The diversity of the instruments used to assess acceptance of evolution and knowledge about evolution in Europe makes the comparison within and between countries and educational groups rather complicated or even questionable regarding its validity. Another crucial point in this regard is the often lacking evidence for local validity and reliability that was discovered in the present review (see Additional files 3, 4, and 5). Moreover, only five of the 13 most commonly used instruments (Mead et al. 2019) were found to have been applied to European samples (ACORNS, CINS, I-SEA, KEE, MATE): this may be partly explained by the fact that some instruments have been only recently developed and published (as is the case for CANS and GAENE). This, along with a generally low number of studies per country across Europe (both as regards knowledge and acceptance of evolution, see Fig. 1 and 2) indicate that much more research is still needed i) to expand and diversify samples, ii) to unify already available ones and compare among them and iii) to apply standards to provide appropriate sources of evidence for reliability and validity. This way it will be possible to get a clearer picture of the European educational context and to make sound and reliable inferences on how different instructional settings impact learning.
Having these methodological limitations in mind (see paragraph on validity issues for a deepened discussion), our results show that the current state of research regarding knowledge and acceptance of evolution of students and teachers in Europe is diverse. However, there are in particular some major points of concern that emerge from our results. As we detail below, pre-service teachers show low to moderate levels of knowledge about evolution in some samples of several European countries (Turkey, Germany, Greece, Slovenia, Czech Republic, Slovakia). In some surveyed samples (Greece and Turkey), undecided attitudes or even rejection of evolution are recorded. As regards knowledge about evolution of primary education in-service teachers, scores range unsatisfyingly from very low to moderate. Teachers, and in particular biology teachers, play a key role in correcting misleading notions and conceptual schemas of evolution from the early stages of education, adjusting instruction to respond to their students’ inquiries and needs. The persistence of various misconceptions through all educational stages that we found in our study must be interrogated by future research also in light of these critical aspects, along with a more detailed understanding of the educational offer about evolution across various curricula.
Knowledge about evolution
School students
The level of knowledge about evolution in European school students has not been much explored yet. The present review resulted in ten publications in six European countries on the assessment of early childhood, primary and secondary education students’ knowledge about evolution (Croatia and Slovenia: Kralj et al. 2018; Germany: Beniermann 2019; Fenner 2013; Jördens et al. 2016; Kuschmierz et al. 2020; Lammert 2012; Greece: Kampourakis et al. 2012a, b; Italy: Kampourakis et al. 2012a, b; Switzerland: Queloz et al. 2017), gathered with eight different instruments (KAEVO and self-developed). In summary, the data on knowledge about evolution in European school students is limited and not unified. The current state of research reveals mixed levels of knowledge about evolution for secondary education students, from very low (Beniermann 2019; Kuschmierz et al. 2020), moderate (Fenner 2013; Lammert 2012) to high (Rufo et al. 2013). Furthermore, a variety of misconceptions, predominantly teleological and Lamarckian, for primary (e.g., Kampourakis et al. 2012a, b) and secondary education students of various grades (e.g., Beniermann 2019; Fenner 2013; Fischer 2014; Jördens et al. 2016; Lammert 2012; Queloz et al. 2017) is apparent. The persistence of such misconceptions might indicate that European school curricula may not fully succeed in coping with naïve conceptual frameworks (that are known to develop at an early age). Also, the knowledge displayed by pre-service and in-service teachers plays a significant role in this regard. Critical aspects have emerged in this sense (see sections below).
University students
Overall, eight studies on university students (excluding pre-service teachers) in seven countries (Flanders, Belgium: 1; Germany: 3; Greece: 2; the Netherlands: 1; Spain: 1; Sweden: 1; Turkey: 1) were discovered, gathered with four different instruments (CINS, KAEVO, KEE, and ORI). Knowledge about evolution of university students seems to be an issue (low to moderate knowledge about evolution or frequently occurring misconceptions) in several countries: Turkey (Annaç and Bahçekapili 2012), Germany (Beniermann 2019; Fiedler et al. 2017; Göransson et al. 2020; Harms and Fiedler 2019; Kuschmierz et al. 2020), Greece (Athanasiou and Mavrikaki 2014), Spain (Gefaell et al. 2020), and Sweden (Göransson et al. 2020).
