When we ask that most human of questions, “Who am I?”, it’s natural to turn to our family line to find the answers in our ancestors. Genealogies are found in many parts of the Bible: there are nine lists of family lines in the Book of Genesis alone, establishing not only how the Twelve Tribes of Israel descend from Abraham, but giving the origin (at least symbolically) of Noah’s son Ham as the ancestor of all Africans and Abraham’s son Ishmael as the ancestor of Arabs. Later, royal dynasties are traced out in I Chronicles 1 & 2 and Ruth 4. Both Matthew and Luke begin their Gospels by tracing the family line of Jesus back to Abraham – and in Luke’s case, all the way to Adam.

Today it has become very popular to take a genetic test to discover one’s ancestry. You can order a personal genetic test quite cheaply and get a report on where you ‘come from’. But how do these tests work, and what are they actually telling us?

Since the discovery in 1953, that the chemical DNA (deoxyribonucleic acid) exists as a double-helix in the nucleus of living cells, we have learned how to read the ‘blueprint’ that instructs living things how to grow and function. The genetic code consists of an alphabet of four letters, which are arranged into three-letter words, each word indicating a chemical from the family of ‘amino acids’. Those words are arranged into paragraphs (genes) which build the amino acids into large chemical structures called proteins. The paragraphs are grouped together in a number of ‘volumes’ which we call chromosomes – and these are paired up so that we have two copies of each set of instructions. Human cells contain 46 chromosomes – 22 pairs of matched volumes, and our sex chromosomes, two ‘type X’ in females and ‘XY’ with one shorter Y chromosome in males.

Altogether, there are about 3,200 million ‘letters’ in the genetic code of a typical human being, so there’s lots of room for variability. But how can the code change and still make a human? Some of the variations result in visible or measurable changes – the colour of our hair and eyes, our blood type, whether we can roll our tongues into a U-shape and even whether coriander tastes like parsley and citrus, or soap!

Lots of other changes are hidden. The genetic dictionary contains synonyms with variant spellings – several different three-letter words can code for the same amino acid. The ‘volumes’ of our genome contain not only instructions but also sections which pad out the length like ‘word art’ decorating a book. None of these variations affect our humanity but they introduce diversity which can be traced back to different regional populations where they were common. Commercial ancestry companies don’t need to sequence all 3 billion letters in your genetic code – they know where to look for about 700,000 letters which tend to vary between individuals and keep track of what part of the world they come from.

To add to the complexity, every time we beget a child, the genes which will be passed on to the next generation get shuffled (the technical word is recombination). A baby girl produces eggs which will await her maturity, and they will only contain one copy, not two, of the paired chromosomes. But it’s not as simple as randomly picking either Mum’s or Dad’s. Rather, the genetic process is the equivalent of a frenzied librarian shouting: “OK, Volume 3: Let’s have pages 1-20 from Dad, 21-27 from Mum, 28-32 from Dad…” and picking random numbers all the way along the set. A similar process takes place as a man’s body continually produces its seed. The amount of random shuffling means that when you go back more than eight generations, it’s likely that some of your ancestors have contributed nothing at all to your own genetic code.

There are two exceptions – two genetic codes which are not shuffled in the same way. The Y-chromosome is passed from father to son along the male line. There’s also some DNA which is not found in the nucleus of our cells, but lives in the cell body and tells our cells how to burn sugar and fat as their energy source. This is known as mitochondrial DNA and is passed down in the outer layers of the egg cell in the line of our mother’s mother’s mothers. The only changes in these lines take place through accidental changes (mutations), apart from 5% of the tip of the Y chromosome which can swap with the tip of the X as part of the usual shuffling process.

Genealogy companies can map the changes found in these parts of our genome, and how they have spread through the world. They can identify our ‘most recent common ancestor’ – the person whose male or female line is responsible for everyone alive today. That doesn’t mean they were the only person alive back then; they were part of a larger population of thousands, but all the other male-male and female-female lines have now died out. This is why you may hear talk of “Y chromosome Adam” or “mitochondrial Eve”. It seems that everyone alive today is descended from a man who lived on the coast of North-West Africa between 160,000 and 300,000 years ago. We also descend from a woman who lived in East Africa between 100,000 and 230,000 years ago. But scientists prefer not to call these individuals “Adam” and “Eve” because they do not propose that these two individuals formed a couple.

One family line with a particular interest in keeping track of their genealogy are Jewish men who believe they are descendants of Aaron, and therefore inherit the status of priests within Judaism, taking the surname “Kohen” (spellings can vary across cultures). Genetic studies showed that a particular version of the Y chromosome is found in 46% of Jewish men who identify as “Kohen”, much higher than you would expect in a random population. (Why would it not be 100%? Explanations would include mutations in that form of the Y chromosome during the lineage of the priesthood, and the possibility that certain men would have been admitted as early Jewish priests without proving descent from Aaron, as well as infidelity by priests’ wives – which if common, would have drastically lowered the percentage.)

Looking to our ancestry for our identity is both instructive and limiting. Looking just to our parents and our grandparents, we can account for the origins of many of our physical and personality traits. But when we look further back, we soon discover we are descendants of humanity as a whole – some statisticians estimate that we only need to go back 15,000 years to find a time when every human then alive would have been one of our ancestors.

We do not need to be constrained by our genetic heritage. It’s insightful that charting Our Lord’s genealogy mattered so much to both Matthew and Luke, when both tell us that Joseph was not the biological father of Jesus – this shows the strong weight put on adoption in the culture of the New Testament. If Jesus was adopted by a man of King David’s line, then as far as society was concerned, he would be a Son of David.

Even the Hebrew Bible hints at God’s Fatherhood being a question of God’s choice and not genetic heritage. In Deuteronomy 14, Psalm 103 and Jeremiah 31, we see images of God approaching the children of Israel as a Father. St Paul clearly understood that baptism makes us adopted children of God (see Ephesians 1, Galatians 4 and Romans 8). The Catholic Church presents herself as a family open to all, where everyone can become brothers and sisters. Before we understood how genes worked, we used to speak of family being “blood” to one another. In that light, let us listen anew to these words from Hebrews 10 (in The Passion Translation): 

Now we are brothers and sisters in God’s family because of the blood of Jesus, and he welcomes us to come into the most holy sanctuary in the heavenly realm—boldly and without hesitation… And since we now have a magnificent High Priest to welcome us into God’s house, we come closer to God and approach him with an open heart, fully convinced that nothing will keep us at a distance from him. For our hearts have been sprinkled with blood to remove impurity, and we have been freed from an accusing conscience. Now we are clean, unstained, and presentable to God inside and out!

Go back far enough, and we are all descended from the highest nobility and from the vilest members of human society. But by the Father’s grace and the blood of Christ, to those who would accept it, Jesus gave each one of us power to become children of God. Welcome to the family.

Revd Dr Gareth Leyshon is a parish priest in the South Wales Valleys, who read physics at Oxford and completed a doctorate at Cardiff (a study of the structure of distant galaxies) before entering seminary.

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