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human evolution unrepresentative sampling?


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I am currently studying human evolution. There are questions currently puzzling me about the conclusions reached by archeologists from the evidence found by studying ancient skeletons

 

First a few musings..

 

Dogs have been bred for a couple of thousand years or so, a trivial period in evolutionary terms, yet they show a huge variation in shape, size, behaviours etc. I am aware that there are two forms of selection at work, natural selection and human selection, but it seems to me that hominids dont exhibit the same drastic variation in their organism even over vastly greater peridos of time. Over the period of time since Sahelanthropus tchadensis (say 7 million years) I would expect to find huge variations in the skeletal design according to climatic and living conditions - in the human ancestral pathway. From my knowledge of the current evidence, we see some variation but no pekinise bulldog or great dane like extremes - according to the narrative (with the only possible exception being homo floriensis). Rather the lineage is described as a very gradual change in brain size, bipediality (consequentiual effects on the skeleton), molars etc. Lifestyle and nutrition also has a significant effect on the skeletal composition. In the West we currently have an obesity epedemic and this has a signficant effect on the skeleton and this is in one or two generations. I would guess that the normative skeletal range has significantly shifted. When archeologists discover a skeleton from the remote past, for example Lucy, I find that many authors in the field tend to make many conclusions about the height and physique of the species from what could be an unrepresentative sample. I am sixty, my parents generation was significatly shorter than their sibilings this effect is over a single generation. Then there is the whole question of epigenetic switches. Lastly, i play piano and have done since a child. i am willing to bet that this has had a significant impact on the development of my wrist bones, their size and shape. Are there not similar considerations ideosynchratic to each specimin? This last point does not refer to pathological changes, rather to natural and perfectly healthy development.

 

 

 

I am aware that the population was far smaller, perhaps this is the reason that conclusions regarding conformity can be made, but i am wondering if archeological assumptions are way too simplistic?

 

 

 

How do archeologists take account of the above considerations when they often have only a few bones coming from one or two specimins? Its not really discussed in the popular science literature I have read.

 

 

 

Obviously science has encountered the above considerations, I would love to know more..

 

Zero

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Artificial pressures put on dogs by man let to the wide diversity of forms under such a sort period of time, they didn't naturally appear in such a wide range, that's the main difference.

 

Other times where one species produces a wide variety of forms is due to extinction opening several niches for them to evolve into, something that's not happened in human ancestry.

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Artificial pressures put on dogs by man let to the wide diversity of forms under such a sort period of time, they didn't naturally appear in such a wide range, that's the main difference.

 

Other times where one species produces a wide variety of forms is due to extinction opening several niches for them to evolve into, something that's not happened in human ancestry.

 

 

Sorry but I find this answer too simplistic

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  • 3 weeks later...

Sorry but I find this answer too simplistic

 

That doesn't mean it isn't the correct answer. The lack of enforced outside factors (i.e. enforced breeding programs) and the lack of an extinction event in human history have played enormous roles in the overall lack of genetic diversity you assert.

 

You are also implying that physical changes created by environment or activity (your piano playing wrist bones) are somehow transferred to your genetic code. Just because I lose a leg doesn't mean my children will be only be born with one.

 

 

 

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That doesn't mean it isn't the correct answer. The lack of enforced outside factors (i.e. enforced breeding programs) and the lack of an extinction event in human history have played enormous roles in the overall lack of genetic diversity you assert.

 

You are also implying that physical changes created by environment or activity (your piano playing wrist bones) are somehow transferred to your genetic code. Just because I lose a leg doesn't mean my children will be only be born with one.

 

 

 

 

 

? Of course I dont think this, i should have thought that was obvious. Where the evidence for a particular original species is one or two skeletons (or even in some cases partial skeletons), the conclusions reached are based on the dimensions of a particular exemplar and no dna.

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? Of course I dont think this, i should have thought that was obvious. Where the evidence for a particular original species is one or two skeletons (or even in some cases partial skeletons), the conclusions reached are based on the dimensions of a particular exemplar and no dna.

