The first question raised is whether original defendant Vincent states facts sufficient to constitute a cause of action for contribution against additional defendant Jones.
The applicable rules of law are stated in Hayes v. Wilmington, 243 N.C. 525, 91 S.E. 2d 673, as follows:
“1. Liability for contribution under the provisions of G.S. 1-240 may not be invoked except among joint tortfeasors. Therefore, in order for one defendant to join another as a third-party defendant for the purpose of contribution, he must allege facts sufficient to show joint tortfeasorship and his right to contribution in the event plaintiff recovers against him. Hayes v. Wilmington, 239 N.C. 238, 79 S.E. 2d 792.
“2. In order to show joint tortfeasorship, it is necessary that the facts alleged in the cross complaint be sufficient to make the third party liable to the plaintiff along with the cross-complaining defendant in the event of a recovery by the plaintiff against him. Hunsucker v. Chair Co., 237 N.C. 559, 75 S.E. 2d 768. Also, the allegations of the cross complaint must be so related to the subject matter declared on in the plaintiff’s complaint as to disclose that the plaintiff, had he desired to do so, could have joined the third party as a defendant in the action. Hobbs v. Goodman, 240 N.C. 192, 81 S.E. 2d 413; s.c., 241 N.C. *650297, 84 S.E. 2d 904. However, it is established by our decision that when a defendant in a negligent injury action files answer denying negligence but alleging, conditionally or in the alternative, that if he were negligent, a third party also was negligent and that the negligence of such third party concurred in causing the injury in suit, the defendant is entitled, on demand for relief by way of contribution, to have such third person joined as a co-defendant under the statute, G.S. 1-240. Freeman v. Thompson, 216 N.C. 484, 5 S.E. 2d 434; Lackey v. Sou. Ry. Co., 219 N.C. 195, 13 S.E. 2d 234; Wilson v. Massagee, 224 N.C. 705, 32 S.E. 2d 335.”
In applying legal principles to the pleadings in that case, the opinion states:
“True, the allegations to the effect that the negligence of the power company concurred with the negligence of Cooper and Neal are made in the alternative, expressly conditioned upon actionable negligence being found against them. However, we think such conditional plea of concurrent negligence is sufficient to enable Cooper and Neal to invoke the right of contribution finder the statute, G.S. 1-240. There is no merit in the power company’s contention that the conditional plea of joint and concurrent negligence as made by Cooper and Neal is a mere conclusion of the pleader to be disregarded. The form of the plea as made has the sanction of the Court. See Freeman v. Thompson, supra (216 N.C. 484); Lackey v. Sou. Ry. Co., supra (219 N.C. 195); Mangum v. Sou. Ry. Co., 210 N.C. 134, 137, 185 S.E. 644.
“Nor is there any merit in appellee’s further contention that the conditional plea of concurrent negligence made by Cooper and Neal is destroyed by their positive denials of negligence and by their allegations of negligence over against other defendants asserted in other portions of their amended answer. As to this contention, it is enough to say that a defendant who elects to plead a joint tortfeasor into his case is not required to surrender other defenses available to him. Nor may an additional party defendant who is brought in as a joint tortfeasor on cross complaint of an original defendant escape the plea against him by borrowing from contradictory allegations made by the cross-complaining defendant by way of defense against the plaintiff or by way of separate pleas over against other defendants. It is elemental that a defendant may set up and rely upon con*651tradictory defenses. Freeman v. Thompson, supra (216 N.C. 484).”
The cross-action in the instant case states facts sufficient to charge additional defendant Jones with negligence in several particulars, and these facts are so related to the subject matter of plaintiffs’ complaints as to disclose that plaintiffs, had they desired to do so, could have joined Jones as an original defendant in the action. And Vincent also alleges that if it should be found that he was negligent in any respect as charged in the complaints, then the negligent acts and omissions of Jones joined and concurred with his (Vincent’s) negligence in causing plaintiffs’ injuries. Vincent asks that Jones be made a party defendant, according to the provisions of G.S. 1-240, in order that he may be required to make contribution in case of a recovery by plaintiffs against Vincent. In our opinion the demurrer was properly overruled. See Read v. Roofing Co., 234 N.C. 273, 66 S.E. 2d 821.
