just one more time than its neighbor). I want to run it against an idealized "challenging landscape". The challenges are just idealized properties as well; just randomly-invoked events - one knocks these traits up and those ones down, another knocks this set up and that set down. Of course, the sets of traits affected will strongly overlap - in a sense the traits themselves are competing. I want to watch and see if, after 10,000 generations, the critters remaining will have selected traits that equate to advantages. Someday...

 

[Evo]

I've asked Ryan to respond when he has time. In the mean time here's a link he uses to explain evolution. http://evolution.berkeley.edu/evolibrary/article/evo_01

 

[DiracPool]

I guess I can see it at the scale of just a few traits, but the number of individual traits of any complex critter is virtually uncountable. This critter has wider tubes for its lymph nodes, that critter has striations in its liver, another critter has eyes nearer the top of its head, yet another has smaller blood corpuscles. It is virtually unfathomable that these traits can evolve essentially independent of each other in a population, when the traits are essentially competing with each other to "help" the critters survive.

I'm not really sure what your question is. It is what it is, what survives is what survives, and what dies..doesn't not survive. Not all survived traits are independent, many are coupled, e.g., the development of the eye and the visual cortex among many others.

Does this mean that of the one gajillion cowoids that went before it, a statistically significant number of them died or were unable to breed effectively because they had short eyelashes and broom-like tails?

Basically, yes. But it doesn't necessarily mean that the short eyelashes and broom tails caused their demise per se, it just means that another cow cam along that didn't have those traits that had another trait not related to those that allowed it to out-compete the short eyelashed cowoids. You know, like some massive udders or something like that

Terriers are bred for digging. If we assume that this is an instinctive trait (not learned from a parent), then there is something in the wiring of the brain that tells all these dogs to dig. Their DNA, the only thing a breed has in-common with its kin, must encode the genes to build the neural pathways that cause it to want to dig. That, and ten thousand other subtle behaviors must be encoded in the genes, which cause proteins to make pathways, which survive the embryonic process to birth, which cause it to ... what? dig? That subtlety of encoding is virtually inconceivable to me.

There is studied hierarchy of behaviors that run down from mammals to lower vertebrates such as reptiles, amphibians, and fish. It's a science called "neuroethology."

https://en.wikipedia.org/wiki/Neuroethology

There are so-called instinctual neural assemblies that are indeed, encoded by the DNA that lay down neural pathways that, say, "code" for a digging behavior. But these need to be reinforced through training or "imprinting" typically to reach full expression in a process

 

[DiracPool]

Wow, I thought all my effort writing a response to this thread was wasted as Evo closed the thread "in write." I'm glad it's back up and my text wasn't deleted. Hope someone gets something from it

Edit: Oops, re-reading it, it looks like my response got cut off mid way for some reason..and unfortunately, those were the best parts..

 

[Drakkith]

Some day I want to write a program like this. An idealized critter, with a hundred traits, all with some sort of (unknown!) advantage or disadvantage, or both - (traits that, in the real world, might to allow it to - or prevent it from - breeding just one more time than its neighbor). I want to run it against an idealized "challenging landscape". The challenges are just idealized properties as well; just randomly-invoked events - one knocks these traits up and those ones down, another knocks this set up and that set down. Of course, the sets of traits affected will strongly overlap - in a sense the traits themselves are competing. I want to watch and see if, after 10,000 generations, the critters remaining will have selected traits that equate to advantages. Someday...

Here are a couple of links to programs that simulate evolution, though they may not have 100 traits.

http://boxcar2d.com/
http://wiki.darwinbots.com/index.php/Main_Page
http://sepuplhs.org/high/sgi/teachers/evolution_act11_sim.html
http://biologyinmotion.com/evol/
http://rednuht.org/genetic_walkers/
http://rednuht.org/genetic_cars_2/

 

[Graeme M]

DaveC, on the matter of dreaming noted in your point 2, I have no knowledge of the science and history of dreaming, but it may have evolved long ago. Michael Graziano postulates the development of a complex attentional processing system for neural signal enhancement which laid the foundation for what he describes as the "attention schema - an internal model of attention. This model constitutes what we might call awareness or consciousness. If this idea is anywhere close to right, and dreaming uses that process (which I assume it might given the similarities between conscious awareness and dreaming), then dreaming may have evolved upwards of several hundreds of million years ago... I rather like Graziano's proposal.

