the unscientific american watches a mammal walk into the water and grow fins.

[Karis]

Natural selection or even evolution (depending on how the term is used) is not problematic (for me) as I see this in science.

 

The Big Question is one of Origin - the when and exactly how and quite possibly why? is not explained by science.

 

 

Wouldn't a lack of a verifiable explanation/ observation of the beginning also be outside of the realm of what evolutionists consider true science.

 

I understand that the evolutionary model totally contradicts the Biblical model. (as far as chronology - from what I've read) That's one thing, but I honestly don't see how evolution can firmly explain origination. Can someone address this for me?

 

For me, it doesn't address this question. (gotta run Be back later)

[Iucounu]

That's a different topic, called abiogenesis. There are scientific explanations for it, although of course it's going to be tough to verify from the geologic and fossil record exactly how it occurred. Scientific understanding evolves all the time. :)

[ravinlunachick]

I grew up in the Bible Belt as well, and I recall being taught about evolution in high school biology (mostly comprised of juniors, btw). Guess what the US History (class required of all juniors) teacher did that week? Tossed his lessons plans out the window and spent every class reading aloud anti-evolution books and "refuting" every single thing that was being taught by the biology teacher. :glare:

 

Anyway, I read a book (I think it was Why Evolution is True by Jerry Coyne) that absolutely blew my mind about the whale issue. To be honest, I'd never given it much thought; I just assumed they were mammals who sort of um....stayed in the water, if you know what I mean. I remember gasping loudly as I read that whales *returned* to the ocean, and that they have pelvises similar to us, and sometimes grow legs! :blink: What a lightbulb moment for me!

 

I appreciate those who have taken the time to answer questions in this thread, and I hope it can stay open. :)

[ravinlunachick]

I suppose I should count myself lucky to have any exposure to evolutionary theory at all in high school. At that time, our state had not developed state-wide standards, and it was still up to each individual teacher to decide what to teach, or what parts of the textbook to use.

 

Lucky me, our bio teacher thought we should know about it. Of course, he also protested the lack of any sex-ed by spending a day discussing STD's and condom usage. His lecture was punctuated by the very dramatic unrolling of a condom over his head and shoulders, and pointing out that no boy should EVER say he was "too big" for a Trojan to accomodate. Yeah, good ol' Mr. Brady. He was a memorable one.

[Trish]

Wait, I thought the dolphin GREW legs and arms, sprouted lungs etc. Not the other way around!

 

Do most Evolutionists believe one species can "become" another? Intra-species evolution would make more sense to me than inter-species evolution.

[kiana]

Lucky me, our bio teacher thought we should know about it. Of course, he also protested the lack of any sex-ed by spending a day discussing STD's and condom usage. His lecture was punctuated by the very dramatic unrolling of a condom over his head and shoulders, and pointing out that no boy should EVER say he was "too big" for a Trojan to accomodate. Yeah, good ol' Mr. Brady. He was a memorable one.

 

Hah! Nice.

[BethG]

I see evolution and find it very believable and IMO incontrovertible and compatible with Scripture ---which is generally looked upon as

:smash:

:ack2:

anathema among fundamentalist.

[nmoira]

Wait, I thought the dolphin GREW legs and arms, sprouted lungs etc. Not the other way around!

Some whale species have vestigial hind limb bones.

 

http://bergenmuseum.uib.no/fagsider/osteologi/hvaler/e_bekken.htm

 

 

Do most Evolutionists believe one species can "become" another? Intra-species evolution would make more sense to me than inter-species evolution.

Depends what you mean by "become." As much as I need a nap, Homo sapiens is not going to "become" Phascolarctos cinereus (the only animal cuter than a cat. Species is generally defined as a group of organisms capable of reproducing fertile offspring. For a number of reasons, a population of organisms can become sufficiently genetically distinct from another (of a common ancestor) that they have "become" a new species. Edited February 6, 2012 by nmoira

[lewelma]

Ok, so many questions, and I am in the middle of teaching.

 

The Big Question is one of Origin - the when and exactly how and quite possibly why?

 

First of all, lets make the origins of life a different thread, please, as it could get a bit more difficult to keep on topic.

 

Next,

Do most Evolutionists believe one species can "become" another? Intra-species evolution would make more sense to me than inter-species evolution.

 

No. Species share a common ancestor species. Later I will give you an example of a ring species for intra-species evolution, but I'm a bit busy now. The concept actually connects to this next question.

