Are They Cousins? Exploring University Students’ Acceptance of Common Ancestry in Evolution

Abstract

Efforts to measure student acceptance of evolution have led to the development of several surveys. One persistent challenge has been constructing a survey that accurately characterizes not only students who accept or reject evolution in its entirety, but also those who accept only certain aspects. This study sought to inform these efforts by exploring how students delineate between what they perceive as acceptable versus unacceptable claims of shared ancestry. We conducted semistructured interviews with U.S. university students in which participants were shown pairs of organisms, asked to explain whether they think the two shared a common ancestor, and explain why or why not. We found that 1) most participants accepted common ancestry for closely related species but rejected it for distantly related species, 2) participants frequently rejected common ancestry between terrestrial and aquatic species, citing habitat differences, 3) participants who rejected common ancestry between humans and chimpanzees often expressed acceptance of human microevolution, and 4) participants who later claimed no creationist beliefs displayed views on evolution similar to those of self-described creationists. These findings can inform ongoing efforts to improve the measurement of student evolution acceptance, particularly those measuring both conceptual knowledge and personal assent.

INTRODUCTION

Why Does Measuring Evolution Acceptance Matter?

The theory of evolution is the “central organizing principle of modern biology” (National Academy of Sciences, 2008) and, as such, the American Association for the Advancement of Science (AAAS) has deemed it to be one of the five core concepts of an undergraduate biology education in its Vision and Change report (AAAS, 2011). Nevertheless, evolution is one of a few well-established scientific theories that many people in the United States continue to reject. Studies at both secular and religiously affiliated institutions have found that introductory biology students commonly exhibit low acceptance of macroevolution (at scales ranging from speciation to the shared ancestry of all life) and human evolutionary history (Siciliano-Martina and Martina, 2020; Ferguson and Jensen, 2021; Grunspan et al., 2021; Aini et al., 2024). This prevalence of evolution hesitance and denial is also reflected among the general public, with nationwide polls showing that more than a third of Americans reject human evolution (Miller et al., 2022; Gallup Inc., 2024).

In evolution education, it is important for students to both understand evolution and adopt it as their working, scientific explanation for the unity and diversity of life. Students with a better understanding of and attitudes toward evolution tend to do better in postsecondary biology courses (Carter et al., 2015). Furthermore, even individuals who understand evolution well enough to pass exams are unlikely to want to apply it in their postgraduation career if they do not accept the scientific validity of what they have learned. For example, studies with preservice K-12 science teachers have found that science teachers who do not accept evolution are less likely to teach it in a thorough and scientifically accurate manner (Berkman and Plutzer, 2011; Plutzer et al., 2020). This is concerning because evolution has applications for many biology-related professions, not only in education, but also in agriculture (e.g., importance of crop biodiversity), biomedical research (e.g., antibiotic resistance, selection of animal models), and public health (e.g., managing disease outbreaks) (Graves et al., 2016; Johnson, 2022; Natterson-Horowitz et al., 2023). As such, undergraduate biology students need to not only understand evolution but also accept it if they are to make full use of their biology education after graduation. Furthermore, the issue of evolution acceptance among teachers and the general public is of great importance because while evolution is included in the Next Generation Science Standards for K-12 education (National Research Council, 2013) and the teaching of it is endorsed by U.S.-wide teachers’ organizations (National Science Teachers Association, 2003; National Association of Biology Teachers, 2019), recent legislative efforts have attempted to introduce intelligent design into science instruction (West Virginia SB 280, 2024; North Dakota, 2025).

Due to the educational importance of evolution acceptance, a substantial portion of evolution education research seeks to 1) identify the causes of evolution rejection and 2) develop instructional strategies that will help increase evolution acceptance among students (Lloyd-Strovas and Bernal, 2012; Nadelson and Hardy, 2015; Fiedler et al., 2019; Lindsay et al., 2019; Sbeglia and Nehm, 2020; Barnes et al., 2021; Ferguson and Jensen, 2021; Laidlaw et al., 2022). Although research questions and methods vary across studies, nearly all such research relies upon surveys designed to measure evolution acceptance. Evolution acceptance surveys form the bedrock of research on evolution acceptance because they are the primary means for collecting data on the outcome variable.

How is Evolution Acceptance Currently Measured?

Currently, researchers can choose from several surveys that were designed to measure evolution acceptance and have been validated for use among university students in the United States: the Measure of Acceptance of the Theory of Evolution [original MATE: (Rutledge and Warden, 1999); MATE 2.0: (Barnes et al., 2022)], the Inventory of Student Evolution Acceptance [I-SEA: (Nadelson and Southerland, 2012)], and the Generalized Acceptance of EvolutioN Evaluation [original GAENE: (Smith et al., 2016); GAENE 3.0: (Glaze et al., 2020)].

The MATE and the GAENE (original and revised versions) are structurally similar in that each survey measures evolution acceptance using a series of statements about evolution, to which the survey-taker responds using a five-point Likert scale ranging from strongly agree to strongly disagree. Furthermore, both the MATE and the GAENE report evolution acceptance as a single construct, such that a survey-taker's result consists of a single composite score that falls on a continuous range representing a spectrum of “high acceptance” to “low acceptance” of evolution (Rutledge and Warden, 1999; Smith et al., 2016; Glaze et al., 2020; Barnes et al., 2022). One limitation of using a single composite score is that many different combinations of responses can lead to identical scores. For example, on the GAENE 3.0, a student who agrees with the item “Everyone should understand evolution” and disagrees with the item “Evolution is a good explanation of how humans first emerged on the earth” could have the same composite score as a student who provides the opposite responses for both of these items (Glaze et al., 2020). This lack of distinction means that while a very high or very low composite score may be fairly informative of a student's views, scores towards the middle of the range cannot provide information on what aspects of evolution students accept, reject, or are unsure about (Barnes et al., 2022; 2024). This provides a practical limitation for researchers and instructors who seek to use one of these surveys to identify and instructionally target areas of low evolution acceptance.