http://www.princeton.edu/~graziano/Graziano_JCN_2014.pdf (Journal of Cognitive Neuroscience)

Speaking of neuroethology, Graziano also has an interesting paper about ethological action maps:

http://www.princeton.edu/~graziano/graziano_2015.pdf (Trends in Cognitive Sciences)

 

[Andy Resnick]

So I have some rather naive thoughts that I'll phrase in the form of incredulity. They are simplified, for the sake of brevity; I understand that it's a nuanced topic.

I don't for a second doubt that it's the case, I just have to ... trust in the science.

1] Dogs are bred for different things. <snip>

2] Complex mammals dream; cats do; dogs do. <snip>

3] Cows have tufted tails, the better to swat flies away with, and over-large eyelashes that help keep flies out of their eyes (pick any other subtle traits). <snip>

My understanding is that describing evolution in terms of 'survival fitness' only has meaning in terms of large-scale population dynamics; applying 'survival fitness' to a single member of a population (or even a single species) is generally problematic.

Dogs actually present a few subtle challenges: first, they are intentionally bred and cross-bred, and the particular trait selected for breeding is an entirely artificial construct- many breeds suffer from specific disorders (cataracts, glaucoma, hip dysplasia...) that would cause problems in the absence of domestication. Second, dogs, of all species, have the largest variability in physical size. The extensive history of domestication and breeding provides an interesting 'laboratory' for canine genetics:

http://genome.cshlp.org/content/15/12/1706.full.html
http://www.nature.com/nature/journal/v438/n7069/full/nature04338.html

As for dreaming, I don't know that the function is understood; assigning an evolutionary status may not make sense unless it is posited as a necessary function of the central nervous system. Currently, existence of REM sleep is a proxy for dreaming, which is about the best we can currently do.

http://www.ncbi.nlm.nih.gov/pubmed/15798942

Regarding cow physiology, tufted tails are not unique to cows. Perhaps more interestingly, lions are the only members of Panthera with a tufted tail, and male lions are the only members with a mane. Asking 'why is this?' has no obvious answer- evolution-as-survival fitness cannot plausibly respond, but that's because it's not the right question. Similarly: if walking on two legs confers a significant survival advantage, why are there only a few living mammalian species (AFAIK) that exclusively walk upright? Evolution is not a directed process- it does not 'act' to solve a problem, and it is not an intermittent process.

Personally, I'm interested in comparing the genome of a modern alligator (or Ginkgo) to one that lived 100 Myr (250 Myr) ago- what genomic changes have occurred in the interim?

"Evolution" type algorithms exist in a variety of contexts to solve a variety of problems, likewise experiments.

 

[Drakkith]

Dave, I'll ask my boss if he's in today about some of this and see what he says. He was a biologist and we've talked about evolution before.

 

[atyy]

I have read some amount of literature on evolution and natural selection over the years and, while I certainly learn a lot, it never seems to quite help me grok the breadth of change over deep time.

3] Cows have tufted tails, the better to swat flies away with, and over-large eyelashes that help keep flies out of their eyes (pick any other subtle traits). They evolved these things as an evolutionary advantage (granted, this is oversimplified). Does this mean that of the one gajillion cowoids that went before it, a statistically significant number of them died or were unable to breed effectively because they had short eyelashes and broom-like tails? I should find a better example but, in essence, does it not hold true that a critter has some subtle trait because .9999 gajillion of its ancestors dies whereas of those that di not have that trait a whole gajillion died? I am aware that many traits evolved alongside other traits, without any apparent advantage. Still, the net outcome is that advantageous traits - even ridiculously subtle ones - were selected for.

If you can't show that the trait is an adaptation (eg. increases survivability of the organism), the question of natural selection does not arise.
https://www.blackwellpublishing.com/ridley/a-z/Adaptation.asp
https://www.jstor.org/stable/77447?seq=1#page_scan_tab_contents

Furthermore, one should be aware that natural selection is not as fundamental a concept as evolution.