 

One question I have is what is the line between species and something less differentiated, for example a breed (as in dog and cat breeds). Is this a rather permiable division?

I understand, for example that there are different species of bee that generally don't breed, but then my understanding of the "killer bee" developments was that it was one type of South American bee mixing with North American bees and producing something new.

 

Another example of the question might be the division between wolf and dog.

 

The reason I ask is I've tried to get my head around why anthropologists consider different hominids (sp?) to be different species (homo sapiens and neanderthal for example) but then there will be an article saying research suggests they interbred (which to me indicates that they were part of the same species but had different traits emphasized by developing in geographic isolation (much as how we have Asian, African and Nordic populations which have distinct traits that can be very different, but have no issue with interbreeding because they are all one species). [i'm not sure how my tone reads. These are genuine, not baiting, questions.

 

This one I want to tackle. really really good question, but I will need to do it in a few hours.

 

Ruth in NZ

Edited February 6, 2012 by lewelma

[nmoira]

Oh sure...crush my dreams. :glare:

Sorry. I edited just for you. :001_smile:

[lewelma]

I see evolution and find it very believable and IMO incontrovertible and compatible with Scripture

 

Beth, you have said this so very kindly, but I think that we need to not bring up compatibility with Scripture if this thread it to stay open.

 

Hope not to offend....

 

Ruth

[leeannpal]

That's a different topic, called abiogenesis. There are scientific explanations for it, although of course it's going to be tough to verify from the geologic and fossil record exactly how it occurred. Scientific understanding evolves all the time. :)

 

And this is where the evolution debate comes full circle. I've had more than one person say that I can't "know" that God created the world. O.K., if you mean "know" by recognizable, quantifiable data, then, no I can't. But, then, neither can these people explain with certainty how the universe began. So, we each have to have a bit of faith as to what we think happened:)

[kiana]

And this is where the evolution debate comes full circle. I've had more than one person say that I can't "know" that God created the world. O.K., if you mean "know" by recognizable, quantifiable data, then, no I can't. But, then, neither can these people explain with certainty how the universe began. So, we each have to have a bit of faith as to what we think happened:)

 

The issue being raised, however, is that the theory of the origin of the universe and the theory of evolution don't really have a lot to do with each other. One is much more physics/geology, the other is biology.

 

No, evolution doesn't explain where the universe came from. That's like asking your Maytag repairman why, since he can fix your washing machine, doesn't he fix your laptop as well?

[lewelma]

The issue being raised, however, is that the theory of the origin of the universe and the theory of evolution don't really have a lot to do with each other. One is much more physics/geology, the other is biology.

 

No, evolution doesn't explain where the universe came from. That's like asking your Maytag repairman why, since he can fix your washing machine, doesn't he fix your laptop as well?

 

This is why I would like to see a new thread started on origins. Don't discuss it here please.

[AmericanMom]

First of all, the mutation rate varies within species. And since it really only matters when the mutation is in sperm and egg cells, the mutation rate also depends on the generation length. This can lead to very complicated calculations. I copied some details below on just bacteria to demonstrate that there is more than enough variability for evolution to work on. Obviously there is less variability in organisms like humans because our generations are very long compared to bacteria and there are not nearly as many of us. But then in our lifetime we have seen new bacteria and virus species evolve to attack humans. So speciation in bacteria and viruses is very quick compared to humans.

 

When you get a chance, though, I'd really like to know about humans and animals. I get the bacteria and virus thing. But how can it have happened that fast for humans, or even other animals? It seems like it would have to have happened at a statistically impossible rate to accomplish all this in 4 and a half billion years. This has been my big question about this all along, and I've never seen an answer that made sense to me. I appreciate you taking the time to answer!

[Matryoshka]

When you get a chance, though, I'd really like to know about humans and animals. I get the bacteria and virus thing. But how can it have happened that fast for humans, or even other animals? It seems like it would have to have happened at a statistically impossible rate to accomplish all this in 4 and a half billion years. This has been my big question about this all along, and I've never seen an answer that made sense to me. I appreciate you taking the time to answer!

 

I think it's very hard for us to wrap our heads around how long the Earth has been around.

 

I did a great demonstration for my kids - I got the scale from a science curriculum I borrowed from the science museum. Stand up and raise your hand over your head. The time from the beginning of the Earth to the Cambrian time is from your foot to your wrist. The amount of time humans have been around since Life began is so small that it could be represented by what you could take off the end of your fingernail with a file.

