It was for quite some time thought that when chickens hatched and immediately began pecking the ground for food, this behavior must have been instinctive. In the 1920s, a Chinese researcher named Zing-Yang Kuo made a remarkable set of observations on the developing chick egg that overturned this idea. He found that rubbing heated Vaseline on a chicken egg caused it to become transparent enough so that he could see the embryo inside without disturbing it. (A) ? he was able to make detailed observations of the chick's development, from fertilization to hatching. One of his observations was that in order for the growing embryo to fit properly in the egg, the neck is bent over the chest in such a way that the head rests on the chest just where the developing heart is encased. As the heart begins beating, the head of the chicken is moved up and down in a manner that mimics the movement that will be used later for pecking the ground.
(B) ?Thus the "innate" pecking behavior that the chicken appears to know miraculously upon birth has, in fact, been practiced for more than a week within the egg.

이문제 있잖아요
마지막 Thus 뒤에 빈칸이 있다면
The pecking behavior is learned rather than innate on birth.
이거 틀리나요 어순이??
On birth 가 pecking behavior 뒤에 와야만 맞는 걸까요??