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We demonstrated that sand lizards (Lacerta ugilis) are more likely to have malformed offspring when they mate with siblings. Offspring with malformations, such as deformed limbs and heads, have zero survival in a natural population. Normal-looking siblings of malformed hatchlings also had a reduced survival in the wild, compared to offspring from clutches in which all siblings appeared normal.

This study has important implications for the interpretation of every study of mortality among immigrants based on official mortality statistics. Using information about income as an indicator of residence in the country appears to be a method which can be pursued further in order to achieve a more accurate understanding of mortality among immigrant groups.

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