Brethren have traditionally based much of their doctrine on the teachings of John Nelson Darby. With few exceptions, particularly in regards to whom to accept into fellowship, exclusive brethren have continued to hold the same beliefs that inspired the early Plymouth Brethren. Exclusive Brethren reject evolution, and if their children attend state schools they are withdrawn from lessons on this. They do not believe that women should have authority over men. They hold to the concept of the Rapture and the End Times. In the 1960s, the group's teachings were that members could not join trade unions or professional associations, as this was mixing too much with the world. The centrality of the Lord's Supper (Holy Communion) is one of the primary linking threads between the different Brethren groups; however, it is also one of the primary differentiators between the various Exclusive Brethren sub-groups: there are exclusive groups which receive all professing Christians to communion, and there are exclusive groups which restrict access to communion to those who are known to be in their fellowship. The PBCC are generally regarded as having the most stringent and uncompromising views on this. However, only two of their services are closed to those who are not members in good standing, the Lord's Supper and the monthly Care Meeting, with well-disposed members of the public free to come into Gospel Preachings and other meetings. Most Exclusive Brethren groups have no formal leadership structure. In many assemblies, matters up for debate may be discussed at special meetings attended solely by adult males called, in some groups, "Brothers Meetings". As a result, schisms can occur in the Brethren over disagreements about church discipline and whether other sister groups in other locations have authority to intervene in these disagreements. There are often global family connections due to the emphasis among members to marry within the Exclusive Brethren, and family connections often influences which side of the issue members will take. The PBCC avoid this trend by having a structured leadership with a central authority figure which has maintained unity through the upholding of a universal standard. Some Exclusive Brethren assemblies "commend" men who are dedicated to the work of preaching. Although they usually do not receive a salary, gifts are often given to them by the separate assemblies where they preach and teach. Exclusive Brethren do not generally name their meeting rooms or Halls except by reference