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<Martin A. Nowak> works on mathematical models of <evolution>, including the evolution of <cooperation>. His 2006 synthesis separated five mechanisms: <kin selection>, <direct reciprocity>, <indirect reciprocity>, <network reciprocity> and <group selection>. Each mechanism changes which interactions contribute to an individual's evolutionary success.<Five rules for the evolution of cooperation by Martin A. Nowak>[Abstract and mechanism-specific sections]{ref}

A simple <direct reciprocity> calculation shows how repeated encounters can change incentives. Suppose cooperation costs $c$, benefits the partner by $b>c$, and an encounter continues with probability $w$. Two cooperating reciprocators obtain expected payoff $(b-c)/(1-w)$. An unconditional defector against a strategy that stops helping after a defection obtains $b$ initially and no later benefit. The first payoff exceeds the second precisely when $w>c/b$. With $b=3$, $c=1$ and $w=1/2$, these payoffs are four and three.

This calculation depends on the specified repeated-interaction model and retaliation rule. It identifies a mechanism by which cooperation can be favored, without asserting that a single inequality describes every biological system. His institutional research profile also lists mathematical work on infection and cancer.https://www.oeb.harvard.edu/people/martin-nowak[Research description]{ref}

\Image[https://www.oeb.harvard.edu/sites/g/files/omnuum6811/files/styles/hwp_4_5__320x400/public/oeb/files/martin_nowak.jpg?itok=tACXeyQo]
{title=Martin A. Nowak, portrait identified by Harvard University}
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Portrait source: https://www.oeb.harvard.edu/people/martin-nowak .


 Martin A. Nowak (source code)