The level of knowledge about evolution of European university students varies between and within the different fields of study. Knowledge about evolution was very low (Germany: English language and literature, and mathematics students, Kuschmierz et al. 2020; Turkey: psychology majors, Annaç and Bahçekapili 2012) and low (Germany: different study programs, Beniermann 2019; Spain: chemistry, history, and English philology students, Gefaell et al. 2020) in university students from different non-biology related study programs. Biology-related university freshmen showed low knowledge about evolution (Belgium: Pinxten et al. 2020). Biology majors showed very low (Germany: Kuschmierz et al. 2020), moderate (first- to third-year and postgraduate biology majors, Greece: Athanasiou and Mavrikaki 2014; Spain: Gefaell et al. 2020) to rather high knowledge about evolution (fourth-year biology majors, Greece: Athanasiou and Mavrikaki 2014; Lazaridis et al. 2011). The finding of Nehm and Ha (2011) for university students in the USA that examples of evolutionary adaptation including the loss of traits are more challenging than examples that include the gain of traits, was also confirmed for German university students (Göransson et al. 2020).
Misconceptions, predominantly teleological misconceptions, were also present among university students of different fields of study (Athanasiou and Mavrikaki 2014; Beniermann 2019; Kuschmierz et al. 2020; Pinxten et al. 2020). Also, some evolutionary concepts, as for example ‘biotic potential’ (Athanasiou and Mavrikaki 2014; Lazaridis et al. 2011), change in a population, and origin of species (Athanasiou and Mavrikaki 2014; Pinxten et al. 2020) seemed to be difficult to understand across multiple samples. Summed up, it can be stated that the knowledge about evolution increased with biology education level across different European university student samples.
Pre-service teachers
Pre-service teachers, especially future biology teachers, play a special role in terms of knowledge about evolution and are the most assessed group of university students in this regard, with numerous studies in Turkey (Akyol et al. 2010, 2012; Deniz and Sahin 2016; Graf and Soran 2010; Keskin and Köse 2015; Tekkayaet al. 2011) and Germany (Fiedler et al. 2017; Graf and Soran 2010; Großschedl et al. 2018; Nehm et al. 2013). Pre-service teachers showed low to moderate knowledge in Turkey and low to rather high knowledge in Germany. In other countries, the database is very thin or no publications were found. Overall, 15 studies on pre-service teachers were discovered in six countries (Czech Republic: 1; Germany: 6; Greece: 2; Slovakia: 1; Slovenia: 2; Turkey: 7), gathered with ten different instruments (CINS, ECKT, KAEVO, ORI, ACORNS, and self-developed).
With this in mind, the results for pre-service teachers show partly alarmingly low levels of knowledge about evolution. Knowledge about evolution of pre-service teachers seems to be an issue (low to moderate knowledge about evolution or frequently occurring misconceptions) in several countries: Turkey (Akyol et al. 2010, 2012; Deniz and Sahin 2016; Graf and Soran 2010; Keskin and Köse 2015; Šorgo et al. 2014; Tekkaya et al. 2011), Germany (Beniermann 2019; Fiedler et al. 2017; Graf and Soran 2010), Greece (Athanasiou et al. 2012; Athanasiou and Mavrikaki 2014) Slovenia (Šorgo et al. 2014; Torkar and Šorgo 2020); Czech Republic (Šorgo et al. 2014); and Slovakia (Šorgo et al. 2014). Pre-service teachers of different fields showed very low knowledge about evolution in two studies (Greece: Athanasiou and Mavrikaki 2014; Slovenia: Torkar and Šorgo 2020), low knowledge in two studies (Germany and Turkey: Graf and Soran 2010; Greece: Athanasiou and Mavrikaki 2014), and moderate knowledge in one study (Nehm et al. 2013). Studies that focused on pre-service science or pre-service biology teachers revealed a variety of knowledge about evolution, from unexpectedly very low (Greece: Athanasiou et al. 2012; Turkey: Akyol et al. 2010; Akyol et al. 2012; Deniz and Sahin 2016), low (Turkey: Tekkaya et al. 2011), to moderate (Germany: Nehm et al. 2013; primary and lower secondary education, Großschedl et al. 2018), and rather high knowledge about evolution (Germany: upper secondary education, Großschedl et al. 2018). Results from open response instruments confirmed that the context effects in evolution assessment found in European university students (Göransson et al. 2020), were also present in pre-service teachers. The examples of evolutionary adaptation in animals apparently were easier to explain than examples in plants (Großschedl et al. 2018; Nehm et al. 2013). The same effect was found for examples including the gain of traits in contrast to the loss of traits (Großschedl et al. 2018; Nehm et al. 2013). These results indicate that the ratio of gain/loss and animal/plants items in an instrument will control measurement outcome to a large degree, which should be taken into account in future standardized assessments across Europe (see also Nehm et al. 2012).
