How does the attempt to control and modify plants and animals lead to eugenics?

A short essay (employing an Introduction, Body, and Conclusion and provide citation (use the CMS format) All links for the reading are below: https://www.britishcouncil.org/ http://sourcebooks.fordham.edu/halsall/mod/spencer-darwin.asp http://www.uvm.edu/~lkaelber/eugenics/ https://www.ushmm.org/wlc/en/article.php?ModuleId=10007057 https://www.ushmm.org/wlc/en/article.php?ModuleId=10007062 https://www.ushmm.org/wlc/en/article.php?ModuleId=10007064 The following question needs to be answered: How does the attempt to control and modify plants and animals lead to eugenics? How are both of these views optimistic? Pessimistic?