The developers of the I-SEA sought to address this limitation by dividing their survey into three subscales that measure acceptance of macroevolution, microevolution, and human evolution (Nadelson and Southerland, 2012). The theory of evolution is a unified theory that ties together mechanisms that shape allele frequency (e.g., natural selection, genetic drift), speciation, and evolutionary changes across lineages over millions of years; evolutionary biologists often do not delineate between “microevolution” and “macroevolution” since the latter is the outcome of the former (Carroll, 2001). Micro- and macroevolution are nevertheless often treated as distinct concepts within evolution education. For example, the National Academies of Sciences (NAS) define macroevolution as “large-scale evolution occurring over geologic time that results in the formation of new species and broader taxonomic groups” and microevolution as “changes in the traits of a group of organisms within a species that do not result in a new species;” UC Berkeley's online resource Understanding Evolution defines them similarly (National Academies, 2025; University of California Berkeley, n.d.). This and prior research showing that nonscientists may perceive differences in evolution based on scale (macro vs. micro) and context (human vs. nonhuman) led Nadelson and Southerland to implement separate subscales for macro- and microevolution that align with the NAS definitions, along with a subscale that focuses on human evolution (Sinatra et al., 2003; Nehm and Ha, 2011; Nadelson and Southerland, 2012). The human evolution subscale of the I-SEA includes items both at the “macro” scale of shared ancestry with other primates and at the “micro” scale of evolutionary mechanisms acting within the human species; it appears to equate the term “human” with Homo sapiens and makes no mention of other hominins.

Studies that use the I-SEA have found that acceptance of microevolution tends to be higher than acceptance of macroevolution and human evolution across a variety of university populations, which supports the utility of using multiple subscales (Nadelson and Hardy, 2015; Romine et al., 2018; Barnes et al., 2019; Ferguson and Jensen, 2021; Beniermann et al., 2022). However, additional investigations into the I-SEA suggest that the three subscales used therein may not represent the most accurate subdivision of student evolution acceptance. Some studies have found that the human evolution subscale shows signs of being multidimensional, with survey items clustering into two sets that approximately align with human macroevolution (common ancestry with nonhuman primates) and human microevolution (evolutionary changes within Homo sapiens) (Sbeglia and Nehm, 2019; Aini et al., 2024). Other studies have found that positively worded items that involve accepting claims that support evolution perform differently than negatively worded items that involve rejecting claims that do not align with evolution (Romine et al., 2025; 2018).

These issues with the delineation of subscales may originate in the earliest phases of developing the I-SEA. Survey development standards in educational research state that before survey items are drafted, individuals from the target population should be systematically interviewed about the construct of interest in order to identify the range of views that the survey needs to be capable of measuring (American Educational Research Association, 2014; Artino et al., 2014). The creators of the I-SEA did conduct student interviews to guide item development. However, the decision to create the macroevolution, microevolution, and human evolution subscales preceded the interviews, and interview data were analyzed using a priori codes instead of allowing the subscales to arise from the data (Nadelson and Southerland, 2012).

An indication of how a more open-ended approach may impact findings comes from two of T.M's previous studies, which qualitatively evaluated the original MATE, the I-SEA, and the GAENE. These studies included an open-ended interview question in which students were asked to describe their views on evolution in their own words. We found that, of the students who did not accept all aspects of evolution, some stated that they accept speciation but believe that higher taxa, such as orders or classes, were created separately (Barnes et al., 2022; Misheva et al., 2023). Like the NAS definition of macroevolution, the macroevolution subscale of the I-SEA lumps together everything from recent speciation (e.g., “I think that new species evolved from ancestral species”) to evolution at the largest scale (e.g., “I think all complex organisms evolved from single-celled organisms”) (Nadelson and Southerland, 2012). These findings suggest that the macroevolution subscale may potentially obscure relevant variation in student views, as some students have claimed to perceive a meaningful difference between geologically recent speciation events and shared ancestry among broader taxonomic groups. The question of where, on the tree of life, students draw this distinction and why they do so led to the current study.

Research Questions

Prior research suggests that while the use of subscales enables a survey to produce a more fine-grained—and thus, actionable—measure of student acceptance of evolution, the three subscales of macroevolution, microevolution, and human evolution used on the I-SEA may be somewhat misaligned with the range of views present among undergraduate students in the United States (Sbeglia and Nehm, 2019; Barnes et al., 2022; Romine et al., 2018; 2025). With the current study, our goal was to better inform future work on the measurement of evolution acceptance by systematically investigating patterns in student awareness and acceptance versus rejection of common ancestry between organisms. This led to the following research questions:

When college students who DO NOT fully accept evolution are asked to evaluate whether it is likely or unlikely that two organisms share a common ancestor…

1. For nonhuman organisms, do students shift from accepting common ancestry to doubting or rejecting common ancestry approximately at the species level, as would align with the use of speciation to delineate between microevolution and macroevolution, or does the shift in acceptance typically occur at higher taxonomic levels? What cues do students use when deciding whether they find common ancestry to be probable?

2. For modern humans, do students shift from accepting common ancestry to doubting or rejecting common ancestry in comparison with extinct hominins, other extant apes, or more distantly related species? What cues do students use when deciding whether they find common ancestry to be probable?

MATERIALS AND METHODS

Recruitment

Before data collection, we conducted seven practice interviews with introductory biology students to check the quality of the interview materials. Participants were paid $25 for their time. Student feedback was used to enhance the variety and relevance of organism comparisons used, and to adjust how information about the organisms is provided so as to better balance providing necessary context versus not railroading student reasoning.

