We would like to thank Dr. Lorenzo Lolli for his interest in our article entitled “The First Allometric Analysis in Newborns Rejects the Allometry Hypothesis for 2D:4D: Strong Developmental Evidence for Prenatal Hormonal Programming” (Özener et al. 2026) and for raising important methodological considerations regarding the use of ratio-based indices and allometric assumptions. We appreciate the opportunity to clarify several points that we believe are central to the interpretation of our findings. We fully agree that simple ratio indices can be problematic when the relationship between numerator and denominator does not pass through the origin, as clearly articulated in the allometric and statistical literature (e.g., Tanner 1949; Albrecht et al. 1993; Curran-Everett 2013). For this reason, our analyses were not based solely on the interpretation of raw 2D:4D ratios. Importantly, we explicitly reported the nonzero y-intercepts in the regression of 2D on 4D and acknowledged that this pattern indicates a departure from strict isometry. However, our primary conclusions do not rely on the assumption that the 2D:4D ratio represents a size-free metric. Instead, the central aim of our study was to evaluate whether the observed sexual dimorphism in 2D:4D among newborns could be accounted for by digit size-related allometric effects. To address this directly, we employed analyses of covariance (ANCOVA), using fourth digit length as a covariate. Our neonatal findings are consistent with and extend the results of our earlier large-scale study in adults (Aksoy and Özener 2025), where, after controlling for allometric effects using ANCOVA, significant sexual dimorphism in 2D:4D persisted. These analyses demonstrated that the sexual dimorphism in 2D:4D remained statistically significant even after controlling for 4D length in both hands. Moreover, when the effect of 4D was held constant, second digit length itself differed significantly between sexes, indicating that digit-specific developmental processes contribute to the observed dimorphism. In this context, the presence of a nonzero y-intercept does not invalidate our conclusions. Rather, it reinforces the importance of using appropriate statistical controls when testing allometric explanations. Our results show that although 2D and 4D are strongly correlated and share a common regression slope across sexes, variation in absolute digit size does not account for the sex difference in 2D:4D in this neonatal sample. Therefore, the data do not support the claim that the observed dimorphism can be attributed to simple differential growth of the fourth digit. Thus, while the statistical limitations of ratio-based indices are well recognized, they do not, in themselves, constitute evidence against the existence of sexual dimorphism in digit proportions. Furthermore, we addressed the issue of nonzero y-intercepts by performing additional regression analyses with centered independent variables (C4D = 4D−Mean 4D). While a y-intercept at 4D = 0 is biologically nonexistent and thus a poor point of comparison, centering the data at the mean allows for a biologically meaningful test of differences at a typical digit length. Our results from these centered models confirm that the intercepts differ significantly between sexes (p < 0.001), reinforcing that sexual dimorphism is not an artifact of scaling at extreme or hypothetical values. Even if males and females share a common allometric slope, they occupy distinct positions (centroids) along that line. As clearly illustrated in our regression analysis (see Figure 1a,b), the vertical displacement between the male and female lines confirms a robust biological signal that persists across the entire range of digit lengths, independent of the scaling model. As our ANCOVA results also indicate, at any given 4D length, the 2D length of females is significantly different from that of males, a finding that Dr. Lolli appears to have overlooked by focusing exclusively on ratio-based statistics. Finally, we wish to clarify that our use of ANCOVA was not intended to model the form of the allometric relationship itself, but rather to test whether allometric variation in digit size could plausibly account for the observed sex differences. From this perspective, ANCOVA represents an appropriate and conservative approach to evaluating size-related confounding. Whether alternative modeling strategies (e.g., log–log regressions) might further characterize scaling relationships does not alter the central finding that sex differences persist after controlling for digit size. Accordingly, methodological concerns regarding the optimal description of allometry do not bear directly on the biological question addressed in our study. Our findings demonstrate that sexual dimorphism in 2D:4D is a primary developmental signal of prenatal origin, rather than a secondary artifact of scaling—a distinction that remains clear regardless of the specific allometric model employed. We respectfully disagree with the assertion that our findings substantiate a lack of empirical support for sexual dimorphism in 2D:4D. On the contrary, by demonstrating that sex differences persist under conditions where postnatal growth, mechanical loading, and size-related confounds are minimal, our study provides developmental evidence that is inconsistent with a purely allometric explanation. In this sense, our results align with a growing body of large-sample and multivariate research suggesting that 2D:4D dimorphism is largely independent of allometric scaling. We thank Dr. Lolli for stimulating further discussion on this important methodological issue and hope that this exchange contributes constructively to ongoing debates regarding the interpretation of digit ratios in human biology. Barış Özener: conceptualization, formal analysis, methodology, visualization, writing – original draft, writing – review and editing. Berna Ertuğrul: conceptualization, formal analysis, visualization, writing – original draft, writing – review and editing. Görel Aksoy: conceptualization, formal analysis, visualization, writing – original draft, writing – review and editing. The authors have nothing to report. The ethics approval of this study was obtained from the Ethics Committee of Sivas Cumhuriyet University (04-E.416797). All procedures were performed in accordance with the ethical standards of the Declaration of Helsinki. The authors declare no conflicts of interest. The data that support the findings of this study are available from the corresponding author upon reasonable request.
Özener et al. (2026) studied this question.