 

Heck, here's a scan of the image (picture's worth a thousand words!)

Edited February 7, 2012 by matroyshka
boo boo

[AmericanMom]

here's a scan of the image (picture's worth a thousand words!)

 

I can't view this for some reason?

 

I think it's very hard for us to wrap our heads around how long the Earth has been around.

 

I'm not saying people have been around a long time. I'm saying I don't understand how 4.5 billion years is long enough for this kind of thing to happen, at least not without it being so fast as to be statistically impossible. I'm asking, mathematically, how could it have happened this fast? How could we have gone from 0 to people in only 4.5 billion years, with these kinds of generational mutations?

[*lifeoftheparty*]

.

[Matryoshka]

I'm not saying people have been around a long time. I'm saying I don't understand how 4.5 billion years is long enough for this kind of thing to happen, at least not without it being so fast as to be statistically impossible. I'm asking, mathematically, how could it have happened this fast? How could we have gone from 0 to people in only 4.5 billion years, with these kinds of generational mutations?

 

Well, the first geologic evidence of life is actually about 3.5 billion years ago, after the earth had already been hanging out by itself for a billion years. Took about another billion and a half years for life to go from simple bacteria to eukaryotic cells. For those cells to become simple multicelluar life took almost another billion. Here's a great website with a pictoral timeline I just found while making sure I got my facts right.

 

Seemingly paradoxically, things seem to be speeding up as they get more complex. Once the basic templates are in place, and the more complex life becomes, there is more diversity in the genes themselves, so more ways already built in to adapt, and also more opportunities for replication errors (mutations).

 

There's a great PBS special on dogs about a scientific experiment trying to replicate how the domestic dog evolved (or perhaps was bred) out of the wolf. They took foxes and bred them only for tameness. Within just a few generations, they had different colored coats (like dogs, but not wild foxes), started to bark like dogs (wild canids rarely if ever bark). Selecting for just one thing brought on a host of changes that were completely unexpected. This was artificial selection, but things happen naturally that select for one trait but can lead to more change, and more rapidly, than you'd think.

[Matryoshka]

I can't view this for some reason?

 

Well, darn. Maybe try a different browser? On mine it shows up as a thumbnail attachment, and if I click it, it gets big enough to see clearly.

[lewelma]

When you get a chance, though, I'd really like to know about humans and animals. I get the bacteria and virus thing. But how can it have happened that fast for humans, or even other animals? It seems like it would have to have happened at a statistically impossible rate to accomplish all this in 4 and a half billion years. This has been my big question about this all along, and I've never seen an answer that made sense to me. I appreciate you taking the time to answer!

 

Well, here are some ball parks for you. I am not a geneticist, so this is just a rough guide to get you thinking.

 

Humans have

3,200,000,000 base pairs in a haploid sperm or egg

The mutation rate per base pair per generation (about 20 years) is about .00003 (which shows you how good the checking mechanism is)

That means in a generation there are about 96,000 mutations

 

Humans have about 20 to 25,000 genes (98% of the base pairs are in the non-coding DNA which does not code for proteins, but does have other functions)

 

Humans vary from our closest ancestors, chimps, by only 2.5%

Humans diverged around 15 million years ago

 

ok, now the math. Please know that there are major complications to all this. This is just giving you a feel for the numbers.

 

25,000 genes total, 2.5% different from chimps = 625 different genes (I'm not quite clear on how the 2.5% difference is calculated, it could be 2.5% of the base pairs which is 80 million base pairs different, I also don't know whether in includes the non-coding DNA which mutates at a much faster rate because selection does not act on it)

 

With 96,000 mutations per generation (98% of which would be hidden in the non-coding DNA) , we have 1920 mutations available for natural selection to work on each generation.

 

15 million years divided by 20 year generations = 750,000 generations

 

750,000generations * 1920 mutations/generation = 14,400,000,000 mutations for natural selection to work on. We need about 625 gene changes (maybe 80million base pairs) to make us as different from chimps as we are.

 

Obviously, most mutations would be deleterious but we have enough to make it work.

 

As I said before, this is not my line of expertise, and I don't want to argue about the numbers. I am sure I have messed up somewhere (probably more than once :tongue_smilie:) and I definitely have not included all the complications, but the numbers support all the other lines of evidence for human evolution.

Edited February 7, 2012 by lewelma

[lewelma]

One question I have is what is the line between species and something less differentiated, for example a breed (as in dog and cat breeds). Is this a rather permiable division?

