Neanderthal DNA breakthrough

[Royston]

Please have a look at the BBC article below...

 

If there is / or even isn’t a genetic link between Neanderthal man and us, the results if successful will definitely be a step forward in piecing together our ancestry.

 

Studying the Neanderthal genome will shed light on the genetic changes that made our species what it is' date=' after the evolutionary lineages of Neanderthals and modern humans diverged from one another.

 

It could also reveal what colour hair, eyes and skin Neanderthals had, whether they were capable of modern speech, shed light on aspects of their brain function and [u']determine whether they contributed to the modern human gene pool. [/u]

 

 

http://news.bbc.co.uk/1/hi/sci/tech/6146908.stm

[michael]

There is a genetic link, and interestingly it is the gene to brain size.

 

Is this why we have so much trouble giving birth?

 

Squeezing a huge neanderthal brain trough a H. sapiens pelvis??

[lucaspa]

There is a genetic link, and interestingly it is the gene to brain size.

 

Is this why we have so much trouble giving birth?

 

Squeezing a huge neanderthal brain trough a H. sapiens pelvis??

 

No. Neandertals and H. sapiens are both descended from H. erectus. We are sibling species, not ancestor-descendent. We, and neandertals, had trouble giving birth for the same reason: large head, small pelvis.

 

From the news article:

 

"The two teams basically agree, within their margins of error, that the evolutionary lineages of Neanderthals and modern humans split somewhere around 500,000 years ago. This fits with previous estimates from mtDNA and archaeological data"

 

See? NOT ancestor-descendent, but two sibling species descended from a common ancestor. Neanderal and sapiens is analogous to chimp and sapiens, except the common ancestor is more recent.

[michael]

OK

Thanks

you would think that the DNA, RNA, protein expression etc could have worked out a better pelvis by now!

[lucaspa]

OK

Thanks

you would think that the DNA, RNA, protein expression etc could have worked out a better pelvis by now!

 

At 20 years per generation and 150,000 years since H. sapiens appeared, that's 7500 generations. Quite a few but not all tht many. The problem is that, from a population standpoint, the pelvis isn't that bad -- most women survive childbirth and the survival of the child is even higher. IOW, altho the mother may die, the kid usually comes thru. So this is a tragedy for individual humans -- the woman and her mate -- but it is not a huge selection pressure. And pain in childbirth is an even lower selection pressure. Natural selection doesn't care if the woman is in pain, only that she has the kid. And the sex drive ensures she has the kid. Yes, women who have no pain in childbirth are going, on average, to have more kids. But it's going to take A LOT of generations for that to become fixed.

[Glider]

It's not only natural selection that plays a role either. Sexual selection plays a large role in evolution, and the selection by males of thinner females (as the social ideal changed) has resulted in a the narrowing of female pelvic girdles over the last 200 years or so. Births are becoming more difficult and the necessity of medical/surgical intervention more frequent.

[lucaspa]

It's not only natural selection that plays a role either. Sexual selection plays a large role in evolution, and the selection by males of thinner females (as the social ideal changed) has resulted in a the narrowing of female pelvic girdles over the last 200 years or so. Births are becoming more difficult and the necessity of medical/surgical intervention more frequent.

 

I would question this. I would need to see some quantitative data on female pelvic girdles. The human population is so large and 200 years so short (10 generations) that I doubt there has been an overall shift in pelvic girdles.

 

Yes, there is sexual selection, no doubt about it. And I would even say that recently men in the West are choosing as you describe. What I question is whether that selection has been strong enough and long enough to shift the mean in female pelvic girdles.

 

Also, the ideal you are describing is in Western civilization. That's a growing segment of the human population, but hardly all humans!

 

It is true that medical/surgical intervention is becoming more frequent, but that has nothing to do with narrower pelvi. Instead, there is a huge number of factors that are coming into play in the West for that:

1. Reimbursement (a surgical procedure can be billed at a much higher rate than natural childbirth)

2. Avoiding malpractice suits (the baby is less likely to have problems with C-section)

3. Convenience for the obstetrician (no waiting for hours while the woman does labor and missing his tee time)

4. The instant gratification and avoidance of pain in modern culture: women sometimes demand C-section so they don't have to go thru labor and can schedule when to have the birth

5. The idea that even one death in childbirth is too many. Therefore we aren't allowing evolution, and natural selection, to take their course.

