The girl found out that she was an adopted daughter because of the shape of her ears 
sister learned the truth about her birth thanks to one fact she heard in biology class. The girl realized that she was adopted when she compared her ears to those of other family members.
The author of the post said that his family adopted the girl when she was 5 months old. According to him, a few weeks ago, his sister asked him if she was adopted. “I was shocked because I was sure that she already knew about it,” the guy said and added that he asked her why she thinks so.
The sister explained that she only suspected this, because outwardly she was different from the rest of the family. Finally, the girl was convinced of this after a biology lesson, where they talked about genetics. “She realized that she had a fused lobe, while the others didn’t,” the guy conveyed the words of his sister about the shape of the ears.
“I told her the truth and warned her that it didn’t change anything. She is still my little sister and the daughter of our parents, ”said the author of the post. He added that he did not want to lie to his sister, although he was not sure how to answer her question.
Later, the girl told her father that she knew the truth and asked why she hadn’t been told about it before. According to the author of the post, his sister did not look angry or sad, she asked about it more out of curiosity. The father said that he and her mother were waiting for her to come of age to tell her the truth, and she calmly accepted this answer.
At the same time, the narrator noted that their mother was angry when she learned about what happened. She accused her son of not having the right to tell his sister about adoption. “We tried to explain to her that it wasn’t even I who raised this topic, but she didn’t listen,” the narrator complained and added that their mother now does not speak to him or to other family members. He believes that she had no intention of telling his sister that she was not his own daughter.
In the comments under the post, many users supported the hero of the story and assured him that he did the right thing by telling his sister about adoption. However, some have condemned the storyteller's mother for her behavior.