Eric S. Haag's "The Other Big Bang"

Eric S. Haag is professor of biology and director of the Biological Sciences Graduate Program at the University of Maryland, College Park. He has conducted research on the evolution of sex and reproduction in animals such as sea urchins, roundworms, and hermaphroditic fish for three decades.

Haag applied the “Page 99 Test” to his new book, The Other Big Bang: The Story of Sex and Its Human Legacy, and reported the following:

Page 99 is the second page of Chapter 7, “Land Ho.” Its first paragraph reads:

[As] I rounded a bend, what was left of a puddle a few feet across came into view. I bent down to discover a sad tableau of mass tadpole mortality. One hundred or so whip-tailed, jet-black blobs were cradled in the drying mud, dead or dying and on their way to becoming pollywog jerky. They were optimistically produced by a pair of red-spotted toads a couple of weeks before, and a few even had managed to start sprouting their hind legs before the dry warm air, breezes, and lack of more rain doomed their bid.

While unlucky tadpoles may seem to be unrelated to sex, by the end of the page we learn how the evolution of a different way of reproducing strongly conditions how humans experience sexuality. So, I’d argue that The Other Big Bang passes the Page 99 Test with flying colors.

The passage, recounting a hike in the Mojave Desert, underscores how the need for standing water limits where amphibians can live. It is frankly amazing that any of them succeed there. The vignette sets up the rest of the page, which introduces the evolution of a new type of vertebrate, the amniote. Amniotes include familiar desert animals like lizards, rattlesnakes, tortoises, roadrunners, jackrabbits, coyotes, and other mammals (including humans). They became the dominant land vertebrates by evolving new anatomies that allow internal fertilization (e.g. penises) and new protections for embryos (membranes and the egg shell). With such “reproductive superpowers” amniotes could reproduce virtually anywhere, including very arid or very cold places.

Before amniotes, males and females often differed only in gamete type: males make sperm, and females eggs. In present-day fish the sexes cannot be distinguished until months after hatching, and even then only by closely examining the developing gonads. Fish and amphibians generally lack external genitalia, and the ducts that carry sperm or eggs to the outside are shared between the sexes. Any sex differences in color or body shape develop only with adulthood, under the control of hormones. In the laboratory, adult fish can be easily sex-reversed with hormones. For example, females can be permanently converted into fertile males by adding testosterone to their water. Outside of the lab, hundreds of fish species naturally change sex over their lifetime, with individuals living as both fertile female and fertile males.

In contrast, amniotes develop sex-specific tissues, inside and out, early in embryonic development. At birth it is easy to tell male and female apart (rare intersex cases excepted). This early developmental divergence is associated with the loss of the sexual plasticity found in our ancestors. Like it or not, much of how we experience sex and gender directly connects to these anatomical sex differences, differences that first evolved in our ancient amniote ancestors. Imagine what it would be like if, instead, we humans retained the sexual plasticity of fish. From this one page, the broader message of The Other Big Bang is apparent: we understand ourselves and our human predicament better when we know how we got here.

Visit Eric S. Haag's website.

--Marshal Zeringue