darwin problem

line6

it seems to be accepted that darwin's theory of evolution is the last word on the origin of species

a few years ago now i heard of an argument along these lines - if the survival of the fittest principle were true then we would see a much larger array of different species; ie links are missing between species on evolutionary chains

so if humans evolved from lemurs for example, we would see many examples of species in between these two instead of just a small handful of apes

has this argument been refuted or does it still stand?

Improbable

line6 wrote: »

it seems to be accepted that darwin's theory of evolution is the last word on the origin of species

a few years ago now i heard of an argument along these lines - if the survival of the fittest principle were true then we would see a much larger array of different species; ie links are missing between species on evolutionary chains

so if humans evolved from lemurs for example, we would see many examples of species in between these two instead of just a small handful of apes

has this argument been refuted or does it still stand?

But humans didn't evolve from lemurs. Humans and lemurs had a common ancestor from which they both evolved. And there are many examples of transitional fossils. But the problem is that every time you fill in a "gap" in the fossil record, 2 more "gaps" appear.

Nolanger

There's a reason it's called a THEORY!

Mena

Nolanger wrote: »

There's a reason it's called a THEORY!

You're thinking hypothesis...

line6

line6 wrote: »

if the survival of the fittest principle were true then we would see a much larger array of different species

Why?

Can you give proof or elaborate on how this conclusion came about? I can't see what the reasoning behind this is...

darjeeling

line6 wrote: »

it seems to be accepted that darwin's theory of evolution is the last word on the origin of species

It's a bit more complicated than that.

It is accepted that all species today have evolved from one common ancestor (or a very few). There's compelling data from gene sequences behind this, and the fossil record (though very incomplete) gives no reason to doubt it.

What is more complicated is that there are more forces at work than just Darwinian natural selection (though this is the main driver). Random demographic effects play a part too - some animals have more offspring by chance rather than through selection. So does 'genetic hitchhiking', where selection for one version of a particular gene can lead to mutations at neighbouring genes becoming more common, even though they're not under strong Darwinian selection themselves.

line6 wrote: »

a few years ago now i heard of an argument along these lines - if the survival of the fittest principle were true then we would see a much larger array of different species; ie links are missing between species on evolutionary chains

so if humans evolved from lemurs for example, we would see many examples of species in between these two instead of just a small handful of apes

has this argument been refuted or does it still stand?

I don't think there's any reason to expect more or fewer living species. We predict that there were once many intermediate species between modern and ancestral species, and palaeontologists go looking for these with varying degrees of success. We know that we've only found a small fraction of the species that have ever lived, but we also know that fossilisation is a rare event, so we expect that most ancestral species will not show up in the fossil record and that we'll only see a sparse sampling of what once existed.

The test of evolution is not proving it by finding examples of all ancestral species, but disproving it by finding ancestral species that make a nonsense of the family tree of life, and that hasn't ever happened.

.

mcmoustache

line6 wrote: »

it seems to be accepted that darwin's theory of evolution is the last word on the origin of species

a few years ago now i heard of an argument along these lines - if the survival of the fittest principle were true then we would see a much larger array of different species; ie links are missing between species on evolutionary chains

so if humans evolved from lemurs for example, we would see many examples of species in between these two instead of just a small handful of apes

has this argument been refuted or does it still stand?

I'll deal with the bit in bold because another user has dealt with the question about links. The idea that survival of the fittest would lead to more diversity isn't strictly true.

Lets say we had two species which were similar in that they inhabit the same area and eat the same food. Wolves and Hyenas for example. If they lived in the same area, they would compete for the same food and eventually one species (the least fit) would go extinct. This example is just to illustrate that natural selection causes extinction and reduces the bio-diversity especially with large animals.

Another example which might be easier to relate to would be what happens when a foreigh species is brought in to an eco-system that can't sustain it. Lets say you brought a predator to an island which had no other predators. It wouldn't take long before lots of defenceless creatures went extinct. Again this is just an example of the bio-diversity getting reduced by natural selection.

line6

many thanks for your considered replies

Quote:
Originally Posted by line6
if the survival of the fittest principle were true then we would see a much larger array of different species

true-or-false wrote: »

Why?

