Abstract
Introduction:
Organ donation and other altruistic behaviors may be influenced by multiple factors, such as demographic characteristics, religious beliefs, and social norms.
Research Question:
We sought to examine the role of genetic factors on altruism by studying identical and fraternal twin pairs.
Design:
We surveyed 296 twins at a twins festival about organ donation and other altruistic behaviors.
Results:
The rate of concordance for stage of change with respect to organ donation was 65% among identical twin pairs versus 33% among fraternal twin pairs (p=0.004). Rates of concordance were also higher among identical vs. fraternal twin pairs for several altruistic behaviors, including giving directions to a stranger (63% vs. 24%, p<0.001), giving money to a stranger (51% vs. 29%, p=.048), donating goods to charity (46% vs. 16%, p=0.005), and offering a seat on the bus (46% vs. 24%, p=0.04).
Discussion:
We conclude that genetic factors play a role in decisions about organ donation and other altruistic behaviors.
Keywords: Organ donation, altruism, twins, survey
Introduction
Even though most individuals perceive organ donation positively, just over half of adults in the United States are registered organ donors.1 Understanding why individuals choose to be organ donors may help to develop interventions to increase organ donation. There may be some overlap between willingness to be an organ donor, willingness to donate blood and bone marrow, and the willingness to engage in other altruistic behaviors. For example, registered bone marrow donors tend to also donate blood regularly and are frequently willing to donate kidneys after death.2 Multiple factors, such as demographic characteristics, religious beliefs, and social norms, may contribute to decisions about organ donation and other altruistic behaviors.3,4 Previous research suggests that genetic factors may also play a role in altruism.5–7 However, these studies did not specifically examine organ donation.
Specific Aim
We sought to examine the role of genetic factors on organ donation and other altruistic behaviors by studying twin pairs. If genetic factors contribute to altruism, we would expect that identical twins would be more alike than fraternal twins in willingness to donate organs, blood, and bone marrow as well as in other altruistic behaviors.
Methods
Design
We performed a survey study that the institutional review board of MetroHealth Medical Center granted exempt status.
Setting/Population
The study was conducted August 5–6, 2017 at an annual twin’s day festival in Twinsburg, Ohio. The festival is the largest gathering of twins in the world and includes both identical and fraternal twins. Twins were recruited via signage in the research plaza area of the festival. Participants were each given a US $2 bill for answering the survey. Each twin gave verbal consent for participation.
Data Collection
Each participating twin was asked to complete a survey. Survey questions asked about demographic characteristics; stage of change with respect to organ, bone marrow, and blood donation; and altruistic behaviors. Stage of change questions, based on the transtheoretical model, have been used extensively to study smoking cessation and other health behaviors.8–10 The transtheoretical model posits that individuals move through a series of stages in decision making, ie pre-contemplation, contemplation, preparation, action, and maintenance. Each stage reflects a particular level of readiness to act so interventions can be tailored to subject responses.11 The stage of change items were from a reliable questionnaire used previously that asked subjects 1) if they had already decided not to be an organ donor, 2) if they were contemplating being an organ donor or needed more information about organ donation, 3) if they were thinking about being an organ donor, 4) if they were interested in being an organ donor, and 5) if they were already registered to be an organ donor.12 Similar questions were asked about bone marrow and blood donation.
The other altruistic behaviors were from a validated scale.13,14 We used 14 relevant items from the scale that did not overlap with questions asked in other parts of our survey and were considered time- and age-appropriate altruistic behaviors for the year that the survey took place and age range of participants. This self-reported survey asked about how often twins engaged in altruistic acts. Participants responded to these questions with one of the following choices: “Never”, “Once”, “More than Once”, “Often”, and “Very Often”. Responses for each of the questions were scored on a 0 to 100 scale. 0 meant that the participant “Never” engaged in the altruistic behavior. 100 meant that the participant responded “Very Often” to the altruistic behavior. The score for each question increased by 25 points for each increase in frequency on the scale. All responses were summed together and higher scores meant more altruism. The highest possible score would be 100. We also examined each participant’s driver’s license to determine if he/she was registered as an organ donor. A total of 68 (23%) participants did not have a license to review. In these cases, self-report of donor status was used as a proxy.
Analysis
Demographic information is reported as frequencies for categorical variables and means for continuous variables. We used the chi square test or the t test to compare the demographic characteristics of identical and fraternal twins. Overall concordance was defined as each twin in a pair providing the same response to a specific question. We used the chi square test to compare overall concordance among identical twins versus fraternal twins. In addition, we examined concordance separately for altruistic and non-altruistic responses. Positive concordance was defined as each twin in a pair selecting one of the top two stages of change for organ, blood, or bone marrow donation (interested in being a donor or already donated) and frequency of altruistic behaviors (often and very often). Negative concordance was defined as each twin in a pair selecting responses in any of the other stages of change or frequency of altruistic behaviors. Data were analyzed using JMP Pro 13.0.0 (SAS Institute, Cary, North Carolina). For two twin pairs, only one twin completed the survey. As a result we excluded these two twin pairs (total of 4 individuals) from all analyses.