 

[mfb]

if walking on two legs confers a significant survival advantage

Is that true in general? It is true for modern humans, but I see no evidence that it is true in general. Humans are quite slow compared to many animals of similar size, for example.

Their DNA, the only thing a breed has in-common with its kin, must encode the genes to build the neural pathways that cause it to want to dig.

We inherit more than the DNA. We also get the epigenome.

For your specific example, I don't know if terriers dig (more than other dogs) if they don't learn it from others. The larger concept "explore the world around you" is certainly inherited, if you do that exploration more below the ground, at the ground, on trees or whatever is a different question.

 

[Andy Resnick]

Is that true in general? It is true for modern humans, but I see no evidence that it is true in general.

Since hominds are one of the few bipedal mammals, post-hoc rationale is generally restricted to primates. It's commonly asserted as being beneficial, also the lack of rationale as to why it occurred for hominids.

http://www.livescience.com/1702-walk-upright-beats-chimp.html
http://elucy.org/Main/WhyBipedalism.html

I could not find similar excuses for kangaroos (bipedal) or pandas (quadrupedal), which also have opposable thumbs and so could hold tools with all the supposed benefits accruing unto.

 

[Pythagorean]

Is that true in general? It is true for modern humans, but I see no evidence that it is true in general. Humans are quite slow compared to many animals of similar size, for example.We inherit more than the DNA. We also get the epigenome.

Slow, but... we still were able to maintain predation over most of the animal population with our legs using a persistence hunting strategy. But this strategy is used by furry four legged animals like wolves too, so to what extent two legs are better I don't know. I think one thing that helps us a lot (and maybe one reason other apes don't persistence hunt) is sweating (a low energy process) instead of panting (a high energy activity) makes cooling during persistence hunting more efficient.

 

[DaveC426913]

Basically, yes. But it doesn't necessarily mean that the short eyelashes and broom tails caused their demise per se,

But it does, ultimately.

Whether because it couldn't breed due to its short-eyelashe or because some one long-eyelasher bred more, using up resources, the outcome is the same.

it just means that another cow cam along that didn't have those traits that had another trait not related to those that allowed it to out-compete the short eyelashed cowoids. You know, like some massive udders or something like that

Same thing. In a turbulent world of competition, the cows with short eyelashes lost to cows with long eyelashes. The massive udder thing should not factor in.

Say you've got four cows:
short eyelashes, normal udders
short eyelashes, massive udders
long eyelashes, normal udders
long eyelashes, massive udders

The udder trait will evolve independently of the eyelash trait. (again, this is not always so, but mostly traits have degrees of freedom not constrained by other traits)
Which means that, when all is said and done, the long eyelashers outcompeted the short-eyelashers.

 

[DaveC426913]

There is studied hierarchy of behaviors that run down from mammals to lower vertebrates such as reptiles, amphibians, and fish. It's a science called "neuroethology."

https://en.wikipedia.org/wiki/Neuroethology

[PLAIN]https://en.wikipedia.org/wiki/Neuroethology[/PLAIN]
Do you mean that digging is an instinctive trait passed down to descendants of all mammals?

But these need to be reinforced through training or "imprinting" typically to reach full expression in a process

Except that terriers naturally dig. To what extent, I'm not concerned, the point is, they have that trait to a level noticeably higher than other dogs.

 

[DaveC426913]

My understanding is that describing evolution in terms of 'survival fitness' only has meaning in terms of large-scale population dynamics; applying 'survival fitness' to a single member of a population (or even a single species) is generally problematic.

Yes. The problem is, that - ultimately - that is what is happening.

Our population models involve large populations, but in reality, the variations in species is actually occurring on an individual basis, as each critter breeds or doesn't.

 

[DaveC426913]

Is that true in general? It is true for modern humans, but I see no evidence that it is true in general.

This is an interesting point, methinks.

