Final answer:
The fact that adopted children resemble their biological families more in terms of weight than their adoptive families suggests genetics play a key role in determining body weight.
Step-by-step explanation:
The observation that adopted children are more similar in weight to their biological families than to their adoptive families supports the claim that genetics play a significant role in determining body weight. This implies that hereditary factors, which are passed down from biological parents, have a greater influence on an individual's weight compared to the environmental factors provided by the adoptive family. This conclusion is often drawn from studies that investigate the nature vs. nurture debate, indicating a strong genetic component to physical characteristics such as weight.