[Mike Collins]

Mike Collins  asked the Naked Scientists:
   
Dear Dr Chris,

I newbielink:http://www.thenakedscientists.com/HTML/podcasts/ [nonactive], but not the live programme.  I have asked this question before, but - well, I understand there's a limit on how may subjects you can treat in a week.

Evolution has done such a fantastic job on so many aspects of life that it leaves us in wonderment.  Even Darwin struggled to see how the eye could have evolved to its current perfection, yet there is one blatant shortfall in what evolution has done - the probability of a successful, unassisted childbirth.

It is said that evolution depends on survival of the fittest, but it could be seen from the other side of the hypothesis - death of the inept.  Now, some women can deliver children easily enough, yet some are still born with too small a pelvic opening for childbirth, and there are the difficulties of breach birth (and many others) that limit the chance of a successful delivery.  Of course, modern medical procedures remove most of the danger - but evolution was not influenced by modern medicine.  Death in childbirth is a guaranteed way killing off any lineage with this biological ineptitude, so how does it happen that we have not evolved the perfection in child delivery that is seen in so many other aspects of life?

I would really like to hear your comments on it.

Best regards,

Mike Collins
Basingstoke.

What do you think?

[imatfaal]

My first reaction would be that evolution through natural selection can only act upon a genetic trait. if the chances of breach birth or other complications have little to do with the mother's genotype but are in fact environmental or just bad luck, then there are no genes that can be "selected" through increased survival of progeny. 

If the mother's genotype does influence the ease of birth one could be very hard-hearted and speculate that children who could survive a "difficult birth" would be the very strongest babies - therefore mothers with a predisposition to trouble in childbirth would have fewer surviving children but they would be very strong and perhaps more likely to successfully breed.

Matthew

[Make it Lady]

The problems with human evolution is that of compromise. We have evolved into the best compromise for a tricky problem. We evolved the ability to walk on two legs and we evolved to be big brained, thinking animals. The two actually don't fit together so well when we give birth. Getting a big head, containing a big brain, out of a pelvis designed for upright movement has to be a compromise. Hence the skull of a baby is flexible, to a point, at birth and babies heads are delicate for some time after birth. Womens pelvis's have a wide cavity to allow the passage of said head. Evolving beyond this has it's limitations as our brains can't get smaller and we would not revert back to being on all fours. I think our massive population shows that nature actually allowed for a number of deaths at child birth. This is not to say that I'm not ungrateful for the fact that this has lessened with medical advance. Give me an epidural any day!   

[LeeE]

Evolution has done such a fantastic job on so many aspects of life that it leaves us in wonderment.  Even Darwin struggled to see how the eye could have evolved to its current perfection, yet there is one blatant shortfall in what evolution has done - the probability of a successful, unassisted childbirth.

It seems paradoxical that whilst Evolution is one of the most widely known scientific principles it is also one of the most widely misunderstood.

The most widely held misunderstanding is that Evolution is directed towards the constant improvement and development of species when the truth of it is that Evolution is purely concerned with random changes (mutations) of individuals within species and furthermore, it is only when such a random change in an individual confers an advantage over other individuals.

Neither can the advantages, of what may be termed evolutionary development, be considered to be absolute, for what may be an advantage in one environment might be a disadvantage in a different environment.  For example, an organism that has evolved to thrive by exploiting the environmental conditions in hot wet places, such as an equatorial rain forest, will not thrive in arctic conditions.  Neither may evolved defenses against the predators of one region be effective against the predators of another region.

In fact, far from Evolution resulting in what may be thought of as highly developed, or even 'perfect' organisms, for the most part it more usually produces organisms that are merely adequate.  Whilst it may seem that, when looking at the life around us, Evolution has done a "fantastic" job, most life is extremely fragile, and far from being perfect, everything is a compromise.

Let's just look at one example of how Evolution has produced something that's both advanced but is also flawed, and also subjective: the spine.

While we may say that encasing the spinal column in bone and then making the spine articulated so that it is very flexible is a Good Thing, the fact that if it does get broken, then anything below that break becomes useless too.  Now this could be avoided if we had two spines instead, or even better, three.  But then, of course, our ideas of perfection in beauty and attractiveness in the opposite sex would be completely different.

With respect to childbirth, if it were not for our highly developed medical services (for those that can afford them) then it is likely, but not certain, that the rate of childbirth problems would drop to the point where it became statistically irrelevant (because you have to draw a limit where a death during childbirth is due just to the childbirth process, or whether it is due to a non-childbirth condition that would result in death anyway).  And the reason it would only be likely is that it is possible that all further mutations in the species had relatively negative primary or secondary effects.  It is, however, more likely that amongst all of the negative mutations there will eventually be one that does confer an advantage.

[Mike Collins]

"imatfaal" says

"If the chances of breach birth or other complications have little to do with the mother's genotype but are in fact environmental or just bad luck, then there are no genes that can be "selected" through increased survival of progeny."

But I would have expected that a mother's ability to bear children *would* be affected by her genes.  If we select just one of the things that ca influence childbirth - the pelvis - surely, genes control whether a woman has a wide or narrow pelvis?  After all, we are all born different - some are better euipped to pass on their genes, and some are more poorly equipped.  Those in the latter case are less likely do do so, and without medical intervention, any woman who dies in childbirth due to that cause will clearly not pass on the genes that gave her a narrow pelvis.