 

The species concept is a human overlay on top of the continuity of genetics. Technically, breeds or subspecies can breed viable, fertile offspring. But the question often is whether they ever would. Some species are classified that way because in the wild they never ever meet up, but you could breed them in the lab. Other species can breed but their offspring are infertile (mule). Sometimes the breeding produces viable and fertile offspring but these offspring are less fit and will be weeded out of the population because they can't compete for mates or resources etc. Sometimes, you can get a ring species, when the range is long and thin and population A can breed with B, and B with C, and C with D, but D cannot breed with A. These are simply called ring species because they just don't fit the clear cut notion of a "species."

 

About as clear as mud.

[lewelma]

I understand, for example that there are different species of bee that generally don't breed, but then my understanding of the "killer bee" developments was that it was one type of South American bee mixing with North American bees and producing something new. [/Quote]During a range expansion (cause by whatever reason), species can encounter another related species that have not diverged fully enough to limit reproduction.

 

In addition, the species concept often does not work well for plants because when 2 species mate and the offspring is not going to be viable, the zygote can double its chromosome number (called polyploidy) so that all the mismatched chromosomes can now line up. And POOF in one generation you have a new species. This why there has been some concern about genetically modified species of plants cross breeding with other species of plants and spreading the introduced modified genes.

Edited February 7, 2012 by lewelma

[Ariston]

OK, so here I am--average mom, homeschooling the people, learning latin, and mainly doing experiments on whether or not I can buy healthy food for my 8 and stay under budget.

 

In my spare time, though, I burn the midnight oil reading books like, "North and South Pole," "The Disappearing Spoon," and last but not least "The Faith of Scientists." (The last book is a collection of scientists' own writing on their faith or non-faith.)

 

I really enjoy reading about how the earth's spreading seafloor records earth's changing magnetism over billions of years. It's explained in detail and I get it. It makes sense to me. I can read a huge volume explaining scientists' thoughts on faith and religion and I can get it--both of them, the faithful and those who are secure in the belief that the earth was not created. I can read a book about chemistry and understand how we know how elements form, break down, spread throughout the universe--it makes sense to me and I get it.

 

But when I put a video on for my kids and a picture of a mammal pops up and the slow drone of the announcer tells us all (while the pictures show it) how this mammal lost its legs, grew fins, etc, etc, etc, and turned into a dolphin, I JUST DON"T GET IT. I am looking at this science, I am listening, but the whole thing seems so ridiculously, hilariously, miraculously walking on water ridiculous to me. Yes, I will use the word ridiculous twice.

 

Apparently, I am one of those many generic unscientific Americans who look at the theory of evolution and question how "believable" it is. But it's not just me. I can't think of a single science teacher I had in public school who ever gave evolution more than a cursory nod. It was such a non-issue.

 

I wish that there was some writing for people like me--people who are willing to study and learn, but really wrestle with the whole "believability" factor."

 

I have not read the rest of this thread and don't know if its been recommended, but I would definitely recommend that you read Darwin's The Origin of Species if you're interested in the subject. Its very accessible.

Elena

[lewelma]

The reason I ask is I've tried to get my head around why anthropologists consider different hominids (sp?) to be different species (homo sapiens and neanderthal for example) but then there will be an article saying research suggests they interbred (which to me indicates that they were part of the same species but had different traits emphasized by developing in geographic isolation

Well, to be considered a different species, they cannot completely interbreed or the 2 populations would have genetic mixing and merge back into one. So there is some barrier to reproduction.

 

Very occasional interbreeding could still allow for the 2 groups to be considered species. It really depends on how much genetic mixing we are talking about. It is a continuum. The 2 groups can remain genetically distinct if they are large populations and the interbreeding is very slight.

Edited February 7, 2012 by lewelma

[lewelma]

Do most Evolutionists believe one species can "become" another? Intra-species evolution would make more sense to me than inter-species evolution.

 

I've given this some more thought and believe I was too hasty before. I am letting my own personal opinions cloud the issue. The name for one species "becoming" another is called anagenesis. The main requirement is that the entire population changes, not just a subset. And the entire population must be significantly differentiated from the ancestral population. A series of such species is called an evolutionary lineage.

 

I personally don't believe that this description can be met in most instances, especially with large populations. Large populations often cover many different types of habitats which will have different selecting pressures. And, large populations need to be very mobile to maintain genetic homogeneity (similarity) in the face of these different selection pressures.

