Why Do Older Mothers Produce Less Robust Offspring?

It is well understood that an older maternal age at birth results in offspring that are less robust, meaning a shorter life expectancy, lesser degrees of reproductive success, and so forth. The question asked here is how this effect can have persisted in the face of evolutionary competition: why do we not see organisms that can produce equally viable offspring at later ages? This is one slice of the broader evolutionary question of why aging happens at all, and why it is near universal in the animal kingdom. The present consensus on the evolution of aging, insofar as there is a consensus, is the antagonistic pleiotropy hypothesis. Selection pressure is stronger in younger individuals, leading to mechanisms and biological systems that are beneficial in youth but harmful in later life. This, of course, is entirely adequate to explain the observation that older mothers have less robust offspring; it is one narrow manifestation of aging.

In many species, survival and reproduction decrease with advancing age, a process known as "senescence." The evolution of senescence is a long-standing problem in life history theory and has been studied extensively in the laboratory, with mathematical models, and in the field. The evolution of senescence is explained by the age-specific patterns of the strength of selection, measured as selection gradients. Age-specific selection gradients on mortality and fertility decrease with age. Thus, traits expressed early in life have a larger impact on fitness than those expressed later. As a result, selection will favor traits that lead to negative effects on survival and fertility at older ages if there are even small beneficial effects in youth.

"Maternal effect senescence" is defined as the reduced success or quality of offspring with advancing age of the mother. Advanced maternal age has known negative effects on offspring health, lifespan, and fertility in humans and other species. In many taxa, including rotifers, Daphnia, Drosophila, and soil mites, offspring from older mothers have shorter lives, lower reproductive success, or both. Field studies of several species of mammals and birds have shown that offspring with older parents exhibit lower survival and recruitment and increased rates of senescence. In humans, advanced maternal age is associated with reduced lifespan and health. In Caenorhabditis elegans, Daphnia, and rotifers, advanced maternal age also increases offspring size, alters development time, and increases variability in gene expression.

Maternal effect senescence remains an interesting problem in life history evolution. Producing high-quality offspring that live long and prosper should, all else being equal, provide a selective advantage. Thus, the reduced quality of the offspring of old mothers demands an evolutionary explanation. We developed a more general multistate model that can incorporate maternal age effects on age-specific survival and fertility throughout the life cycle and with which we can easily calculate selection gradients on any of those rates as joint functions of age and maternal age.

We fit these models to data from individual-based culture experiments on the aquatic invertebrate, Brachionus manjavacas (Rotifera). By comparing models with and without maternal effects, we found that maternal effect senescence significantly reduces fitness for B. manjavacas and that this decrease arises primarily through reduced fertility, particularly at maternal ages corresponding to peak reproductive output. We also used the models to estimate selection gradients, which measure the strength of selection, in both high growth rate (laboratory) and two simulated low growth rate environments. In all environments, selection gradients on survival and fertility decrease with increasing age. They also decrease with increasing maternal age for late maternal ages, implying that maternal effect senescence can evolve through the same process as in the theory of the evolution of age-related senescence.

Link: https://doi.org/10.1073/pnas.1919988117


The same thing happens with older fathers.

Posted by: mcmp at July 9th, 2020 10:44 AM

This is a real concern considering people are having children later.

Posted by: J at July 9th, 2020 12:13 PM

My favorite pet theory is that this might be an adaptation to increase species fitness. The longer an individual lives, the more chances were there to reproduce and spread the more or less stable genetic material. Since there was enough time to procreate with low mutation rate at younger age, now at the older the mutation rate is increased which reduces the overall fitness but increases the variability of the species and allows for addressing more edge conditions and niches. All this could be a side effect of the antagonistic pleiotropy and yet bring the benefits of boosted mutation rates...

@mcmp the pregnancy is very critical, so the effects might much stronger for an older mother than father. But yes, you are right.

by having children later the people are self selecting to breed longer lifespans . It was the original experiments with the flies (removing the children until older age) that breed them to live much longer. So in the end, if we never have any anit-aging improvements and we continue with similar society in 10 to 20 generations people will be living longer and aging slower.

Posted by: cuberat at July 9th, 2020 2:03 PM

Hey there! Just a 2 cents.