Data for this study were collected through two sets of student interviews during the Fall 2023 and Spring 2024 semesters at a large, private, research-intensive (Carnegie R1) institution in the U.S. northeast. For the Fall 2023 interviews, participants were recruited from an introductory psychology course. At the time of the study, all introductory biology courses at this institution were taught by one of the authors (J.W.), who addresses evolution acceptance as part of the curriculum. Although students from J.W.’s course were recruited for the pre-data collection practice interviews, students outside of biology were sought for inclusion in the main dataset to avoid biasing the results with explicit instruction. A presurvey consisting of the macroevolution and human evolution subscales of the I-SEA was distributed to the entire class. At the end of the survey, students were asked to provide their email address if they were interested in participating in a follow-up interview. The purpose of the presurvey was to identify potential participants who exhibit lower levels of evolution acceptance. We used this screening method because previous studies have found relatively high overall rates of evolution acceptance at this institution (Dunk and Wiles, 2018; Grunspan et al., 2021). Students who received an average score of <3.75 on either subscale and provided their email were contacted individually with an offer to participate. On the I-SEA, items are scored on a five-point Likert scale, with higher values, indicating higher levels of acceptance. We used 3.75 as the cutoff because it indicates that a student scores below agreement with some aspect of evolution. Twenty students were contacted, eleven of whom participated in the study. Participants received a $25 gift card. Participants were asked to complete a brief online demographic survey after the interview.

We conducted a second set of interviews in the following spring semester to increase both the size and diversity of our sample. The postinterview demographic survey revealed that most participants identified as Christian. To increase the religious diversity of our sample, we contacted the leaders of ten religious student organizations on campus and asked them to share a recruitment flyer for the study with their members. We opted to forgo the presurvey because the recruitment flyer explicitly stated that we were interested in religious students’ views on evolution. The second round of recruitment yielded ten additional interviews. For the second round, we increased participant compensation to a $30 gift card because we expected the interviews to run slightly longer due to minor adjustments to the protocol. The Institutional Review Board of Syracuse University approved the procedures for this study (SU IRB #23-340).

Data Collection

Data collection consisted of a total of 21 semistructured interviews that were conducted virtually on Zoom by T.M. Semistructured interviewing is a flexible, interactive format in which the interviewer uses a set of prepared questions to guide discussion, yet has the flexibility to pose spontaneous follow-up questions in dialogue with the interviewee (Lewis-Beck et al., 2004). All interviews were recorded and transcribed.

Interviews centered on a series of comparisons involving pairs of organisms, usually of different species. In selecting species to compare, our priorities were to 1) primarily use examples that are likely to be familiar to limit cognitive load, and 2) include a wide variety of plants and animals, along with some bacteria and fungi. Species were initially identified using scientific names that align with the biological species concept, or the taxonomically relevant equivalent. During interviews, common names were used to ease recognition (e.g., Red Squirrel vs. Sciurus vulgaris), and names were occasionally shortened when doing so did not factor into the comparison (e.g., sea lion vs. Steller sea lion for Eumetopias jubatus). Scientific names were used for species that lack a common name (e.g., Tyrannosaurus rex). (See Table 1) PowerPoint slides were used to show pairs of organisms, with a picture and a common name for both. Twenty pairs were used in each interview. The presentation sequence roughly corresponded to decreasing relatedness, with closely related species (e.g., same genus) shown first and distantly related species (e.g., share only a kingdom) shown later. Comparisons involving humans were placed at the end of the sequence so that participants could discuss their views on shared ancestry between nonhuman species before turning their attention to human evolution. Previous research has shown that student acceptance of and reasoning about human evolution commonly differs from that of nonhuman evolution (Betti et al., 2020; de Lima and Long, 2023; Wingert et al., 2023; Aini et al., 2024). One same-species comparison was included (two modern humans), not because we expected many to reject the common ancestry of all humans, but to investigate participants’ reasoning about the causes of shared ancestry. This pairing also included a follow-up question about whether they think evolution has shaped variation within the human species. A comparison between domestic dogs and gray wolves was included for similar reasons.

TABLE 1.

Species comparisons were presented during the interviews, along with the purpose of each comparison

Pairing	Reason for pairing	Fall 2023	Spring 2024
Domestic dog (Canis familiaris); Gray wolf (Canis lupus)	Same genus; animals; result of artificial selection	X	X
Tiger (Panthera Tigris); Lion (Panthera leo)	Same genus; animals	X	X
Bristlecone pine (Pinus longaeva); Scots pine (Pinus sylvestris)	Same genus; plants	X	X
Burrowing owl (Athene cunicularia); Great gray owl (Strix nebulosa)	Same family; birds with matching names	X	X
Red squirrel (Sciurus vulgaris); Himalayan marmot (Marmota himalayan)	Same family; mammals with different names	X	X
Sunflower (Helianthus annuus); Lavender (Lavendula angustifolia)	Same order; plants	X	X
Sea lion (Eumetopias jubatus); Red fox (Vulpes vulpes)	Same order; animals; terrestrial versus aquatic	X	X
Atlantic Salmon (Salmo salar); Orange Clownfish (Amphiprion percula)	Same class; animals; (ray-finned) fish	X	X
Fly agaric (Amanita muscaria); Shaggy bracket (Inonotus hispidus)	Same class; fungi	X	X
Giraffe (Giraffa tippelskirchi); House mouse (Mus musculus)	Same class; animals; mammals	X	X
Velociraptor (Velociraptor mongoliensis); Shoebill stork (Balaeniceps rex)	Both archosaurs; extant versus extinct species	X
Tyrannosaurus rex; Mallard duck (Anas platyrhynchos)	Both archosaurs; extant versus extinct species		X
Streptococcus; Salmonella	Same domain; bacteria	X
Salmonella; Giant amoeba (Chaos carolinensis)	Prokaryote versus eukaryote; both unicellular	X
Oak tree (Quercus robur); Sphagnum moss (Sphagnum spp.)	Same kingdom; distantly related plants	X	X
Honeybee (Apis mellifera); Moose (Alces alces)	Same kingdom; distantly related animals	X	X
Texas bluegrass (Poa arachnifera); Giant Pacific Octopus (Enteroctopus dofleini)	Same domain; plant versus animal	X	X
Two modern humans (Homo sapiens)	Common ancestry of humans; human microevolution	X	X
Modern human (Homo sapiens); Neanderthal (Homo neanderthalensis)	Same genus; modern human versus extinct hominin	X	X
Modern human (Homo sapiens); Chimpanzee (Pan troglodytes)	Same family; human versus nonhuman primate	X	X
Modern human (Homo sapiens); Manatee (Trichechus manatus latirostris)	Same class; human versus aquatic nonprimate	X	X
Modern human (Homo sapiens); Red fox (Vulpes vulpes)	Same class; human versus terrestrial nonprimate		X
Chimpanzee (Pan troglodytes); Manatee (Trichechus manatus latirostris)	Same class; nonhuman primate versus nonprimate		X
Modern human (Homo sapiens); Clownfish Amphiprion percula	Same phylum; human versus fish		X