Misconceptions, predominantly teleological misconceptions, were also present among pre-service teachers (Germany: Graf and Soran 2010; Greece: Athanasiou and Mavrikaki 2014; Turkey: Keskin and Köse 2015; Tekkaya et al. 2011; Slovenia: Torkar and Šorgo 2020). In contrast to other university students, knowledge about evolution did not consistently increase with biology education level across different European pre-service teacher samples.
In-service teachers
Seven studies on in-service teachers were found in four countries (Greece: 4, Serbia: 1, Turkey: 1, the United Kingdom: 1), gathered with four different instruments (CINS, ECKT, self-developed). Very low (Greece: Athanasiou et al. 2016; Serbia: Stanisavljevic et al. 2013), low (Greece: Athanasiou et al. 2016; Prinou et al. 2011; Stasinakis and Athanasiou 2016; Serbia: Stanisavljevic et al. 2013; Turkey: Tekkaya et al. 2012) or moderate (Greece: Athanasiou et al. 2016; United Kingdom: Buchan et al. 2019) knowledge about evolution was reported for different groups of in-service teachers in several countries.
The level of knowledge about evolution among in-service teachers differed according to the type of school education. While very low knowledge about evolution was stated for early childhood education (Greece: Athanasiou et al. 2016; Serbia: Stanisavljevic et al. 2013), primary education teachers showed very low (Serbia: Stanisavljevic et al. 2013), low (Greece: Athanasiou et al. 2016; Turkey: Tekkaya et al. 2012), and moderate knowledge about evolution (the United Kingdom: Buchan 2019). Very low (physics, Serbia: Stanisavljevic et al. 2013), low (biology, chemistry, Serbia: Stanisavljevic et al. 2013; Turkey: Tekkaya et al. 2012), moderate (Greece: Athanasiou et al. 2016; the United Kingdom: Buchan 2019) and rather high (Greece: Venetis K, Mavrikaki E. Oi gnoseis ton ekpaideytikon thetikon epistimon shetika me tous exeliktikous mixanismous ton zontanon organismon. Sto A. Polyzos, L. Anthis (epim.), Praktika Ergasion 4th Panelliniou Synedriou “Biologia stin Ekpaideysi” [Knowledge of secondary education science teachers regarding the evolutionary mechanisms of living organisms. In: Polyzos A, Anthis L, editors. Proceedings of the 4th Panhellenic Conference “Biology in Education”]. Piraeus: Panhellenic Association of Bioscientists 2017) to high (Greece: only biologists, Venetis et al. 2017) knowledge about evolution was also presented for secondary education teachers. Even in-service teachers showed mainly teleological misconceptions (United Kingdom: Buchan 2019; Greece: Prinou et al. 2011), and also anthropomorphic and Lamarckian misconceptions (United Kingdom: Buchan 2019). This illustrates the persistence of misconceptions through all education levels that is likely to affect the quality of evolution instruction offered to the various groups of students.
Cross-country studies
Five publications include samples from two or more European countries, four of them compare two countries in terms of knowledge about evolution (Croatia and Slovenia: Kralj et al. 2018; Germany and Turkey: Graf and Soran 2010; Belgium and the Netherlands: Pinxten et al. 2020) or with a focus on misconceptions (Germany and Sweden: Göransson et al. 2020; Belgium and the Netherlands: Pinxten et al. 2020). One study compares four countries regarding knowledge about evolution (Czech Republic, Slovakia, Slovenia, and Turkey: Šorgo et al. 2014).