[Glider]

I would question this. I would need to see some quantitative data on female pelvic girdles. The human population is so large and 200 years so short (10 generations) that I doubt there has been an overall shift in pelvic girdles.

The data exist in the field of Obstetrics and medicine in general (see for example Leong, A. (2006) Sexual dimorphism of the pelvic architecture: A struggling response to destructive and parsimonious forces by natural & mate selection. McGill Journal of Medicine. 9: 61-66. ).

 

Sexual selection is a powerful force in species morphology. Consider it ‘Turbo Evolution’. Sexual selection can bring about comparatively rapid changes in a population. For example, look what we have done with plants by deliberately selecting specimens with ‘desirable’ qualities. Hundreds of new cultivers appear each year. Look also at the results of the process in animals such as dogs, cats, horses, cattle, sheep and so-on. Changes that left to random selection would take millions of years can be forced in a few generations.

 

Those are deliberate manipulations, but the same thing can be seen on the wild. For example, look at the anole lizards of Cuba, where groups of the same species were separated due to elevated sea levels. There are now many distinct sub-populations. Look also at Darwin’s finches of the Galapagos Islands.

 

The same thing happens in humans. There are natural forces, of course, but these take a lot longer for effects to occur. Mate selection on the other hand is an incredibly fast and effective driving force for change.

 

I should have been more specific though. I never meant all females. Sexual selection is itself driven by social ideals and these differ between cultures (and change over time).

 

The social ideal in the west has been for more slender females. This is driven by a number of factors; the emphasis and value placed on ‘eternal youth’ in the West and the almost pathologically underdeveloped body form that is presented as the ideal in the fashion world for example.

 

Yes, there is sexual selection, no doubt about it. And I would even say that recently men in the West are choosing as you describe. What I question is whether that selection has been strong enough and long enough to shift the mean in female pelvic girdles.

No, not in all females, but within distinct sub-populations, particularly in the West (e.g. UK). Ten generations is easily enough for sexual selection to produce measurable change. This is because sexual selection driven by cultural ideals in a lot more specific than natural selection. It rules out variation by definition.

 

I should point out that sexual selection is not the only driving force, there are nutritional factors also and the increasing levels of sex hormones entering the (intensively farmed and processed) food chain.

 

Also, the ideal you are describing is in Western civilization. That's a growing segment of the human population, but hardly all humans!

Yes, sorry, my bad (see above).

 

It is true that medical/surgical intervention is becoming more frequent, but that has nothing to do with narrower pelvi. Instead, there is a huge number of factors that are coming into play in the West for that:

1. Reimbursement (a surgical procedure can be billed at a much higher rate than natural childbirth)

The price of a surgical procedure is not grounds for performing it.

 

I would question the ethics and legality of performing a surgical procedure simply because it costs more. In the UK the higher cost of a surgical procedure is actually grounds for avoiding it if possible (UK hospitals being under so much pressure to keep to budget). Further, labour wards in the UK do not charge the patient (which is why we are subject to so many ‘Health Tourists’, particularly, in the case of labour, from the USA).

2. Avoiding malpractice suits (the baby is less likely to have problems with C-section)

Performing invasive surgery that is not necessary is malpractice.

 

In the UK surgical sections are done only where necessary as they carry their own inherent risks. Moreover there is an increasing trend for ‘natural births’ and surgical sections (as with all invasive procedures) require informed consent, which can be withheld.

3. Convenience for the obstetrician (no waiting for hours while the woman does labor and missing his tee time)

You seem to have a somewhat tenuous grasp of ethicolegal concepts in medicine. Under no circumstance is the practitioner’s ’convenience’ grounds for surgery. Tea time even less so. (note the spelling).

4. The instant gratification and avoidance of pain in modern culture: women sometimes demand C-section so they don't have to go thru labor and can schedule when to have the birth

’Can schedule when to have the birth’? Hmmm. There are plenty of analgesic drugs and procedures available and these are often requested. In fact, women very rarely ‘demand’ surgical section (at least in the UK). It leaves a scar. It tends to be left until there are signs of foetal distress or where scans have shown that there is little chance of a natural birth.

5. The idea that even one death in childbirth is too many. Therefore we aren't allowing evolution, and natural selection, to take their course.