If my understanding of evolution is correct, there are few general advantages. The proof (of survival) is in the pudding (of actually surviving). Humans survived because of a large number of traits in conjunction with its upright stance - for example good binocular vison, developed hands that can be used once freed from locomotion, large brain to make tools. Some other critter with upright stance but none of these other traits would find themselves at a disdvantage. Too much of their energy budget would be being wasted on a vertical stance if they have poor eyes or clumsy hands.

The suvival happens on an individual basis, since the "landscape" (both literal and virtual) of drivers (distant mastodons, thick fur, wide plains, clever competing predators, etc.) is nearly limitless. In other words, there is no "formula" that works generally, just de facto successes.

Most of the common traits that disparate species share are not independent at all - they were handed down from a common ancestor.

In my opinion.

 

[DiracPool]

The udder trait will evolve independently of the eyelash trait. (again, this is not always so, but mostly traits have degrees of freedom not constrained by other traits)
Which means that, when all is said and done, the long eyelashers outcompeted the short-eyelashers.

Yeah, that's probably correct. There's no real reason to think that eyelash length and udder size are linked-traits (in cows at least, if you're a human female stripper, maybe )

The point is that, so what? What's your point? Eyelash length may confer an advantage to keep dust or bugs out of your eyes or serve as a secondary sexual characteristic. In either case, it's a trait subject to natural selection as is udder size, and they may be selected for independently or partially independently. That kind of goes without saying. What's your quandary?

 

[jim mcnamara]

I think Dave's problem is assumptions, one is: there is meaning or direction or intention or any kind of logic to Natural Selection. It is random. No logic or predestination whatsoever.

A meteor falls on a population of cattle. They all had short eyelashes. That gene now becomes rare and whatever selection pressure there was in the past to preserve the trait is no longer there. Long eyelashes "win" for no reason at all( to put it in a really bad sentence with wrong meaning).

Think Yoda: There is no win - only live to reproduce. And. Reproduce more than the next cow.

You cannot focus on traits, only environment and maybe trends in the environment.

Does that help?

 

[DaveC426913]

The point is that, so what? What's your point? Eyelash length may confer an advantage to keep dust or bugs out of your eyes or serve as a secondary sexual characteristic. In either case, it's a trait subject to natural selection as is udder size, and they may be selected for independently or partially independently. That kind of goes without saying. What's your quandary?

Yeah, it's just weird to think that it happens to individuals in the population. Literally, more short-eyelashed cows died (from short-eyelash problems) before they could reproduce (otherwise, that is not the trait that would be selected-for).

 

[DaveC426913]

I think Dave's problem is assumptions, one is: there is meaning or direction or intention or any kind of logic to Natural Selection. It is random. No logic or predestination whatsoever.

Mm. No I'm not assuming that.

To be clear, I'm adequately well-read in evolution and natural selection, and there's no doubt of its veracity. Its just when I start looking closely - a at human scale, of individuals, rather than the overarching million years of populations - that it gets hard to fit in my head.

A meteor falls on a population of cattle. They all had short eyelashes. That gene now becomes rare and whatever selection pressure there was in the past to preserve the trait is no longer there.

Random events like this would balance out in the long-term. Next century, a flashflood wipes out a population of long-eyelashed cattle.

You cannot focus on traits, only environment and maybe trends in the environment.

That's one of the things I'm getting at.

Our models deal with populations.
But the actual mechanism of selection acts upon individuals.

 

[Ygggdrasil]

1] Dogs are bred for different things. (Not the best starter topic, since this involves artificial selection) Terriers are bred for digging. If we assume that this is an instinctive trait (not learned from a parent), then there is something in the wiring of the brain that tells all these dogs to dig. Their DNA, the only thing a breed has in-common with its kin, must encode the genes to build the neural pathways that cause it to want to dig. That, and ten thousand other subtle behaviors must be encoded in the genes, which cause proteins to make pathways, which survive the embryonic process to birth, which cause it to ... what? dig? That subtlety of encoding is virtually inconceivable to me.

To what extent DNA and genetics control behavior is still very much an active area of research. While we've dissected some of the genetics that control the development of neural circuits in animals such as fruit flies and nematode worms, we understand much less about mammals (like mice, dogs, and humans). In part, this is because much of neuronal development in mammals is experience-dependent. In other words, whereas the wiring diagrams for the neuronal circuits of simpler animals are genetically programmed, the wiring diagrams of mammalian brains are not pre-programmed and instead form in response to learning.

