Cellular Senescence: As cells undergo stress, they occasionally become "senescent," both losing their ability to divide and, simultaneously, becoming resistant to death. These "zombie cells" can't be removed from the body. They build up over time, infect neighboring cells, and ultimately create a zombie apocalypse of inflammatory debilitation.

DELETING THE ZOMBIE SENESCENT CELLS IN OLD TISSUES. Thanks to the primordial survival circuit we've inherited from our ancestors, our cells eventually lose their identities and cease to divide, in some cases sitting in our tissues for decades. Zombie cells secrete factors that accelerate cancer, inflammation, and help turn other cells into zombies. Senescent cells are hard to reverse aging in, so the best thing to do is to kill them off. Drugs called senolytics are in development to do just that, and they could rapidly rejuvenate us.

Small numbers of senescent cells can cause widespread havoc. Even though they stop dividing, they continue to release tiny proteins called cytokines that cause inflammation and attract immune cells called macrophages that then attack the tissue. Being chronically inflamed is unhealthy: just ask someone with multiple sclerosis, inflammatory bowel disease, or psoriasis. All these diseases are associated with excess cytokine proteins.

Known as senolytic therapies, these drugs destroy the inflammation-producing zombie cells believed to be one of the causes of aging.

Stem Cell Exhaustion: As we age, our supply of stem cells plummets, in certain cases by a ten thousandfold decline. Worse, the ones we do manage to hang on to become far less active. This means that the body's internal tissue and organ repair system loses its ability to do its job.

Stem Cell Exhaustion: As we age, our supply of stem cells plummets, in certain cases by a ten thousandfold decline. Worse, the ones we do manage to hang on to become far less active. This means that the body’s internal tissue and organ repair system loses its ability to do its job.

When our cells sense sustained danger, they divert resources to defense and alarm pathways instead of normal functions that generate sustainable health. Given this, no matter how pristine your dietary intake is, how much you’re moving, how much sunlight you’re getting, or how many hours of quality sleep you’re getting, if the cells are bathed in a stew of stress created by the way psychology translates to biochemistry (via hormones, neurotransmitters, inflammatory cytokines, and neurologic signals), all the other healthy choices will fall

Without apoptosis, life would not be possible. ...when cells lose their ability to die, they run rampant, assuming that life-threatening form we call cancer. ...The process of apoptosis by which life and development are governed is profoundly communal. ...Cells ...need to be "encouraged" to live.

(5) In environments where extrinsically induced mortality is frequent, selection against senescence is comparatively weak as few individuals live long enough to suffer a substantial phenotypic decline. The weaker the selection against senescence, the further the optimal balance point moves toward shorter telomeres and increased tumor suppression. The stronger the selection against senescence, the farther the optimal balance point moves toward longer telomeres, increasing the capacity for tissue repair, slowing senescence and elevating tumor risks.

A dying organism is often observed to be capable of extraordinary endurance and strength. ... When any living organism is attacked, its whole function seems to aim toward reproduction.

Youth → broken DNA → genome instability → disruption of DNA packaging and gene regulation (the epigenome) → loss of cell identity → cellular senescence → disease → death.

Have you heard this one, Psycho? How do a blonde's brain cells die? [... A] blonde's brain cells die alone.

It is not the germ cell itself, but the bodily accretion or appendage, which is abandoned by life, and which accordingly, dies and decays.

Here's the important point: there are plenty of stressors that will activate longevity genes without damaging the cell, including certain types of exercise, intermittent fasting, low-protein diets, and exposure to hot and cold temperatures (I discuss this in chapter 4).