Altogether, results of 15 different European countries on evolutionary knowledge were documented in the current review. In only three of these countries three or more publications are discovered (Germany: 11, Greece: 7, Turkey: 9; see Fig. 1). This implies that there is only few or even no information available concerning knowledge about evolution in most European countries. Thus, evolution education research in Europe should fill this gap in the future by conducting cross-country studies on a comparable target group by use of the same instrument and providing evidence for local validity.
Acceptance of evolution
School students
Our review resulted in ten studies focusing on acceptance of evolution of school students that were discovered in six countries (Austria: 1, France: 1; Germany: 5, Italy: 1, Turkey: 1, the United Kingdom: 1), gathered with eight different instruments (MATE and self-developed).
Evolution acceptance in school students is rather high in three European countries (Germany: Beniermann 2019; Fenner 2013; Konnemann et al. 2016; the United Kingdom: Mead et al. 2018; Italy: Rufo et al. 2013). In three countries, studies reported moderate acceptance (Germany: Konnemann et al. 2016; Lammert 2012), mixed attitudes towards evolution (Austria: Eder et al. 2011) or even rejection (Turkey: Köse 2010) for this sampling group. The conflicting results for Germany support an issue, which has also been found in previous studies (e.g., Barnes et al. 2019; Mead et al. 2019; Smith et al. 2016): besides other reasons, the application of different measuring instruments can lead to inconsistent results. Konnemann et al. (2016) used a self-developed instrument as well as the MATE, reporting moderate acceptance of evolution for the MATE and at the same time positive attitudes towards evolution for a great majority of the students (87.6%) based on the self-developed instrument. In both studies that revealed moderate acceptance (Konnemann et al. 2016; Lammert 2012), the MATE was used. Beniermann (2019) and Fenner (2013), who reported rather high acceptance, used self-developed measurement instruments.
The results show that only a few school students in Europe seem to reject evolution. Predominant rejection occurred only in one Turkish study (Köse 2010), where evolution was recently banned from textbooks (Genç 2018). Although there is only one study on Turkish school students, the results shown by Köse (2010) are in accordance with results of studies on Turkish pre-service teachers (e.g., Akyol et al. 2012; Deniz and Sahin 2016; Graf and Soran 2010).
University students
Only five studies on university students who are not pre-service teachers, were reported in four countries (Germany, Spain, Turkey, and the United Kingdom), gathered with five instruments (I-SEA and self-developed). According to the authors, in all samples surveyed students largely accept evolution (Germany: Beniermann 2019; Spain: Gefaell et al. 2020; Turkey: Annaç and Bahçekapili 2012; the United Kingdom: Betti et al. 2020; Southcott and Downie 2012). Despite the fact that this is generally good news, the explanatory power of a total of five studies is pretty low. More research on university students would be necessary to strengthen this tendency.
Furthermore, a crucial point when comparing studies using different instruments, is the categorization of the mean scores. For example, Annaç and Bahçekapili (2012) reported a “high acceptance” for a mean score that reflects a low to moderate acceptance of evolution based on the MATE scale (see Table 2). This issue displays that it is important to standardize comparative studies across countries.
Pre-service teachers
Fifteen studies on pre-service teachers’ acceptance of evolution were discovered in four countries (Germany: 5, Greece: 2, Turkey: 7, the United Kingdom: 1), gathered with three different instruments (MATE and self-developed).
In contrast to the other university students, many studies have been conducted on European pre-service teachers. Additionally, the situation is more diverse than for school students and other university students. In some countries, the surveyed samples largely accept evolution (Germany: Graf and Soran 2010; Großschedl et al. 2014; Großschedl et al. 2018; Konnemann et al. 2018; Nehm et al. 2013; the United Kingdom: Arthur 2013), in some countries the surveyed samples have undecided positions or rather reject evolution (Greece: Athanasiou and Papadopoulou 2012; Athanasiou et al. 2012; Turkey: Akyol et al. 2010, 2012 Deniz et al. 2011; Deniz and Sahin 2016; Graf and Soran 2010; Irez and Bakanay 2011; Bilen and Ercan 2016; Yüce and Önel 2015). These alarming results for Greece and Turkey should be investigated further, especially in view of the particularly important role of pre-service teachers in evolution education. In both countries, evolution only plays a minor role in school curricula.
