Letters to the editor from the August 2018 issue of Scientific American

Readers Respond to the August 2018 Issue


In “Bringing Darwin Back” [Special Education Report 2018], Adam Piore discusses how a majority of American teachers do not fully teach evolutionary theory. He also reports on groups promoting strategies for preparing teachers to do so in communities that are biased against the subject.

To teach evolution effectively and productively, the sequence of topics should be changed. The first should be ecology and then genetics, with the latter’s last chapter covering evolution. Integrating evolution with those two subjects would show students that evolution is needed for ecological adaptation and that the way for it to occur over the long term is through natural selection for those traits that are adaptive at a given time. And it should be impressed on them that evolution is an absolute necessity because the planet is always changing and that for a living system to be successful it must also change.

I doubt that any students would profess to not “believe” in genetics and ecology. And they could be asked if they think that humans are “apart from nature” or “a part of nature.” I think many would accept that they are a part of nature and have evolved because the evidence is overwhelming.

BRIAN MYRES Professor emeritus of biology, Cypress College

As a retired biology teacher with 20 years of experience teaching evolution in high school, I have found an ideal way to present the topic: I begin my three-day lesson by announcing that the earth itself has embedded a key part of biology in its record. It has documented the natural process of evolution at work in all life-forms on the planet. I then ask the kids to define “evolution.” Some do so accurately; a few proclaim that it says people come from monkeys. I then define it: “Evolution is simply a natural change in the design of species over time, in response to changes in their environment.” That’s it! The kids don’t complain about something so simple.

I then spend two days outlining exactly how species change over time in response to the environment, including through natural selection. I give the students graphic slides showing organisms changing. I challenge them to identify what long-term changes would make sense in an organism if its environment, for example, got colder or warmer. They discover for themselves why organisms get bigger, or smaller, or smarter, or more colorful.

Kids are exquisitely sensitive to their peers. As they logically progress through the examples as a group, they become hesitant to voice any religious objection to a process so obvious and rationally innocent as the realization that species change over time in response to their environment. As a result, when I finally introduce them to the evidence that people, too, have evolved in design over time, they get it.



In “Is Dark Matter Real?” Sabine Hossenfelder and Stacy S. McGaugh compare two explanations for how stars orbit in galaxies and galaxies orbit in clusters: a long-assumed theory involving invisible particles having mass (dark matter) and theories that change the mathematical description of gravitational forces (modified gravity).

Einstein tells us that gravity is only an apparent force that results from the curvature of spacetime and that mass causes such curvature. Might it be that things other than mass (dark energy, for one) can cause it as well? Could dark energy’s distortive effects on galactic scales result in a kind of local “bubbling” of spacetime?

KEITH BACKMAN Bedford, Mass.

I find it surprising that the authors have nothing to say about the influence of the darkest of the dark: black holes. In particular, the lack of density peaks in a galactic core might be affected by the presence of a central black hole, which could gorge itself on the dark matter distribution.


THE AUTHORS REPLY: Regarding Backman’s question: According to Einstein’s theory of gravity, all kinds of energy and mass cause spacetime to curve. Dark energy does affect the curvature, but it does not do so in the right way to give rise to the effects attributed to dark matter. Actually “dark energy” and “dark matter” are just names that physicists have given to what they conclude is necessary to explain the observations, and they have different properties. Dark energy is the stuff that causes the accelerated expansion of the universe. Its influence is negligible inside of galaxies.

In response to Turchi: The center of the Milky Way hosts a supermassive black hole that weighs in at about four million solar masses and that heats up surrounding gas as it falls in. Mind-boggling as that is, neither its gravitational influence nor the hot gas has much of an effect on the overall motion of the galaxy. The central black hole really plays a role for only the innermost regions of the galaxy, and the mass of the hole is tiny compared with the mass of dark matter needed to explain our observations.


“Capture That Carbon,” by Madison Freeman and David Yellen [Forum], discusses carbon capture, utilization and storage (CCUS), in which carbon captured from the smokestacks or removed directly from the air is turned into useful products or something that can be stored long term.

It should now be clear to all who follow the trends in climate change that we have long since passed the point where simply reducing emissions will be enough to solve the problem. The authors cite the difficulty of securing the investment funds needed to fully develop CCUS technologies to the level necessary to have the desired effect.

But there is another very low-tech, well-established approach that could be implemented immediately: forestry management. By ensuring that a new tree is planted for every mature tree cut, lumber going into construction could effectively be stored carbon. A critical element of this method is, of course, ensuring that all cut mature trees are replaced. One of the most destructive trends in the current situation is the conversion of tropical forest into pastureland or other agricultural use.

The technology of forest management is available right now. But we do need to change the economic value placed on forests in all regions. They could make an important contribution to sustaining a habitable planet.

PAUL M. MARTIN Springfield, Mass.


In “That’s Life” [Anti Gravity], Steve Mirsky notes a study asserting that it “found no reports of primary data relating to health aspects of the use of sex robots.” In response, I would like to point out that absence of evidence is not evidence of abstinence—or even evidence for absence.



“Is Dark Matter Real?” by Sabine Hossenfelder and Stacy S. McGaugh, should have referred to the theory of particle dark matter predicting many more small dwarf galaxies than are observed rather than fewer. Further, the units for the graph in the box “A Problem for Dark Matter” should have been given as meters per second squared rather than meters per second.

Stephen Ornes’s “Art by the Numbers” should have said that there will never be a finite number of primes rather than a countable number.