How I traced my ancestry back to the Stone Age

Carol's father and grandmother
Image caption Kashuki... Russian-Poland.... my grandmother's answers were hard to understand

I recently had a genetic test to find out more about where my ancestors came from. The results confirmed what I already knew - I am from a family of European Jews. But there was also a surprise - a Neanderthal forebear.

In many families, there seems to be one person who is interested in genealogy. In my family, it's me.

When I was 11, I conducted my very first interview with my grandmother, Ray Zall, who graciously answered all my questions about her childhood in Belarus.

The recording, which I still have , begins rather grandly: "This is Carol Zall interviewing Ray Zall, my grandmother, or 'Bobe' in Yiddish. Now Mrs Zall, could you tell me about your childhood?"

"What can I tell you?" asked my grandmother in her heavily-accented English. "I was born in a small village called Kashuki."

I'd never heard of Kashuki. And I still can't find it on a map.

"What country is it near?" I asked, confused.

"Russian-Poland, Russian-Poland," she answered.

My grandmother was born in the early 1900s, in what is now Belarus, but was then Poland (and part of the Russian Empire).

Some other ancestors of mine came from similarly vague places in countries that no longer exist, like Austria-Hungary. All of this has made it very hard to trace my roots.

Thirty-four years after I recorded that interview with my grandmother, there are new and revealing ways of finding out about your family tree.

Advances in the field of genomics have made it possible to use a person's DNA to find out where their ancestors may have come from. A number of companies now offer these tests, and there are a few rules of thumb you can use to separate science from the snake oil .

Image caption Carol the young genealogist and her "Irish" sister... where do those freckles come from?

The question is, would this work for me?

For about $200 (£125) I signed up with a company called 23andMe (the name derives from the fact that we all have 23 pairs of chromosomes).

The next thing I knew I was spitting into a plastic tube and posting my saliva sample to the company.

"The first thing we do is extract the DNA from the saliva," says Joanna Mountain, Senior Director of Research at 23andMe.

"The DNA gets cut up into little pieces and put on to what we call a chip."

Human DNA is like a code made up of three billion letters.

Testing companies like 23andMe don't look at all those letters (or positions, as they call them). They look at a small percentage of them - about a million - a process known as "genotyping". The positions are studied to find out all kinds of information - from diseases we may be at risk of in the future, to details about our past.

I've always known that my family was Jewish. My entire family tree, so far as I know, consists of European Jews, also known as Ashkenazi Jews. I've always imagined my ancestors as people who spoke Yiddish, lived in Eastern Europe, and listened to klezmer music.

However, since Ashkenazis spent centuries wandering around Europe, living among different populations, I've often wondered if they might have married or had children with people who were not Ashkenazi.

After all, my mother's mother and all her siblings had red hair and blue eyes. And my own sister - a redhead with freckles - is always assumed to be Irish.

A few weeks later, the results of the test came back.

"It looks like about two-thirds of it can be traced back to Ashkenazi-Jewish ancestry in Russia, Poland, Belarus, and other nearby countries," says Joanna Mountain.

"This is where your Jewish ancestry really pops out," says Mountain as she shows me my chromosomes displayed as separate bars, each one of them covered with bright blue sections, representing all the gene segments I share with other people in her company's database whose known ancestry is Ashkenazi Jewish.

This is how testing companies determine ancestry, by comparing your genes to known reference populations, to see which ones they resemble most.

No surprises there or any hints about where the red hair came from.

That's not to say that I had no overlap with other groups. My DNA did bear some resemblance, for instance, to the genes of Moroccan Jews, but that overlap was trivial compared to the number of identical gene segments I shared with Ashkenazis.

"There's always been some little degree, at least, of interchange between Ashkenazi populations and all these different peoples that they have lived amongst," says David Goldstein, director of the Centre for Human Genome Variation at Duke University. "So it is an incredibly complicated history of input from all sorts of different populations."

I couldn't help feeling a little disappointed.

Two hundred dollars and a vial of spit later, the big headline is something I already knew - that my ancestors were mostly Jews from different parts of Eastern Europe, though there was some interesting finer detail.

My "mitochondrial DNA" (the special piece of DNA that's handed down from mother to child) traces back to a common female ancestor somewhere on the Iberian peninsular - today's Spain or Portugal - about 15,000 years ago.

Another exciting thing I've learned goes all the way back to the Stone Age. The test I used has added a feature that lets you see what percentage - if any - of your DNA comes from Neanderthals, and 2.7% of mine is Neanderthal.

While that's not unexpected - almost everyone of non-African descent does have a little bit of Neanderthal DNA in them - I find it fascinating to think that somewhere up the line, I was a twinkle in a Neanderthal's eye.

As genome research continues at a greater pace than ever before, sometime in the next decade the cost of having your whole genome sequenced - all three billion letters of the code - will become affordable. When that happens, it will change genetic genealogy all over again, the experts I talked to say.

"What you'll be able to do is look at an individual's genome and say, all right, they have this mutation, which arose in a particular village in the south of France, for example," says Harvard genetecist Joe Pickrell.

"You'd be able to say with nearly 100% certainty that you have some ancestor who came from that particular village."

Now I'm waiting for the day when I can have my entire genome sequenced, and finally find out where my family might have been - before Kashuki.

Additional reporting by Rob Hugh-Jones.

Listen to more on this story, and hear some of Carol Zall's interview with her grandmother, at PRI's The World, a co-production of the BBC World Service, Public Radio International, and WGBH in Boston.

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