Can you give proof or elaborate on how this conclusion came about? I can't see what the reasoning behind this is...

environments can be seen as continuums - ie variables such as water availability or mean temperatures change continuously across space

it would seem natural that the variety of species would form a continuum also, in order to maximise survival within those environments

instead we see a relatively small number of distinct and discrete species rather than a much larger number of slightly differing ones - even allowing for extinction rates this seems to be antithetical to darwin's theory

at least this is how i remember the argument but the brain is not guaranteed at this stage

line6

darjeeling wrote: »

... 'genetic hitchhiking', where selection for one version of a particular gene can lead to mutations at neighbouring genes becoming more common, even though they're not under strong Darwinian selection themselves...

thanks darjeeling but can you clarify this part for me please

Capt'n Midnight

line6 wrote: »

it would seem natural that the variety of species would form a continuum also, in order to maximise survival within those environments

why ?

seriously why ?

that would only happen if every species was suited to a particular niche and could displace less suited species from that niche

there are a lot of generalist omnivores out there , like us , that can survive in many different ecosystems, and can use resources from one to drive their usage in another, or they could migrate seasonally - one could imagine a world full of mice, rats and cats animals that survive almost anywhere



yes you find more species at boundries between ecosystems but because those species can use resources from more than one ecosystem


roll the clock back to just after the permian extinction, many deposits consisted almost entirely of lystrosaurus more than ten times the numbers of fossils of every other animal in the area at the time. You also have to remember it's very hard to compete with the market leader, you can't establish a colony in a new environment even if you are more suited to it, if there is no room at the inn, because you need enough resources to have a stable breeding population.

amacachi

darjeeling wrote: »

What is more complicated is that there are more forces at work than just Darwinian natural selection (though this is the main driver). Random demographic effects play a part too - some animals have more offspring by chance rather than through selection. So does 'genetic hitchhiking', where selection for one version of a particular gene can lead to mutations at neighbouring genes becoming more common, even though they're not under strong Darwinian selection themselves.

If there are "external forces" then they're very inefficient.

darjeeling

amacachi wrote: »

If there are "external forces" then they're very inefficient.

Not sure what you mean by 'external' here.

The role of genetic drift (wiki link) and of mechanisms such as genetic hitchhiking (wiki link) in increasing evolutionary divergence is well documented in the literature. As I commented though, natural selection is generally agreed to be the main driver of evolutionary change, with all these other mechanisms playing a lesser role.

line6 wrote: »

can you clarify this part [(genetic hitchhiking)] for me please

The wiki page actually explains it quite nicely and very concisely - not sure I could do a better job.

We might see the effects most extremely in our domesticated animals, where very strong selection for traits that we found useful have led inadvertently to increased frequency of undesirable genetic defects in nearby genes.

line6

thanks again everyone - i appreciate your patience

i shoulda coulda woulda read up on this first - what i'm referring to here is the missing link phenomenon, and how it impinges on the creationist/evolutionist debate

still struggling with concepts here - wiki tells us

Henry M. Morris and other creationists have claimed that evolution predicts a continuous gradation in the fossil record, and have misrepresented the expected partial record as having "systematic gaps".[14] Due to the specialized and rare circumstances required for a biological structure to fossilize, only a very small percentage of all life-forms that ever have existed can be expected to be represented in discoveries and each represents only a snapshot of the process of evolution. The transition itself can only be illustrated and corroborated by transitional fossils, but it will never demonstrate an exact half-way point between clearly divergent forms.

and goes on to explain how and why species are discrete in their variations

what still confuses me is not the fossil records which are understandably patchy in this regard, but the currently existing species showing no intermediate phases as might be expected

if evolution goes on, then surely we would see many examples of "half baked" traits, as the process selected out ever better examples of, say arms or eyes or whatever

sorry if this has already been addressed, i'm just not getting it

it's almost as if current species were predetermined in some way, but that's patent nonsense

amacachi

darjeeling wrote: »

Not sure what you mean by 'external' here.

The role of genetic drift (wiki link) and of mechanisms such as genetic hitchhiking (wiki link) in increasing evolutionary divergence is well documented in the literature. As I commented though, natural selection is generally agreed to be the main driver of evolutionary change, with all these other mechanisms playing a lesser role.

I was talking about a "guiding hand" for mutations :pac:

The wiki page actually explains it quite nicely and very concisely - not sure I could do a better job.

