At the LessWrong European Community Weekend 2018, I gave a talk explaining the intuition behind non-adaptive theories of the evolution of ageing. This blog post and its followup are adapted from that presentation.

When people find out that I did my PhD in the biology of ageing, they tend to ask one of two questions. First, they ask what they can do to live longer. Second, they ask why people age in the first place. My answer to the first question is unfortunately fairly boring at present -- don't smoke, eat well, get enough exercise, get enough sleep, et cetera -- but when it comes to the second I think I have more of interest to say. So let's dive into the important and fractious question of why we age.

What is ageing?

It is a curious thing that there is no word in the English language that stands for the mere increase of years; that is, for ageing without its connotations of increasing deterioration and decay.
—Peter Medawar, "An Unsolved Problem in Biology"

When people talk about "ageing", there are broadly speaking three different things they might mean^[1]. Firstly, there is the simple process of getting older -- of the amount of time since you were born inexorably increasing. Let's call this process "temporal ageing". Ageing in this way has a lot of benefits: more memories, more experience, and with luck more self-knowledge and more wisdom.

Unfortunately, the benefits conferred by temporal ageing are currently inextricably tied to the physical changes denoted by the second meaning of "ageing": a generalised physiological deterioration, characterised by a wide range of unfortunate symptoms affecting almost every system of the body. As a result of this second kind of ageing, we become slower, more fragile, more prone to disease, and generally more likely to experience impaired health and wellbeing as we get older, eventually leading to death. As we as a civilisation have gradually eliminated more and more extrinsic forms of suffering and death, the depredations of ageing have gradually become the primary cause of ill health and death in developed countries by an overwhelming margin. This is the kind of ageing people mean when they worry about getting cancer or dementia, buy "anti-ageing" skin cream, or invest in real anti-ageing research; it's the province of doctors, physiologists, and molecular biologists. Let's call it "physiological ageing".

Finally, th

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Sarah Collins

Sarah Collins