Appellant contends that the court erred in overruling his motion for nonsuit of original defendant’s cross-action.
The evidence considered in the light most favorable to the original defendant (he occupies the position of plaintiff in his cross-action for contribution) discloses the following facts:
Testimony of original defendant Vincent: He was travelling east and first observed the bus and the Chevrolet stopped behind it when he was about six car lengths away. He was going slightly upgrade. The highway had three lanes, but the center lane was blocked out with yellow marks and there were only two lanes for traffic. When he was five or six car lengths away he took his foot off the accelerator and his car began to slow down; he began to apply brakes when he was four or five car lengths away and he intended to stop behind the Chevrolet. His brakes were holding at first. When he was three or four car lengths from the Chevrolet his car dashed forward and his head snapped back; he was applying his brakes but they were not stopping the car. At that time he did not realize that his car had been struck behind. He wanted to turn left but this movement was delayed momentarily to allow a meeting car to pass. He turned as soon as he could, but the right front of his car struck the left front of the Chevrolet. He then crossed the highway and came to rest in the ditch. While at the scene a highway patrolman showed him red paint on his rear bumper, and the bumper was dented. He then saw a red Ford standing about one and one-half car lengths behind the Chevrolet. The whole front of the red Ford was smashed in, “the hood was slightly ajar and the front end bent *652in.” The front end of the Chevrolet was up against the right rear of the bus.
Testimony of additional defendant Jones on adverse examination, introduced by Vincent: Jones owned the red Ford and was driving it on this occasion. He was going east. Jones’ car struck the rear of Vincent’s car. The Vincent car and the Jones car were both moving when they collided. The Vincent car was in the middle lane when it was struck; it then veered to the left and off the highway. After Jones’ car struck Vincent’s car it stopped immediately; it did not hit the Chevrolet.
Plaintiffs’ evidence is not included, in the récord. But the verdict established the actionable negligence of Vincent and he did not appeal. Plaintiff’s complaint alleges that Vincent was negligent as to lookout, control and speed. From the unchallenged verdict and judgment we must assume that one or more of these specifications of negligence on Vincent’s part was a proximate cause of the collision of Vincent’s car with the Chevrolet in which plaintiffs were seated and that a collision would have occurred regardless of the activities of Jones.
Vincent alleges that Jones was negligent as to lookout, control, speed and following interval. From the evidence it was permissible for the jury to find that when Vincent’s car was three or four car lengths from the stopped Chevrolet, it was struck in the rear by Jones’ Ford, knocked forward with added momentum, its brakes rendered ineffective and its control rendered more difficult, and the added momentum continued effective to the moment of the impact of Vincent’s car on the Chevrolet. The fact that Jones’ Ford collided with the rear of Vincent’s car furnished some evidence that Jones was negligent as to speed and control, was following too closely, or failed to keep a proper lookout. Powell v. Cross, 263 N.C. 764, 140 S.E. 2d 393; Dunlap v. Lee, 257 N.C. 447, 126 S.E. 2d 62; Clark v. Scheld, 253 N.C. 732, 117 S.E. 2d 838; Clontz v. Krimminger, 253 N.C. 252, 116 S.E. 2d 804. There may be two or more proximate causes of an injury. These may originate from separate and distinct sources or agencies operating independently of each other, yet if they join and concur in producing the result complained of, the author of each cause would be liable. Barber v. Wooten, 234 N.C. 107, 66 S.E. 2d 690. If any degree, however small, of causal negligence is attributable to a person, he incurs liability thereby. Rattley v. Powell, 223 N.C. 134, 25 S.E. 2d 448. The evidence is sufficient to justify a finding that Jones’ negligence remained active and effective to the moment of plaintiffs’ injuries, concurred with the negligence of Vincent and contributed to the injuries sustained.
*653The assignments of error relating to the admission of evidence and the charge are not sustained.
No error.