 

My apologies - I understood your argument inverse to what you were trying to say. Your point, and correct me if I am wrong, is that external factors, such as piano playing, may lead to incorrect conclusions based solely on an examination of the bone structure of the skeleton.

 

If that's correct, then I'd have to say that it probably doesn't fall outside the realm of normal variance in the species, but I'm not an expert on that. Then again, there's that subjective term normal.

 

Of course, you could make the same argument about any skeletal or fossil remains ever found. Of course they're only a small subset of the possible number of skeletons based on potential numbers of creatures that have ever lived, but you can't (or at least you shouldn't) form scientific conclusions based on information you don't have. That's why scientists try and leave the door open for new information that contradicts the presently accepted model.

Edited by Greg H.
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"I'd have to say that it probably doesn't fall outside the realm of normal variance in the species"

 

Apols accepted Greg the first poster did not understand either, maybe its me.

 

I can see how, on the evidence of a very small sample - even as little as a jaw bone - they can extrapolate to make claims about the features of a species. If the jaw bone is an outlier it will not represent the norm. In other statistical sciences a representative sample is required ot make valid conclusions and I am feeling that in the conclusions reached by archeologists this is often not considered, or if it is tenously. Also the environmental factors on the expression of the genome. Presently, because this matter is not discussed in the text books I have read, I am doubting the veracity of the evidence. I can see there is a difference between robustus and gracile forms and of course there are dental differences, but beyond this, I am currently hesitent to accept the conclusions of what I am reading. There seems to be a lot of 'wish fulfilment' in the conclusions reached and dare I say it some 'anthropomorphising' - if I dare use this term of our ancestors. I mean inferring 'modern human' qualities from scant evidence.

 

 

Perhaps an expert on the examination of bones could correct me on this (i dont know the term dfor such an expert0

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so your concern is that small and possibly non-random sampling of physiological artifacts, as well as post-genetic influences, can all effect morphology. This is a problem when your goal is studying the evolution of genetically-derived forms.

 

This is a valid concern, but I don't think evolutionary anthropologists are unaware of these issues.

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so your concern is that small and possibly non-random sampling of physiological artifacts, as well as post-genetic influences, can all effect morphology. This is a problem when your goal is studying the evolution of genetically-derived forms.

 

This is a valid concern, but I don't think evolutionary anthropologists are unaware of these issues.

 

I have a number of concerns. If anthropologists are aware (I presume they are) then why dont they discuss these issues in the popular science? After all the public are often educated people.

 

The more I examine the 'evidence' the more I find issues with the presentation of the data and the claims that are made - even by the most respected sources.

 

 

 

NB: In case you are wondering, I am no creationist, i go by facts and valid data.

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If you just consider animals recognised as dogs in the wild (i.e. those not influenced genetically by man) then (IMO) you won't find that much variation,

 

 

So they will be no dogs with heavy bone structure or light? No short, no tall? All uniform?

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Perhaps an expert on the examination of bones could correct me on this (i dont know the term dfor such an expert0

 

Osteology is the study of bones, but it's often studied by other specialties as well, such as paleontologists, anthropologists, and archaeologists.

 

One thing to keep in mind is that it's not as if the people making these conclusions can just whip up a random sample like they can with, for instance, demographics. We only have a limited number of fossils to work from (though according to the Smithsonian, this is around 6000 fossils, so it's not exactly a jawbone and a couple of fingers). Out of necessity, the conclusions drawn will be influenced by that sample, but as new finds are made, they are added to our body of knowledge - if adjustments to the current model are needed, they will be made on the body of the evidence at hand.

 

Your argument that the sample size is limited is not an unforeseen problem in this instance. It's simply the nature of the beast, unfortunately.

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I have been making some further enquiries. Evidently sometimes species have been incorrectly defined (at least in sharks). Here is a paper regarding sharks teeth that raises the issues which could applyto hominids - I claim:

 

it states

 

" The great diversity of tooth forms they found spurred them into naming many questionable species."