Note: “X” indicates that the pairing was presented in a set of interviews.

At the beginning of each interview, participants were provided with a definition of “common ancestor” (see Supplementary Materials), and it was explained that we are interested in students’ personal views on evolution. As pairs of organisms were presented, participants were asked whether they think the two shared a common ancestor, and to explain why or why not. Follow-up questions were posed as needed to clarify participants’ responses. At the end of the interview, the interviewer posed a series of open-ended questions in which the participants were asked to describe their personal views on how life on Earth came about. Participants were encouraged to elaborate on 1) whether they believe a higher power was involved, 2) if so, what that involvement consisted of, 3) how they perceive their views to intersect with evolution, and 4) to clarify any inconsistencies between their self-described views and their previous answers. The interview script is included in the Supplementary Materials.

Though we sought to maintain consistency across interviews, several patterns that emerged during the first set of interviews prompted us to make several minor adjustments to the materials before embarking on the second set. The changes were as follows:

1. DELETED “streptococcus and salmonella” and “salmonella and giant amoeba.” Initial trends strongly suggested that many participants lack firm views and struggle to provide reasoning for single-celled organisms due to a lack of familiarity.

2. ADDED “human and red fox” and “chimpanzee and manatee.” Based on initial patterns, we wanted to more closely examine participants’ views on human versus primate, human versus nonprimate, and (nonhuman) primate versus nonprimate relationships.

3. REPLACED “velociraptor and stork” with “tyrannosaurus and duck” for the comparison between a non-avian dinosaur and a modern bird. The initial, more visually similar pair was swapped out for a less visually similar pair to check for differences in reasoning.

One additional comparison—modern human and clownfish—was added partway through the second set of interviews to further investigate a common line of reasoning involving species in terrestrial versus aquatic habitats. Though the sample size for this comparison was small (the last three participants), responses were consistent with the ongoing findings.

Analysis

Interview transcripts were qualitatively coded using a combination of the constant comparative method and content analysis (Saldaña, 2021). Content analysis of responses to the question "Do you think these organisms/species share a common ancestor?” was used to quantify the qualitative data in order to measure frequency, identify patterns, and make comparisons more systematic. Answers to this question fell into three main codes: yes, no, and undecided. The frequency of each answer was calculated for each pairing. The constant comparative method was used to analyze explanations of reasoning as well as participants’ self-described views. The constant comparative method is based on grounded theory, which is an inductive approach in which researchers seek to build a theoretical understanding of a phenomenon based on patterns that emerge from qualitative data (Glaser and Strauss, 1967). We opted for this approach because our goal was to discover potentially unforeseen patterns in student reasoning for accepting or rejecting common ancestry. The constant comparative method is well-suited for this goal because it does not constrain the analysis into using a priori codes based on researchers’ predictions.

Coding occurred in two cycles: initial (or open) coding followed by axial coding (Saldaña, 2021). During initial coding, one researcher (T.M.) used the interview transcripts to assign codes to every new answer or piece of reasoning provided. For each comparison, explanations were given one or more codes, depending on how many distinct reasons the participant gave. During axial coding, codes from the first cycle were grouped into higher-level codes. For example, the first-level codes “different growth” and “different reproduction” were grouped into the second-level code “life cycle—different.” In coding participants’ self-described views, a code was assigned for each distinct concept that the participant explicitly voiced. These codes were not mutually exclusive.

To affirm code reliability, a second researcher (K.C.) used an interview transcript to assign first-level codes from the codebook. K.C. and T.M. met to compare and unite on code application, and K.C. assigned first-level codes to four more interview transcripts from the sample. Second-level codes for the four latter interviews were grouped into topic codes, and all agreements and disagreements were recorded. For example, “life cycle—different” and “life cycle—similar” were grouped into the topic code “life cycle—discussed” to determine 17 topic codes. Inter-rater reliability was assessed by calculating Cohen's kappa (κ) for each of the topic codes; the overall kappa was κ = 0.927. Kappa values between 0.60 and 0.79 are considered moderately accurate, or substantial agreement (McHugh, 2012).

The following results include quotes from students who participated in the study; some quotes have been lightly edited for clarity, and participants selected their own pseudonyms. Table 2 provides a summary of the participants.

TABLE 2.