 

My other problem is that large enough genetic change to produce a new species usually requires a changing environment. If the environment does not change, the species has no need to adapt (the horse shoe crab is an example of a very very old species that has hardly changed at all in millions of years.) But the problem is that when you have a changing environment, there are often new niches that are created that lead individuals of the species (that happen to have a mutation that is adaptive for the new niche) to move into the new niche. This often creates a speciation event.

 

It is currently unclear in the research how much genetic drift plays in anagenesis. Obviously more in small populations.

Edited February 7, 2012 by lewelma

[ekfk]

You can watch the full PBS documentary What Darwin Never Knew for free from the PBS website to get an explanation.

[TKDmom]

There's a great PBS special on dogs about a scientific experiment trying to replicate how the domestic dog evolved (or perhaps was bred) out of the wolf. They took foxes and bred them only for tameness. Within just a few generations, they had different colored coats (like dogs, but not wild foxes), started to bark like dogs (wild canids rarely if ever bark). Selecting for just one thing brought on a host of changes that were completely unexpected. This was artificial selection, but things happen naturally that select for one trait but can lead to more change, and more rapidly, than you'd think.

 

National Geographic had an article about that experiment last year. It was fascinating.

[Trish]

I see evolution and find it very believable and IMO incontrovertible and compatible with Scripture ---which is generally looked upon as

:smash:

:ack2:

anathema among fundamentalist.

 

I guess I consider myself an Old Earther with a God Start and God Intervention...

 

For some reason I feel this has not been adequately explained from a religious standpoint. I'd be curious to know how you (or anyone else who considers themselves Christian) view the "general" timing of things. So God starts things, they are either off with a Bang, or a Precisely Controlled Whoosh. Then. Is "Adam" one real person? Or an allegory for...WHAT? A whole race of prehistoric people collectively sinning? That just doesn't feel right. But, if he is ONE person, at what point is he inserted into history?

 

And if there is NO original sin, then (speaking hypothetically) what would Jesus be redeeming us from? Just sinful tendencies that we're born with? If he isn't the Redeemer, there's really no point to Christianity at all, so...I lean toward a very definite sin, but committed when?

 

At this point religious folk say it doesn't MATTER when it was committed, which is true, I suppose, but wasn't there PERFECTION prior to the Fall of Adam and Eve? This means even the animals not eating each other, but getting along, along with no diseases/disasters. But doesn't the fossil record go against that? So that would indicate a MUCH earlier Adam (pre-dating carnivorous dinosaurs).

 

Unless Eden was a separate, non-earthly location. After Adam leaves Paradise, perhaps then he is banished to Earth, which is already functioning imperfectly? Eh.

 

On the other hand, do we have evidence for abiogenesis, or is that an assumption based on everything else evolutionists believe "must" be true?

[lewelma]

I guess I consider myself an Old Earther with a God Start and God Intervention... [snip] Is "Adam" one real person? Or an allegory for...WHAT? [snip] And if there is NO original sin, then (speaking hypothetically) what would Jesus be redeeming us from? [snip] but wasn't there PERFECTION prior to the Fall of Adam and Eve?

 

Please take this to a different thread. We are discussing evolution here, NOT origins of life or Christianity.

 

I don't mean this in a mean way, but I do not join the Adam and Eve threads and start discussing evolution. Mutual respect would be appreciated.

 

Ruth in NZ

[Dana]

If you are sincerely interested, I will spend some time to explain it. But I do not want to get into an argument, and I have no interest in being tricked or cornered. I have a PhD in evolutionary ecology and have taken about 10 evolution classes and read around 3000 pages about evolution. All this was of course many moons ago. :glare: How to summarize such a massive topic would be a challenge, but I am willing. We could also do this privately, unless others are sincerely interested.

 

Ruth in NZ

 

I just wanted to say thank you so much for your posts here. I really appreciate the time you're taking to explain things.

 

(And now back to lurking ;) )

[Trish]

Please take this to a different thread. We are discussing evolution here, NOT origins of life or Christianity.

 

I don't mean this in a mean way, but I do not join the Adam and Eve threads and start discussing evolution. Mutual respect would be appreciated.

 

Ruth in NZ

 

Thanks for the PM!

 

:lol:

[lewelma]

Thanks for the PM!

 

:lol:

 

oops. Didn't even think about it. :001_huh: sorry.