I'd also question whether Terriers are genetically programmed to dig. For example, the AKC says that "Their ancestors were bred to hunt and kill vermin," and neither that page nor Wikipedia make any mention of terriers being bred for or having any particular proclivity toward digging. So the assumption that this is an instinctive trait (vs a learned trait) is probably wrong. Certainly genetics might influence the general disposition of a breed, but it is unlikely that breeding would affect learned behaviors such as digging (other than changing physical characteristics that might make them more adept at digging).

2] Complex mammals dream; cats do; dogs do. I suppose rodents do too. I'm not sure about non-mammals. That means that the process for dreaming must have come from their common ancestor - that shrew that lived alongside the Tyrannosaur 80 million years ago. If more distant animals - such as any of the mammals' classificationary cousins - also dream, that means dreaming was well-established even before mammals split off. Unless we are going for convergent evolution here...

3] Cows have tufted tails, the better to swat flies away with, and over-large eyelashes that help keep flies out of their eyes (pick any other subtle traits). They evolved these things as an evolutionary advantage (granted, this is oversimplified). Does this mean that of the one gajillion cowoids that went before it, a statistically significant number of them died or were unable to breed effectively because they had short eyelashes and broom-like tails? I should find a better example but, in essence, does it not hold true that a critter has some subtle trait because .9999 gajillion of its ancestors dies whereas of those that di not have that trait a whole gajillion died? I am aware that many traits evolved alongside other traits, without any apparent advantage. Still, the net outcome is that advantageous traits - even ridiculously subtle ones - were selected for.

4] I imagine an idealized critter, with only two traits, say, a blob that has a skin-texture and a leg-length.
The smooth-skinned has a slight advantage over pebbly-skin, but long legs has an advantage over short legs. (Let's say they live on the surface of fast-running water or some such). Smooth skin prevails over pebbly-skin, but in doing-so, wipes out a bunch of long-legged, pebbly-skinned varieties. Ultimately, the two traits evolve independent of each other. Skin gets smoother, legs get longer, even though many of both kinds of being wiped out.

I guess I can see it at the scale of just a few traits, but the number of individual traits of any complex critter is virtually uncountable. This critter has wider tubes for its lymph nodes, that critter has striations in its liver, another critter has eyes nearer the top of its head, yet another has smaller blood corpuscles. It is virtually unfathomable that these traits can evolve essentially independent of each other in a population, when the traits are essentially competing with each other to "help" the critters survive.

Some day I want to write a program like this. An idealized critter, with a hundred traits, all with some sort of (unknown!) advantage or disadvantage, or both - (traits that, in the real world, might to allow it to - or prevent it from - breeding just one more time than its neighbor). I want to run it against an idealized "challenging landscape". The challenges are just idealized properties as well; just randomly-invoked events - one knocks these traits up and those ones down, another knocks this set up and that set down. Of course, the sets of traits affected will strongly overlap - in a sense the traits themselves are competing. I want to watch and see if, after 10,000 generations, the critters remaining will have selected traits that equate to advantages. Someday...

As others have mentioned before, not all traits we carry are adaptive. Natural selection is not the only mechanism for evolution. http://discovermagazine.com/2014/march/12-mutation-not-natural-selection-drives-evolution probably plays as big a role in evolution as selection. Furthermore, a common fallacy is to assume that functions and selective pressures stay constant over time. There are certainly examples of traits that were adaptive in the past but still persists in some vestigial form in the present (e.g. humans have tail bones and appendixes. Human embryos have gill like structures that eventually go away). Similarly, there are examples of traits that evolved for one purpose and have taken on a completely different purpose later in evolution (a process called exaptation). An example here is the evolution of feathers, which was originally for warmth and insulation, and only later were used for flight. There are also traits that are not adaptive themselves but occur as a byproduct of an adaptive process (called spandrels). Sometimes these spandrels occur because the trait is closely linked (genetically or otherwise) to a separate adaptive trait (in reference to your point #4).