Description of participants’ religious identities and college biology backgrounds

Pseudonym	Religious identity	Biology background	Pseudonym	Religious identity	Biology background
Annie	Christian (Pentecostal)	1 course	Sarah	Atheist; raised Christian (Catholic)	none
LP	Nothing in particular; raised Christian (Catholic)	1 course	Victoria	Christian (LDS)	1 course
Olivia	Christian (Lutheran)	none	Lemon	Christian (Orthodox)	none
Sam	n/a	n/a	Rob	Muslim	1 course, incl. evo
Wild Frog	Christian (Catholic)	none	Mario	Muslim	none
Honey	Jewish	no bio; yes evo	Batman	Atheist	4+ courses; incl. evo
John	Christian (Catholic)	none	Red Apple	Muslim	3 courses
CZ	Christian (Catholic)	none	Jack	Muslim	none
Aubrey	Nothing in particular; raised Buddhist	2 courses	Layla	Nothing in particular; raised Christian (Adventist)	4+ courses
Senti	Christian (nondenominational)	1 course

Note: Sam did not provide demographic information.

RESULTS AND DISCUSSION

Participants

Out of the 21 students who participated in the study, two were removed from the final results. When asked to describe their views, both participants stated that they believe God created all life on earth, including humans, through the process of evolution and that all life shares the same set of single-celled ancestors. For example, one of these students said, “I think that life came from single-celled organisms and then over just years of development, it just kept growing into the many different organisms that we have. I'm Muslim, but … I believe that evolution could have been used as a tool to be able to create organisms.” These views were reflected in the pairwise comparisons; both students accepted common ancestry for every pair. Although these individuals’ reconciliation of scientifically accurate evolution with their religious beliefs reflects a suitable end-goal for efforts to increase student acceptance of evolution, their responses were removed from the present analysis because this places them outside of the intended participant demographic (that being students who do NOT fully accept evolution).

The final sample for this study thus consists of nineteen students from one private R1 university in the U.S. northeast (Table 2). Of these, eight identified as Christian, four as Muslim, one as Jewish, and five as nonreligious. Of the five who identified as currently nonreligious, four indicated that they were raised in a religious tradition (one Buddhist, three Christian). For gender, eleven identified as women and seven identified as men; nonbinary and open-response options were offered but not selected. For race and ethnicity, five participants identified as Black/African American, five as white, five as Asian/Asian American, one as Middle Eastern or North African (MENA), and two identified with more than one option (white/MENA and white/Pacific Islander). A majority of participants (13) were in their first or second year of college, four were in their third or fourth year, and one was a graduate student. Three participants had taken three or more college-level biology courses, six had taken one or two, while the remaining nine had taken none. Three had taken a course focused on evolution. One participant, Sam, did not complete the demographic survey; this participant is included in the results, but is not reflected in the demographic summary. Table 2 provides a summary of participants using their self-selected pseudonyms.

Finding 1: Most Participants Accepted the Common Ancestry of Closely Related Species

As expected, 100% of participants said that dogs and wolves share a common ancestor (Table 3). Most gave reasoning based on anatomical similarity and/or domestication. For example, Olivia said that the two share a common ancestor because “humans domesticated dogs to be companions [and] to help them with hunting.” This shows that all participants accepted and understood the concept of two divergent lineages sharing a common ancestor within the relatively uncontroversial context of animal domestication. This provides a useful baseline for participants’ eventual shifts from acceptance to rejection for the later comparisons.

TABLE 3.

Percentages of participants who accept, reject, or are undecided about common ancestry for various example pairs of organisms

Pairing (common names)	N	Accept	Reject	Und.	Pairing (common names)	N	Accept	Reject	Und.
Domestic dog and Gray wolf	19	100%	0%	0%	Streptococcus and Salmonella	11	73%	27%	0%
Tiger and Lion	19	90%	10%	0%	Salmonella and Giant amoeba	11	36%	45%	18%
Bristlecone pine and Scots pine	19	80%	10%	10%	Oak tree and Sphagnum moss	19	37%	63%	0%
Burrowing owl and Great gray owl	19	95%	5%	0%	Honeybee and Moose	19	5%	95%	0%
Red squirrel and Himalayan marmot	19	68%	21%	10%	Bluegrass and Giant Pacific Octopus	19	0%	100%	0%
Sunflower and Lavender	19	26%	63%	10%	Two modern humans	19	100%	0%	0%
Sea lion and Red fox	19	5%	84%	10%	Modern human and Neanderthal	19	90%	5%	5%
Salmon and Clownfish	19	37%	37%	26%	Modern human and Chimpanzee	19	58%	26%	16%
Fly agaric and Shaggy bracket	19	68%	21%	10%	Modern human and Manatee	16	25%	75%	0%
Giraffe and Mouse	19	21%	68%	10%	Modern human and Red fox	8	12%	88%	0%
Velociraptor and Shoebill stork	11	100%	0%	0%	Chimpanzee and Manatee	8	12%	88%	0%
Tyrannosaurus rex and Mallard duck	8	25%	50%	25%	Modern human and Clownfish	3	0%	100%	0%

Note: Some values do not add to 100 due to rounding.

Similarly, over three-quarters of participants accepted common ancestry for the lion and tiger (90%), the two pines (80%), and the two owls (95%) (Table 3). For these, shared classification and similar anatomy were the most commonly cited explanations for accepting shared ancestry. For example, for the lion and the tiger, Wild Frog said, “I think at one point they could have had a similar ancestor because they're both cats. I think that they could have had a common ancestor because their noses look similar, and their paws are the same and also their tails, it's just like the look of them is a little different but similar anatomy.” Likewise for the Great Gray owl and the burrowing owl, Annie said, “Yes, they do share a common ancestor. They share very similar physical characteristics. They are both birds, so they do share common broad characteristics like that, but they also have similar patterns and colors on their wings. They have the same eye color.” Scientific classification, which is based on evolutionary history, commonly overlaps with lay classification that is largely based on easily observable morphology. Though it was not entirely clear whether participants were thinking about classification in a scientific sense, a lay sense, or a blend of both when they described examples as “both cats” or “both birds,” these clearly arose as conceptual categories that participants used to sort species into groups with plausible common ancestry.