We might see the effects most extremely in our domesticated animals, where very strong selection for traits that we found useful have led inadvertently to increased frequency of undesirable genetic defects in nearby genes.

On the molecular level it's fairly obvious that genes that indirectly cause an advantage will also survive I would've thought.

Improbable

line6 wrote: »

thanks again everyone - i appreciate your patience

i shoulda coulda woulda read up on this first - what i'm referring to here is the missing link phenomenon, and how it impinges on the creationist/evolutionist debate

still struggling with concepts here - wiki tells us

Henry M. Morris and other creationists have claimed that evolution predicts a continuous gradation in the fossil record, and have misrepresented the expected partial record as having "systematic gaps".[14] Due to the specialized and rare circumstances required for a biological structure to fossilize, only a very small percentage of all life-forms that ever have existed can be expected to be represented in discoveries and each represents only a snapshot of the process of evolution. The transition itself can only be illustrated and corroborated by transitional fossils, but it will never demonstrate an exact half-way point between clearly divergent forms.

and goes on to explain how and why species are discrete in their variations

what still confuses me is not the fossil records which are understandably patchy in this regard, but the currently existing species showing no intermediate phases as might be expected

if evolution goes on, then surely we would see many examples of "half baked" traits, as the process selected out ever better examples of, say arms or eyes or whatever

sorry if this has already been addressed, i'm just not getting it

it's almost as if current species were predetermined in some way, but that's patent nonsense

The reason you don't see intermediates in between current species is because of the fact that the middle ground in which they meet is located in the past. There is no direct link between different species in the present, if that makes sense at all. Imagine a single species. That single species evolves over time and gives rise to both humans and lemurs. From what I gather, you're asking why there are no species in the present day that are 50% human, 50% lemur. One possible reason that I can think of is that allopatric speciation would mean that the 2 populations would be under different selective pressures and evolve into completely different species, given enough time.

But in a way, these things do exist. Take a group of primitive humans. Separate them into 2 different groups. Put one group in the desert and put the other in the arctic circle. Given enough time, because of dissimiliar selective pressures, they will evolve into different species. Say if one group fed only on berries nuts and leaves and the other group only fed on wild game. Then take each of those groups and separate them so that 1 group from each can only come out at night time and that the other group from each can only come out during the day. Given enough time, they would form 4 different species.

Now obviously this is a very simplistic view and even over a fairly long period of time, those different species would still look relatively similiar compared to humans and lemurs. But nature is not simple. There are so many different types of selective pressures and external factors such as genetic drift, differing models of speciation and probably, stuff that we don't even know about that over the vast amounts of time involved when dealing with matters regarding evolution, that it's not surprising that we don't see organisms that visually look a like 50% human, 50% lemur.

The simpler answer is that you don't get species that look 50% human and 50% lemur because humans and lemurs don't mate.

IrishKnight

line6 wrote: »

if evolution goes on, then surely we would see many examples of "half baked" traits, as the process selected out ever better examples of, say arms or eyes or whatever

Er, we do! In many organisms we see eye development at a number of different stages. So in Euglena sp. we see "eyespots", where are basically proteins that sense light. These are rather crap compared to our eyes but shows one of the earliest stages of eye evolution.

Next up is Planarian sp. which have gone one better and have photoreceptors that reside in a cup shape. They can slightly differentiate the direction and intensity of light because of their cup-shaped. Still no clear image, but an improvement on the eyespots.

Next in line of eye evolution would be to create a pin-hole eye. This would allow the organism to achieved true imaging forming, allowing for fine directional sensing and even some shape-sensing. This can be seen in the Nautilus Family.

This pit eye likely went on to develop a lens, to allow for fine imaging formation and what not and slowly evolve into the eye we see in humans. (See what I did there, eye, see, oh never mind)

But to call anything "half-baked" isn't really right. Nothing is half-baked in terms of evolution, each stage gives the organism an advantage over those without.

Indeed, I always find it funny that people look to the eye (ah look eye, ba, suit your selves) as this great marvel that could only have been make by a creator. But the human eye is a bit crap. The method by which it is "wired" means that all the light from the outside world has to travel through said wired to get to the light sensing part of the cells. It would be a bit like if I was putting up a light in a room, but have all the electrical cables, rather than going into the roof, hanging infront of the bulb, blocking the light.

