Who was the first human ancestor?

Well, we know 30,000 years ago

our ancestors were making early cave paintings.

About 60,000 years ago, some were migrating out of Africa.

Even before that, some of our recent ancestors,

like Homo erectus, were chipping away at stone tools.

And, going back much further,

we were swinging around in trees like chimps, right?

The idea of humans evolving from a chimp-like ancestor

has pervaded scientific thought since the time of Charles Darwin.

And given 6 to 10 million years, it seems at least plausible

that we could have evolved from wild apes into our current, refined selves.

But, new fossil evidence suggests

we didn't come from chimps any more than they came from us.

Let's start with the classic hominid ancestor, Lucy.

She lived about 3.2 million years ago and she looks

like she could have evolved from an animal resembling a chimp.

But a newly-described hominin, nick-named Ardi, is a million years older.

Given that she is older than Lucy,

it stands to reason that she should look more like a chimp.

But, she doesn't entirely fit the bill.

Although she lived part of the time in the trees,

she could probably walk upright.

And when she was down on all fours,

she would've padded around on the palm of her hand

rather than on her knuckles like chimps do.

So, if our forebearers didn't look like chimps,

did they look like Ardi?

Um, well...maybe not.

Just last year, scientists discovered eight fossil bones of a strange foot.

This foot looked an awful lot like Ardi's foot

and had a sideways pointing big toe for climbing trees.

The only problem is the owner lived at the same time as Lucy.

This suggests that Ardi could be

on an entirely separate line from Lucy's and ours.

So, who were the first human ancestors?

Were they Lucy's, Ardi's, or what?

The short answer is, it's complicated and we might never know.

Unfortunately, the more fossils we find, the bushier our family tree becomes.

For Scientific American's Instant Egghead, I'm Katherine Harmon.