As a starting point, I'd suggest reading the following blog post for a more detailed explanation. Here's an exerpt:

In 1979, Stephen J. Gould and Richard C. Lewontin saw a growing problem in the field of biology. To combat and point out the problem they saw they co-authored the paper entitled, "http://www.aaas.org/spp/dser/03_Areas/evolution/perspectives/Gould_Lewontin_1979.shtml " which is now a classic and somewhat controversial paper in the field of biology. Gould say's in I Have Landed that it's his second most referenced paper behind only his paper with Eldredge on punctuated equilibrium.

The problem was that every part of an animal's anatomy was being broken up and explained as having an evolutionary purpose. The tyrannosaur's small arms were to help it get up from sleeping, or the female hyena's masculinized genitalia created aggressive and larger than would be expected hyena, are the types of explanation's being put forward. Each piece or feature of an animal was broken up and weighed; if something existed it existed for a Darwinian reason and the animal as a collective whole was never thought about. Noses were created to hold glasses and ears to fit earplugs.

http://themoralskeptic.blogspot.com/2012/02/biological-spandrel.html

 

[Ygggdrasil]

We inherit more than the DNA. We also get the epigenome.

This is quite a controversial topic in biology. It is certainly true that histone and DNA modifications are important regulatory components of cells, but whether these are the cause or the effect of the regulation is still an area of active research. While epigenetic modifications have been observed pass down through several generations, most of these experiments show the effects diminishing with time, raising doubt about whether such mechanisms could contribute to adaptive change over evolutionary timescales.

 

[atyy]

Our models deal with populations.
But the actual mechanism of selection acts upon individuals.

That is a classic position. However, given that natural selection is not fundamental, I think one should be careful about this, eg. it has been argued that the unit of selection can be the gene, as well as the population.

https://www.blackwellpublishing.com/ridley/tutorials/The_units_of_selection_Summary.asp

 

[OCR]

It is what it is, what survives is what survives, and what dies..doesn't not survive.

Lol, and no, I'm not a grammar cop ... but[COLOR=#black].[/COLOR] isn't not [COLOR=#black].[/COLOR]what I bolded in your quote, a double negative ?[COLOR=#black] ...[/COLOR]

Just a simple typo ... correct ? [COLOR=#black]..[/COLOR]

 

[Andy Resnick]

Yes. The problem is, that - ultimately - that is what is happening.

Our population models involve large populations, but in reality, the variations in species is actually occurring on an individual basis, as each critter breeds or doesn't.

I'm not sure I understand your meaning. Yes, genetic variability/heritability applies to single(-ish) organisms (call it microscale), but evolution in terms of a macro-scale drift in genome content applies to a much larger population.

How about this- 'sequencing the human genome'. Given that you and I have different genes (as we must, since we are different people with different ancestries), what does that phrase really mean? Is there such a thing as 'baseline normal'? Does it make sense to average small-scale variations, or does that actually produce nonsense?

Or this: the evolution-as-adaptation process is often couched in terms of antibiotic resistance: a small number of bugs are resistant to some drug, those small number reproduce more efficiently and thus, over time, the population of bugs is transformed into an antibiotic resistant strain. This is similar in spirit to replacing a thermodynamic process with just the equilibrium states, using the assumption that the process is path-independent. It's unclear (to me) that this is a valid abstraction for adaptation. Why must there be only a single version of resistant strain- why can't multiple bugs develop resistance independently, with independent 'solutions'?

Edit- in fact, this is exactly the case for eyes: refractive eyes and compound eyes are two indpendent and equivalent 'solutions to the problem of vision'.

 

[Andy Resnick]

Its just when I start looking closely - a at human scale, of individuals, rather than the overarching million years of populations - that it gets hard to fit in my head.

<snip>

Our models deal with populations.
But the actual mechanism of selection acts upon individuals.

I agree, it's tough to go macro -> micro. But it's also usually true that the characteristic being selected (bred?) for acts uniformly across the population. When it doesn't, you end up with species-level differentiation, as the case for Darwin's finches.