In-service teachers
Seven studies on in-service teachers’ acceptance of evolution were found in four countries (Greece: 1, Serbia: 1, Turkey: 1, the United Kingdom: 2), gathered with two different instruments (MATE and self-developed). In almost all of these countries, in-service teachers showed moderate (Serbia: Stanisavljevic et al. 2013; Turkey: Tekkaya et al. 2012) to high acceptance (Germany: Beniermann 2019; Greece: Athanasiou et al. 2016; Serbia: Stanisavljevic et al. 2013; the United Kingdom: Buchan 2019; Downie et al. 2018). In one study, the majority of biology teachers rejected evolution (Turkey: Köse 2010). Despite the crucial importance of in-service teachers to foster knowledge about evolution and acceptance of evolution, the amount of studies in Europe is quite low. The partly alarming results concerning pre-service teachers in the present review lead to the assumption that this issue could arise also in future studies on in-service teachers in Europe.
Comparing acceptance among different education levels, a rejection of evolution was mainly found in university students, but rather not in school students and in-service teachers (but see Köse 2010). Comparable with the topic of knowledge about evolution, the number of studies in different countries varied among European countries. Much research has been conducted in Turkey (especially for university students) and Germany. In all other countries, a sharp image of evolution acceptance is missing. Only two publications compare acceptance of evolution among European countries by means of the same instrument within comparable groups (Clément 2015a; Graf and Soran 2010).
Results of 35 different European countries on evolution acceptance were documented in this article. An amount of three or more publications are found in only four of these countries (Germany: 9, Greece: 3, and Turkey: 10, the United Kingdom: 6; see Fig. 2). Similar to evolutionary knowledge, it has been shown that there is only few or even no information available about acceptance of evolution in most European countries.
Relationship between acceptance of evolution and knowledge about evolution
European studies that investigated both acceptance of and knowledge about evolution reported very different results concerning the existence and strength of the relationship between these factors. However, some trends are visible, for example the lacking or weak correlation between acceptance and knowledge for primary and secondary school students in Germany indicating an increase of strength of the relationship the higher the educational level (Beniermann 2019; Fenner 2013; Lammert 2012). This assumption is supported by the fact that based on the same instruments (ATEVO and KAEVO) Beniermann (2019) showed an increase of the correlation coefficient from lower secondary students to in-service biology teachers. Other studies on pre-service or in-service teachers in Europe showed weak (Germany: Graf and Soran 2010; Großschedl et al. 2014; Turkey: Akyol et al. 2012; Greece: Athanasiou et al. 2012) or moderate (Germany: Großschedl et al. 2018; Nehm et al. 2013; Turkey: Deniz and Sahin 2016; Serbia: Stanisavljevic et al. 2013; the United Kingdom: Buchan 2019) positive relationships between acceptance and knowledge. Based on these results there is no effect of the used instruments visible as the mentioned studies applied either a combination of the MATE and the ECKT or utilized the MATE and the CINS. Both combinations of instruments lead to weak as well as moderate positive correlations between acceptance and knowledge.
However, in contrast to these results, there are contradicting studies reporting no significant correlation for pre-service and in-service teachers in Turkey (Akyol et al. 2010; Graf and Soran 2010; Tekkaya et al. 2012) and Greece (Athanasiou et al. 2016). Except for Graf and Soran (2010) who used deviant instruments, all of these studies used a combination of ECKT and MATE to assess knowledge and acceptance. Even though the combination of ECKT and MATE for almost all non-significant correlations is noteworthy, it should be considered that for a valid comparison between combinations of instruments, these instruments should be applied to comparable or ideally the same samples.
Overall, the results emphasize the difference between knowledge about evolution and accepting evolution as two separate constructs, since there is no clear connection between these two variables visible. This once more demonstrates the importance for measuring instruments that clearly distinguish between acceptance of evolution and knowledge about evolution, as discussed in several methodological considerations (Beniermann 2019; Kahan 2015; Konnemann et al. 2012; McCain and Kampourakis 2018; Roos 2014; Smith 2010).
