Transcript Lecture 8: Life-History Evolution

The Evolution of Aging
A GK-12 Project Presentation
Michael R. Rose
Dept. of Ecology and Evolutionary Biology
University of California, Irvine
The survival and fertility of plants and animals
usually changes with age, typically getting worse
So why do animals and plants often
fall apart with age?
Some Organisms Don’t Age
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This creosote bush has
lived for more than
10,000 years.
It grows in the Mojave
Desert of California
It started life as a small
bush, and grew
outwards in a circle.
Some species age slowly,
some very quickly
The Longest Lived Human
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Madame Jeanne
Calment lived 122
years, dying in 1997.
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She sold paintbrushes to
Vincent Van Gogh in
her home town of Arles,
France.
Of course we’re interested in aging
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Aging has
been studied
from very
different
perspectives,
including
evolutionary
biology
Facts About Human Aging
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Life expectancy now
(US): pushing 80 years
Life expectancy without
aging: 1,200 years
based on the survival
rate at age 12
Here is what aging looks like
medically
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Noncontagious
diseases hit
older people
with greater
and greater
force, killing
us off, and
making us
debilitated
Freedom from Major Diseases
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Freedom from
cardiovascular disease,
cancer, kidney disease,
etc.
At age 60 years, more
than 50% of the
population is free of
major disease
By 85 years, only about
30%
There are plenty of quack “cures”
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Ginseng,
shown on the
left, has been
prescribed as
a “cure” for
aging by
Chinese
traditional
medicine for
centuries.
Timing of Reproduction Controls the Evolution of Aging
Early Life
Later Life (post-reproduction)
Reproduction
X
Lethal gene not
passed on
Lethal gene(s)
passed on
Later Generations
Here is a case of an early acting
lethal gene
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The disease is known as
Hutchinson-Gilford’s
progeria
It starts to affect young
children (3-5 years of age)
Kills by 20 years of age
Due to a single bad copy of
the gene at the Lamin A
locus
This is a very rare disease,
with just dozens of progeric
children alive at one time
Here is a case of a late acting lethal
gene
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The disease is known as
Huntington’s Disease
It starts to affect the brain of
middle-aged adults over 30
years of age
Takes years to kill victims,
breaking down coordination,
IQ, personality, as it goes
Due to a single bad copy of
gene at the Huntington locus
This is a common genetic
disease, with many
thousands of victims alive at
one time
Timing of Reproduction Controls the Evolution of Aging
Early Life
Later Life (post-reproduction)
Reproduction
X
Lethal gene not
passed on
Lethal gene(s)
passed on
Later Generations
Why some organisms don’t age
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Aging
should not
evolve in
fissile
organisms
because
natural
selection
stays
strong; it
has to
Evolution of Aging is predicted for
all strictly non-fissile organisms
Postponing Reproduction forces early
acting deleterious genes out
Reproduction
Deleterious
Mutations
= Longer, more robust lifespan
Changing the force of natural selection can
produce rapid evolution of aging patterns
Here’s Where Young Flies Live
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We rear our flies in
vials with controlled
densities
The food goes in the
bottom of the vial and
the top is plugged so
they can’t fly out
Our Fruit Fly Old Age Home
How we control reproduction
larval rearing
Day 14
Egg collection
Day 14
Day 70
Egg collection
Later egg collection
Postponing Reproduction forces early
acting deleterious genes out
Reproduction
Deleterious
Mutations
= Longer, more robust lifespan
Changing the force of natural selection can force the
evolution of aging patterns: data after 80 long generations
Meaning of the Experimental Result
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This result showed that the idea of aging being
timed by the force of natural selection is the
best available theory as to the cause of aging
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Also showed that adult life is characterized at
first by a weakening force of natural selection
But can we stop our own aging?
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Does
evolution
offer us any
hope for
changing our
own pattern
of aging?
What if we were to delay human
reproduction?
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It would take many generations – now more
than 700 fruit fly generations have gone by in
my delayed-breeding experiments
In human terms, that would be around 700 x
25 years: 17,500 years
So even if we set about confining female
reproduction to women over 40 and male
reproduction to over 60, we would have to
wait tens of thousands of years for such a big
improvement in human aging by evolution
Proposed Methuselah Mouse:
Delayed breeding to let evolution tell
us how to slow mammalian aging
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Let Evolution by
Natural Selection
supply us with the
answer to the question
of how to build a
longer-lived mammal
And then reverseengineer its answer to
develop anti-aging
therapies for genetically
unaltered humans
Conclusions
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We know now why aging happens: the
declining force of natural selection with age
And we know that we can experimentally
manipulate both the rate and the end of aging
There are ways in which could postpone
human aging, and I have described one of
these approaches
This is not a “should” argument, just a “could”