Which kind of supports my point. Because surgical section as a procedure is available, males can continue to select waiflike partners and avoid the natural consequences of trying to push larger babies through smaller spaces.

 

Whilst surgical intervention not the first recourse in labour (at least in this country), it is becoming more frequently necessary as difficult births become more common, due largely to the increasingly android female pelvis in Western sub-populations.

[lucaspa]

The data exist in the field of Obstetrics and medicine in general (see for example Leong, A. (2006) Sexual dimorphism of the pelvic architecture: A struggling response to destructive and parsimonious forces by natural & mate selection. McGill Journal of Medicine. 9: 61-66. ).

 

Apparently this is not indexed in PubMed. Can you find some other articles that are indexed in PubMed? The title of this one suggests that it is looking at the differences between male and female pelvi -- the "sexual dimorphism" and that mate selection has given us the general dimorphism, not anything within the last 200 years. So, please, post some other articles.

 

Sexual selection is a powerful force in species morphology.

 

Next time, let me suggest you read my entire post before you start to reply. If you had read the next paragraph,you would have seen that I was NOT questioning sexual selection in general, ONLY the specific comment that the mean width of female pelvi had changed within the last 200 years.

 

Consider it ‘Turbo Evolution’. Sexual selection can bring about comparatively rapid changes in a population. For example, look what we have done with plants by deliberately selecting specimens with ‘desirable’ qualities.

 

First, I agree that sexual selection can be a powerful selective tools.

Second, the examples you gave is artificial selectio, not sexual selection. That the changes you do to "random selection" are not that. Selection itself is not random. It's just that the humans are making a very severe environment. Artficial and natural selection are the same thing: artificial selection is natural selection where humans dictate the environment. And yes, in nature the environment rarely imposes selection pressures that are so severe but, when they are, evolution is just as fast. See this paper:

Evaluation of the rate of evolution in natural populations of guppies (Poecilia reticulata). Reznick, DN, Shaw, FH, Rodd, FH, and Shaw, RG. Science 275:1934-1937, 1997. The lay article is Predatory-free guppies take an evolutionary leap forward, pg 1880.

 

Those are deliberate manipulations, but the same thing can be seen on the wild. For example, look at the anole lizards of Cuba, where groups of the same species were separated due to elevated sea levels. There are now many distinct sub-populations. Look also at Darwin’s finches of the Galapagos Islands.

 

Again, this is natural selection, not sexual selection. From your examples, I think you are confusing the terms.

 

I agree that humans are under natural selection. I'm questioning whether there has been enough time for natural and/or sexual selection to change human female pelvi in 200 years. Remember that we are talking number of generations. Evolution is change in populations from generation to generation. Both lizards and the finches have generation times that are 1 year or less. Thus, you can get 20 or more generations in 20 years. And the populations are relatively small -- in the few thousands. In contrast, humans have a generation time of 20 years and the population in the last 200 years has been in the tens to thousands of millions. It's diffficult for new changes to spread so fast thru such a large population.

 

Mate selection on the other hand is an incredibly fast and effective driving force for change.

 

The problem is that NONE of your examples of mate selection was really mate selection.

 

No, not in all females, but within distinct sub-populations, particularly in the West (e.g. UK). Ten generations is easily enough for sexual selection to produce measurable change. This is because sexual selection driven by cultural ideals in a lot more specific than natural selection. It rules out variation by definition.

 

OK, let's look at mate selection. In mate selection only particular members of the opposite sex are chosen to mate with. What you have to have is just a small proportion of one gender producing all the offspring. Now, how many women in the UK are unmarried? Of the married women, what proportion are having babies? For your hypothesis to work, especially in 10 generations, you need ONLY the narrow hipped females to find mates and have kids. Just as an observation here in the US, which has the same culture for beauty as the UK, I don't see this. Yes, men may chase slim hipped women, but the fact is that men who don't get the "ideal" mate do not go mateless. Remember, the gender ration is close to 50:50. Since slim-hipped women would make up a small percentage of the women, say even 50%, that means you should see 50% of men be bachelors because they would not get the mates they want. I don't see this. Instead, the men who do not "get" the slim-hipped women marry and have kids with women who have wider hips.

 

The price of a surgical procedure is not grounds for performing it. ... .