Based on this review, the relation between acceptance of evolution and knowledge about evolution remains open (see Barnes et al. 2019; Dunk et al. 2019) to investigation in Europe and needs a more standardized way to assess both factors allowing for a more comparable database.
Religiosity and other factors influencing acceptance of evolution
As a negative relation between religious faith and acceptance of evolution was discovered for primary and secondary education students (Eder et al. 2011; Lammert 2012), university students (Annaç and Bahçekapili 2012; Beniermann 2019; Betti et al. 2020; Graf and Soran 2010; Southcott and Downie 2012) including biology pre-service teachers (Athanasiou et al. 2012; Deniz et al. 2011; Deniz and Sahin 2016) as well as in-service teachers (Athanasiou et al. 2016; Clément et al. 2012) across European countries, the close relationship between these constructs becomes visible. However, it was shown before in the USA (McCain and Kampourakis 2018) as well as Europe (Germany, Beniermann 2019) that religious faith alone is no predictor for a rejection of evolution and a huge percentage of religious believers do accept evolution.
Acceptance of evolution differed between denominations for primary and secondary education students, as well as university students in Austria, Germany and the UK with lowest acceptance scores for Muslims (Eder et al. 2011; Fenner 2013; Lammert 2012; Southcott and Downie 2012) or Christian Free Churchers (Beniermann 2019; Konnemann et al. 2016) and highest scores for students without a denomination (Beniermann 2019; Lammert 2012; Konnemann et al. 2016). It should be emphasized that, subsamples of Muslims and Christian Free Churchers in European samples are normally very small and therefore difficult to generalize.
Clément (2015a) and Clément et al. (2012) showed how in-service teachers in Europe differed concerning their acceptance of evolution depending on the predominant affiliation in the country samples. For example, Orthodox teachers in Russia showed the most creationist positions (Charles and Clément 2018) and European countries with a large share of Catholic (Poland, Malta) or Orthodox (Georgia, Romania) respondents tend to reject evolution more often (Clément 2015a). However, in their cross-country comparison Clément et al. (2012) showed that even countries with a comparable share of Orthodox teachers as members of a conservative religion (Cyprus, Georgia, Romania and Serbia) differ highly in their creationist positions (between 54% in Georgia and 11% in Serbia). Clément (2015a) concluded that the observed differences between countries are mostly related to the countries and not to the denomination: “Globally, in the less economically developed countries, teachers are more believing in God and practicing their religion, whatever is this religion, and they are more creationist and more often against a separation between science and religion” (Clément 2015a, p. 286). Although some religious affiliations are important parts of several national backgrounds, they cannot be separated from other important factors like national history, politics and economy (Clément 2015b). This “strong influence of the national socio-cultural context” (Clément et al. 2012) was also confirmed by comparison of Catholic, Protestant and Muslim teachers in different countries (Clément 2015a).
Another important path of investigation for future research within Europe consists in assessing which factors mainly influence the acceptance of evolution. Besides religiosity, conceptions on the nature of science (NOS; Smith 2010; Smith and Siegel 2004)—generally regarded as fundamental components of scientific literacy—may also play a critical role in this sense. Akyol et al. (2010) as well as Graf and Soran (2010) identified a statistically significant positive contribution of understanding of the nature of science to the acceptance of evolution among pre-service teachers. Moreover, attitudes towards science have found to be a significant predictor for acceptance of evolution for German (Graf and Soran 2010; Großschedl et al. 2014) and Turkish (Graf and Soran 2010) pre-service teachers. Therefore, future studies should further explore the correlation between understanding the nature of science (in its epistemological and sociological aspects), attitudes towards science and acceptance of evolution in Europe.
Cross-country studies
Overall, in only four studies samples from more than one country were surveyed in terms of acceptance of evolution and/or knowledge about evolution (Clément 2015a; Göransson et al. 2020; Graf and Soran 2010; Pinxten et al. 2020; Šorgo et al. 2014). Even if the results of Clément (2015a) are based on several multiple-choice questions and no established measurement instrument, they show that teachers’ views on evolution and religiosity are highly connected to their national socio-cultural background.
Numerous studies have been conducted in only a few countries (mainly Greece, Turkey, and Germany). Very few instruments have been used multiple times and the target groups are very diverse. Further research will be necessary to get a clear overview of the status of knowledge and acceptance of evolution among different education levels in Europe.