 

I thought that you (and possibly others) had not seen my previous requests about starting a new thread. The moderators closed the last thread where evolution and creationism were discussed simultaneously, and I am hoping to keep this one open by keeping the discussion focused on evolution only.

Edited February 7, 2012 by lewelma

[lewelma]

I just wanted to say thank you so much for your posts here. I really appreciate the time you're taking to explain things.

 

 

Thanks for this. I usually keep my head down about evolution here, and was quite nervous about discussing it given how contentious these types of conversations have gotten in the past.

[meggie]

Thanks for this. I usually keep my head down about evolution here, and was quite nervous about discussing it given how contentious these types of conversations have gotten in the past.

 

I would also like to thank you for your posts. And everyone else who has been explaining things. It has been such a fascinating thread; I've loved reading all of it (and loved that it hasn't gotten argumentative)

[bpskowski]

I thank you too. I've got a long list of books to read now. Already have one DVD and one book ordered from the intrlibrary loan system. I am stunned at my lack of knowledge.

[Joules]

I just wanted to say thank you so much for your posts here. I really appreciate the time you're taking to explain things.

 

(And now back to lurking ;) )

:iagree: Thank you so much, Ruth. I'm a physicist, so don't deal with the squishy stuff too much, but I've become fascinated with evolution and population genetics lately. I know most of what you've posted here, but you've made it so clear and simple that it will help me explain it to others (if I'm ever as brave as you've been here ;) )

[kubiac]

Another thank you, including a thank you for handling the Adam and Eve topic with haste and grace. I was going to jump in with what I consider the obvious answer, but your approach was much, much better!

[msrift]

(Really enjoying this thread! Thanks for sharing your expertise.)

 

Former biochemist popping in here to add a little tidbit about science that the general public frequently misunderstands:

 

Science does not explain everything.

 

What I mean by that is that our current understanding and knowledge of science is constantly changing and growing. There are millions of unanswered questions about the world around us. And scientists love it that way! Scientists love coming across a puzzle and digging in to see if they can figure it out. Think about it - if we could answer everything, what would all those poor graduate students do for their research projects?;)

 

When scientists come across a question they can't answer using the current knowledge base, they admit they don't know the answer. (Trying not to offend anyone - but this does not mean they assign a supernatural explanation for the phenomenon.) It does not mean a failure of 'science'. It just means that our current scientific understanding does not adequately explain the problem, and leaves open the possibility of future scientists one day expanding that knowledge so the question is answerable.

 

(going back to lurking...I found evolution boring in college, but you make it so interesting!)

[Happy Scientist]

What a marvelous thread! Lewelma, you have done an incredible job of explaining and keeping things on track.

[Wheres Toto]

What a marvelous thread! Lewelma, you have done an incredible job of explaining and keeping things on track.

:iagree:

 

Have you seen how many have viewed this thread? Great job!

[TC5]

It took me two nights to read this whole thread, but I am glad I did. I have learned and re-learned so much and see many options for more study. Thank you to all those who have asked and answered questions, especially to Ruth. It was worth your time! You've done us a great service this week.

[lewelma]

Well, thanks for the kind words, everyone.

 

Of course, I find it fascinating as to what was asked, and what was not asked. Lots of questions about speciation, but no questions about phylogenetics or cladistics (the classification of organisms into Phylum, class, order etc). Questions about convergent evolution, but none on co-evolution (bees and flowers for example). Questions about genetic mixing, but none about genetic separation especially biogeography and the implication of continental drift. And no questions about molecular evolution, viruses, jumping genes, etc.

 

Also, no questions about societal issues: how evolution works in antibiotic resistant strains, the new flu vaccine every year, or genetically engineered organisms. And no questions about the implication of modern medicine in human evolution, the possible success of eugenics, or even the implication of small population size (bottlenecks) to the evolution of endangered species.

 

Luckily with all the book recommendations that were given, there will certainly be answers to all these questions and MORE. So enjoy some new bedtime reading!

 

Having stayed in the lime light for a couple of days, I am now ready to go back to my typically quiet (or mostly quiet) self. :001_smile:

 

Ruth

Edited February 9, 2012 by lewelma

[Dana]

And no questions about the implication of modern medicine in human evolution,

 

I've at least encountered the other ideas before... but what do you mean by this?

 

Is it how things may change with people living due to medicine who otherwise would have died? (Like without surgery as an infant, my husband wouldn't be here.) Or is it something else?