At 68%, acceptance of common ancestry was slightly lower for the red squirrel and marmot, who are scientifically classified within the same family, Sciuridae. Participants who accepted shared ancestry once again mostly cited anatomical similarities and shared classification as rodents or mammals. The four who doubted that the two were related cited anatomical differences as their reasoning. For example, Aubrey said, “It doesn't look like they have any shared characteristics. The red squirrel's legs look more compressed. And then looking at the arms too, the marmot's look stubbier than the red squirrel's. And [the marmot's face] is a different shape than the squirrel's.”

These findings suggest that often, students who reject evolutionary relatedness for at least some groups of organisms may take no issue with speciation itself, and may have little difficulty with accepting shared ancestry for closely related species that share clearly visible anatomical similarities. This limited acceptance of macroevolution aligns with an approach to Christian creationism called baraminology, which was initially developed in the 1940s to explain how the multitude of species alive today all descended from the animals rescued on Noah's Ark (Marsh, 1944). This idea is still espoused by creationist organizations such as Answers in Genesis, which draws a distinction between the biological species concept and what they call “created kinds,” with one article on their website stating, “Created kinds correspond roughly to the family level of the current classification taxons [sic] but may vary from order to genus level” (Mitchell, 2011).

Finding 2: Most Participants Rejected Common Ancestry Between Plants and Animals, as Well as Distantly Related Animals

All but one of the participants (95%) rejected common ancestry for a moose and a honeybee (vertebrate vs. arthropod, animal kingdom), and every single participant rejected common ancestry for a grass species and an octopus species (plant vs. animal, eukaryotic domain). When comparing a moose and a honeybee, participants mainly cited differences in size, body plan, and feeding behaviors as the primary reasons for why mammals/vertebrates and insects have never shared ancestry. For example:

Honey, a Jewish student, said, “I just feel like they couldn't ever possibly come from a common ancestor with one walking, one flying, one being an insect.”

Victoria, a Latter-Day Saints Christian student, said: “I would say no, [because of] the different kinds of things that they feed off of and the way they organize themselves. Honeybees, they live in hives, they pollinate, they're very group-oriented. Moose actually, I dunno, but they're just very different. So I would say no.”

Jack, a Muslim student, said: “They're just very different. The things that they eat, one can fly [and] is a bug, the other one isn't. One has antlers, one has a stinger. [It] seems to me as if they don't have the same ancestor.”

When comparing a species of octopus and a species of grass, most participants focused on the fact that one is a plant while the other is an animal, with a few specifically citing plants’ and animals’ differences in energy acquisition as reasons why the two have never shared a common ancestry. For example, Senti said, “No, I don't think these are related at all, just because they don't have the same diets. One is a plant and one is an animal; I don't think those were ever related at any point.” Additionally, several students included these species’ different habitats (aquatic vs. terrestrial) as one of their reasons for rejecting common ancestry. Olivia explained, “I don't believe these two are related at all. Octopi are sea-dwelling, very intelligent creatures. Bluegrass is grass that is tall and long and stationary, and it's a plant. So I don't see these two being related at all.” This, together with the previous finding, suggests that students who are willing to accept evolution in the context of shared ancestry within a genus or family may nevertheless reject evolution in the context of shared ancestry between organisms classified in different kingdoms or domains.

Finding 3: Most Participants Rejected Common Ancestry Between Terrestrial and Aquatic Species, Citing Habitat Differences as one of their Primary Reasons for Rejection

When presented with comparisons in which one organism is primarily terrestrial and the other is primarily aquatic, a majority of participants rejected the possibility of the two sharing a common ancestor. When providing the reasoning for their rejection, most cited this difference in habitat, often along with anatomical traits that are adaptations to life in terrestrial versus aquatic environments (e.g., having paws vs. flippers).

This pattern was most starkly visible when comparing a sea lion with a red fox. Eighty-four percent of participants stated they do not believe that these species have ever shared an ancestor, while an additional 10% were undecided. All but one of these participants explicitly mentioned the species’ different habitats as part of their reasoning. Two examples come from Mario and Sam; in their self-described views, both said they believe that God created a number of initial species, and evolution followed after. For the sea lion and the fox, Mario said: “I would say they're not related as far back as we go, just because one of them [is] a creature that mainly lives in the water and the other one's a creature that mainly lives on land.” The importance of habitat was further highlighted in Mario's answer for the next comparison of salmon and clownfish. For this pair, he was undecided, saying “That's a tough one. I do see that they're both creatures that live in the water and I do see a lot of similar characteristics, but those are just all the characteristics of a fish … It's possible that there was just one kind of fish [in the beginning], but it could be that they're just two completely different kinds of fish.” Meanwhile, Sam was undecided on the relatedness of sea lions and foxes. Sam connected their reasoning to what they had previously learned about evolution, saying, “this is the part of evolution where I sometimes question whether or not it's true … I've been told about how [in] evolution everything was in the ocean and then eventually fish evolved to breathe and walk on land … And I just find that really difficult to believe … Sometimes it makes sense and I understand that that happens over the course of millions of years … But that's something I've always kind of questioned.” Though ‘aquatic animal’ and ‘terrestrial animal’ are not scientifically valid taxa, these responses demonstrate that for many students, these habitat categories are highly salient features that can play an important role in informing whether they find claims of common ancestry to be believable.

