Carbon monoxide is lethal for big oxygen breathing mammals, like us, so it seems reasonable that the build up of the gas to toxic levels would inhibit complex lifeforms around other stars. What seems reasonable at first glance, isn’t always so upon further analysis.
The Claim – CO Build Up and the Absence of Complex Life… A Limited Habitable Zone for Complex Life
Carbon dioxide is shown quite clearly to be a limiting variable for higher organisms. Quite low levels are toxic in the long term – even 1% CO2 levels are restrictive. Carbon monoxide is proposed as another limiting variable, but this can be disputed… as per the comment.
The Counter-claim Comment on “A Limited Habitable Zone for Complex Life”
Carbon monoxide toxicity is a feature of one oxygen carrier biomolecule, hemoglobin, but not of other oxygen carriers. Thus complex life isn’t limited by CO abundance if its chemistry is tweaked away from the unique ‘defect’ of hemoglobin and its fugacity for CO.