That's solid points there, all. I believe that sexual reproduction is (evidently) much more costly for women, as such there is selection pressure as said to birth while still fertile (in young age), it is mainly because of the resource cost that it would Have to happen earlier with women; the body will invest a substantial amount of (sexual) resources for the gestation/pregnancy period; these resources will taken Away from the subject (the mother, herself), thus, it is self-less act, whereby she dispenses her resources (somatic ones for tissue repair) towards pregnancy...it is important to understand that there Is a 'Balance' between the 2; the body diverts whatever resources to whatever end; in the case of pregnancy; the reproduction cost will be at the (cost) of tissue repair/longevity/self (herself). If you spend those resources for reproduction, this are Less available for her(self). This Will have an impact on (her) longevity; most centenarian women had no children; only few had 1 or 2 child...very Very few had a Gigantic 15 kids...family...and lived to be centanarian; this explains it; reproduction is costly - it accelerates telomere loss, it creates mitochondrial lesions (high gravidity women/women that make Lots of kids - are self-sacrificing themselves/their own bosy somatic-tissue maintenance/DNA repair resources - for their Own longevity; the selfless act is having all these children, and it taking a Hit on the mother).

Now, a young woman has More resource Right Now in her young age...then an old woman that Needs whatever little left resources - for her own longevity to continue; thus, at older age, its very strenuous and 'limiting' because there is Less resources now (at old age) for a woman.
The children that will be born from an older mother may suffer premature diseases because the mother could Only give what she could at her older age (in terms of resources, for her child(ren)).
Thus, in old age, resources are now 100% allocated to longevity because evolutionary wise...(as with the antagonist pleiotropy) there will be deleterious diseases of aging happening, but as we saw in studies there is SLowing of metabolism at the person ages..thus the body Compensates for the early 'youth fast metabolism' (aroudn puberty where we lose up 5kb of telomere in less than 5 years...that's the tell you how fast we grow and how fast we would die If we had puberty for life...i.e. it would not be a long life..because we would burn our telomeres so fast..like mouse),
Thankfuilly, after puberty every slows down to near a 'stall'...well almost...thus, the body does its best to 'age gracefully and slowly' for the remainder of the decades up to 100 years old...because Normally speaking if that did not hapepn we would die at 20-25 years old because we would erode telomeres DNA so quickly (beause of ultra-fast growth/metabolism in teenager age).

The way I see it we 'coast', we 'glide', or said (badly but nicelty), we 'age gracefully' after puberty until we hit a 100. We run out of fuel after 18...so, after, we glide/coast it....until crash (at 100 years old). A long slope/tail, gliding it 'to make it to a 100'....and that requires the body slowing.

An older woman, less energy, slower metabolism - not much energy left...but for self/sustenance of life/dna repair/tissue repair maintenance...

not big family reproduction of 20 children...costly, in sex resources. And as shown the more children a woman has - the shorter her lifespan (detected as mitochondrial lesions (8-oxodG) proportional to the Number of gestations/pregnancies - this willa ccelerate telomere shortening rate of the mother; thus, having many kids is ultimate sacrifice of mother('s) own resources for her lifspan). Big family = costly on mother lifespan.

Just to tell you how Limited and how the female gender/women are Under The Evolution Selection Pressure...they only carry a 'set number' of eggs...women that are more fertile have more eggs/ovules and bigger ovaries. Thus women have to 'Ration' the resources for sexual reproduciton3pregnancy - And - Have Some Left for Themselves and live a long life...to reach grand-ma age.

With fathers it's more ambiguous and muddied, an older father can give defects to the child..and compromise his child(ren) by defective DNA in his sperm (spermatozoid cells)/his testicules (sertolli/leydig cells responsable for sperm formation) having damage...likewise for his prostate responsable for the presemen/inal fluid that mixes with the spermatazoid ejac fraction to form, the sperm. Semen quality is Crucial for the whole pregnancy to work/the child to be born correctly, things going as pallened; with that said..older sperm from age fathers is much more ambiguous than women's reproduction organs....

Aged sperm (from an elder father) has Evolution advantage (if we remove the age as causing defects) which is that Telomerase in the leydig/sertolli/stem/germ cells of gonad/testicules Increase the Length of the telomers of the spermatozoid cells; thus, older men have we call telomere elongation With Age; or also called 'sperm maturation' which is that the sperm is 'stronger' and 'more capable' of fertilizing a woman because taller telomeres in spermatozoids...
A yougn man..has shorter sperm telomeres - but offsets that lacking - by being young, thus Less DNA defects/mutations possible in the sperm; but not necessarily 'yougner sperm'...taller telomers means younger sperm;; as such, and Older Man Had Younger sperm than a younger man (because telomerase processivity (over teh years) in testicules). So it'S like a 'inverted balance'...evolution foudn a awy to make men 'not useless/disposable' with age..while a woman is crucial for only Her births/gives birth to humanity...I mean a man can't birth...but he gives the sperm..which is requires/essential..But..in the future..it may not be so anymore, if sperm cells can be 'made in the lab'...and likewise...a woman many not be indispensable anymore (like a man); a baby could be made 'in lab'...very possible in the fture by making in lab sperm and in lab eggs/ovules...you just need incubation/a in lab uterus to simulate the 9 months period and all the fluids/amnytoic liquid and body resources (DNA, maternal fluid/vitamin/minerals/fake umbellical cord).... of course that is the 'ethics' domain, many people would refute that and says it'S morally not ok/against god (like Eugenics) and women should always 'humanely' make birth and well, men, should (?) always have the sperm 'ready'..not a lab...but it's going to happen in the future; Both Genders will be 'not needed' anymore for birthing a child,. Only a lab full of cells 'Recycled/resourced/restarted/cultured' infinitely. This is very akin to the cloning and 'Dolly Sheep' clone, making 'twins' in labs...it will happen, for humans at some point. Ethics/morals/religious people will block that of course.

