FEA­TURE

Does hu­man palaeon­tol­ogy per­plex? Don’t know your hob­bit from your ha­bilis, or Ne­an­derthal from naledi? DYANI LEWIS ex­plains what we know about the hu­man ori­gin story.

Cosmos - - Contents -

— Where hu­mans came from

MOD­ERN HU­MANS, Homo sapi­ens, are a sin­gle twig on a branch of the evo­lu­tion­ary tree that reaches back some seven mil­lion years, to when we split from our clos­est liv­ing rel­a­tives, the chim­panzees and bono­bos.

Hu­man evo­lu­tion, how­ever, “is not a line of car­toons from a bent-over chim­panzee to a mod­ern hu­man,” says Fred Spoor, a palaeoan­thro­pol­o­gist from Univer­sity Col­lege, Lon­don. “It’s a com­plex busi­ness.” So what do we know? We know that Homo sapi­ens evolved in Africa per­haps as far back as 300,000 years ago, and then trav­elled north into Eura­sia. They dis­persed though Europe and Asia, reach­ing Aus­tralia about 55,000 years ago and the Amer­i­cas about 15,000 years ago.

Most cur­rent ac­counts, drawn from the fos­sil record and stud­ies of an­cient and mod­ern hu­man DNA, sug­gest two waves of global mi­gra­tion. The first mi­gra­tion had Homo sapi­ens reach­ing the Mid­dle East as early as 125,000 years ago, and China 80,000 years ago. By the time a sec­ond wave of Homo sapi­ens left Africa around 60,000 years ago, the first wave had prob­a­bly ei­ther re­treated or be­come ex­tinct.

Ge­netic stud­ies that de­ter­mine how liv­ing pop­u­la­tions have in­ter­bred and mixed through­out his­tory sug­gest most non-africans liv­ing to­day can trace their her­itage to the sec­ond ex­o­dus from Africa. A re­cent study sug­gests the founders of Sahul (the an­cient con­ti­nent com­pris­ing Aus­tralia and Pa­pua New Guinea) might have been part of the first mi­gra­tion.

Trac­ing a di­rect line of an­ces­try for Homo sapi­ens back along our branch of the evo­lu­tion­ary tree is dif­fi­cult, be­cause the fos­sil record is a patchy mo­saic of in­com­plete skele­tons. Few early hu­mans died at the right time and place for their re­mains to be pre­served.

En­tire species prob­a­bly be­came ex­tinct with­out leav­ing a sin­gle toe bone for us to dig up in the smat­ter­ing of places we are look­ing.

The fos­sil record for two to three mil­lion years ago, when our old­est Homo – or “upright” – an­ces­tors emerged, is par­tic­u­larly sparse, says Spoor, mak­ing it “one of the least un­der­stood parts of hu­man evo­lu­tion”.

Early hu­man species that have been dis­cov­ered are just as likely to be an­cient “cousins” – off­shoots of the branch lead­ing to us – as they are an­ces­tors.

Here’s a short guide to the most prom­i­nent mem­bers of the the ex­tended an­cient hu­man fam­ily.

Aus­tralo­p­ithe­cus africanus Homo rudolfen­sis Ekembo hes­eloni Adapis an Eocene lemur

Homo sapi­ens Mod­ern Omo 1 Homo sapi­ens 195,000 year old Homo erec­tus

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