Interestingly, students' emphasis on habitat differences was also present in the examples that include humans. Of the eleven students who said they DO accept the shared ancestry of humans and chimpanzees, seven said that they DO NOT accept shared ancestry between humans and manatees or clownfish. For example, when asked whether humans and chimpanzees share a common ancestor, Layla said, “Probably distantly, yes. … They're very social animals, just like humans. And I know that they're very intelligent animals as well.” Yet she rejected shared ancestry for humans and clownfish, saying, “Fish are aquatic animals … humans are terrestrial. And I'd say we have a lot more close relation to primates than fish.” Layla presented similar reasoning for chimpanzees and manatees, stating that they share no ancestry because “manatees have flippers and chimpanzees have fingers,” which are anatomical differences that are directly connected to these habitat differences. Layla self-described as being in the process of figuring out her views regarding evolution and creationism. Similarly, Sam was undecided on whether humans and chimpanzees share a common ancestor, but outright rejected common ancestry between humans and manatees. Sam said, “It definitely makes more sense for God to have put us on [Earth] as monkeys and us evolved from that than God having put us all on the earth as just fish.”

Finding 4: Students who Rejected or Were Undecided About our Common Ancestry with Chimpanzees Often Accepted Evolution Within the Human Lineage

Eight out of nineteen students (42%) either rejected or were undecided about the common ancestry of humans and chimpanzees. Of these eight, six indicated that they accept the idea of evolutionary processes acting on anatomically modern humans, as well as common ancestry between modern humans and Neanderthals (Table 3). Two examples come from Victoria and Mario; in their self-described views, both said they believe that evolution proceeded from an initial set of created species, and that humans were created separately from all other species.

When explaining his views regarding the common ancestry of all modern humans, Mario, a Muslim student, expressed a blend of scientific and religious views, stating, “I've learned that humans all originated from Africa, from what I've learned in science. And then I'd also say there's some religious influence to my belief, where it's like I believe in Adam and Eve.” He made room for Neanderthals within the category of ‘human,’ saying, “Yeah, so I would say [Neanderthals] are related just mainly based on their cognitive capacity,” and stated that variation within the human species is “mainly based on evolutionary factors.” Mario further summarized his views on human evolution and the role of earlier hominins at the end of the interview with, “I do believe that humans, the way we look now and the way we behave now might not have been the same as we behaved in the beginning of our creation. So obviously we might've had different proportions, a different way of communicating.” Victoria, a Latter-day Saint Christian student, expressed similar views. She said, “I think we are all ancestors of the first humans, Adam and Eve … I would say the majority [of modern human variation] is evolutionary … I believe that [Neanderthals] existed, but that they are more human than we think they are. They just maybe [had] animal tendencies because they were cavemen.” As these quotes demonstrate, these students believe that humans were created separately from all other animals, yet they perceive evolutionary change within the human lineage (broadly defined to include extinct hominin branches) as being consistent with their creation beliefs.

In contrast, both Mario and Victoria drew the line at accepting common ancestry between modern humans and chimpanzees. Victoria mainly cited her creationist beliefs, stating, “I think they were created separately. I think humans came from Adam and Eve; I think chimpanzees are a whole separate lineage.” Meanwhile, Mario cited cognitive differences between species as his reason for rejection, saying, “I would say [chimpanzees] are not related [because of] just them being nonverbal. And even though they might have a certain level of cognitive capability, [there are] a lot of scenarios where their primal instincts tend to take over rather than them having control of a situation.”

These explanations demonstrate that when it comes to evolution acceptance, evolutionary scale and species context can intersect, such that some students have different views regarding evolution within the hominin lineage versus common ancestry between modern humans and other extant species. This finding provides qualitative support for previous quantitative work that found that items in the human evolution subscale of the I-SEA cluster into two sets that approximately align with human macroevolution and human microevolution (Sbeglia and Nehm, 2019; Aini et al., 2024).

Finding 5: Students Both With and Without Creationist Beliefs Expressed Similar Views on Evolution with Regard to Acceptance of Common Ancestry

Two participants from the initial total of 21 were removed from the sample because they accepted the shared ancestry of all life on earth. On average, the remaining participants rejected common ancestry for ∼42% of comparisons (range, 10 – 70%). Yet rejection of common ancestry was not always associated with having a religious identity or expressing creationist views. In the demographic survey, five participants did not identify with any religion. In their self-described views, three of the five said that life on earth arose through purely natural evolutionary processes with no direct involvement from a higher power, while one said that a higher power guides evolution, and another said that they are still figuring out their views. One participant who identified as a Catholic Christian likewise said they believe that life arose through natural evolutionary processes alone.

Of the four who said that life arose only through natural evolution, all four rejected common ancestry for a sea lion and a fox, a moose and a honeybee, and an octopus and grass. These students offered the same reasons for rejection as most other participants, as illustrated by Batman's anatomy-based reasoning for the moose and honeybee: “I do not believe they have a common ancestor because [of] very, very different anatomy. The moose has four legs and antlers, whereas honeybees are relatively smaller compared with the moose, and they have wings.” When asked to elaborate on how these answers fit in with her self-described views, Batman said, “they came to life separately. They never crossed paths,” implying that certain taxa originated and evolved in parallel without any distantly shared ancestry. This appears to reflect a lack of knowledge about the shared ancestry of life on earth, more so than creationism-based evolution rejection. The role of limited knowledge appears in Aubrey's explanations as well. When asked to reflect on the relationship between her answers and her self-described views, Aubrey—who rejected shared ancestry for humans and manatees—said, “I feel like, I'm not sure where a manatee would derive from, if I'm completely honest. I feel like it's something to do with my current belief is that it's something to do with the dinosaurs and stuff, but I don't really have a full grasp on the jump between dinosaurs to Neanderthals to et cetera.” This explanation suggests that she accepts the existence of evolutionary relationships between broad taxonomic groups such as mammals and dinosaurs, but struggles to think through the implications of how broad taxonomic groups might evolve across deep time.