 

www.paleosoc.org/Fossil_Shark_Teeth.pdf

 

 

 

There does seem to be discussion in the expert literature but its not reaching the popular press. Perhaps someone somewhere is trying to find the 'standard deviation curves' for the data.

 

I still hold there must be tall and short wolves. When I said that there were sometimes only a few jaw bones I was referring to instances of the more remote fossils such as Ardipithecus.

 

One point to bear in mind is that the gene pool was much smaller -presumably

 

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The problem with sharks is overly exacerbated by the fact that of the entire body, only the vertebrae, jawbones and teeth remain, so they don't even have the entire animal to look at. It's no wonder they had trouble with them. Even normal variances with a species can look like whole new members of the family when you possess so little data. Lining the teeth up in the jaw wrong, or in the wrong jaw (which was, apparently common with early attempts to reconstruct megalodon), would add even more confusion to the mix.

 

As for the assertion that there must be tall and short wolves - I'm sure there are/were - within the norms of variation for the species.

 

Keep in mind that your comparison to dogs is not the way we would expect a natural system to behave. Dogs were selectively bred for certain characteristics (size, speed, sense of smell), and breeding of undesirable traits was actively selected against by ensuring the animal in question not only did not breed, but had no opportunity to breed (either by neutering or euthanasia).

 

In the wild, this second limiting factor isn't present. "Less than perfect" members of the species still get the opportunity to mate, so while there will be some variation, unless that particular mutation provides some overwhelming advantage or detriment, it's probably not going to selected for or against with Nature running the show. It may hang around in the gene pool for millenia until something changes that makes it either a benefit or a detriment, in which case natural selection will take over.

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The problem with sharks is overly exacerbated by the fact that of the entire body, only the vertebrae, jawbones and teeth remain, so they don't even have the entire animal to look at. It's no wonder they had trouble with them. Even normal variances with a species can look like whole new members of the family when you possess so little data. Lining the teeth up in the jaw wrong, or in the wrong jaw (which was, apparently common with early attempts to reconstruct megalodon), would add even more confusion to the mix.

 

As for the assertion that there must be tall and short wolves - I'm sure there are/were - within the norms of variation for the species.

 

Keep in mind that your comparison to dogs is not the way we would expect a natural system to behave. Dogs were selectively bred for certain characteristics (size, speed, sense of smell), and breeding of undesirable traits was actively selected against by ensuring the animal in question not only did not breed, but had no opportunity to breed (either by neutering or euthanasia).

 

In the wild, this second limiting factor isn't present. "Less than perfect" members of the species still get the opportunity to mate, so while there will be some variation, unless that particular mutation provides some overwhelming advantage or detriment, it's probably not going to selected for or against with Nature running the show. It may hang around in the gene pool for millenia until something changes that makes it either a benefit or a detriment, in which case natural selection will take over.

All in the field know there is much speculation involved when there is little skeletal evidence. All one can do is listen to what they claim as evidence to support their conclusions and whether it seems like a logical or likely possibility. Evolution over millions of years developed the wolf. Man's domestication of dogs is thought to have been at least 10,000 years ago and many believe much longer. We learned to breed dogs for work and protection qualities so the best dogs became very valuable. In maybe just 10,000 years since we were able to change dogs by selective breeding. Our ability to do this is because dogs sexually mature in 6-12 months instead of 13-15 years old for humans.

 

For the last couple of thousand years there have been few recorded attempts lasting only at most 10 generations concerning the breeding of human slaves for strength and stamina for the fields, and for looks as house servants. Hitler attempted "eugenics" for looks, health, and intelligence, but was stopped after just one generation.

 

So I expect if long-lived aliens wanted to breed humans for some reason, they probably could produce the variety that we see in dogs in the same number of generations which it took us for dogs, which was about 10 to 15 thousand generations of selective breeding. If we get down to understanding genetics better we could breed into animals favorable characteristics in a much shorter time period, with fewer trial and errors, and fewer unfavorable inbreeding traits. Today screening takes place to some extent concerning human amniotic analysis for genetic disease traits which can be selected out by abortion in early pregnancy.

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Edited by pantheory
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