We Are All Descended From an Actual “Eve”

She lived between 100,000 and 200,000 years ago in southern Africa. These days she’s known as Mitochondrial Eve, but that’s a little misleading. Unlike the Biblical Eve, she wasn’t the first woman nor was she the only woman alive at the time—and there were plenty of men around as well. Still, Mitochondrial Eve was an actual person. We don’t know much about her except that she is the most recent woman to whom everyone alive today—male and female, all 7.6 billion of us—is connected through their mothers by a speck of DNA.

But as important as such a linkage may be to scientists, and despite the role that her namesake plays in Christianity, how significant is she for us? I’m not sure. See what you think.

Every cell in any organism contains small particles that keep the cell alive. The  nucleus, carrying the genetic DNA masterplan of the body, is the cell’s control center. Smaller particles carry out other functions. Mitochondria produce energy for the cell. They contain their own, separate bit of DNA because millions of years ago they themselves were free-floating bacteria that were engulfed by cells, proved useful, and took a permanent place in the cell anatomy.

Mitochondria in a cell (Flickr)

Mitochondria in a typical cell. The long thread of genetic DNA in the nucleus is shown but not the bits of mitochondrial DNA, which are incidental and much smaller. (Flickr)

Over time and across countless cell divisions, the DNA in the mitochondria  changed in small ways unrelated to the genetic DNA in the nucleus. As a result, the early apes, then the pre-humans, then the earliest modern Homo sapiens all carried the slight variations in mitochondrial DNA that they inherited.

But they inherited them only through he females. Males couldn’t pass theirs along. Why? Because we inherit our cellular structure from mom’s egg. While fathers may deliver their genetic DNA by sperm to the egg, it’s mom’s egg cell itself that grows into the embryo and into all human cells. Complete with the mother’s mitochondria.

Over the course of five thousand generations or so, women around the world passed their variations of mitochondrial DNA to their daughters. Along the way, though, some mothers bore only sons and other women had no children at all. Gradually, all the variations of mitochondrial DNA fizzled out, except one. We all carry it, as did a woman a long time ago, Mitochondrial Eve.

What to make of all this? Compared to the Biblical Eve and her list of firsts—first woman, first human to be curious, first mother—we have little to show for our ancestry from the other Eve, Mitochondrial Eve. And the merging of genetic DNA from our mother and father has by far a greater influence on who we are and what we’re like. By comparison, Mitochondrial Eve is just a woman a very long time ago whom we all happen to be linked with inconsequentially on our mother’s side.

Still, as Siddhartha Mukherjee writes in The Gene, without elaborating, “I find the idea of such a founding mother endlessly mesmerizing.” For Mitochondrial Eve is one of our Most Recent Common Ancestors—an MRCA. The MRCA for any group of organisms, whether the same species or not, is the individual or type after which subsequent generations evolved in different directions. The MRCA of primates (humans as well as chimps, apes, monkeys, baboons) lived 65 million years ago. The MRCA of all animals lived 600 million years ago. And the MRCA of all living things, 3.6 billion years ago. For many people, interesting to know but not so easy to imagine.

But it is possible with some effort to envision the Most Recent Common Ancestor who looked a lot like us. Maybe Mitochondrial Eve’s value lies here: by thinking about her, we may be getting better at wrapping our heads around the reality of even older ancestors who seem impossibly ancient yet who made us what we are.

The Biology Of Suffering

“Where does suffering come from? Why do we suffer?” The questions open biologist Ursula Goodenough’s essay “The Biological Antecedents of Human Suffering” (in The Routledge Companion to Religion and Science (2012)). Through the ages, people have looked to religion for the answers, with no easy satisfaction. But under a biologist’s eye, the questions look more manageable.

Goodenough proposes two categories of suffering, the biological and the experienced. Biological suffering comes to all living things. Bacteria, plants, and people all seek out what they need—water, food, light—and withdraw from what harms them—poisons, enemies. Any organism with too little of what it needs or too much of what will weaken it is struggling, under stress.

Durer_Revelation_Four_Riders (sciencemediacentre.co.nz)

The Four Horsemen of the Apocalypse by Albrecht Dürer  (sciencemediacentre.co.nz)

For animals with developed nervous systems, however, such suffering not only occurs biologically but is also experienced. The biological struggle announces itself through the nervous system. Vertebrates (with a backbone, head, and skeleton) carry neurons called nociceptors in their skin and internally in muscles, joints, and the gut. When nociceptors tell the brain that something is very wrong, the brain interprets the message as paina slice in a finger, a twisted ankle, sudden nausea. In addition, for humans—social creatures that we are—the sources of such experienced pain include social and psychological feelings (envy, guilt) as well as bodily injury.No

Fortunately, for most of the difficulties that organisms endure, antidotes are available. Organisms will move towards water if they need it, try to compensate for an injury, muster immune responses to fight infections, call a friend if they are lonely. Goodenough calls these corrective measures amelioration systems; they make things better. But often at a price. We humans will likely feel the amelioration process at work more uncomfortably at first, ironically, than the adversity that triggered it. We suffer through a fever because the higher body temperature strengthens the immune response to an infection that might otherwise be barely noticeable at the start.

No matter their inconvenience, though, amelioration systems are indispensable. To paraphrase Goodenough, organisms whose amelioration systems fail to cope with adversity will die. Organisms whose amelioration systems are inactive because they have all they need enjoy well-being. But it is organisms whose amelioration systems are at work “actively dealing with difficult circumstances” that are in a state of biological suffering.

Sometimes the suffering is not felt: “The food-deprived amoeba or the bacterium, the plant plunged in darkness or subject to a wound, pays the suffering price, but does not feel the price.” In other cases, for humans and other vertebrates, the price is acute pain. Pain alone won’t ameliorate a condition but calls attention to it—and may teach a lesson that brainy creatures can remember about what to do differently next time.

In still other cases, though, continuous or recurring pain is a scam. Chronic pain is “physical pain that is not obviously in the service of amelioration systems and is unresponsive to analgesics or other practices….Here we encounter an example of things gone awry.” With chronic pain, “Suffering has become uncoupled from resolution.”

Goodenough closes, “The long evolutionary view of suffering is that it is an inherent feature of life….[It] is part of the package, the price paid for the gift of being alive at all.” Up to a point, we knew this already—that at least some suffering goes with being alive. But Goodenough’s naturalism presents suffering in an earthly mode, with less mystery and without guilt. Still, we are left to reckon with the irony that often what we suffer from are the very processes by which the body goes about repair and renewal.

These highlights amount to only a partial summary of Goodenough’s rich essay, which is here at Google Books.