Overall, this finding suggests that judgments about shared ancestry from people with limited knowledge about evolution can closely resemble those from people with creationist views. This, in turn, has implications for both past and future efforts to measure student evolution acceptance. Multiple prior studies have found positive correlations between acceptance and understanding of evolution (Nadelson and Southerland, 2010; Romine et al., 2017; Fiedler et al., 2023). Yet researchers have also raised the issue of conflation between acceptance and understanding by highlighting how students who are uncertain about the scientific accuracy of survey items sometimes opt for more neutral answers, even when they verbally indicate an overall willingness to accept the scientific consensus (Smith, 2010; Misheva et al., 2023). This finding presents an additional complicating factor that ought to be considered when examining the relationship between acceptance and understanding of evolution: religious students with some creationist beliefs and nonreligious students without creationist beliefs can at times engage in nearly identical reasoning about macroevolution, particularly at the larger, less intuitive scales of evolution due to a lack of knowledge about the science.

Limitations

Though this study has important implications for the conceptualization and measurement of student acceptance of evolution, it also comes with several important limitations. First, although interviews enabled us to identify the presence of certain views on evolution among undergraduate students, this study's relatively small sample size is not suitable for ascertaining the prevalence of each of these views within larger student populations. Second, the fact that there are millions of living species means that the number of different pairwise comparisons that could have been used is functionally infinite. Though we were intentional in our selection of pairwise comparisons, a different set of comparisons may have yielded additional patterns or revealed other nuances in student reasoning. For example, we did not find any clear differences in how students reason about common ancestry within plants versus within animals. It is possible that a different set of comparisons could have revealed a noteworthy pattern. Third, though all participants volunteered to take part in a 30-min interview about evolution, their exposure to college-level biology was highly varied, with many having never taken a college-level biology course. It is possible that a sample limited to biology majors—who may have a better factual understanding of evolution, regardless of personal acceptance—would have yielded somewhat different results.

CONCLUSION

Implications for Measuring Evolution Acceptance

In this study, we found that religious students who express having some creationist beliefs can accept “macroevolution” that produces speciation at lower taxonomic levels, such as within a family or genus, yet reject “macroevolution” that pertains to shared ancestry between higher taxa, such as classes and kingdoms. Students used similar anatomy (especially with regard to body plan) and shared membership within a commonly known taxonomic family (e.g., felines or owls)—or, perhaps, nonscientific categorization that aligns with such—as reasons to accept common ancestry between species that share a family or genus. Conversely, they used classification differences at higher taxonomic levels (e.g., insect vs. mammal) and clear differences in size and body plan as reasons for believing that two species descended from separately created first ancestors. This suggests that measuring evolution acceptance in a way that delineates between macroevolution and microevolution using speciation and the biological species concept may be somewhat misaligned with how creationist students reason about what can be attributed to evolution versus creation. To better align survey results with the range of student views, a measure of evolution acceptance could reallocate the concept of “shared ancestry between species in the same taxonomic family” as part of the microevolution subscale, and reserve the macroevolution subscale for the idea that evolution leads to major differences in anatomy, habitat, and lifestyle across broad lineages over very long periods of time. In particular, we found that whether a species is found in a primarily terrestrial or primarily aquatic habitat can be a particularly salient distinction for students, with many students being more hesitant to accept shared ancestry between a terrestrial species and an aquatic species.

Yet the responses we received from students who do NOT believe that life on earth was created by a higher power complicate the measurement of macroevolution acceptance. We found that students who lack creationist beliefs can be factually unaware that distantly related taxa share common ancestry, and use similar lines of reasoning as students with creationist beliefs when trying to determine whether shared ancestry is probable in such scenarios. This further highlights the highly nuanced relationship between acceptance and understanding of evolution—individuals with creationist beliefs and those without may, on a certain level, display very similar views on evolution that nevertheless have different philosophical underpinnings (belief in an alternative creationist account versus a lack of knowledge about the scientific account). Similarly, previous research has found that college students both with and without creationist beliefs often struggle with scientific reasoning related to deep time (Jaimes et al., 2020). This in turn suggests that survey items addressing the relatedness of plants and animals or the relatedness of all life on earth may measure evolutionary knowledge as much as evolution acceptance.

Additionally, we found that students who believe that humans were created by a higher power separate from all other animals may nevertheless accept microevolution within the human species. This is not necessarily surprising, since certain creationist organizations likewise accept the notion of human populations being affected by at least some evolutionary processes (e.g., genetic drift) despite firmly rejecting human descent from nonhuman ancestors (Purdom, 2010).

Given this information, subscales for human microevolution and human macroevolution could enable researchers to distinguish between these two aspects of human evolution acceptance.

Therefore, to differentiate between knowledge and acceptance, a survey should have items that separately measure awareness of the scientific consensus and acceptance of the scientific consensus for each major concept in evolution. This would enable researchers to differentiate between students who are unaware of yet willing to accept the scientific consensus, and students who reject certain evolutionary concepts because they hold alternative beliefs. A similar approach has been used in the Evolutionary Attitudes and Literacy Survey (EALS), which includes subscales that measure young-earth creationist beliefs, intelligent design fallacies, evolutionary knowledge, and genetic literacy, among others (Hawley et al., 2011). An important distinction, however, is that the knowledge-related items on the EALS focus exclusively on understanding of evolutionary processes (e.g., natural selection), with items across subscales that are not designed to separately measure awareness and acceptance of concepts such as the shared ancestry of all life or multicellular species’ descent from unicellular ancestors. Essentially, acceptance of evolution involves awareness/understanding, as well as assent and adoption of a range of evolutionary concepts. This notion is incorporated in the definition of evolution we established in a recent Delphi study (Misheva et al., 2024). Furthermore, it indicates that a robust measure of evolution acceptance that would be well-suited to inform teaching practice should simultaneously report on both student awareness and assent with regard to these aspects of evolution.