[Sebastian (a lady)]

Well, to be considered a different species, they cannot completely interbreed or the 2 populations would have genetic mixing and merge back into one. So there is some barrier to reproduction.

 

Very occasional interbreeding could still allow for the 2 groups to be considered species. It really depends on how much genetic mixing we are talking about. It is a continuum. The 2 groups can remain genetically distinct if they are large populations and the interbreeding is very slight.

 

So here's what I'm trying to wrap my head around: it seems to me that we have relatively few remains of ancient man. They come from diverse geographic areas and from widely separated times.

 

I see some charts that list almost a dozen different types of "humans" (please forgive the uninformed word choice). But when I look at a reconstruction of a Neanderthal woman, I see a face that isn't that dissimilar to faces that were all around me when we visited Central Europe.

 

When we visited the Bone exhibit in the Smithsonian Natural History Museum (on a different floor from the Human Evolution exhibit) there were great cases showing the impact of environment, illness and useage on bone structure.

 

Then I think of how my husband stands a head or more taller than everyone else on a Japanese train and yet how our Scandanavian friends tended to dwarf him.

 

All of this gets me wondering what is being looked at to make anthropologists think that the variety of human remains found represent separate branches or stages on the human family tree rather than natural variation of a single species under developing technologies, nutritional challenges and lifestyles.

 

In other words why are the bits of bone in the cases considered to be different types when a 6'6" Scandanavian and a 4'10" North Korean are seen as the same?

 

Have "human types" been merged by scientists over the years? Or does dna typing allow us greater fidelity in determining what is what?

 

(And thank you for playing Dr. Answergirl. This is a topic I've long avoided and I find that I don't even know how to think through reasonable questions.)

[momto2Cs]

I'm sorry I don't have anything at the moment to really contribute to this thread, other than seconding the recommendations for the Loxton Evolution book, and The Magic of Reality, but I wanted to thank everyone on this thread for such an interesting, eye-opening, and respectful thread! I have really enjoyed reading it. :)

[lailasmum]

Dr Alice Roberts has done several good TV series, She has a book called Evolution the Human story which may be worth a look.

[lewelma]

I thought the thread was dead. Too much stirring of the pot on my part. I thought just to spur everyone to reading a good scientific book. :001_smile:

 

I've at least encountered the other ideas before... but what do you mean by this?

 

Is it how things may change with people living due to medicine who otherwise would have died? (Like without surgery as an infant, my husband wouldn't be here.) Or is it something else?

 

Oh, this is just a question people seem to ask me. The logic goes something like this: if natural selection cannot work to remove bad genes, then evolution will stop occurring in humans. But what people often don't realize is :

 

1) most medicine is done on treating people past child bearing age. And as has been mentioned before, any trait that affects you after reproductive age, cannot be selected for by natural selection because it cannot prevent you from having children. And natural selection requires a reduction in the number of offspring, to reduce your genes in the next generation. (well you can have kin selection, but that is a different question)

 

2) Medicine that helps with recessive diseases like Cystic Fibrosis, and allows these children to one day have their own children, would not raise the percentage of this trait enough to matter at all. The percentage is soooo low that even doubling it in the population still would keep it incredibly low.

 

3) Although evolution occurs more quickly when the environment kills individuals with less adaptive traits, evolution probably occurs more frequently with a reduction (not cessation) of reproduction in individuals with less adaptive traits.

 

4) Also, the path of evolution is usually not clear during the process. People are as different on the inside as the outside, so evolution might currently be increasing the size of the liver to help filter all the toxins out of your body (just an example, I have no idea), and you would not really know which of your friends has a large or small liver. :001_smile:

 

5) Natural selection cannot always maximize a trait. New born head size is a great example. The larger the brain the better, but too large means that the baby cannot get out of the birth canal without damaging itself or its mother. There is a physiological constraints on increasing the birthing canal much bigger, because of the starting point of early human physiology. Natural selection never completely reconstructs and builds a better system. It has to lay improvements on what already exists.

 

6) Natural selection can also act to make people MORE similar through stabilizing selection. Evolution occurs when the gene frequencies in a population change. So if they change to be more similar, they are still changing. There may be no major changes in humans until we have a changing environment or a catastrophe.

 

7) Finally, don't forget to add TIME, lots and lots of TIME. Don't even try to think you can figure out where humans are headed.