My sister has two daughters, both born by cesarean section,and she was told that without it, her genes most certainly would not have been passed on.

If you were re-designing the human being, to go forth and be a more successful species, I'm sure you would incorporate ideas that would prevent such things as breach birth.  As long as you can conceive (no pun) of a design that would prevent it, then you must accept that a design is possible.  I don't know anything about gynecology, but I'll bet that some women are less prone than others to allowing a baby to present itself bottom first.  And as everything about us seems to be dependent on genes, it is amazing to me that such an obvious way of putting a stop to a genetic line has not done so.

If the mother's genotype does influence the ease of birth one could be very hard-hearted and speculate that children who could survive a "difficult birth" would be the very strongest babies - therefore mothers with a predisposition to trouble in childbirth would have fewer surviving children but they would be very strong and perhaps more likely to successfully breed.

I have heard of babies being brain-damaged by a difficult birth - an effect that certainly does not make them more attractive as potential mates.

[Mike Collins]

I just spend more than an hour writing a further reply, explaining what I don't understand, with much reference around the web, and consideration of other people's viewpoints - to be told "Your session has timed out.  Please re-enter your post" - but I can't - it's GONE!

Sheesh!

[Mike Collins]

The most widely held misunderstanding is that Evolution is directed towards the constant improvement and development of species when the truth of it is that Evolution is purely concerned with random changes (mutations) of individuals within species and furthermore, it is only when such a random change in an individual confers an advantage over other individuals.

But surely, an inability to survive childbirth gives any genetic line a very distinct disadvantage, compared with those that survive, even quite poorly.

Eyebrows are not vital to survival, yet partly due to their practical application to diverting sweat from the eyes, and partly due to our predilection to their aesthetic attractiveness, they have evolved to what we have now - it is rare to see eyebrows that are exaggerated well ouside of the norms - even though such an exaggeration would not be life-threatening - yet life-threatening difficulties in natural childbirth are not uncommon.  My sister has two daughters and a grandson, but her doctors left her in no doubt that without the assistance of a cesarean section, none of them would be carrying the gene today that gave her too small a pelvis.

I can see that really unattractive eyebrows might disfavour the genetic line, and even if it didn't die out, it would survive less successfully than lines of really attractive people.  But death in childbirth stops the continuance of those genes point blank.  They don't diminish over a time.  They end there.

what may be an advantage in one environment might be a disadvantage in a different environment.

... but death in childbirth is a disadvantage in any environment.

I accept, of course, that things are what they are, but I haven't had that "Oh - of course!" moment yet.  There's clearly something I just don't get.

[LeeE]

But surely, an inability to survive childbirth gives any genetic line a very distinct disadvantage...

That is something of an understatement, as you clarify later...

But death in childbirth stops the continuance of those genes point blank.

But I'm not sure what point, that is at odds with what I said, you're trying to make.

Although with...

Eyebrows are not vital to survival, yet partly due to their practical application to diverting sweat from the eyes, and partly due to our predilection to their aesthetic attractiveness, they have evolved to what we have now

you still seem to be setting the horse before the cart.  Our eyebrows haven't evolved in response to a need i.e. because there was a need to become more effective at diverting sweat or because there was a need to become more attractive, but rather that a random mutation occurred, which just happened to make the eyebrows of the mutated individual more effective at diverting sweat, or more attractive to others.  The eyebrows didn't evolve due to a reason or need, but once the mutation did occur it conveyed an advantage and because of that advantage the mutation was subsequently preserved.

Evolution doesn't occur due to pressure, for there is no guarantee that the 'right' mutation will occur to meet and counter any given environmental pressure.  Were it to be so then there would have been many less extinctions than there have been, for the pressures that resulted in those extinctions should have spurred the mutations that would have permitted the survival of the extinct species.  As it happened though, the particular mutations that might have saved the extinct species just didn't happen, because the nature of the mutations are random, so the species died out and became extinct instead.

Of course, this isn't to say that environmental pressures play no part in evolution, but the part they play only becomes a factor after a mutation that conveys an advantage in the context of those environmental pressures has occurred.

It's not Environmental Pressure -> Mutation = Survival

but Mutation + Environmental Pressure = Survival

[wolfekeeper]

Child birth is a trade-off between delivering a large head and being able to run/walk.

Having wide hips helps with child birth, but is a disadvantage when you want to run (most athletes have narrow hips).

Having a large head is advantageous because humans have big brains, and big brains have been a successful trait.

So... it may actually be that childbirth is optimum right now, relatively few women/children die during childbirth (in evolutionary terms a couple of percent isn't necessarily enough for evolution to bother) and there presumably is advantages from the increased intelligence.

[JnA]

It has also been speculated that babies who are birthed through the birthing canal are stronger and healthier than c-section babies. I recall that it has to do with the big squeeze, helping the lungs..   sometimes a 'struggle' is exactly the right evolutionary advantage.
Evolution has to be looked at on a species level.. not an individual level. On an individual level species advantages can seem cruel and inconsistent. 

[wolfekeeper]

Actually, mostly, evolution is looked at at the gene level. The problem is that there are competing genes, narrow hips/wide hips big head/small head etc. etc. and each of them can be a win, depending on what other genes there are active in the embryo/mother.