The full title is She Has Her Mother’s Laugh: The Powers, Perversions and Potential of Heredity. It’s written by Carl Zimmer, a science journalist, who also teaches at Yale. I heard Zimmer interviewed on NPR recently, and what appealed to me was that our family did the ancestry test with 23andMe. In fact, Santa gave the tests to all of us and to my sister this past Christmas. I learned so much about genetics and biology in Zimmer’s book, and that really says something for someone who barely squeaked out a C in freshman biology in college- actually it may have a D. I mean, the class met at 8:00 in the morning. How was I supposed to help shut down my favorite bar and then learn molecules, chromosomes and cells mere hours later? It’s not humanly possible! My disclaimer is I know nothing about all this stuff, so any errors are mine, not Zimmer’s.

I want to talk about two aspects of this hugely informative book, emphasis on the hugely part. It’s 656 pages, BUT the last 100 pages consist of endnotes and bibliography. Truth is- it’s a fascinating read because it’s all told in story form. It’s not a textbook. It’s a composite of stories about the people who have worked in biology and genetics for the past several hundred years with plants, animals and humans. Zimmer has an incredible ability to make really complicated information understandable to non-science people.

So one of the aspects I want to talk about is Neanderthals. I always thought they were some sub-human hominid, but they are not. They mated with modern humans, made their own tools, hunted large game, wore jewelry and made sculpture out of stalagmites. According to 23andMe, I’m part Neanderthal- 292 variants. The highest number of Neanderthal variants 23andMe has seen is 400. I have more than 75% of their DNA. So other than knowing how to cook game, use tools, love sculpture and wear jewelry, what else do I have in common with my ancient family? I have straighter than normal hair and less than average height. If I were a guy I would have back hair, but I don’t since I’m not. It’s thought that Neanderthal DNA is good for our immune system because it has a lot of immune fighting genes. Zimmer says thanks to 23andMe, Neanderthal pride is a real thing. Zimmer also says the Neanderthal test is not very accurate. But nevertheless….

In 1856, Neanderthal bones were first discovered in Neander Valley in southern Germany, hence their name. There is evidence that Neanderthals bred with modern humans during three different time periods in three different places- Europe, Near East and East Asia. At the turn of the 20th century in a cave on Mount Carmel in Israel, bones were discovered with modern human DNA and Neanderthal DNA. In 1995 mitochondrial (from females) DNA was taken from Neanderthal fossils from the Neander Valley, and by 2010 scientists had 60% of the entire Neanderthal genome built. A genome is “the complete sequence of DNA in an organism.” This is remarkable considering we’re talking about fossils that are several hundred of thousands of years old.

The second aspect I want is to talk about is “leaky” placentas. When pregnant, the circulation system connecting mom to baby is not a one-way highway. Cells migrate back and forth. What does this mean? According to Zimmer’s research, mothers of biological sons may carry some of their boys’ Y chromosomes in their bodies until they die. Research as shown that sons’ Y chromosomes lodge in their mothers’ organs and have been found through autopsies. Two things about this. Women are more prone to autoimmune conditions. Some scientists think our bodies COULD be fighting off our sons’ Y chromosomes since women do not have any Y chromosomes. Females are XX and males are XY. Other scientists think the sons’ Y chromosomes could help their mothers fight off cancer and other diseases. There are Y chromosomes that have been found in healthy breast tissue of women fighting breast cancer.

So this swapping of chromosomes between mothers and sons helps explain why my son, He Who Must Not Be Named and I stay in each other’s heads. Because we do! Brains are one of the organs Y chromosomes have been found. He tries unsuccessfully to influence me to think more to the right, and I try unsuccessfully to influence him to think more to the left. Not sure where stubbornness shows up on the human genome, but it’s there somewhere. Now Zimmer doesn’t say this, but I have deducted (remember the biology grade!)that during pregnancy mothers are also swapping out cells with their daughters. But since all females are XX, I’m assuming scientists can’t tell whose X is whose. Meaning scientists can’t tell apart the cells my daughter Ellie gave me and what were mine to begin with. Taking that step further, I would have X chromosomes my mother Shirley shared with me. Right? Share and share alike….

This chromosomal sharing makes for some interesting ramifications. We like to think surrogacy is like baking your bread in your neighbor’s oven, but it’s more than that. Zimmer doesn’t shy away from discussing this. He writes, ” In 2009, researchers at Harvard did a study on eleven surrogate mothers who carried boys but who never had boys of their own. After the women gave birth, the scientists found Y chromosomes in the bloodstreams of five of them…surrogates-to-be need to give informed consent that’s truly informed. It may come as a surprise to them that their own DNA could have a long-term influence on the health of an unrelated child, and that they may end up with some of the child’s cells-complete with a separate genome. These women need to know that heredity’s tendrils can’t be pruned as easily as we might imagine.”

Fascinating, yes? Also there is good information in this book about genetic screening to rule out disease-causing mutations in yet unborn children. There’s discussion about the desire of some to create a super-child who is brilliant, beautiful and disease free. This may be obtainable to couples in affluent developed countries, but what about the masses of humanity whose children would continue to suffer with diseases without adequate medical care in developing countries? Lots of ethical discussions that Zimmer handles eloquently.

I’ve never read a book like She Has Her Mother’s Laugh. It’s taken me all summer to read it and wrap my head around it. It has been the most meaningful endeavor of my summer. I find myself thinking about what I’ve learned all throughout my day. It’s not for everyone, but I highly recommend tackling this fascinating subject.

#carlzimmer #shehashermotherslaugh #genetics #neanderthals #surrogacy #23andMe