 

[mfb]

This is quite a controversial topic in biology. It is certainly true that histone and DNA modifications are important regulatory components of cells, but whether these are the cause or the effect of the regulation is still an area of active research. While epigenetic modifications have been observed pass down through several generations, most of these experiments show the effects diminishing with time, raising doubt about whether such mechanisms could contribute to adaptive change over evolutionary timescales.

I never claimed any long-term effects. Passing down things by one generation would already be sufficient to get parent->child influences that are not encoded in the DNA and not learned.

 

[Pythagorean]

I believe epigenetic effects are found to influence grand children even, since grandparents provide sex cells to their own offspring which will produce the grandchildren. Iirc, a specific case related famine in the early 20th century to obesity today. I'll give it a search when I'm at a computer.

 

[jim mcnamara]

@Pythagorean - Sweden - data from church roles from the 1700's(?) onward, with periodic famines influencing grandchildren's longevevity. IRRC. I can't find the paper either.
May you have better luck.

 

[Pythagorean]

Apparently there's a couple different examples, including Sweden. This article references it's examples as in line links:

http://theconversation.com/how-your-grandparents-life-could-have-changed-your-genes-19136

 

[rbelli1]

more short-eyelashed cows died (from short-eyelash problems) before they could reproduce

Or some small percentage of long eye lashed cows survived just so slightly longer that they were able to produce just one more offspring. You don't need a trait to be terminal to have an effect over millions of years.

BoB

 

[Ygggdrasil]

@Pythagorean - Sweden - data from church roles from the 1700's(?) onward, with periodic famines influencing grandchildren's longevevity. IRRC. I can't find the paper either.
May you have better luck.

Apparently there's a couple different examples, including Sweden. This article references it's examples as in line links:

http://theconversation.com/how-your-grandparents-life-could-have-changed-your-genes-19136

Here's a review article on the topic:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4157403/

On the Swedish studies:

Compelling historical findings of paternal transgenerational effects in humans come from the Överkalix population in northern Sweden27–31 using samples of individuals born in specified years. Longevity and specific causes of death were linked to detailed historical records of harvests and food supply experienced by previous generations in early life. This series of studies is summarised in table 1.

 

[DaveC426913]

Or some small percentage of long eye lashed cows survived just so slightly longer that they were able to produce just one more offspring. You don't need a trait to be terminal to have an effect over millions of years.

Exactly.

But again, break it down to the actual cause and effect there. In a population (granted, one jillion cows over one jillion years), a statistically significant number of animals literally were unable to breed at least one season because of the some eyelash-related problem. Maybe short-lashed cows get more infections, or maybe they just walk into trees slightly more because can't see where they're going as well. The problem may be seemingly small, but it is pervasive in the population.

 

[Fervent Freyja]

Is that true in general? It is true for modern humans, but I see no evidence that it is true in general. Humans are quite slow compared to many animals of similar size, for example.We inherit more than the DNA. We also get the epigenome.

We also evolved to sleep significantly less than other animals, where that extra time allowed us to cover more distance- the advantage in traveling couldn't be just the speed/bipedalism like you said. Juvenile male primates are well known for wandering off to explore their surroundings. So, I imagine that it wouldn't be so different for the young male homo sapiens.

Bipedalism does have a few advantages: "What our research has been showing is that many of the anatomical characters of great apes and our ancestors, the early hominins (such as bipedal posture, the proportions of our hands and the shape of our faces) do, in fact, improve fighting performance..." I don't exactly see how it would help fight off a pack of wolves though.

Yeah, that's probably correct. There's no real reason to think that eyelash length and udder size are linked-traits (in cows at least, if you're a human female stripper, maybe )

DiracPool, what are you, some sort of primate?

 

[DaveC426913]

Bipedalism does have a few advantages: "What our research has been showing is that many of the anatomical characters of great apes and our ancestors, the early hominins (such as bipedal posture, the proportions of our hands and the shape of our faces) do, in fact, improve fighting performance..." I don't exactly see how it would help fight off a pack of wolves though.

Having hands on long arms that are free means we have much better reach than a wolf, who must move into within biting range.
Essentially, humans have three "mouths" to attack and defend with, two of which have a reach of several feet.

And you'll survive bites the to arms, if that's all an attacker can get near.