This paper examines the use of evidence by students in the context of causal explanations about human performances and the influence of environment in gene expression. Argumentation is an integral part of science (Jiménez-Aleixandre & Erduran, 2008). Science learning involves mastering concepts and models, but also the appropriation by students of epistemic practices, which according to Kelly (2008) include knowledge production, evaluation and communication. Explanations and models of scientific phenomena are constructed through social discourse (Berland & Reiser, 2009).

Argumentation can be characterized in different ways, for the purposes of this study, it is considered as the evaluation of knowledge claims in the light of available evidence (Jiménez-Aleixandre, 2008). It needs to be noted that argumentation and the use of evidence are framed in scientific competence, a notion central to PISA (OCDE, 2006) international evaluation, as well as one of the eight key competences recommended in 2006 by the European Union as a central core of lifelong learning (EU, 2006). Engagement in argumentation requires the appropriation of criteria and of evidence for the evaluation of arguments (Kunh, 1993). Conditions for supporting argumentation are dependent on the use of evidence in the process of building explanations (Duschl & Osborne, 2002).

An emerging literature in science education dedicated to the application of argumentation to educational processes has identified the importance of student's learning how to use, evaluate and critique evidence (Kelly, Regev & Prothero, 2008). In a previous study (Jiménez-Aleixandre & Puig, 2011) we analyzed the arguments of students, with a focus on the challenges that they encountered in building justifications and integrating evidence in their arguments. In order to increase our knowledge about students' difficulties in using evidence and in integrating them in their arguments, this paper seeks to examine another dimension of this scientific practice: the metaknowledge about the use of evidence. In other words, the knowledge about the role of evidence, about the epistemic criteria for evaluating knowlege, for distinguishing evidenced claims for opinions. 

There is also a socio-scientific (SSI) dimension, which deals with social representations impliying determinism views about human races. We view argumentation about socio-scientific issues (SSI) as contributing to scientific literacy (Kølsto, 2006;) and also to the development of an independent opinion in order to critically examine scientific opinions and arguments (Jiménez-Aleixandre & Puig, 2010).

This paper aims to explore the criteria (implicit or explicit) expressed by students in their arguments about the causes of the outstanding achievements of black people sprinters.  The research objectives:

1) to examine how students interpretate each piece of information in terms of gene-environment interaction

2) to explore the criteria expressed in the arguments by students about what constitutes appropriate evidence.

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