In “The Biomass Bottleneck,” Eric Toensmeier and Dennis Garrity address the strategy of drawing down billions of tons of carbon dioxide by using biomass for energy and carbon capture. Their analysis concludes that the amount of biomass required would leave the world with inadequate arable land to grow food. And they indicate that available biomass waste that currently has no other use is not available in sufficient quantity to make a significant dent in the climate change crisis.

I wish to call attention to a recent analysis by a consortium of scientists collaborating with Lawrence Livermore National Laboratory entitled Getting to Neutral: Options for Negative Carbon Emissions in California. The goal of this work was to create a cost-effective plan to bring California to carbon neutrality by 2045. In the report, the biggest contributor to attaining this goal is the conversion of waste biomass to fuels. The CO2 generated in producing such fuels can then be sequestered underground, leading to a net removal of CO2 from the atmosphere without impacting food production. I also wish to make the general point that some fraction of the biomass that is currently used for certain applications, such as animal feed, might need to be directed to clean energy generation and carbon capture in a carbon-constrained future.

I wholeheartedly agree with the authors that improvement in agricultural practices is profoundly important. Solving the climate crisis will require many different activities, whose nature can vary with geographical location. Utilizing waste biomass can play a significant role in allowing California to achieve its goal of carbon neutrality.

JOFFRE BAKER Montara, Calif.

Toensmeier and Garrity omit an important variable in their discussion of the potential for biomass energy. If people were to adopt a plant-based diet, the amount of agricultural land needed for food production would be greatly reduced. When crops are fed to animals, the loss of efficiency is staggering. And cattle are a major source of methane emissions. If people ate less meat, much existing cropland could be used for biomass energy with no harm to human welfare.

M. BARTON LAWS Brown University School of Public Health


In “Survival of the Friendliest,” Brian Hare and Vanessa Woods imply that a lack of friendliness led to the extinctions of at least four other known human species that were mutually extant with our own. But there are anthropologists who attribute our singular success to pursuing the genocidal destruction of all the other competing species. Similarly, many present-day religions claim superiority over all other competing religions, often seeking to eliminate the competition. Is there a genetic linkage between species domination and religious domination?

ROY BRUNO Redmond, Wash.

The authors refer to our species succeeding, but they never directly define what human success is, unless it is some crude Darwinian measure of reproduction and the displacement of other species. We can look around and see the impact of the “success” of eight billion people: We have the capacity for culture and can cooperate. Yet our cooperation has been used to wage war and commit genocide (even slaughtering people halfway across the globe); to cause extinctions and greatly diminish the numbers of other species; to turn complex ecosystems into monocultures; and to wreck a planet's climate. We have lost the ability to control the narcissists we produce. If this is cultural prowess and success, let's say that the story is not over yet. And it does not seem particularly friendly. There is good evidence we have become less emotionally mature as a species.

DAVID JOHNS McMinnville, Ore.


Thank you for “Black Health Matters,” by the Editors [Science Agenda], as well as the powerful imagery used to visually highlight the discrepancy in health care as it pertains to race. The illustration should be hung in research institutions and policy-making rooms around the country.

I agree that many of the health care disparities stem from systemic racism and policies, such as those that prevented Black people, in particular, from purchasing Federal Housing Administration–insured mortgages in our country until 1968—forcing many to live in segregated and overcrowded communities that have now become a breeding ground for pandemic-related illness. As a result of these policies, neighborhood schools became rife with underfunded, poor-quality education. That problem, in turn, led to the inability of many of those neighborhoods' residents to access higher education or jobs with decent wages, and they had far fewer opportunities to receive adequate health insurance and health care. The result was a reduced ability to learn about such health impacts as vitamin D deficiency, high blood pressure, and so on. Additionally, previously redlined neighborhoods have been surrounded by food deserts—with stores providing minimal access to fresh fruits and vegetables and rampant with an overabundance of processed and sugar-laden foods and drinks—which has led to disproportionate rates of type 2 diabetes. All these factors affect how Black and brown people are impacted by SARS-CoV-2, the virus that causes COVID-19.

I would love to see a recurring section of Scientific American that would analyze what information is available to doctors and scientists around the world pertaining to health consequences for Black and brown people. For example, you could examine the role that thrombosis plays in COVID-19 in this population and explain why, for many Black and brown individuals, the disease is vascular in nature rather than respiratory.

I concur that there will be another pandemic. And if all lives truly matter, addressing the science behind why COVID-19 is disproportionately affecting those of us in Black and brown communities will be one of the first steps in finding how to fix it and other ailments through the art of science. Imagine the impact an ongoing publication highlighting concurrent sociological and biological research on this population would have 20 years from now. And for those who don't care about the actual people being affected and whose primary concern is the impact on the economy, such information would inform how to keep businesses open and staffed with healthy employees because the frontline workers come predominantly from these communities.

KELLY ECTOR via e-mail


“Step Spy,” by Sophie Bushwick [Advances; July 2020], reports on sensors that identify people by their walking gait, which is unique for each person. I had to laugh when I read the article! I am now 77 years old. When I was seven, my mother went out one day to visit a neighbor in our building. She told me not to answer the door to anyone but her. I was to make absolutely sure it was her before I answered the door. An hour later I heard her come down the stairs and approach the door, so I opened it. Of course, I was punished—despite insisting that I did know it was her because I recognized her gait.

I can't undo the spanking I got, but after 70 years it feels good to be vindicated at last.

JUDY ANDERSON via e-mail