[GRG] NewAbs: More on the Evolution of Menopause

To Members and Friends of the Los Angeles Gerontology
Research Group:  More on
the evolution of menopause… — Steve Coles

“Putting the Men in
Menopause:

Can Mating Behavior Explain the
Evolution of Menopause in Humans?”by
Jon Stone
© CLAIRE ARTMAN/CORBIS
September 1, 2013; (The Scientist) — Menopause puzzles
evolutionary biologists. After all, avoiding mortality and ensuring
reproduction are the two most fundamental tenets of Darwinian natural
selection. Theoretically, species should evolve so that individuals live
only as long as they reproduce. So why did humans evolve a long adulthood
with females becoming nonreproductive about halfway through?Menopause,
quantified as the proportion of expected time in adulthood during which
an individual is nonreproductive, is remarkable in humans relative to
most other species in the animal kingdom. Among the many hypotheses that
have been proposed to explain the origin of menopause, two have garnered
substantial attention. According to the most popular explanation, known
as the Grandmother Hypothesis, older females increase their
genetic contribution to future generations by assisting in rearing their
grandchildren rather than continuing to bear and rear children of their
own. This scenario requires that older females become grandmothers twice
for each forgone additional opportunity to become mothers themselves, as
grandmothers typically share half as many genes with their grandchildren
as with their own children. The other leading explanation, called the
lifespan artifact hypothesis, implies that menopause is the by-product of
an increase in life expectancy. This scenario assumes that over the
history of our species, only males have extended fertility coupled with
increased longevity, possibly to father more children. Research into
these hypotheses has yielded equivocal results.
Dissatisfied with either explanation on its own, my colleagues Richard
Morton and Rama Singh and I recently published a novel hypothesis,
formulated on the basis of a thought experiment involving the effects of
a change in mating behavior
(
PLOS Comp Bio, 9:e1003092, 2013). Imagine a population in
which individuals lived long lives, throughout which they were able to
reproduce. In this scenario, any gender-specific mutations that
diminished fertility late in life would be selected against. If a mating
behavior change were introduced, however, such that females reproduced
only at a young age, natural selection would become relaxed in older
females. Consequently, effects from the female-specific mutations that
diminished fertility late in life would become effectively neutral, and
such mutations would accumulate over time. Eventually, female fertility
would decline with age; in other words, menopause would evolve.Because
older males would continue to reproduce late in life, natural selection
would continue to operate negatively on corresponding male-specific
mutations that diminished fertility late in life, as well as on any
non-gender-specific mutations that diminished survival late in life;
neither, therefore, would become effectively neutral nor accumulate in
males.Theoretically, species should evolve so that individuals
live only as long as they reproduce. So why did humans evolve a long
adulthood with females becoming nonreproductive about halfway
through?  To formalize this new hypothesis, we developed a
computational model and assessed, through computer simulation, the idea
that menopause originated as a consequence of a change in mating
behavior. Data that mimic real-world survivorship and fertility were
generated by evolving virtual populations. From a behavioral perspective,
the mating-behavior change that was introduced in the computer
simulations could be viewed as a male preference for young females or as
young females outcompeting older females for access to males. Ultimately,
the model showed that, when only young females mate, menopause arises.
Intriguingly, the reverse scenario also holds true: if only young
males mate then male menopause will arise -­ an observation that
could be  tested by investigating whether menopausal male fruit
flies could be evolved in a laboratory setting.This
“change in mating behavior” explanation is a nonadaptive hypothesis for
the origin of menopause: it requires neither inclusive fitness benefits
through which older, nonreproducing women assist younger women in their
reproductive efforts (i.e., the grandmother hypothesis), nor an
assumption that fertility always diminished at a typical, prescribed age
in older women and remained so despite increased survival through
extended reproduction by males (i.e., the lifespan artifact hypothesis),
possibly accompanied by increased male fitness. A change in mating
behavior allows alleles that diminish fertility to accumulate in an
effectively neutral manner. Similar genetic mechanisms are theorized as
the ultimate causes for other conditions, including senescence.Of course,
the different hypotheses for why menopause evolved are not mutually
exclusive, but the neutral, change-in-mating-behavior hypothesis, itself,
provides a sufficient, mechanistic explanation for how menopause could
arise. Why older women historically stopped reproducing and the precise
temporal relationship between the origin of grandmothers and extended
life spans in human populations are puzzles that remain unsolved, but
that will now

invite much speculation.From a
practical perspective, real-world counterparts for deleterious mutations
that arise during the computer simulation, if such mutations do exist,
might have effects on traits other than fertility. So, if corresponding
candidate mutant alleles responsible for the onset of menopause were
suspected to reside in human genomes, then the novel hypothesis may be
received as a challenge to researchers to identify and study those genes,
ultimately promoting research in human health.