Indeed, some aspects of humans could be considered "half-baked" as there a rats that don't have the Y chromosome yet somehow can develop into both female and male...

"Nothing in biology makes sense except in the light of evolution" -- Dobzhansky

(Again, light, eye evolution! Ugh, my humour is lost on you people :P )

line6

line6 wrote: »

it would seem natural that the variety of species would form a continuum also, in order to maximise survival within those environments

what i'm referring to here is the missing link phenomenon, and how it impinges on the creationist/evolutionist debate

what still confuses me is not the fossil records which are understandably patchy in this regard, but the currently existing species showing no intermediate phases as might be expected

if evolution goes on, then surely we would see many examples of "half baked" traits, as the process selected out ever better examples of, say arms or eyes or whatever

Ok, so based on this I think I see what you're getting at: That there should be species alive today that show a midway between the divergence of two species?

I think the main thing you're missing is the concept of niches. I'm not sure whether I'm telling you something you already know or not, but bear with me. Species A is in an ecosystem. Let's say the ecosystem is half blue and half yellow. Let's say species A is half blue half yellow. A mutant species A is born all blue. It survives predation far better than the normal As because it blends into the blue perfectly. Through selection, it forms a new species B over time. At the same time as the first blue mutant arose, a yellow mutant arose, and like species B forms a new species C over time, as it survives predation far better on the yellow part of the ecosystem. As this is on an evolutionary timescale, the two species B and C are completely separate, as each has been slowly separated by the blue/yellow boundary of the ecosystem, and they haven't interbred in a very long time. So species B is hard to find for predators and survives well in the blue niche, and species C is hard for predators to find and survives well in the yellow niche. So I think your question is where is species A gone now?
Species A evolved into B and C. It's not extinct in a "the species was wiped out" sort of way, it went extinct because the natural selection that allowed B and C to survive, made A the most visible prey around. It has no niche. It hasn't been wiped out, it has evolved. The A individuals that were half blue half yellow were either killed by predation etc, or bred with an all blue mutant or all yellow mutant, and so when it died it left only all blue or all yellow offspring. And over time B and C became established as new species.

It's late, I'm not sure if I answered your question or even made the slightest bit of sense, but I'll be back tomorrow to edit this out of shame/confusion!

Do have to add though, I saw an episode of Celebrity Big Brother (don't judge, it was my sister watching it) a few years ago and Stephen Baldwin was on it. He said, knowingly, something along the lines of "if evolution was real, and we really evolved from apes, tell me this. How could there still be monkeys today???" And proceeded to act as though he had just disproved evolution.

RocketFalls

Well, the fossil record is inherently sketchy, and finding 'missing links' is highly unlikely at this point due to the the high levels of specialisation undergone by established organisms. We've all settled into our niches, if you know what I mean.
Molecular phylogenetics is your best bet, though it doesn't shed light on the morphology of these intermediate creatures..

nozzferrahhtoo

line6 wrote: »

so if humans evolved from lemurs for example, we would see many examples of species in between these two instead of just a small handful of apes

has this argument been refuted or does it still stand?

No not at all. Species diverge over time from common ancestors, meaning the differences between them to us will appear greater over time. There is nothing in it that suggests there should be a still living constant continuum of development at any one time.

Natural selection also tells us that most species go extinct too. I have heard figures like 99% of all species that ever lived are now extinct.

For each species that goes extinct, the apparent "gap" between other species will be bigger, because the kind of transitions you are imagining in this post are gone.

Imagine a rainbow, it is almost impossible to find a point in that rainbow where one color stops and another starts. This is what you are imagining... that there should be some smooth horizontal pathway between any two species. This is not how it works.

The animal kingdom is more like what you would get if you puncture holes in a rainbow.... all the colors came from a common ancestor... white light... but now there are different colors with gaps punctured between them.

Improbable

nozzferrahhtoo wrote: »

No not at all. Species diverge over time from common ancestors, meaning the differences between them to us will appear greater over time. There is nothing in it that suggests there should be a still living constant continuum of development at any one time.

Natural selection also tells us that most species go extinct too. I have heard figures like 99% of all species that ever lived are now extinct.

For each species that goes extinct, the apparent "gap" between other species will be bigger, because the kind of transitions you are imagining in this post are gone.

Imagine a rainbow, it is almost impossible to find a point in that rainbow where one color stops and another starts. This is what you are imagining... that there should be some smooth horizontal pathway between any two species. This is not how it works.