Results
Participant characteristics
Of 296 twins who participated in the survey, 246 (83%) were identical twins and 50 (17%) were fraternal twins. The mean age was 36 years (Table 1). Most participants were female non-Hispanic whites. Most had a religious affiliation, and three-fourths completed additional education beyond high school. There were no statistically significant differences between identical and fraternal twins in demographic characteristics.
Table 1:
Characteristics of participants.
| Characteristic | Overall (n=296) | Identical Twins (n=246) | Fraternal Twins (n= 50) | p-value |
|---|---|---|---|---|
| Mean age, years (SD) | 36 (18) | 36 (18) | 35 (18) | 0.52 |
| Female, n (%) | 235 (80%) | 200 (81%) | 35 (71%) | 0.12 |
| Race, n (%) | 0.55 | |||
| White | 259 (87%) | 214 (87%) | 45 (90%) | |
| Black | 22 (7%) | 18 (7%) | 4 (8%) | |
| Other | 17 (6%) | 14 (6%) | 1 (2%) | |
| Hispanic, n (%) | 3 (1%) | 3 (1%) | 0 (0%) | 0.45 |
| Religion, n (%) | 0.24 | |||
| Catholic | 73 (26%) | 66 (28%) | 7 (15%) | |
| Protestant | 118 (42%) | 96 (41%) | 22 (46%) | |
| Jewish | 6 (2%) | 5 (2%) | 1 (2%) | |
| Other | 24 (8%) | 21 (9%) | 3 (6%) | |
| None | 63 (22%) | 48 (20%) | 15 (31%) | |
| Highest Education, n (%) | 0.07 | |||
| High school graduate | 70 (24%) | 54 (22%) | 16 (32%) | |
| Some college or vocational training | 56 (19%) | 42 (17%) | 14 (28%) | |
| College degree | 110 (38%) | 97 (40%) | 13(26%) | |
| Graduate degree | 46 (19%) | 49 (20%) | 7 (14%) |
Organ donation
Among all twins, 23 (8%) did not want to be an organ donor, 27 (9%) had not contemplated being an organ donor or needed more information, 34 (11%) were thinking about being an organ donor, 34 (11%) were interested in being an organ donor, and 176 (59%) were already registered to be an organ donor. The overall concordance for stage of change for organ donation was 65% among identical twin pairs versus 33% among fraternal twin pairs (P=.004; Table 2). Overall concordance for stage of change for bone marrow donation and blood donation did not differ significantly among identical vs fraternal twin pairs. There was no difference in overall concordance for being a registered organ donor among identical vs fraternal twin pairs. The results for positive and negative concordance are presented in Table 3.
Table 2:
Concordance of twin pairs for stage of change, organ donor registration, and other altruistic behaviors.
| Concordance among identical twins (%) | Concordance among fraternal twins (%) | p value | |
|---|---|---|---|
| Stage of change | |||
| Organ Donor | 79/122 (65%) | 8/24 (33%) | 0.004 |
| Bone Marrow Donor | 53/122 (43%) | 13/24 (54%) | 0.33 |
| Blood Donor | 74/123 (60%) | 15/24 (63%) | 0.83 |
| Registered Organ Donor | 98/119 (82%) | 18/25 (72%) | 0.23 |
| Altruism Behaviors | |||
| Given directions to a stranger | 77/123 (63%) | 6/25 (24%) | <0.001 |
| Given money to charity | 80/123 (65%) | 12/25 (48%) | 0.11 |
| Given money to a stranger | 63/123 (51%) | 7/24 (29%) | 0.048 |
| Donated goods to charity | 56/121 (46%) | 4/25 (16%) | 0.005 |
| Done volunteer work for charity | 61/120 (51%) | 8/24 (33%) | 0.12 |
| Delayed an elevator and held door for stranger | 57/123 (46%) | 10/25 (40%) | 0.56 |
| Allowed someone to go ahead in line | 64/121 (53%) | 12/25 (48%) | 0.66 |
| Given a stranger a lift in car | 86/122 (70%) | 14/24 (58%) | 0.24 |
| Pointed out a clerk’s error in undercharging for item | 55/122 (45%) | 6/24 (25%) | 0.07 |
| Let a neighbor borrow an item of value | 50/120 (42%) | 7/25 (28%) | 0.20 |
| Voluntarily looked after a neighbor’s pets or children without being paid | 47/123 (38%) | 7/25 (28%) | 0.33 |
| Offered to help a handicapped or elderly stranger across street | 49/122 (40%) | 7/25 (28%) | 0.25 |
| Offered my seat on a bus or train to stranger | 55/120 (46%) | 6/25 (24%) | 0.04 |
| Helped an acquaintance to move households | 50/123 (41%) | 6/25 (24%) | 0.12 |
Missing data (e.g. one or both twins in pair did not answer question) were omitted from analysis.
