Study 1

In Study 1 (US sample, n = 183, mean age 38.2, 50.81% female), we studied the general public’s judgments of the badness of human extinction. A large majority of the participants (78.14%, 143/183 participants) found human extinction to be bad on a binary question (bad vs. not bad), and we got similar results on a seven-point scale (1 = definitely not bad, 4 = midpoint, 7 = definitely bad; M = 5.61; SD = 2.11). Participants also felt strongly that human extinction needs to be prevented (1 = not at all, 4 = midpoint, 7 = very strongly; M = 6.01, SD = 1.65), that they have a moral obligation to prevent it (1 = definitely no, 4 = midpoint, 7 = definitely yes; M = 5.69, SD = 1.86), and that funding work to reduce the risk of human extinction is more important than funding other areas of government, such as education, health care and social security (1 = much less important to fund work to reduce the risk of human extinction, 4 = midpoint, 7 = much more important; M = 5.43, SD = 1.72). Participants believed that provided that humanity will not go extinct, the future is going to be roughly as good as the present (1 = much worse than the present world, 4 = about as good as the present world, 7 = much better than the present world; M = 4.48, SD = 1.57), and the better they thought the future would be, the worse they considered extinction to be (r = 0.51, P < 0.001), as measured by the seven-point scale. Similarly, more optimistic26 participants judged extinction to be worse (r = 0.32, P < 0.001). Participants’ responses to the question whether the world gets better if a happy person comes into existence were close to the midpoint (1 = definitely not better, 4 = midpoint, 7 = definitely better; M = 4.45, SD = 1.73), and people who thought that that would make the world better were more likely (r = 0.22, P = 0.003) to find extinction bad. For further details about the results, see Supplementary Materials.

Study 2a

Having thus observed that people do find human extinction bad, we turned to studying whether they find it uniquely bad relative to non-extinction catastrophes in Study 2a (pre-registered at https://osf.io/hj2n4; British sample). Participants (n = 1,251, mean age 36.6, 35.33% female) were randomly divided into a control condition and four experimental conditions: “the animals condition”, “the “sterilization condition”, “the salience condition” and “the utopia condition” (see below for explanations of the manipulations). Participants in the control condition (257 participants) were presented with the three outcomes described above—no catastrophe, a catastrophe killing 80%, and a catastrophe killing 100%—and were asked how they would rank them from best to worst. As Parfit expected, a large majority (82.88%, 213/257 participants, cf. Fig. 1) ranked no catastrophe as the best outcome and 100% dying as the worst outcome. However, this was just a preliminary question: as per the discussion above, what we were primarily interested in was which difference participants that gave the expected ranking found greater: the first difference (meaning that extinction is not uniquely bad) or the second difference (meaning that extinction is uniquely bad). (Recall that the first difference was the difference between no catastrophe and a catastrophe killing 80%, and the second difference the difference between a catastrophe killing 80% and a catastrophe killing 100%.) We therefore asked participants who gave the expected ranking (but not the other participants) which difference they judged to be greater. We found that most people did not find extinction uniquely bad: only a relatively small minority (23.47%, 50/213 participants) judged the second difference to be greater than the first difference.

Figure 1 Proportions of participants who found extinction uniquely bad. (This means that they found the difference, in terms of badness, between a catastrophe killing 80% and a catastrophe killing 100% to be greater than the difference between no catastrophe and a catastrophe killing 80%.) Laypeople consistently did not find extinction uniquely bad in the control condition (Control), but did so in a scenario where the future would be very long and good conditional on survival (Utopia). The animals condition (Animals), sterilization condition (Sterilization) and salience condition (Salience) yielded in-between results. People explicitly devoted to existential risk reduction (Existential risk mitigators) consistently found extinction uniquely bad. Full size image

As stated, we included four experimental conditions aiming to explain these results. We thought that one reason why participants do not find extinction uniquely bad in the control condition is that they feel strongly for the victims of the catastrophes. Therefore, they focus on the immediate suffering and death that the catastrophes cause, which leads them to judge the difference between no one dying and 80% dying to be greater than the difference between 80% dying and 100% dying. To test this hypothesis, we included two conditions designed to trigger a weaker focus on the immediate harm. First, we included a condition where the catastrophes affected an animal species (zebras) rather than humans (“the animals condition”; otherwise identical to the control condition; 246 participants). (We chose zebras because zebra extinction would likely have small effects on humans; in contrast to extinction of, for example, pigs or dogs.) We hypothesized that people focus less on the immediate harm that the catastrophes cause if the catastrophes affect animals rather than humans27. Second, we included a condition where the catastrophes led to 80%/100% of the world’s population being unable to have children, rather than getting killed (“the sterilization condition”; otherwise identical to the control condition; 252 participants). We hypothesized that people would focus less strongly on the immediate harm that the catastrophes cause if they lead to sterilization rather than death.

