They're not too healthy, however they don't really live as long, or else they will have fewer offspring themselves. A long standing mystery is why development would retain this Hormone impact in a great number of species, since these late-born offspring tend to be less fit to survive and replicate.

They confirmed that this effect of older maternal age, called esophageal effect senescence, does reduce evolutionary fitness of the offspring in all environments, chiefly through diminished fertility throughout their peak reproductive period. In addition they imply a molecular mechanism for why this might occur.

To address this, Hernández and collaborators assembled mathematical models to calculate, for the first time, the strength of natural selection stress on the fertility and survival of offspring inhabitants as part of this age in these mothers. They found this pressure, called the choice gradient, decreases with maternal age.

<span style="color: #ff6600;"><a style="color: #ff6600;" href="https://www.pnas.org/content/early/2020/06/26/1919988117">"Since the selection anxiety decreases since the mothers era, it may well not be strong enough to clear away these less-fit [offspring] from the people," Hernandez says.</a></span>

<span style="color: #ff6600;"><a style="color: #ff6600;" href="https://www.pnas.org/content/early/2020/06/26/1919988117">"Due to this, Hormone impact senescence will last and continue to evolve in the people, though it contributes to decreased fitnesscenter," Gribble adds. They do not yet fully understand the genetic mechanisms that cause off spring caliber to diminish in maternal age.</a></span>

The models which the team developed might be applied to a wide range of species to rate the physical fitness consequences of maternal effect senescence. "As long as you have experimental data, as we did, on life span and fecundity of hens from mothers of all different ages, you can address this specific question in most organisms," Gribble states.

<strong>Source:</strong>
Marine Biological Laboratory

<strong>Journal reference:</strong>
Hernández, C.M., et al. (2020) A demographic and evolutionary analysis of maternal effect senescence. PNAS. doi.org/10.1073/pnas.1919988117.