Table 3:
Positive and negative concordance of twin pairs for stage of change and other altruistic behaviors.
| Positive concordance among identical twins (%) | Negative concordance among identical twins (%) | Positive concordance among fraternal twins (%) | Negative concordance among fraternal twins (%) | |
|---|---|---|---|---|
| Stage of change | ||||
| Organ Donor | 76/122 (62%) | 21/122 (17%) | 11/24 (46%) | 2/24 (8%) |
| Bone Marrow Donor | 15/122 (12%) | 73/122 (60%) | 2/24 (8%) | 14/24 (58%) |
| Blood Donor | 67/123 (54%) | 27/123 (22%) | 15/24 (63%) | 2/24 (8%) |
| Registered Organ Donor | 66/119 (55%) | 32/119 (27%) | 10/25 (40%) | 8/25 (32%) |
| Altruism Behaviors | ||||
| Given directions to a stranger | 37/123 (30%) | 54/123 (44%) | 5/25 (20%) | 8/25 (32%) |
| Given money to charity | 47/123 (38%) | 52/123 (42%) | 7/25 (28%) | 11/25 (44%) |
| Given money to a stranger | 9/123 (7%) | 91/123 (74%) | 2/24 (8%) | 19/24 (79%) |
| Donated goods to charity | 66/121 (55%) | 17/121 (14%) | 13/25 (52%) | 1/25 (4%) |
| Done volunteer work for charity | 46/120 (38%) | 42/120 (35%) | 6/24(25%) | 9/24 (38%) |
| Delayed an elevator and held door for stranger | 73/123 (59%) | 14/123 (11%) | 14/25 (56%) | 3/25 (12%) |
| Allowed someone to go ahead in line | 49/121 (40%) | 38/121 (31%) | 15/25 (60%) | 5/25 (20%) |
| Given a stranger a lift in car | 1/122 (1%) | 112/122 (92%) | 0/24 (0%) | 23/24 (96%) |
| Pointed out a clerk’s error in undercharging for item | 8/122 (7%) | 96/122 (79%) | 2/24 (8%) | 17/24 (71%) |
| Let a neighbor borrow an item of value | 5/120 (4%) | 104/120 (87%) | 3/25 (12%) | 20/25 (80%) |
| Voluntarily looked after a neighbor’s pets or children without being paid | 13/123 (11%) | 85/123 (69%) | 2/25 (8%) | 12/25 (48%) |
| Offered to help a handicapped or elderly stranger across street | 14/122 (11%) | 88/122 (72%) | 6/25 (24%) | 16/25 (64%) |
| Offered my seat on a bus or train to stranger | 10/120 (8%) | 75/120 (63%) | 3/25 (12%) | 9/25 (36%) |
| Helped an acquaintance to move households | 15/123 (12%) | 74/123 (60%) | 4/25 (16%) | 11/25 (44%) |
Other altruistic behaviors
The mean total altruism score was 50 among identical twins and 52 among fraternal twins (P=.47) on a scale from 0 to 100, where 100 is highest level of altruism. Rates of concordance were higher among identical vs fraternal twin pairs for several altruistic behaviors, including giving directions to a stranger (63% vs 24%, P<.001), giving money to a stranger (51% vs 29%, P=.048), donating goods to charity (46% vs 16%, P=.005), and offering a seat on the bus (46% vs 24%, P=.04; Table 2).
Discussion
We found that the rate of concordance in stage of change for organ donation was significantly higher among identical twins versus fraternal twins. Rates of concordance were also higher for several other altruistic behaviors among identical twins as compared to fraternal twins, including giving directions or money to a stranger, donating goods to charity, and offering a seat on the bus. By contrast, there was no statistically significant difference in rates of concordance among identical as compared to fraternal twins for stage of change for bone marrow donation and blood donation; organ donor registration; and several other altruistic behaviors. The strengths of our study include a large sample size of twins, use of driver’s licenses to confirm organ donor registration, and assessment of a variety of altruistic behaviors.
Previous research suggested that genetic factors may also play a role in altruism. A Spanish study on genetics and altruism found that identical twin pairs were more willing to self-sacrifice for each other than fraternal twin pairs. However, there was no difference between identical and fraternal twin pairs in willingness to fight for each other.7 A study of Danish twins showed that rates of concordance for blood donation were higher among identical twin pairs (42%) than among fraternal twin pairs (23%).6 An English study on self-reported altruistic behaviors concluded that about half of the variance in subject responses was associated with genetic factors.5
Since there is a genetic component to altruism and organ donation, our findings suggested that efforts to improve organ donation registration may focus on members of the same family and even through family discussions. Future research to address attitudinal, socioeconomic, or religious differences among genetically similar or identical individuals in willingness to register as organ donors may be important.
Several limitations must be considered in interpreting our findings. We enrolled a convenience sample of participants. The modest number of fraternal twin pairs may have limited our ability to draw statistically significant conclusions. The proportion of participants who were registered donors is very high and may not be representative of the general population.1 This high level of registration may also have limited the power of study to find a difference in concordance between identical and fraternal twin pairs.
Conclusion
Genetic factors appear to play a role in decisions about organ donation and other altruistic behaviors. Future work is needed to better quantify the relative importance of genetic vs non-genetic factors and to use this information to help develop interventions to increase organ donation.
Acknowledgments
Grant information: Grants U54MD002265, P60MD002265, and K23DK101492 from the National Institutes of Health and grant R390T26989 from the Health Resources and Services Administration.
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