 

Ethically, no. In practice, yes. In order to survive, the hospital/doctor in the US has to bring in money to survive. If there is some justification for a procedure that can be billed, that becomes an indication to do the procedure. Reimbursement is higher in the US for C-sections than normal delivery. Now, you said "Further, labour wards in the UK do not charge the patient" That implies that patients ARE charged for C-sections. Is that true? Or are they not charged no matter what happens to the patient?

 

C-sections is a gray area. What constitutes "necessary"? How much risk to the baby is deemed "necessary" in order to decide to do a C-section? Any risk at all? Something greater than that? If it is the first, then all delivery is a risk to the baby and C-sections are "necessary".

 

Performing invasive surgery that is not necessary is malpractice

 

In this case, it is trivial. The overwhelming source of malpractice suits in obstetrics is harm to the baby: cord wrapped around the throat, narrowing of the head as it passes thru the birth canal -- with possible neural problems, use of forceps and possible neural problesm, etc. So, cesearian sections remove all that and make it much safer for the baby. And, since the cesearian is done to protect the baby, it is necessary.

 

You seem to have a somewhat tenuous grasp of ethicolegal concepts in medicine. Under no circumstance is the practitioner’s ’convenience’ grounds for surgery. Tea time even less so. (note the spelling).

 

You should have noted the spelling. "tee time" in the US is when you tee off in a golf game.

 

On the contrary, I work in a surgical department and we have 4 ethicolegal Grand Rounds per year. I am quite familiar with the situation. There is the ideal and then there is what actually happens. You seem to be familiar with the ideal; I'm familiar with the real world.

 

And yes, doctors have their own lives to live. Why do you think Family Practice doctors have office hours during regular Mon-Fri work hours? It's inconvenient to the patients, but convenient to the doctors. Most surgery is scheduled during normal working hours for the same reasons. There is also the consideration of the support staff for surgery. Remember those UK hospitals who want to keep their costs down? Do they have to pay overtime? Do staff on the evening and night shift get more pay (to compensate them for the odd hours)? What happens when they have to keep the support staff past quitting time in cases that may, or may not, end in a C-section. Assuming they do, then the hospital and doctor have motives for converting the birth that may be C-section into a C-section.

 

There are plenty of analgesic drugs and procedures available and these are often requested. In fact, women very rarely ‘demand’ surgical section (at least in the UK).

 

1. Analgesics make the birth process easier, but it doesn't remove the uncertainty of which day labor is going to start, does it? From the 9th month onward, women could go into labor anytime.

 

2. Again, can you give me some data on that "rarely demand"?

 

It leaves a scar. It tends to be left until there are signs of foetal distress or where scans have shown that there is little chance of a natural birth.

 

Actually, no. It seems to depend on "progress". Here is a study -- conducted in England. First, women who had a cesaerean were just as satisfied with their delivery experience as women who had normal birth. See the first bolded section in the abstract. Also note that cesaerian is pretty low in England: <10%. This argues AGAINST your contention of high cesaerian birth rate due to narrow pelvi. Instead, the decision to have a cesaerian depends on whether labor is "progressing" in a timely matter, not fetal distress or concerns about width of the birth canal.

 

Effect of different partogram action lines on birth outcomes: a randomized controlled trial.Lavender T, Alfirevic Z, Walkinshaw S.

University of Central Lancashire, Preston, United Kingdom. Tinalav@yahoo.co.uk

 

