\( % groupings of objects. \newcommand{\set}[1]{\left\{ #1 \right\}} \newcommand{\seq}[1]{\left(#1\right)} \newcommand{\ang}[1]{\langle#1\rangle} \newcommand{\tuple}[1]{\left(#1\right)} \newcommand{\size}[1]{\left| #1\right|} \newcommand{\comp}{\circ} % numerical shortcuts. \newcommand{\abs}[1]{\left| #1\right|} \newcommand{\floor}[1]{\left\lfloor #1 \right\rfloor} \newcommand{\ceil}[1]{\left\lceil #1 \right\rceil} % linear algebra shortcuts. \newcommand{\change}{\Delta} \newcommand{\norm}[1]{\left\| #1\right\|} \newcommand{\dprod}[1]{\langle#1\rangle} \newcommand{\linspan}[1]{\langle#1\rangle} \newcommand{\conj}[1]{\overline{#1}} \newcommand{\der}[1]{\frac{d#1}{dx}} \newcommand{\lap}{\Delta} \newcommand{\kron}{\otimes} \newcommand{\nperp}{\nvdash} \newcommand{\mat}[1]{\left[ \begin{smallmatrix}#1 \end{smallmatrix} \right]} % derivatives and limits \newcommand{\partder}[2]{\frac{\partial #1}{\partial #2}} \newcommand{\partdern}[3]{\frac{\partial^{#3 #1}}{\partial #2^{#3}}} \newcommand{\gradient}{\nabla} \newcommand{\subdifferential}{\partial} % Arrows \newcommand{\diverge}{\nearrow} \newcommand{\notto}{\nrightarrow} \newcommand{\up}{\uparrow} \newcommand{\down}{\downarrow} % gets and gives are defined! % ordering operators \newcommand{\oleq}{\preceq} \newcommand{\ogeq}{\succeq} % programming and logic operators \newcommand{\dfn}{:=} \newcommand{\assign}{:=} \newcommand{\co}{\ co\ } \newcommand{\en}{\ en\ } % logic operators \newcommand{\xor}{\oplus} \newcommand{\Land}{\bigwedge} \newcommand{\Lor}{\bigvee} \newcommand{\finish}{\Box} \newcommand{\contra}{\Rightarrow \Leftarrow} \newcommand{\iseq}{\stackrel{_?{=}}} % Set theory \newcommand{\symdiff}{\Delta} \newcommand{\setdiff}{\backslash} \newcommand{\union}{\cup} \newcommand{\inters}{\cap} \newcommand{\Union}{\bigcup} \newcommand{\Inters}{\bigcap} \newcommand{\nullSet}{\phi} % graph theory \newcommand{\nbd}{\Gamma} % Script alphabets % For reals, use \Re % greek letters \newcommand{\eps}{\epsilon} \newcommand{\del}{\delta} \newcommand{\ga}{\alpha} \newcommand{\gb}{\beta} \newcommand{\gd}{\del} \newcommand{\gp}{\pi} \newcommand{\gf}{\phi} \newcommand{\gh}{\eta} \newcommand{\gF}{\Phi} \newcommand{\gl}{\lambda} \newcommand{\gm}{\mu} \newcommand{\gn}{\nu} \newcommand{\gr}{\rho} \newcommand{\gs}{\sigma} \newcommand{\gth}{\theta} \newcommand{\gx}{\xi} \newcommand{\gw}{\omega} \newcommand{\sw}{\sigma} \newcommand{\SW}{\Sigma} \newcommand{\ew}{\lambda} \newcommand{\EW}{\Lambda} \newcommand{\Del}{\Delta} \newcommand{\gD}{\Delta} \newcommand{\gG}{\Gamma} \newcommand{\gW}{\Omega} \newcommand{\gS}{\Sigma} \newcommand{\gTh}{\Theta} % Bold english letters. \newcommand{\bA}{\mathbf{A}} \newcommand{\bB}{\mathbf{B}} \newcommand{\bC}{\mathbf{C}} \newcommand{\bD}{\mathbf{D}} \newcommand{\bE}{\mathbf{E}} \newcommand{\bF}{\mathbf{F}} \newcommand{\bG}{\mathbf{G}} \newcommand{\bH}{\mathbf{H}} \newcommand{\bI}{\mathbf{I}} \newcommand{\bJ}{\mathbf{J}} \newcommand{\bK}{\mathbf{K}} \newcommand{\bL}{\mathbf{L}} \newcommand{\bM}{\mathbf{M}} \newcommand{\bN}{\mathbf{N}} \newcommand{\bO}{\mathbf{O}} \newcommand{\bP}{\mathbf{P}} \newcommand{\bQ}{\mathbf{Q}} \newcommand{\bR}{\mathbf{R}} \newcommand{\bS}{\mathbf{S}} \newcommand{\bT}{\mathbf{T}} \newcommand{\bU}{\mathbf{U}} \newcommand{\bV}{\mathbf{V}} \newcommand{\bW}{\mathbf{W}} \newcommand