Thus, we hypothesized that a greater share of the participants who gave the expected ranking would find extinction uniquely bad in the animals condition and the sterilization condition than in the control condition. We found, first, that a large majority ranked no catastrophe as the best outcome and 100% dying as the worst outcome (the expected ranking) both in the animals condition (89.84%, 221/246 participants) and the sterilization condition (82.54%, 208/252 participants). Subsequently, we found that our hypotheses were confirmed. The proportion of the participants who gave the expected ranking that found extinction uniquely bad was significantly larger (χ2(1) = 8.82, P = 0.003) in the animals condition (44.34%, 98/221 participants) than in the control condition (23.47%, 50/213 participants). Similarly, the proportion of the participants who gave the expected ranking that found extinction uniquely bad was significantly larger (χ2(1) = 23.83, P < 0.001) in the sterilization condition (46.63%, 97/208 participants) than in the control condition (23.47%, 50/213 participants).

We had another hypothesis for why control condition participants do not find extinction uniquely bad, namely that they neglect the long-term consequences of the catastrophes. To test this hypothesis, we included a condition where we made the long-term consequences salient (“the salience condition”; 248 participants). This condition was identical to the control condition, with the exception that we added a brief text explicitly asking the participants to consider the long-term consequences of the three outcomes. It said that if humanity does not go extinct (including if it suffers a non-extinction catastrophe, from which it can recover) it could go on to a long future, whereas that would not happen if humanity went extinct (see the Methods section for the full vignette). We also wanted to know whether participants see empirical information about the quality of the future as relevant for their judgments of the badness of extinction. Does it make a difference how good the future will be? We therefore included a maximally positive scenario, the “utopia condition” (248 participants), where it was said that provided that humanity does not go extinct, it “goes on to live for a very long time in a future which is better than today in every conceivable way”. It was also said that “there are no longer any wars, any crimes, or any people experiencing depression or sadness” and that “human suffering is massively reduced, and people are much happier than they are today” (in the scenario where 80% die in a catastrophe, it was said that this occurred after a recovery period; see the Methods section for the full text). Conversely, participants were told that if 100% are killed, then “no humans will ever live anymore, and all of human knowledge and culture will be lost forever.” We hypothesized that both of these manipulations would make more participants judge extinction to be uniquely bad compared with the control condition.

We found again that a large majority ranked no catastrophe as the best outcome and 100% dying as the worst outcome (the expected ranking) both in the salience condition (77.82%, 193/248 participants) and the utopia condition (86.69%, 215/248 participants). Subsequently, we found that our hypotheses were confirmed. The proportion of the participants who chose the expected ranking that found extinction uniquely bad was significantly larger (χ2(1) = 29.90, P < 0.001) in the salience condition (50.25%, 97/193 participants) than in the control condition (23.47%, 50/213 participants). Similarly, the proportion of the participants who chose the expected ranking that found extinction uniquely bad was significantly larger (χ2(1) = 30.30, P < 0.001) in the utopia condition (76.74%, 165/215 participants) than in the control condition (23.47%, 50/213 participants). We also found that there was a significant difference between the utopia condition and the salience condition (χ2(1) = 29.90, P < 0.001).

Our interpretation of these results is as follows. The utopia manipulation effectively does two things: it highlights the long-term consequences of the outcomes, and it says that unless humanity goes extinct, those consequences are going to be extraordinarily good. The salience manipulation only highlights the long-term consequences. Thus, we can infer that merely highlighting the long-term consequences make people more likely to find extinction uniquely bad, and that adding that the long-term future will be extraordinarily good make them still more likely to find extinction uniquely bad.

Lastly, we found that across all conditions, the more cognitively reflective the participants were (as measured by the Cognitive Reflection Test28), the more likely they were to judge extinction to be uniquely bad (Exp(B) = 0.15, P = 0.01, Odds ratio = 1.6).

In conclusion, we find that people do not find extinction uniquely bad when asked without further prompts, and have identified several reasons why that is. As evidenced by the animals and the sterilization conditions, they focus on the immediate harm that the catastrophes cause, because they feel strongly for the victims of the catastrophes—and on that criterion, near-extinction is almost as bad as extinction. As evidenced by the salience condition, they neglect the long-term consequences of the outcomes. We also find that participants’ empirical beliefs about the quality of the future make a difference: telling participants that the future will be extraordinarily good makes them significantly more likely to find extinction uniquely bad.