OBJECTIVE: The World Health Organization recommends partograms with a 4-hour action line, denoting the timing of intervention for prolonged labor; others recommend earlier intervention. We assessed the effect of different action line positioning on birth outcomes. METHODS: A randomized trial of primigravid women with uncomplicated pregnancies, in spontaneous labor at term, was conducted in the northwest of England. Women were assigned to have their labors recorded on a partogram with an action line 2 or 4 hours to the right of the alert line. If progress crossed the action line, diagnosis of prolonged labor was made and managed according to standard protocol. Primary outcomes were rate of cesarean delivery and maternal satisfaction. RESULTS: A total of 3,000 women were randomly assigned to groups; 2,975 (99.2%) were available for analysis. Questionnaires were completed by 1,929 (65%) women. There were no differences in cesarean delivery rate (136/1,490 compared with 135/1,485; relative risk [RR] 1, 95% confidence interval [CI] 0.80-1.26) or women dissatisfied with labor experience (72/962 compared with 81/967; RR 0.89, 95% CI 0.66-1.21). More women assigned to the 2-hour arm had labors that crossed the action line (854/1,490 compared with 673/1,485; RR 1.27, 95% CI 1.18-1.37); received more intervention (772/1,490 compared with 624/1,485; RR 1.23, 95% CI 1.14-1.33); and, if admitted to the midwife-led unit, were transferred for consultant-led care (366/674 compared with 285/666; RR 1.26, 95% CI 1.13-1.42). CONCLUSION: In this birth setting, for primigravid women selecting low intervention care, the 2-hour partogram increases the need for intervention without improving maternal or neonatal outcomes, compared with the 4-hour partogram, advocated by the World Health Organization. CLINICAL TRIAL REGISTRATION: Current Controlled Trials, http://www.controlled-trials.com/isrctn/trial/|/0/78346801.html, ISRCTN78346801.

 

Because surgical section as a procedure is available, males can continue to select waiflike partners and avoid the natural consequences of trying to push larger babies through smaller spaces.

 

What happened to your ethics? The "natural consequences" are traumatized or dead babies! How ethical is it to refrain from a surgical procedure if such restraint is going to harm the baby!

 

Whilst surgical intervention not the first recourse in labour (at least in this country), it is becoming more frequently necessary as difficult births become more common, due largely to the increasingly android female pelvis in Western sub-populations.

 

That cause is not listed in the obstetrics literature. According to this article, what matters is the experience of the obstetrician, not the pelvic size. New obstetrician, more cesearians.

 

J Obstet Gynaecol. 2005 Oct;25(7):666-8. Links

A prospective observational study of emergency caesarean section rates and the effect of the labour ward experience.Griffiths AN, Avasarala S, Wiener JJ.

Department of Obstetrics and Gynaecology, Royal Gwent Hospital, Gwent, UK. Dr@anthony36.freeserve.co.uk

 

The National Sentinel Audit found that one in five births in England and Wales was by caesarean section. The reasons for the increase in caesarean section rates are multi-factorial. Anecdotally, it is suggested that obstetric intervention rates and caesarean section rates vary among obstetricians without a difference in fetal and maternal outcomes. The aim of this prospective observational study of 817 deliveries was to assess the effect of experience on the caesarean section rates for different obstetricians. Obstetricians with greater than 3 years of 2nd on-call labour ward experience had a statistically significant lower caesarean rate than less experienced obstetricians 10.25% vs 25.49%, respectively (p < 0.05). Differences in instrument deliveries was also studied.

 

Here's another article from England. It documents an increase in caesarian births by request.

 

Obstetricians say yes to maternal request for elective caesarean section: a survey of current opinion.Cotzias CS, Paterson-Brown S, Fisk NM.

Institute of Obstetrics and Gynaecology, Imperial College School of Medicine, Queen Charlotte's and Chelsea Hospital, Goldhawk Road, London W6 0XG, UK.

 

AIM: To determine what proportion of obstetricians would agree to elective pre-labour CS for 'maternal request'. METHODS: Every fifth consultant on an alphabetical list of obstetricians in England and Wales obtained from the RCOG (243) was surveyed by post and asked (a) "Would you agree to perform an elective CS on a woman with an uncomplicated singleton cephalic pregnancy at term for 'maternal request?"' and (b) if yes, in relation to this 'Has your practice changed over recent years?" RESULTS: 155 questionnaires were returned (63% response rate -- four unanswered, leaving 151 for analysis). One hundred and four (69%) consultants said they would agree to 'maternal request' for CS. Of the 'yes' respondents, 62 (60%) claimed their practice had changed recently. CONCLUSION: This survey demonstrates that a majority of obstetricians are now prepared to agree to maternal request for CS in the absence of obstetric indications.

 

Here's one showing that affluent women opt for caesarian section birth:

 

Investigating the relationship between affluence and elective caesarean sections.Alves B, Sheikh A.

SpT in Public Health, Brighton and Hove City PCT, Brighton, East Sussex, UK.