{\bX}{\mathbf{X}} \newcommand{\bY}{\mathbf{Y}} \newcommand{\bZ}{\mathbf{Z}} \newcommand{\bba}{\mathbf{a}} \newcommand{\bbb}{\mathbf{b}} \newcommand{\bbc}{\mathbf{c}} \newcommand{\bbd}{\mathbf{d}} \newcommand{\bbe}{\mathbf{e}} \newcommand{\bbf}{\mathbf{f}} \newcommand{\bbg}{\mathbf{g}} \newcommand{\bbh}{\mathbf{h}} \newcommand{\bbk}{\mathbf{k}} \newcommand{\bbl}{\mathbf{l}} \newcommand{\bbm}{\mathbf{m}} \newcommand{\bbn}{\mathbf{n}} \newcommand{\bbp}{\mathbf{p}} \newcommand{\bbq}{\mathbf{q}} \newcommand{\bbr}{\mathbf{r}} \newcommand{\bbs}{\mathbf{s}} \newcommand{\bbt}{\mathbf{t}} \newcommand{\bbu}{\mathbf{u}} \newcommand{\bbv}{\mathbf{v}} \newcommand{\bbw}{\mathbf{w}} \newcommand{\bbx}{\mathbf{x}} \newcommand{\bby}{\mathbf{y}} \newcommand{\bbz}{\mathbf{z}} \newcommand{\0}{\mathbf{0}} \newcommand{\1}{\mathbf{1}} % Caligraphic english alphabet \newcommand{\cA}{\mathcal{A}} \newcommand{\cB}{\mathcal{B}} \newcommand{\cC}{\mathcal{C}} \newcommand{\cD}{\mathcal{D}} \newcommand{\cE}{\mathcal{E}} \newcommand{\cF}{\mathcal{F}} \newcommand{\cG}{\mathcal{G}} \newcommand{\cH}{\mathcal{H}} \newcommand{\cI}{\mathcal{I}} \newcommand{\cJ}{\mathcal{J}} \newcommand{\cK}{\mathcal{K}} \newcommand{\cL}{\mathcal{L}} \newcommand{\cM}{\mathcal{M}} \newcommand{\cN}{\mathcal{N}} \newcommand{\cO}{\mathcal{O}} \newcommand{\cP}{\mathcal{P}} \newcommand{\cQ}{\mathcal{Q}} \newcommand{\cR}{\mathcal{R}} \newcommand{\cS}{\mathcal{S}} \newcommand{\cT}{\mathcal{T}} \newcommand{\cU}{\mathcal{U}} \newcommand{\cV}{\mathcal{V}} \newcommand{\cW}{\mathcal{W}} \newcommand{\cX}{\mathcal{X}} \newcommand{\cY}{\mathcal{Y}} \newcommand{\cZ}{\mathcal{Z}} % Formatting shortcuts \newcommand{\red}[1]{\textcolor{red}{#1}} \newcommand{\blue}[1]{\textcolor{blue}{#1}} \newcommand{\htext}[2]{\texorpdfstring{#1}{#2}} % Statistics \newcommand{\distr}{\sim} \newcommand{\stddev}{\sigma} \newcommand{\covmatrix}{\Sigma} \newcommand{\mean}{\mu} \newcommand{\param}{\theta} \newcommand{\gthEst}{\hat{\theta}} \newcommand{\ftr}{\phi} \newcommand{\est}[1]{\hat{#1}} % General utility \newcommand{\todo}[1]{\textbf{[TODO]}] \footnote{TODO: #1}} \newcommand{\tbc}{[\textbf{Incomplete}]} \newcommand{\chk}{[\textbf{Check}]} \newcommand{\why}{[\textbf{Find proof}]} \newcommand{\opt}[1]{\textit{#1}} \newcommand{\experience}[1]{[\textbf{Personal Experience}]: #1 \blacktriangle} \newcommand{\pf}[1]{[\textbf{Proof}]: #1 \Box} \newcommand{\core}[1]{\textbf{Core Idea}: #1 \Arrowvert} \newcommand{\example}[1]{\textbf{Example}: #1 \blacktriangle} \newcommand{\error}[1]{\textbf{Error alert}: #1 \triangle} \newcommand{\oprob}{[\textbf{OP}]: } \renewcommand{\~}{\htext{$\sim$}{~}} \DeclareMathOperator*{\argmin}{arg\,min} \DeclareMathOperator*{\argmax}{arg\,max} \)

About the Author

Professor David Reich, of the Department of Genetics at Harvard Medical School and the Howard Hughes Medical Institute, is a pioneer in analyzing ancient human DNA to learn about the past. In 2015, Nature magazine named him one of “10 people who matter” in all of the sciences for his contribution to transforming ancient DNA data “from niche pursuit to industrial process.” He has received numerous awards, including the 2017 Dan David Prize in the Archaeological and Natural Sciences for the computational discovery of intermixing between Neanderthals and modern humans.