pose of this appeal, without so deciding, that plaintiffs have made a jury question on such issues.
In order to recover for negligence the burden is upon the plaintiffs to prove that the alleged negligence is the proximate cause of their injury. In Fanelli v. Illinois Central R. Co., 246 Iowa, 661, 666, 69 N.W.2d 13,19, the rule is thus stated:
“ mere negligence which appears to have no causal connection with the injury is not actionable. It must appear that the injury was the natural and probable consequence of the negligence, wrongful act, or breach of duty. ”
In Brewer v. Johnson, 247 Iowa 483, 72 N.W.2d 556, 558, the court states, “To be actionable, the negligence must be a proximate cause of the injury.”
Before considering the evidence we shall discuss the test to be applied in determining the sufficiency of the evidence to support the verdict. The question of whether state or federal law controls in diversity cases on the issue of the sufficiency of the evidence to support a verdict has not been decided by the Supreme Court. Courts of appeal are not in agreement on this problem.
Dick v. New York Life Ins. Co., 359 U.S. 437, 444-445, 79 S.Ct. 921, 3 L.Ed.2d 935. Our present case was tried by all parties on the basis that Iowa law controls. Under such circumstances, particularly where the state and federal standards are substantially alike, the Dick case advises that no determination be made on the question of the applicable law.
The evidence in our present case bearing on the proximate cause issue is all circumstantial. The Iowa rule with reference to the test of the sufficiency of circumstantial evidence to support a verdict has been liberalized in recent years. Iowa has abandoned the “exclusion of every other hypothesis rule” and now follows the “more reasonably probable rule.” Soreide v. Vilas & Co., 247 Iowa 1139, 78 N.W.2d 41, 43; Bokhoven v. Hull, 247 Iowa 604, 75 N.W.2d 225, 227; Little v. Watkins Motor Lines, 8 Cir., 256 F.2d 145, 149; Guyer v. Elger, 8 Cir., 216 F.2d 537, 539. The federal cases just cited involve the Iowa law. In the Bokhoven case, the court states (75 N.W.2d at page 227):
“ we are firmly committed to the rule that plaintiff’s theory of causation need not be proved by evidence so clear as to exclude every other possible theory. The evidence must be such as to make that theory reasonably probable, not merely possible, and more probable than any other hypothesis based on such evidence. ”
It would appear that the test of the sufficiency of circumstantial evidence under federal law would be substantially the same. Pennsylvania R. Co. v. Chamberlain, 288 U.S. 333, 339, 53 S.Ct. 391, 77 L.Ed. 819; Adair v. Reorganization Inv. Co., 8 Cir., 125 F.2d 901, 905; Cudahy Packing Co. v. N. L. R. B., 8 Cir., 116 F.2d 367, 371. In the Adair case, at page 905 of 125 F.2d, the court quotes from the Cudahy case as follows:
“ ‘It is not necessary in establishing a necessary fact by circumstantial evidence that a party upon whom the burden of proof rests shall present evidence to dispel all contradictory inferences. It is necessary, however, that such party produce evidence of facts and circumstances which may be accepted by the trier of the fact as establishing with reasonable certainty the truth of the inference contended for.’ ”
The court then continues:
“If the proven facts give equal support to each of two inconsistent inferences then judgment must go against the party upon whom rests the necessity of sustaining one of these inferences. The essential inference cannot be left to conjecture and speculation. * ”
The task of applying the law as above stated to the evidence remains. We must, of course, observe the well established rule that the party in whose