 

The proportion of women delivering by caesarean section has increased dramatically in England and many westernised countries. It has been suggested that one important reason for this increase is the growing proportion of women opting for elective caesareans for lifestyle reasons, a trend that is, it is argued, most common among the affluent. We investigated the hypothesis that affluent women are more likely to deliver by elective caesarean section. Logistic regression modelling was used to analyse data from half a million women who delivered in English NHS hospitals between 1996 and 2000. We found that women living in the most affluent areas of England were significantly more likely to have an elective caesarean section than their deprived counterparts.

 

All in all, I can't find any support in the obstetrics and gynecology literature for your hypothesis that an increase in caesarian births is due to pelvic size.

 

Wait, here's a study looking at ALL risk factors for caesarian births. Breech presentation is a high risk factor, which has nothing to do with the width of the pelvis, of course. Elective caesarian is high on the list. We do see "Extremes of neonatal birthweight" and "increasing neonatal head circumferences". Both of these don't really indicate smaller pelvi, but rather the baby on the extreme of size. That would be a problem from the baby's side, not the woman's pelvis; it would have been competent to handle a normal sized baby.

 

So, yes, I did look in the obstetrics literature. But I didn't find what you said I would find. Instead, I found support of my hypotheses and refutation of yours. But thanks for the opportunity to do some research and increase my knowledge.

 

1: Int J Epidemiol. 2005 Apr;34(2):353-67. Epub 2005 Jan 19. Links

Prenatal risk factors for Caesarean section. Analyses of the ALSPAC cohort of 12,944 women in England.Patel RR, Peters TJ, Murphy DJ; ALSPAC Study Team.

Division of Obstetrics and Gynaecology, University of Bristol, St Michael's Hospital, Southwell Street, Bristol BS2 8EG, UK. roshni.patel@bristol.ac.uk

 

BACKGROUND: There has been an escalation in Caesarean section rates globally. Numerous prenatal factors have been associated with elective and emergency Caesarean section, some of which may be amenable to change. METHODS: A population-based cohort of 12,944 singleton, liveborn, term pregnancies were used to investigate risk factors for Caesarean section using multivariable logistic regression modelling. Numerous prenatal factors were investigated for their associations with the following outcomes: first, with Caesarean section (both elective and emergency) compared with vaginal delivery (spontaneous and assisted); second, for their associations with elective Caesarean section compared with attempted vaginal delivery; and finally emergency Caesarean section compared with spontaneous vaginal delivery. RESULTS: 11,791 women had vaginal delivery and 1153 had Caesarean section (685 emergency, 468 elective). Non-cephalic (breech) presentation (all Caesareans odds ratio (OR) 36.6, 95% confidence interval (CI) 26.8-50.0; elective Caesarean OR 86.4, 95% CI 58.5-127.8; emergency Caesarean OR 9.58, 95% CI 6.06-15.1) and previous Caesarean section (all Caesareans OR 27.8, 95% CI 20.9-37.0, elective Caesarean OR 54.4, 95% CI 38.4-77.5; emergency Caesarean OR 13.0, 95% CI 7.76-21.7) were associated in all analyses with an increased risk of Caesarean section. Extremes of neonatal birthweight were associated with an increased risk of Caesarean section (all Caesareans and emergency section) compared with vaginal delivery as was increasing neonatal head circumferences. In all analyses increasing maternal age (OR 1.07 per year, 95 % CI 1.04-1.09; OR 1.04 per year, 95 % CI 1.01-1.08; OR 1.11 per year, 95% CI 1.08-1.15) was independently associated with increased odds of Caesarean section. Increasing parity was associated with a decrease in risk for all Caesareans and emergency section (OR 0.63, 95% CI 0.53-0.75 and OR 0.46, 95% CI 0.33-0.63, respectively), as was the outcome of the last pregnancy being a live child. Increasing gestation was independently associated with a decreased risk of both all Caesareans and elective Caesarean (OR 0.86, 95% CI 0.80-0.93 and OR 0.52, 95% CI 0.46-0.58 respectively), whereas diabetes mellitus was associated with increased risk. These variables were not associated with emergency section. However, epidural use was associated with an increased risk of emergency Caesarean (OR 6.49, 95% CI 4.78-8.82) while being in a preferred labour position decreased the risk (OR 0.59, 95% CI 0.49-0.73). CONCLUSIONS: A careful exploration of risk factors may allow us to identify reasons for the increasing rates of Caesarean section and the marked variation between institutions.