Edited February 9, 2012 by lewelma

[lewelma]

This is a cool question. Actually it is a statistics question. Have you studied statistics, probability, bell curves, that sort of stuff? If not, get an book and study up. It is a fantastically useful field. Not only will you understand science better, you will understand social science better (psychology, political science, sociology, etc.) Well worth your time.

 

Ok, here are some things to think about:

 

So here's what I'm trying to wrap my head around: it seems to me that we have relatively few remains of ancient man. They come from diverse geographic areas and from widely separated times.

 

First of all, there are actually LOTS (meaning 1000s of fossils) for many of the species of hominids. Obviously, some of the older species have much fewer (like 10) and then there are those species that only have 1. Obviously, scientists are going to be much more certain of their interpretation if the species under study has more fossils to study.

 

But when I look at a reconstruction of a Neanderthal woman, I see a face that isn't that dissimilar to faces that were all around me when we visited Central Europe.

Well, this is an ARTIST'S reconstruction. But more importantly, humans are as different on the inside as the outside, so just looking at an image is not going to help you see most anatomical differences.

 

Then I think of how my husband stands a head or more taller than everyone else on a Japanese train and yet how our Scandanavian friends tended to dwarf him.

As you know, it is not just the length of bone. There is variability within every trait of every organism on the entire earth. This is the really useful variability that natural selection can act on when the environment is changing.

 

So here is some evolutionary thought: In 2 subspecies, over time natural selection will cause them to separate further and speciate. You can imagine this as a bell curve. If you have a bimodal distribution of the frequency of a trait (people are either very short or very tall but few in the middle), natural selection typically separates this curve into two mostly non-overlapping curves (People are tall OR short) This happens because the hybrids in the middle typically have reduced fertility. I'll just make up an example: small people would have a hard time having the very large babies of tall people, so they would have reduced fertility. So what you see in the variability of a trait between 2 species is typically very little overlap. (Height is not a good example for hominids as there is lots of overlap. Instead, you could think about the spine or how the hips rotate etc. )

 

Thus, when looking at fossils, there will be numerous traits that do NOT overlap in their variability. If they do overlap, then the fossil is classified within one of the species already identified.

 

All of this gets me wondering what is being looked at to make anthropologists think that the variety of human remains found represent separate branches or stages on the human family tree rather than natural variation of a single species under developing technologies, nutritional challenges and lifestyles.

 

In other words why are the bits of bone in the cases considered to be different types when a 6'6" Scandanavian and a 4'10" North Korean are seen as the same?

Now, I am not a palaeontologist, so this is a biologist's answer not an expert's answer. When palaeontologists evaluate skeletons there are many different things they look at: tendon attachment points, location of muscles, design of spine, size of brain case, etc. Many of these traits would change the behavior of the hominid by restricting them physiologically. He could not stand up straight, he could not speak, he could not climb trees, etc. Some issues might be more subtle, like a modern human baby's head could not exit the birthing canal in a different species (I'm just making this up to get you thinking). These are issues that a palaeontologist could identify in a skeleton.

 

So, here is a very poor description of cladistics. You take 3 ancient skeletons (A, B, C) and you look at 50 different features that you think represent the variability in the skeleton, and you load these points into the computer. You then do a cladistic analysis. (These used to be done on paper way back when). The computer maximizes the relationships. Trait 7 and 10 are the same, but trait 11 and 22 are different. 32 is similar to species C but 33 is the same as species A. etc. The more data you can put in, the larger the certainty of the relationships. Because, natural selection cannot reconstruct and must add improvements on top, if all skeletons share a trait, it is likely the ancestral trait and the other traits are added on top. This helps you figure out which species is ancestral and which is more modern. Ok, it is very complicated, but it works and it is cooooool when the answer pops out.

 

Have "human types" been merged by scientists over the years? Or does dna typing allow us greater fidelity in determining what is what?

DNA will be addition evidence to the morphology of the skeletons. But I don't think it will ever override it. DNA is often degraded over time, so there can be a lot of holes.

 

I don't even know how to think through reasonable questions.[/Quote]Well, you did and it was a good enough one to get me writing for a while this morning (good thing it is Friday reading time for the kids :D)

 

Ruth

Edited February 9, 2012 by lewelma

[Stellalarella]

I thought the thread was dead. Too much stirring of the pot on my part. I thought just to spur everyone to reading a good scientific book. :001_smile:

 

.

 

yes. I think I need to get to reading so I can understand even the questions that keep coming. :001_smile: