Naked Science Forum

Life Sciences => Physiology & Medicine => Topic started by: chris on 13/06/2017 08:53:30

Title: Why hasn't evolution selected out painful childbirth?
Post by: chris on 13/06/2017 08:53:30
John is wondering:

I love your show (https://www.thenakedscientists.com/podcasts)! I downloaded all of the podcasts (https://www.thenakedscientists.com/podcasts) for the past 11 and a half years and listened to them while at work every day over the course of a year and a half. You and the team have kept me riveted!

My question is this: As far as I know humans are the only animal who experience great amounts of pain during childbirth. Pain accompanied with torn tissue, bleeding and a long recovery time. I was wondering why this disadvantage hasn't been selected out of our genes by now, because it seams like less evolved species have it down better than we do.

My wife gave birth to our second son a few days ago, so it got me wondering.

Keep up the good work!

-John
Brighten your day.


What does everyone think?
Title: Re: Why hasn't evolution selected out painful childbirth?
Post by: evan_au on 13/06/2017 11:34:05
Most of the birth difficulties are with the baby's head - the rest of the baby's body seems to slip out relatively easily once the head is out.

Perhaps the advantages of a large brain outweigh the disadvantages of a high mortality rate for mothers and babies?
Title: Re: Why hasn't evolution selected out painful childbirth?
Post by: Kryptid on 13/06/2017 15:29:06
I think I would agree with evan_au's explanation.

As far as I know humans are the only animal who experience great amounts of pain during childbirth.

Spotted hyenas also experience pain and potential damage during childbirth due to their unique anatomy.
Title: Re: Why hasn't evolution selected out painful childbirth?
Post by: chiralSPO on 13/06/2017 19:57:54
To add to evan's comment:

Two very strong evolutionary advantages that have been selected for (large heads and walking upright) appear to have outweighed the risks of childbirth.

I would also point out that it is entirely possible* that the dangers of childbirth without medical intervention may actually have increased over the last century due to the elimination of evolutionary forces associated with childbirth. Essentially, because of the prevalence of c-sections (among other interventions) there may now be a segment of the populations that have larger head sizes at birth, or are more likely to be breached or facing the wrong way (to the extent that these are genetically determined...) These babies (and perhaps their mothers) would have very high likelihoods of dying in the 19th century and earlier, but no longer...

*Disclaimer: this second part is only my own thoughts, and may well not be true!!!
Title: Re: Why hasn't evolution selected out painful childbirth?
Post by: Janus on 13/06/2017 20:28:48
As pointed out, the increased cranial size is the cause in the  difficulty in birth.  Evolution never works for the advantage of the individual, but for the advantage of the species as a whole.  The advantage of the greater intelligence outweighs the disadvantages of child birth.  Having said that, evolution did meet us halfway.  Human infants are born without their brains being fully developed.  Presumably waiting until the brain did develop more fully would lead to greater problems in child birth than the advantage gained.  As a result, human infants are a lot more helpless at birth than any other species in exchange for some easing of the birth process.
Title: Re: Why hasn't evolution selected out painful childbirth?
Post by: MayoFlyFarmer on 21/06/2017 16:42:57
great topic. I have a feeling everyone who has posted thus far hit the nail on the head.
Title: Re: Why hasn't evolution selected out painful childbirth?
Post by: Christof Schwiening on 04/07/2017 22:13:38
Why should evolution have selected out painful childbirth? Are you suggesting that women may avoid sex because of the knowledge of the pain of child birth - all evidence seems to suggest that is unlikely.

Evolution results from the survival of the fittest. Why would the offspring which results from a painful birth to the mother have a different survival chance from one born to mother who suffered no pain? I can see two possible links. First, it could be that the painful birth changes the mother's interaction with the baby. One possibility is that the mother may value a baby more as a result of the pain and therefore nurture it more - this might increase the survival chance and therefore also possibly increase the likelihood that genes resulting in 'painful births' are retained within the genome. Another possibility is that, in times past, a painful birth with its attendant noise attracts attention of others to the birth process which may lower the mortality rate and therefore also increase the number of 'pain-inducing' genes within the genome. There are probably lots of other ideas, but I offer these with little expert knowledge on the subject other than being male with three children!
Title: Re: Why hasn't evolution selected out painful childbirth?
Post by: chris on 05/07/2017 00:08:38
Could it not be that a more painful birth means more damage is being done to mother and baby, reducing survival prospects?
Title: Re: Why hasn't evolution selected out painful childbirth?
Post by: mrsmith2211 on 05/07/2017 00:54:16
Remember a teacher,  He was doing field research in New Guinea, He told of field laborors that would squat down give birth, let the baby suckle and continue working.
Title: Re: Why hasn't evolution selected out painful childbirth?
Post by: Christof Schwiening on 05/07/2017 09:12:48
Could it not be that a more painful birth means more damage is being done to mother and baby, reducing survival prospects?

It is important to decouple the higher conscious processing that results in what we call pain from the physical stimulus which results in damage. During birth the forces on various tissues causes the activation of a range of mechanoreceptors, including nociceptors. These sensations are interpreted as pain, but that need not be the case. For instance, in battle, soldiers can suffer far more extreme damage and suffer remarkably little pain. We have neuronal and hormonal pathways that are capable of blocking the feeling of pain regardless of the level of acute damage. The fact that these sensations, leading to the feeling of pain, have not been blocked during childbirth seems to me to suggest that the pain - or the results of it - are useful. My guess is that it has a role in drawing the attention of others to the mother such that she can be helped. There is no doubt that during child birth a woman and baby are vulnerable. I guess the argument against is that each successive birth to a mother tends to be less painful. This is typified by the stories of women, in Third World countries, briefly stopping manual labour to give birth. But, perhaps that also represents the value that evolution has placed on repeat copies of similar genetic material in the gene pool. The first few births from a mother are valuable because they add genetic diversity - subsequent births add only a little more diversity and are therefore less important. This is consistent with the most pain being felt at the first birth when the newest mix of genetic material arrives! This is pure speculation.

Perhaps what is really being asked here is why so much damage has to occur to the mother as a result of child birth. This is a good question, and I suspect it links to another thread to do with nutrition. It is only within the past 100 years that humans have become quite so large. During most of our evolution nutrition was far poorer and birth weights and sizes would have been smaller. It is possible that the current level of damage and pain in child birth is a modern phenomenon resulting from larger babies (due to increased calorie intake during pregnancy)...you need an expert to address this!
Title: Re: Why hasn't evolution selected out painful childbirth?
Post by: evan_au on 05/07/2017 09:52:39
There may be a clash between larger brain size at birth, and size of the birth canal through the pelvis.

Presumably, a wider pelvic opening would allow birth of a baby with a larger skull size (but the soft tissue still needs to stretch a lot).

But a wider pelvis may increase the risk of broken hip, or interfere with running?

Perhaps if and when humans start to live in microgravity, running and broken hips will be less of a problem, so a wider pelvis (with reduced calcium) may become possible?
Title: Re: Why hasn't evolution selected out painful childbirth?
Post by: Christof Schwiening on 05/07/2017 10:52:47
I guess those interested in these arguments might want to look at some articles cited by Graham Burton published as a result of a conference on ‘Human evolution: brain, birthweight and the immune system’.
Search Google with this article code PMC4305162 for the reference. [ironically references to peer-reviewed science seems to be blocked.]

"Trevathan [4] develops this theme and describes how the modern female pelvic configuration necessitates rotation of the fetus during birth to accommodate first the head and then the shoulders. The end result is that the infant emerges facing the opposite direction from the mother, placing a premium on having assistance at delivery to clear the infant's airways."
Thus, whilst there is an obvious conflict between pelvic size (smaller the better) and the infants brain size (bigger the better) the need for pain and its attendant emotional consequences could well be to do with assistance. Evolution could well have produced mechanisms that prevent pain during labour without making the pelvis bigger or the head smaller, but, the fact that child birth is painful suggests that pain has some evolutionary advantage (or at least less of a disadvantage than mechanisms that reduce pain).
Title: Re: Why hasn't evolution selected out painful childbirth?
Post by: chris on 05/07/2017 11:59:05
[ironically references to peer-reviewed science seems to be blocked.]

It's because you are not senior enough (in terms of posts) yet - once you have a few more posts then full links unlock. It's to stop spammers from abusing the forum.