Evolv­ing Ideas

Re­cent dis­cov­er­ies sug­gest early mod­ern hu­mans, our an­tecedents, mixed with other ho­minids... It turns out, we're not so spe­cial

Canadian Wildlife - - BIGGER PICTURE - By Alanna Mitchell

The im­age is iconic, show­ing the march of evo­lu­tion from our knuckle-drag­ging hu­man an­ces­tors of mil­lions of years ago to long-legged mod­ern peo­ple strid­ing up­right. It pa­rades across T-shirts, posters and the pa­le­on­to­log­i­cal lit­er­a­ture.

In fact, it’s so broadly ac­cepted that it’s of­ten par­o­died. One spoof shows that up­right fel­low evolv­ing even fur­ther into a guy hunched over his com­puter.

But with icons come mes­sages. Hu­man­ity’s evo­lu­tion is cast as the march of in­evitabil­ity. The nar­ra­tive goes like this: We are evo­lu­tion’s vic­tors. We sur­vived be­cause we were more ad­vanced than all the types of hu­mans who came be­fore, the glo­ri­ous sum­mit of ge­netic progress to which all the bil­lions of years of lesser crea­tures were in­ex­orably lead­ing.

There are a few flaws in the logic. For one thing, there’s the un­com­fort­able groundswell of find­ings over the past few years show­ing that our species, the anatom­i­cally mod­ern hu­mans who showed up about 200,000 years ago, walked the Earth at the same time as sev­eral other types of hu­mans. Evo­lu­tion did not nat­u­rally lead to us. Another of those hu­man-like species might have been the vic­tor un­der slightly dif­fer­ent cir­cum­stances.

We lived on the Earth at the same time as the tiny hob­bit hu­man, Homo flo­re­sien­sis, whose bones were found in a cave in the In­done­sian is­land of Flores in 2003. They died out about 54,000 years ago. And we shared the planet with both the highly so­phis­ti­cated Ne­an­derthals, who van­ished about 40,000 years ago, and the Deniso­vans, who were still alive when the Ne­an­derthals went ex­tinct. Their dis­cov­ery, through a cou­ple of teeth and a fin­ger bone in a Rus­sian cave, came to light in 2010.

DNA find­ings, which we have for both Ne­an­derthals and Deniso­vans, show that we mated with both those hu­man cousins, pro­duc­ing off­spring that re­pro­duced in their turn. It means we mod­ern hu­mans carry within us the genes of both Ne­an­derthals and Deniso­vans. And that means the evo­lu­tion­ary track of those two sur­vives within us. It may even be what al­lowed us to thrive. The bits that re­main in us ap­pear to have boosted our im­mune sys­tem.

And now, the lat­est find­ing, from the Ris­ing Star ex­pe­di­tion. This is the one led by Lee Berger of the Evo­lu­tion­ary In­sti­tute at the Univer­sity of the Wit­wa­ter­srand in South Africa, whose team re­cov­ered more than 1,500 hu­manoid fos­sils in a nar­row-mouthed cave in the Cra­dle of Hu­mankind World Her­itage Site, the largest stash ever re­cov­ered.

And not just any fos­sils, but those of a whole new species, dubbed Homo naledi. It had the small brain size and curved fin­gers of our more an­cient rel­a­tives but the wrists, legs and feet that char­ac­ter­ize us. When it was dis­cov­ered in 2013, the great mys­tery was where it fit into the hu­man fam­ily tree, tough to solve be­cause the DNA wasn’t pre­served.

In May, Berger and his team re­vealed that the ex­am­ples of Homo naledi could be as re­cent as 236,000 years old, based on the age of the sed­i­ments they lay in. The tan­ta­liz­ing pos­si­bil­ity, then, is that this hu­man cousin might have lived in Africa when we, Ne­an­derthals, Deniso­vans and Homo flo­re­sien­sis roamed Europe and Asia. Other undis­cov­ered hu­man species might still lie hidden in African caves or Chi­nese hills.

The pic­ture that emerges from the find­ings is of an Earth pop­u­lated with many strands of hu­mans, per­haps more like the many va­ri­eties of mon­keys that now live here. Rather than a tree or a march of in­evitabil­ity to­ward the supremacy of Homo sapiens, the hu­man fam­ily is a river, with trib­u­taries break­ing off and re­join­ing the flow, as Berger likes to say.

The other glar­ing flaw in the logic that we are the cho­sen species is that evo­lu­tion con­tin­ues. It did not end

RATHER THAN A TREE OR A MARCH OF IN­EVITABIL­ITY TO­WARD THE SUPREMACY OF HOMO SAPIENS, THE HU­MAN FAM­ILY IS A RIVER, WITH TRIB­U­TARIES BREAK­ING OFF AND RE­JOIN­ING THE FLOW

with us. We are not the high­est and best it can do. We are just a stop along the way.

The plain truth is that evo­lu­tion de­scribes not just the past and present, but also the fu­ture. It will con­tinue long af­ter we have gone ex­tinct, with sur­prises we can’t even imag­ine.

And, to me, it makes it tough to jus­tify the ca­sual stance of dom­i­nance our species has taken to­ward the rest. As a species, we act as though the di­ver­sity of life is here for us to use at will. The truth is, we mod­ern hu­mans are just one piece of a com­plex puz­zle that has evolved to work. What’s un­clear is how many pieces we can take out be­fore we goose evo­lu­tion into another mass ex­tinc­tion when all bets, in­clud­ing the fate of hu­mans, are off.1

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