Study 2b

To find out whether these results would hold up with different demographics, we aimed to replicate them using a sample of the US general public (pre-registered at https://osf.io/8amxs; N = 855, mean age 36.85, 48.65% female) in Study 2b. We found again that large majorities ranked no catastrophe as the best outcome and 100% dying as the worst outcome (the expected ranking) in the control condition (87.80%, 144/164 participants), the animals condition (92.44%, 159/172 participants), the sterilization condition (91.62%, 153/167 participants), the salience condition (83.05%, 147/177 participants) and the utopia condition (89.71%, 157/175 participants). And again we found that only a small minority of the participants who chose the expected ranking judged extinction to be uniquely bad in the control condition (18.75%, 27/144 participants). The proportion of the participants who chose the expected ranking who found extinction uniquely bad was significantly larger in the animals condition (34.59%, 55/159 participants; χ2(1) = 8.82, P = 0.003), the salience condition (39.45%, 58/147 participants; χ2(1) = 14.10, P < 0.001) and the utopia condition (66.88%, 105/157 participants; χ2(1) = 68.72, P < 0.001) than in the control condition. We also again found a significant difference between the utopia condition and the salience condition (χ2(1) = 21.868, P < 0.001). However, in the sterilization condition, only 28.75% (44/153 participants) of the participants who chose the expected ranking found extinction uniquely bad, which meant that the difference with the control condition was not significant on the 0.05-level (χ2(1) = 3.55, P = 0.059). Lastly, we found again that (across all conditions) the more cognitively reflective the participants were (as measured by the Cognitive Reflection Test), the more likely they were to judge extinction to be uniquely bad (Exp(B) = 0.21, P = 0.005, Odds ratio = 1.2).

Study 2c

To further test the robustness of our findings across different demographics, we conducted Study 2c as another replication, this time using a sample of University of Oxford students (N = 196, mean age 24.27, 61% female). We only included the control and the utopia conditions. We found again that most participants ranked no catastrophe as the best outcome and 100% dying as the worst outcome (the expected ranking) both in the control condition (65.7%, 65/99 participants) and the utopia condition (84.5%, 82/97 participants). We then found again that a minority of the participants who chose the expected ranking found extinction to be uniquely bad in the control condition (36.92%, 24/65 participants), though this minority was slightly larger than in the two samples of the general public (cf. Fig. 1). We also found again that the proportion of the utopia condition participants who chose the expected ranking that found extinction uniquely bad (76.83%, 63/82 participants) was significantly larger (χ2(1) = 22.28, P < 0.001) than in the control condition. (These findings were further supported by five supplementary studies; see Supplementary Materials).

Study 3

In Studies 2a to 2c, we thus found that when asked without further prompts, laypeople do not find extinction uniquely bad. In Study 3 (N = 71, mean age 30.52, 14.00% female) we aimed to test whether people devoted to preventing human extinction (existential risk mitigators) judge human extinction to be uniquely bad already when asked without further prompts. (Existential risks also include risks that threaten to drastically curtail humanity’s potential12,13,14,15, without causing it to go extinct, but we focus on risks of human extinction.) This would support the validity of our task by demonstrating a link between participants’ responses and behavior in the real world.

We recruited participants via the Effective Altruism Newsletter and social media groups dedicated to existential risk reduction, and only included respondents who put down reducing existential risk as their “most important cause”. Again we had two conditions, the control condition and the utopia condition. We hypothesized that a majority of participants would find extinction uniquely bad in both conditions. We found again that most participants ranked no catastrophe as the best outcome and 100% dying as the worst outcome (the expected ranking) both in the control condition (90.32%, 28/31 participants) and the utopia condition (92.50%, 37/40 participants). But unlike the samples in Studies 2a to 2c, and in line with our hypotheses, substantial majorities of the participants who chose the expected ranking found extinction uniquely bad both in the control condition (85.71%, 24/28 participants) and the utopia condition (94.59%, 35/37). The difference between the conditions was not significant (χ2(1) = 0.63, P = 0.43). In contrast to laypeople, existential risk mitigators thus found human extinction to be uniquely bad even when the description of the outcomes did not include information about the quality of the future. This suggests that judging human extinction to be uniquely bad, as measured by our task, may be a key motivator for devoting oneself to preventing it.