Children born from older fathers (like me, and my twin sister, we are twins; she girl am boy; my dad has us late (in his 30s); and my grand-ma had my dad late at 41 and a daugher at 39 (my father's sister/my aunt)...yet against all odds my paternal grand-ma (who birther my dad and my aunt) lived 92..thus, it does not mean that a woman ca't live a long life because she had kids at 45...no but it clearly will limit things because there Was a cost to those pregnancies (both in longevity resources being retranslocated towards sexual reproduction and Also, mitochondrial lesions..though she had only two pregnancies, it's when you ahve 4 or more pregnancies that you start to see lots of lesions)...it is possible that my grand-ma could have lived to 112 instead of 92..had she no kids...

But then, I would not exist (thankfully forever, for my grand ma having my dad).

To end, older fathers 'give their tall(er) telomeres' from their older sperm and studies showed that children born from older fathers could be one of two things; Struck/die precipitously/have tons of health problems when they grow up OR be Youthfull and just younger than the rest of the population (and this is measurable in their Extra-telomere chunk, they obtained from older father'S sperm telomeres).

Just a 2c.

Posted by: CANanonymity at July 9th, 2020 9:17 PM


I subscribe too to the view that after some age we slowly degrade physically. I think that it is not 18 but rather 25 years were the body starts to age. ( Though they're are some organs and tissues that age since birth, or some since teens , like teeth) There's some inertia till mid 30s which lets professional athletes reach their peak after 30. And after that we expire, run out of warranty and 40 is the old age. Just a couple of hundred years ago the people were living in such brutal conditions that after 40 -something the death rates were accelerated and the physical condition where quite sad. If you are lucky and age gracefully you can keep on going till 100 y. old . That was happening in the ancient times too. However, the majority of the population had to play procreate and die game. I don't believe that old men have better semen. Rather they are wiser and have proven that can live up to that age, and probably can (could) provide better for the family.

Posted by: Cuberat at July 9th, 2020 10:33 PM

The same thing happens with older fathers

Do you have any evidence for that?

Posted by: anon at July 9th, 2020 11:31 PM

@ anon, there's plenty of evidence; google it.

Posted by: mcmp at July 10th, 2020 1:25 PM

Hi Cuberat! Thanks for that.

That's a solid take. In all cases, just a 2 cents, I believe we live much longer lives now; but, as you said, in the ancient past people also lived very long lifespan (some people did reach 90-100s in antiquity and way before; thus centenarians are not new stuff; just (ancient history) rediscovered today as we see the (extremely) valid point/reason of curing aging and living much longer lives healthy).

Thus to Reason text'S question: Why Do Older Mothers Produce Less Robust Offsprings? It's the age/damage accumulated most likely the largest explanation (such mitochondrial lesions each new pregnancy - not helping), the (more and more) limited resources with advancing age in a woman; that needs to preserve their (more than ever) limited/dwindling resources towards their own lifespan/DNA repair. As such, less left for reproduction and less & less can be given to the child(ren) she births as she advances in age; and, doubly as such, her child(ren) may suffer diseases/age acceleration growing up. I mean a mother may make children at 55 before menopause very soon...but this will be taxing as her limited lifespan resources will be diverted to the reproduction; taking them away from their original purpose (self maintenance/longevity). Compromised DNA from older mothers and older fathers can compromise the child's life by being birthed this late in the parents lifespan. Albeit, fathers it's more ambiguous because telomerase works in testicules (it also works in ovaries...but sperm, you never run out of it; it is recreated - thanks to enzymatic-testicular telomerase; otherwise we would run of sperm too; and would have a 'set number' of spermatozoid capacity just like women's limited umber of ovules). Studies showed that the very start/birth period of child(ren) dictates a, lot, about the future/length of the lifespan of the child, later. Thus, this early fetal period of 'consolidating mother resources/assembling the building blocks/DNA foundations' (in pregnancy/womb) to birth child in substantially determinant of what happens later on the child' life.

Just a 2 cents.

Posted by: CANanonymity at July 10th, 2020 3:26 PM
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