Summed up, a comprehensive overview of knowledge and acceptance of evolution in Europe, conducted with a comparable sample and the same high-quality instrument in each country, is still missing.
Measuring instruments
The identified instruments to measure knowledge about evolution and attitudes towards evolution in European studies focus on different aspects of the target construct. Especially the instruments that aim to measure knowledge about evolution differ concerning the evolutionary concepts they cover (e.g., KAEVO vs. CINS).
With regard to measuring acceptance of evolution, Barnes et al. (2019) already showed in a comparative analysis that different approaches in some cases lead to different results and hence different interpretations. In a German sample, Konnemann et al. (2016) also obtained diverging results based on two different measures. However, even globally there are still only few publications that investigated whether different instruments result in different conclusions about attitudes towards evolution (Barnes et al. 2019; Metzger et al. 2018; Rachmatullah et al. 2018; Romine et al. 2018; Sbeglia and Nehm 2018, 2019) and even these comparative studies came to different conclusions. For example, Romine et al. (2018) concluded that the MATE, GAENE, and I-SEA can be considered as a single scale to measure one or two factors without losing quantitative interpretability, while Barnes et al. (2019) emphasized the partly inconsistent results based on different instruments by use of the I-SEA, GAENE, MATE and the 100-point instrument of self‑defined acceptance. These inconsistent results were mostly visible for Christian and Mormon respondents. However, these differences in results occurred not for all instruments and not between all groups. The effect of different instruments was mainly visible when focusing on the effect of evolution understanding on evolution acceptance. For this relationship, evolution understanding was a better predictor, when evolution acceptance was assessed based on the MATE or the I-SEA microevolution scale. When people identified as Protestant or Mormon, measured values for acceptance of evolution differed depending on the applied instrument.
These reported inconsistent results may be partly explained by the different focus on evolution in general, microevolution, macroevolution or human evolution (Barnes et al. 2019), since several studies in the US showed that levels of acceptance are higher for microevolution than for macroevolution or human evolution (Barnes et al. 2019; Nadelson and Hardy 2015; Nadelson and Southerland 2012). Theoretically, human evolution as well as macroevolution are in conflict with many religious beliefs, while even creationists accept microevolution to some extent (Pobiner 2016; Scott 2008). In Europe this difference was visible in the only study that used the I-SEA (Betti et al. 2020). Furthermore, one European study emphasized the lower acceptance for evolution of the human mind compared to evolution in general (Beniermann 2019).
Another crucial factor regarding the decision for one instrument to measure acceptance of evolution in Europe is the distinction between acceptance of evolution and religious belief. The framing of questions on attitudes towards evolution is of crucial importance, since the way in which the relationship of evolution, faith and creationism is presented, will influence the results of a survey (Elsdon-Baker 2015; Kampourakis and Strasser 2015). While Romine et al. (2017)argued for the US context that the inclusion of explicitly creationist views in assessments of acceptance of evolution may not be a problem, McCain and Kampourakis (2018) showed that publication polls about the acceptance of evolution lead to different results, depending on the inclusion of a statement about God in the questions about evolution. This distinction may be even more important, when investigating the relationship between acceptance of evolution and religious faith in less religious countries (Beniermann 2019), as it is the case in several European countries (Clément 2015a).
The diversity of the instruments used to assess acceptance of evolution and knowledge about evolution in Europe is one major point that makes the comparison within and between educational groups and countries rather complicated or even questionable regarding its validity. One approach to address this issue is to build categories of acceptance and knowledge levels to compare between results derived from different instruments. Most published scales do not recommend categories for interpretation of survey results, so that authors of single studies apply categories (e.g., “low knowledge”, “moderate acceptance”) themselves. This approach serves standardization between studies, even if our standardized categories are in some cases in conflict with interpretation of study authors.