[Glider]

Ok, whatever you say.

[lucaspa]

Ok, whatever you say.

 

Not what I say, but what the data says. Now, if you can post the abstract from the Leong paper to show that they have measured pelvic dimensions of women and show a difference in the last 200 years, then that is different data. Perhaps you could even post some data from tables in the paper.

 

However, since the paper is not available on any database I have access to, I can't check to see if the paper really has that data.

 

WAIT! I found the paper! It's at http://www.medicine.mcgill.ca/mjm/issues/v09n01/crossroads/Pelvis%20sexual%20dimorphism2.pdf

 

OK, so now let's look at it. As I suspected, the article is talking about how pelvic dimorphism (difference between men and women) arose. Leong thinks sexual selection had a lot to do with that, along with natural selection. Leong says BOTH seem to have worked for WIDER pelvi.

 

Leong catalogs the problems that can result in childbirth when there is a baby size/birth canal ("pelvic-fetal anatomy") incompatibility. He then says:

 

"In light of the plethora of injuries associated with

childbirth, it is easy for one to postulate that in the

absence of healthcare, incompatible pelvic-fetal

anatomy could result in significant infant and maternal

mortality and morbidity. Although concrete scientific

evidence does not exist, one has to wonder if medical

practice is indirectly and insidiously introducing

variability to the human anatomy."

 

Leong is making the same speculation you are: modern health care, combined with a tendency to view thin females as desirable, is adding "variability" to human anatomy. Leong won't even go so far as to say that there is directional change, but rather that narrow-hipped women, so far being selected against, are now being kept in the population.

 

Look what I bolded. Even with the much weaker claim Leong is making, he says there is no data. Which is exactly what I was skeptical about.

 

Glider, if you want to present the idea as a speculation/hypothesis, that is fine. In fact, it was fine. I expressed my skepticism towards it, and gave my reasons. Where you got into trouble was 1) trying to say there was supporting data and, therefore, the speculation was fact and 2) trying to use the number of caesarian sections as data.

 

1) doesn't work because there is no direct supporting data. Leong says that outright.

2) the number of caesarian sections doesn't work because of the data and reasons I gave: there are too many alternative hypotheses to explain the rise in the number of c-sections. Even in England (did you notice I limited the papers I used to England?). So we can't say the rise in the number of c-sections is due to an overall decrease in female pelvic size.

 

Some other interesting quotes from Leong's paper:

 

"Natural Adaptive Forces in Shaping Sexual

Dimorphism of the Pelvis:

Bipedalism versus Parturition

An evolutionary pattern towards bipedalism, taking

into account selective pressures of reproduction, has

been demonstrated by the increase of critical

dimensions of the pelvis as the maternal skeleton

becomes larger. ... These adaptations to ease parturition as reflected in

the sexual dimorphism in the human pelvis and femur

are disadvantageous to women in terms of mechanics of

locomotion."

 

"Superficial to the skeleton and musculature of the

pelvis, sexual dimorphism in pelvic morphology is most

apparent in body fat distribution as measured by waist

hip ratio (WHR). The WHR has been shown to be

independent of overall body weight and an accurate

predictor of risk for various diseases, premature

mortality, degree of estrogenicity and fecundity of

women (4). Undoubtedly, healthy women have a

greater propensity to possess rounder hips and a lower

WHR compared to most men (4). ... Finally,

cross-cultural and historical data have suggested that

the relationship between WHR and female

attractiveness is not culture-specific and not inculcated

by what modern Western fashion dictates or media (15)."

 

Now, Leong quotes some surveys:

 

"It has been shown that both

males and females assigned higher ranking for

attractiveness, youthfulness, healthiness, reproductive

capability and intelligence to normal weight figures

with low WHRs. ... Female and male subjects, judged heavier female target

figures with low WHRs as more attractive and healthier

than thinner figures with higher WHRs. Female

subjects perceived heavier female target figures with

low WHR to represent ideal female figures. It is

proposed that female attractiveness and ideal female

shape may be more influenced by WHR than overall

body size (4)."

 

Basically, this says that everyone -- male and female -- regard rounder hips as more desirable. Low weight, rounder hips are what give a low WHR. So the daat presented by Leong says there is NOT sexual selection for narrow hips! Sorry, Glider.