The animal kingdom is more like what you would get if you puncture holes in a rainbow.... all the colors came from a common ancestor... white light... but now there are different colors with gaps punctured between them.

http://www.lassp.cornell.edu/newmme/science/ModelsOfExtinction.pdf

nozzferrahhtoo

Hey Improbable. I am afraid that link is coming up broken for me, regardless of how I try to open it. Maybe you could adumbrate what your point was by posting it rather than me ignoring it and moving on?

IrishKnight

Improbable wrote: »

http://www.lassp.cornell.edu/newmme/science/ModelsOfExtinction.pdf

tl;dr

Improbable

nozzferrahhtoo wrote: »

Hey Improbable. I am afraid that link is coming up broken for me, regardless of how I try to open it. Maybe you could adumbrate what your point was by posting it rather than me ignoring it and moving on?

It's an interesting paper from 1999 about models of extinction. It's in PDF format. Thought you might enjoy reading it. I've attached it as a PDF. It's rather long like IrishKnight says, but if you're interested in the topic, it's fascinating.

line6

line6 wrote: »

what still confuses me is not the fossil records which are understandably patchy in this regard, but the currently existing species showing no intermediate phases as might be expected

The fossil record is actually the wrong place to look for "missing links", because fossils don't preserve well over huge periods of time. If you're looking at life (say) 50 million years ago, your problem is that most of what lived at the time has disappeared, and all we're left with are fossils that provide a limited look at some of the species of the time.

It might be more productive to look at what's around and living today. In one of his books (can't recall which) our old mate Dawkins offers the idea that everything is intermediate, that each generation of a species is a "missing link" between the generation that went before and the generation to come after.

In other words, it might be more productive not to think in terms of missing links at all. The problem with searching for "the missing link" is simple. Each time you add a new fossil to the record of evolution of a species, you also add another missing link.

Try it. You have an older fossil A and a newer fossil Z. Where's the one missing fossil that connects the two? You find a fossil in between, called M. Now you need to find TWO missing link fossils - one aged between A and M, another aged between M and Z. This will keep happening unless and until you have the fossil or genetic record of every single generation.

Improbable wrote: »

Take a group of primitive humans. Separate them into 2 different groups. Put one group in the desert and put the other in the arctic circle. Given enough time, because of dissimiliar selective pressures, they will evolve into different species.

In the realm of popular science, the BBC's Walking With Cavemen series puts forward the idea that the above is exactly how H. Sapiens and H. Neanderthalensis evolved. Two populations of (I think) H. Heidelbergensis were separated into European and African sub-populations while Europe was covered in glaciers and most of Africa was desertified.

The northern population evolved to cope with the extreme cold and limited food supply. Meanwhile, the southern population evolved to cope with extreme heat, limited food supply, and limited and dwindling water resources. Both groups developed bigger brains, but the key difference between the two environments was the lack of water, and the theory is that although the southern population almost became extinct, the creatures who were most likely to survive were those who could develop strategies and advance plans to cope with water shortages - which meant having more creative and imaginative brains. The northern population evolved into Neanderthals, the southern population into modern humans.

It's a plausible (and indeed beguiling) idea, but I don't know how much currency it has in scientific circles these days.

nozzferrahhtoo

Improbable wrote: »

It's an interesting paper from 1999 about models of extinction. It's in PDF format. Thought you might enjoy reading it. I've attached it as a PDF. It's rather long like IrishKnight says, but if you're interested in the topic, it's fascinating.

Ah ta for that. I know this document already as it happens, but no harm having it attached on here for future reference.

skregs

When a species arrives in a new environment, it evolves rapidly to adapt to that environment. (allopatric speciation)

Then the rate of evolution slows down and adaptations are less noticeable. Stuff like disease reistance, improved digestion etc. (sympatric evolution)


The idea of species being in a continuum should be looked at as a chronological concept, i.e. species A 50,000 years ago and species A in the present.


There isn't a continuum between species because sexual reproduction prevents breeding with other organisms outside of your own species.
(crap animals like ligers are almost always sterile and have severe health problems because nature hates them)

If you have two distinct species competing for the same resources in the same location, basic ecology predicts that one of them will eventually become extinct.

This leads to the 'gaps' you see between species.