Validity issues
In total, 26 studies in this review used their own instruments to assess acceptance or knowledge about evolution, making it more difficult to compare results between studies. In addition to studies that used previously published instruments, 31 other instruments were used to assess acceptance or knowledge about evolution in Europe since 2010. Most likely, not all of these instruments have undergone a validation procedure (e.g., based on AERA 2014). The literature review demonstrates that evidence for validity and reliability is at least often not reported in these publications: Only six of the 15 studies identified in the present review that used an own instrument to assess acceptance of evolution provided at least one source of evidence for validity of the instrument (see Additional file 5). For non-established instruments to assess knowledge about evolution nine studies reported at least one source of evidence for validity while seven studies did not provide any evidence (see Additional file 4).
However, there are even validity issues for most of the published scales (Mead et al. 2019), not to mention local validity for the respective studies that used these instruments (see Additional file 3). The present review showed that six of nine studies that used the CINS in a European context did not report any source of evidence for local validity of the CINS within their setting. Those who provided evidence for validity reported results for PCA (internal structure; Athanasiou and Mavrikaki 2014; Pinxten et al. 2020) or referred to an expert review (content validity; Tekkaya et al. 2011). Evidence for reliability in form of internal consistency was reported for five of the nine studies. Altogether, four of these nine studies did neither provide evidence for validity nor for reliability (Annaç and Bahçekapili 2012; Buchan 2019; Lazaridis et al. 2011; Nehm et al. 2013).
The majority of studies utilizing the ECKT did not provide any evidence for validity. Only one out of seven studies reported results for dimensionality (Akyol et al. 2012). In four of the seven studies evidence for reliability was provided via internal consistency (Akyol et al. 2012; Athanasiou et al. 2012, 2016; Tekkaya et al. 2012). Summed up, in three studies neither evidence for validity nor for reliability was provided (Akyol et al. 2010; Deniz and Sahin 2016; Stanisavljevic et al. 2013).
Two of three studies using the KAEVO reported multiple evidence for validity (content validity, internal structure) and reliability (Beniermann 2019; Kuschmierz et al. 2020). One study did not provide any evidence neither for validity nor for reliability (Torkar and Šorgo 2020). Gefaell et al. (2020), who used the KEE, provided one source of evidence for validity (external structure) and reliability (internal consistency). One of three studies using the ORI provided evidence for validity (content validity; Göransson et al. 2020). Göransson et al. (2020) and also one additional study provided evidence for reliability (Fiedler et al. 2017). None of the two studies using the ACORNS provided evidence for validity but both studies provided evidence for reliability (Großschedl et al. 2018; Nehm et al. 2013).
Betti et al. (2020) provided evidence for validity (internal structure) but not for reliability using the I-SEA. Seven of 21 studies using the MATE provided evidence for local validity via internal structure or content validity and reliability (Akyol et al. 2012; Großschedl et al. 2014; Irez and Bakanay 2011; Konnemann et al. 2016; Lammert 2012; Tekkaya et al. 2012; Yüce and Önel 2015). Almost all studies (18) provided evidence for reliability, predominantly via internal consistency (Akyol et al. 2010, 2012; Athanasiou and Papadopoulou 2012; Athanasiou et al. 2012, 2016; Bilen and Ercan 2016; Denizet al. 2011; Deniz and Sahin 2016; Gefaell et al. 2020; Großschedl et al. 2014, 2018; Irez and Bakanay 2011; Konnemann et al. 2016, 2018; Lammert 2012; Mead et al. 2018; Tekkaya et al. 2012; Yüce and Önel 2015). Only three studies provided no evidence for neither reliability nor local validity (Buchan 2019; Nehm et al. 2013; Stanisavljevic et al. 2013).
The importance of providing evidence for local validity and reliability arised in the field of evolution education within the last 12 years (Mead et al. 2019; Nehm and Schonfeld 2008; Smith et al. 2016). Thus, the awareness about the necessity to provide proper evidence for local validity and reliability steadily increased over the years. However, even studies that were published within the last 2 years are in some cases lacking evidence of local validity and reliability.
Furthermore, most published scales have been developed and validated for specific target groups, but are often used for different groups (e.g., different educational levels), even if it is questionable whether they are suitable for these groups (e.g., for MATE: Wagler and Wagler 2013). However, particularly in case of knowledge instruments, this raises the question, whether categories for interpretation of results should be adjusted when applying the same instrument for different educational levels. To date, there are only few instruments that have been developed for multiple education levels (e.g., KAEVO and MATE).