Why might the conclusions of scientific studies, later be viewed as invalid?

The conclusions of some scientific studies could later be viewed as invalid because there could be more studies done that disprove the findings of earlier studies. This would make the earlier studies be viewed as invalid because they no longer are correct in what they state.

Explanation:

since you have not provided the options here i   am going to give you general overview about hormone.hormone are actually the part of endocrine system in our body and produced by the endocrine glands. the hormones act like a chemical messenger   within human body. once produce by the glands they   travel through the blood stream and reach at specific or target tissue and organs   which result in control of our body function. the hormones are specific in their work and work on only the targeted tissue or organ   . with the of hormone endocrine system regulate the heart rate , metabolism, our mood and   growth as well as the development and even the sleeping cycle etc. they actually are the messenger for body cell and organs .