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Meet Your Ancestors

Meet Your Ancestors

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For many of us, it may be hard to imagine that if we went back far enough in time—more than 55 million years, when the first primates are thought to have lived—that our great-a-million-times-over-grandparent was a mouse-sized creature weighing just over an ounce. Yet just as assuredly as if your parents hadn't lived, you wouldn't exist if that putative ancestor hadn't lived.

So, want to meet that very distant relative of yours? Here, we'll lead you back through key stages in your primate heritage, as revealed in the fossil record, till you come face-to-face with your great-to-the-nth-degree-grandparent. Nervous?—Peter Tyson


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Homo sapiens
Present day

This is a modern human. Actually, it's me, the author, about 20 years ago. Don't ask what I'm doing. Instead, imagine your own picture here rather than mine. This is about your ancestors, after all (well, mine too).

Can you "see" yourself in the frame? Okay, now let's just say for the sake of argument that you were born in the year 2000 and that a generation is 25 years. (It will make the math a whole lot easier.) Ready? First read some details about yourself below, then move on to the first of your ancestors shown here.

Your Profile
You are a bipedal primate. Your species, Homo sapiens, also known as modern humans, arose in Africa about 200,000 years ago. Your kind's most defining characteristic is its large brain. That three-pound universe inside your skull enables you, among other things, to speak a language, reason abstractly, and contemplate whatever it is you like to contemplate.




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Homo erectus
1.6 million years ago

Okay, rewind the clock 1,600,000 years. You've gone back 64,000 generations in your family history. Here's what your ancestor of around this time might have looked like.

Your Ancestor's Profile
Your genus, Homo, arose about 2.4 million years ago. Its appearance was marked by a significant, though not huge, increase in brain size from earlier primates. H. erectus dates to 1.9 million years ago, and its best-known skeleton, the so-called Nariokotome boy, is about 1.6 million years old. H. erectus is the first member of your line to show fully modern body size and proportions. Had he lived longer, for instance, the Nariokotome boy would have grown up to be about six feet tall.




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Australopithecus
3.2 million years ago

Now, double that rewind. You're now 128,000 generations of your family into the past. Meet your great-whatever-grandfather. This isn't just a thought experiment—you did have a male forebear in this period, and he might have resembled this individual.

Your Ancestor's Profile
Australopiths are the earliest undisputed members of the human family. Their most standout advance over their predecessors was the ability to stand on two legs. Their brains were still small, however, about the size of a modern chimpanzee's. Lucy, the most famous australopith fossil, designated Australopithecus afarensis, dates to 3.6 to 2.9 million years ago. She would have weighed between about 65 and 110 pounds, similar to a chimp.




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Dryopithecus
9.5 million years ago

Now we'll take a great leap back. Your progenitor—your direct ancestor, remember, removed only by oodles of time—is about the size of a chimp and may have borne a likeness to this fellow. Look like anyone in your family?

Your Ancestor's Profile
We've now moved out of hominids and into ape-like mammals. Dryopithecus was an advanced ape. The best-known skeleton of this genus, uncovered in Spain, is 9.5 million years old. Experts estimate that when it was alive, that individual had a body mass of about 75 pounds, again similar to a living chimp. And like a chimp, it would have hung from its powerful forelimbs while going about its life in the trees.




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Proconsul
20 million years ago

Hang on, we're zipping back through 800,000 generations of your line—a long way down your family tree. Back then your primogenitor was more like a monkey than a chimp, no offense.

Your Ancestor's Profile
Proconsul is the most primitive ape that is well-known from a fossil skeleton. It lived in Africa about 20 million years ago. Like modern apes, it lacked a tail, but it would have been monkeylike in behavior, moving around in the trees on all four limbs. It weighed between 37 and 110 pounds. (There are different species that weighed different amounts. The bigger ones would have approached a modern chimp in size.)




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Aegyptopithecus
30 million years ago

Ever seen a howler monkey? That's what your extended family member would have resembled roughly halfway back to the dinosaurs, temporally speaking.

Your Ancestor's Profile
Aegyptopithecus—the name honors Egypt, where its fossil remains were found—was a primitive anthropoid, the group that includes monkeys, apes, and us. It would have weighed about 15 pounds, roughly the same as a modern howler monkey, and its behavior would have been similar to that of living monkeys.




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Notharctus
45 million years ago

Your great-times-a-very-high-number-
grandparent would have resembled a modern-day lemur. Cute, eh?

Your Ancestor's Profile
Notharctus would have been similar to living prosimians like lemurs. (A prosimian is a lower primate.) It would have weighed perhaps two to four pounds, which is about the same as a golden bamboo lemur. It lived in western North America about 45 million years ago.




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Carpolestes
55 million years ago

We're getting close to your ultimate primate grandparents. But first, meet one of your most primordial ancestors, who may have looked like this mole-sized critter.

Your Ancestor's Profile
Carpolestes is a very early primate, but it has features that set it apart from the most primitive primates of all, including a nail rather than a claw on its big toe. Its closest living analogue would be a woolly opossum from South America. The skeleton this image is based on turned up in Wyoming. When alive, the animal would have weighed about three-and-a-half ounces.




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Dryomomys
55 million years ago

We've now arrived at one of your very earliest precursors, Dryomomys. Something like this creature begot something that begot something that, after that eternity of time, begot you—only time separates the two of you. Now, imagine if you could erase that intervening eternity for a moment and meet your hugely distant forebear. At a smidgen bigger than a mouse, this nearly eldest of all your elders would fit snugly in the palm of your hand.

Your Ancestor's Profile
Dryomomys is the most primitive primate known from good fossil material. (The first known primate, Purgatorius, dating back as far as 65 million years ago, is known only from isolated teeth and jaw fragments.) The animal most like Dryomomys today is a wee being called the pen-tailed tree shrew. Dryomomys would have weighed about 1.3 ounces, roughly akin to that of the smallest living primates, the mouse lemurs of Madagascar. Like its cousin, the roughly contemporary but more advanced Carpolestes, the Dryomomys skeleton that the reconstruction is based on was unearthed in Wyoming.




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The Start of You
4 billion years ago

Forgive us, but we thought that since you've come this far you might like to meet your true ultimate ancestor on Earth. That beyond-imaginably-distant relative may have appeared something like this single-celled protozoan. See any resemblance?

Your Ancestor's Profile
Paleontologists believe the first living cell somehow came to life about four billion years ago. (Explaining that "somehow" is the holy grail of origins-of-life researchers.) Beyond that humble organism, whatever it was, your heritage on this planet, sorry to say, dies out. Or, if it makes you feel better, was yet to be born. But that's 160 million generations of your family in the past, and who can count that high anyway?



Note: Most everything known about our primate heritage remains fragmentary and hotly debated among scholars, more so the farther back in time one travels in the fossil record. The eight fossil primates presented here are often-cited examples of key stages in primate evolution, and their artistic reconstructions are based on careful study of the paleontological evidence. Thanks to Mary T. Silcox of the University of Winnipeg for supplying details on each fossil primate.


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