Advertisements

About Johnny Adams

My full-time commitment is to slow and ultimately reverse age related functional decline to increase healthy years of life. I’ve been active in this area since the 1970s, steadily building skills and accomplishments. I have a good basic understanding of the science of aging, and have many skills that complement those of scientists so they can focus on science to advance our shared mission. Broad experience Top skills: administration, management, information technology (data and programming), communications, writing, marketing, market research and analysis, public speaking, forging ethical win-win outcomes among stakeholders (i.e. high level "selling"). Knowledge in grant writing, fundraising, finance. Like most skilled professionals, I’m best described as a guy who defines an end point, then figures out how to get there. I enjoy the conception, design, execution and successful completion of a grand plan. Executive Director Gerontology Research Group (GRG). Manages Email discussion forum, web site, meetings and oversees supercentenarian (oldest humans, 110+ years) research. CEO / Executive Director Carl I. Bourhenne Medical Research Foundation (Aging Intervention Foundation), an IRS approved 501(c)(3) nonprofit. http://www.AgingIntervention.org Early contributor to Supercentenarian Research Foundation. Co-Founder Geroscience Healthspan Forum. Active contributor to numerous initiatives to increase healthy years of life. Co-authored book on conventional, practical methods available today to slow the processes of aging – nutrition, exercise, behavior modification and motivation, stress reduction, proper supplementation, damage caused by improper programs, risk reduction and others. Fundamental understanding of, and experience in the genomics of longevity (internship analyzing and curating longevity gene papers). Biological and technical includes information technology, software development and computer programming, bioinformatics and protein informatics, online education, training programs, regulatory, clinical trials software, medical devices (CAT scanners and related), hospital electrical equipment testing program. Interpersonal skills – good communication, honest, well liked, works well in teams or alone. Real world experience collaborating in interdisciplinary teams in fast paced organizations. Uses technology to advance our shared mission. Education: MBA 1985 University of Southern California -- Deans List, Albert Quon Community Service Award (for volunteering with the American Longevity Association and helping an elderly lady every other week), George S. May Scholarship, CA State Fellowship. BA psychology, psychobiology emphasis 1983 California State University Fullerton Physiological courses as well as core courses (developmental, abnormal etc). UCLA Psychobiology 1978, one brief but fast moving and fulfilling quarter. Main interest was the electrochemical basis of consciousness. Also seminars at the NeuroPsychiatric Institute. Other: Ongoing conferences, meetings and continuing education. Aging, computer software and information technology. Some molecular biology, biotech, bio and protein informatics, computer aided drug design, clinical medical devices, electronics, HIPAA, fundraising through the Assoc. of Fundraising Professionals. Previous careers include: Marketing Increasing skill set and successes in virtually all phases, with valuable experience in locating people and companies with the greatest need and interest in a product or service, and sitting across the table with decision makers and working out agreements favorable to all. Information Technology: Management, data analysis and programming in commercial and clinical trials systems, and bioinformatics and protein informatics. As IT Director at Newport Beach, CA based technology organization Success Family of Continuing Education Companies, provided online software solutions for insurance and financial professionals in small to Fortune 500 size companies. We were successful with lean team organization (the slower moving competition was unable to create similar software systems). Medical devices: At Omnimedical in Paramount CA developed and managed quality assurance dept. and training depts. for engineers, physicians and technicians. Designed hospital equipment testing program for hospital services division. In my early 20’s I was a musician, and studied psychology and music. Interned with the intention of becoming a music therapist. These experiences helped develop valuable skills used today to advance our shared mission of creating aging solutions.
This entry was posted in Uncategorized. Bookmark the permalink.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s