Answer by taking a quote from the following article:

Theodore John Kaczynski (; born May 22, 1942), also known as the Unabomber, is an American domestic terrorist. A mathematics prodigy, he abandoned an academic career in 1969 to pursue a primitive lifestyle, then between 1978 and 1995 he killed three people, and injured 23 others, in a nationwide bombing campaign targeting those involved with modern technology. In conjunction, he issued a social critique opposing industrialization and advancing a nature-centered form of anarchism.

Kaczynski was born on May 22, 1942, in Chicago, Illinois, to working-class, second-generation Polish Americans, Wanda Theresa (nee Dombek) and Theodore Richard Kaczynski. His parents told his younger brother, David Kaczynski, that Ted had been a happy baby until severe hives forced him into hospital isolation with only limited contact with others, after which he "showed little emotion for months". Wanda later recalled Ted recoiling from a picture of himself as an infant being held down by physicians examining his hives, and said he always showed sympathy to animals in cages or otherwise helpless, which she speculated stemmed from his experience in hospital isolation.  From first to fourth grade, Kaczynski attended Sherman Elementary School in Chicago, where administrators described him as "healthy" and "well-adjusted". In 1952, three years after David was born, the family moved to southwest suburban Evergreen Park, Illinois; Ted transferred to Evergreen Park Central School. After testing scored his IQ at 167, he skipped the sixth grade. Kaczynski later described this as a pivotal event: previously he had socialized with his peers and was even a leader, but after skipping ahead he felt he did not fit in with the older children and was bullied.  Neighbors in Evergreen Park later described the Kaczynskis as "civic-minded folks", one stating that the parents "sacrificed everything they had for their children". Both Ted and David were intelligent, but Ted stood out in particular. One neighbor said she had "never known anyone who had a brain like [Ted's]," while another commented that Ted was "strictly a loner" who "didn't play ... an old man before his time." His mother recalled Ted as a shy child who would become unresponsive if pressured into a social situation. At one point she was so worried about Ted's social development that she considered entering him in a study for autistic children led by Bruno Bettelheim, but decided against it after observing Bettelheim's abrupt and cold manner.

Was David his only sibling?