Out of Eden: An Evolutionary History More Twisted Than a Double Helix

Out of Eden: An Evolutionary History More Twisted Than a Double Helix

Devotional for the United Church of Christ Science and Technology Network

September 21, 2017

Rev. Dr. Ruth E. Shaver

Genesis 3:22-24, NRSV

Then the Lord God said, “See, the man has become like one of us, knowing good and evil; and now, he might reach out his hand and take also from the tree of life, and eat, and live for ever”— therefore the Lord God sent him forth from the garden of Eden, to till the ground from which he was taken. He drove out the man; and at the east of the garden of Eden he placed the cherubim, and a sword flaming and turning to guard the way to the tree of life.

Homo sapiens sapiens are the supposed pinnacle of evolution for the genus Homo. Given that we seem to be hurtling backward toward the good old days of mutually assured destruction, we could easily argue that placement, but for now, at least, we are the most intelligent and most creative species in existence on Earth. But why H. sapiens sapiens and not, say, Homo (sapiens) neanderthalensis or Homo (sapiens) denisova, our closest cousins in the genus? We don’t know. But we do know this: most humans alive today share DNA with one or both of our cousin species because Homo sapiens left the Eden of Africa not once but twice in history.

Africa is, with little argument, the front-runner for the biological Eden of Homo sapiens. Although H. sapiens wandered out of Africa at least one other time, contributing human mitochondrial DNA (mtDNA) to the Neanderthals through the interbreeding of Neanderthal males and human females about 270,000 years ago, the general date given for human migration that “stuck” is 70,000 years ago. The human species spread out from the East African Rift Valley across the southern half of the continent, diversifying as we went (likely making our way off the continent by sea to populate the southern hemisphere), and eventually found our way north again to move into Asia and Europe. Evolution worked its slow and sometimes not-so-slow magic to make us look incredibly different in every climate on every continent but Antarctica, with the most diversity in our genetic makeup found at home in Africa. This makes sense: we’ve been there longer than anywhere else on the planet! Until the advent of intercontinental seafaring and later air travel, the emigrant populations on other continents were often fairly isolated from each other, allowing genetic adaptation to environments and circumstances that only now are spreading among other populations as we meet again in our global village.

Something very interesting shows up thanks to science, however: evidence that we are all related to the same female ancestor and to the same male ancestor a lot more recently than we might think. ALL of us. Genetic studies have allowed us to trace mtDNA along maternal lines in women and Y-chromosome changes along paternal lines in men.

Mitochondrial DNA is passed from mother to child; only females can pass it on through mating. Because mtDNA is passed on only by daughters, we have no way to track lines of mtDNA that died out because only males survived. This leads to fewer lines than one might think and the preservation of female-dominant lines across long stretches of time. It also allows us to find a theoretical Mitochondrial Eve, who was born in Africa around 200,000 years ago and through the thousands of generations since has given every member of H. sapiens a piece of her mtDNA. A substantial proportion of the population of the African continent today carries the longest remnants of this mtDNA, particularly those whose lineage include few or no women born of non-African mothers. Around 63,000 years ago, when some members of H. sapiens walked out of Africa to populate the rest of the world, too, a second mtDNA line developed that is common to all human beings born to a mother whose linage arose on a continent other than Africa. The varying subgroups of mtDNA linage are called haplogroups. These haplogroups show how humans have moved across the face of the Earth from biological Eden in Africa to five other continents.

Y-chromosome Adam, the common ancestor of all men, lived between 100,000-200,00 years ago, depending on which analysis one credits most. As with mtDNA, because the Y-chromosome is carried only from father to son, we have no way to track Y-chromosome lines that ended when a man did not sire a son. But we can track genetic changes back through time and populations, with an estimated mutation rate of one every 125 years, which leads to the general dates above. There are outlier dates proposed at the more recent and much older ends, as well, and there could be some men whose Y-chromosome does not show this link as isolated populations are studied, but as with mtDNA, this genetic wonder leads us to realize just how interconnected all of humanity truly is thanks to the adenine-cytosine and guanine-thymine pairs that make us human. We are all linked back to biological Eden by the twisting and turning of the DNA molecule and its incredible double helix.

Our creation myth from Genesis 2-3 tells us that humanity itself is twisted and in need of turning back to God. Biblical Eve tempted Biblical Adam with an apple after the snake, later interpreted to be Satan, told her that the apple would give her the same knowledge as God. It’s that knowledge, not our creation, that makes us sinful, of course. But this directly contradicts Genesis 1, in which we are created in the image of God. This to me is far more life-giving as a creation story than the fall, not because it removes the necessity of salvation—we have used our creativity and ingenuity to cause more than enough evil through the centuries to be in need of salvation!—but because it reminds me that, just as we are all genetically close cousins whether we were born in Bora Bora, Tora Bora, or Borger, Texas, we are all divinely close cousins because we share in God’s image. No matter how twisted and turned we are by the misuse of God’s image within us, God’s generative love provides a path back to true love and hope for using that image for good instead of evil. It’s in our divine DNA!

Prayer:

Holy One, you wrote the laws of creation to give rise to life, life that is interconnected from smallest to largest and oldest to youngest by DNA. We who have the gift of knowing this all to often forget that we are related to other humans, never mind to every animal and plant and fungus and microbe on Earth. Help us to remember that as we strive to use your divine DNA, your creative and ingenious image within us, for good so that we do not twist and turn our creativity to harm ourselves, our human cousins, or any other life. We ask in the name of Jesus Christ, whose life was not twisted or turned away from you and whose death brings us life anew. Amen.