In chapter 4 of his book Defending the Faith: J. Gresham Machen and the Crisis of Conservative Protestantism in Modern America, D.G. Hart discussed Machen’s views on science, and evolution in particular. Machen, he wrote, received a letter from William Jennings Bryan a few weeks before the 1925 Scopes trial, in which Bryan asked Machen to appear in Dayton as an expert witness. This rather put Machen on the spot. Machen’s well-known scholarly defense of the fundamentals of the historic Christian faith was being recruited by a populist evangelicalism that was deeply skeptical of academia. Though Machen was a proponent of biblical inerrancy like the fundamentalist side Bryan represented, he thought the historicity of Christ in the New Testament was more important than the historicity of Genesis, and was reticent to speak on evolution. Machen wrote back, saying that he would not testify.
Though Machen had generally avoided the subject of evolution in public statements, Machen had thoughts on the matter, and was not a six-day creationist. In The Christian View of Man 
There is… evidence to suggest that Machen avoided the subject of evolution because he was not troubled by alternative views of creation. He grew up in a Christian home where his parents had in all likelihood come to terms with Darwinism. His niece Mary Gresham Machen said that when the General Assembly of the Southern Presbyterian Church (PCUS) met in Baltimore in 1881 the Machen residence was the meeting place for those in sympathy with James Woodrow. The uncle of Woodrow Wilson, Woodrow taught at Columbia Theological Seminary and, despite the efforts of his supporters who met in the Machen home, was dismissed by the General Assembly for his efforts to reconcile Genesis and evolution.
Undoubtedly, another influence upon Machen’s thinking about evolution was the Princeton theologian Benjamin Breckinridge Warfield. While defending the Bible’s inerrancy, Warfield also argued that the Genesis narratives were compatible with the idea that God had providentially superintended evolutionary developments in the origin of the human form and had supernaturally intervened to create the human soul. The only place in the creation of humanity where Warbled thought it necessary to insist upon supernatural and direct divine activity in the evolutionary process, therefore, was in the creation of the human soul, the place that he believed bore the divine image. With that one qualification made, Warfield could assert in 1915 that the Calvinist understanding of creation not only allowed for evolutionism but for “pure evolutionism.” Machen appeared to accept Warfield’s views. When he responded to queries about evolution he usually directed inquirers to Warfield’s writings. Machen did not believe that evolution could explain the origin of human life nor did he believe that evolution was incompatible with divine creation. He thought it possible [p. 98] to accept evolution in providential terms, “as God’s way of working in certain spheres . . . through nature.” And like his mentor, he was careful to distinguish between God’s creative power to bring life into existence out of nothing (ex nihilo) and divine providence, which involved God’s superintendence of existing natural forces and laws. “The uniqueness of redemption in Christianity,” he wrote, depended upon a distinction between supernatural (creative power) and natural causes (providence).
Yet when Machen spelled out his understanding of creation for publication he garbled some of Warfield’s subtleties. The occasion was a series of radio addresses on Christian theology delivered in 1936. In his homily “Did God Create Man?” Machen made the point that God did create humankind in a supernatural sense. Like Warfield, Machen held that the origin of human life depended on both natural developments and divine intervention. And following Warfield, he also thought that the supernatural creation of human life, as distinguished from the providential course of natural development, referred specifically to the creation of the soul, not the human form. Creation in the image of God, he explained, could not refer to the human body because God was spirit.
Unlike Warfield, however, Machen drew back from the idea that the human species had evolved from lower forms of life. His hesitations showed sympathy with fundamentalist hostility to evolution. Machen believed that there were significant gaps in the biological and geological evidence for evolution and that naturalistic presuppositions had led scientists to overlook these problems. Nevertheless, he resisted the tendency of creationists to attack the scientific establishment and to set up a rival science of their own. Machen acknowledged his own incompetence to judge the scientific data even though he did not want the issue to become strictly a matter for scientific experts. For evolution, he believed, ultimately concerned one’s understanding of the nature and meaning of the universe.
So Machen looked to Christ’s birth to reveal the problems of an evolutionary account of human life. Similarities in bodily structure between Jesus and other men had not prevented conservative theologians from accepting the virgin birth. In fact, historic Christianity had always asserted that miracles were interwoven with natural events. In the case of Christ’s birth, this meant that Jesus’ body was produced not merely by the ordinary course of nature but also by a supernatural act of God. Despite great differences, Machen said, this same principle applied to the creation of human life. Physical similarities between human species and lower animals did not disprove God’s supernatural [p. 99] creation of human life. The crucial issue was not the nature and scope of the scientific data but the theological implications of evolutionary theory. If evolution entailed a denial of God’s creative and miraculous power, then it was incompatible with Christian theism, a proposition in keeping with Warfield’s perspective. But machen wavered over the converse idea–one that Warfield would have affirmed–that evolutionary theory was acceptable as long as it made room for divine intervention.
Despite questions about evolution, Machen made points about science more generally in his essay for the New York Times which were closer to those of his newspaper rival, the zoologist Kellogg, than to the views of fundamentalists. Machen did not attack evolution itself but rather the way in which liberal Protestants had selectively accommodated new learning in all spheres of academic inquiry. While professing to offer to the modern world a version of Christianity compatible with advances in science, religious modernists overlooked what was going on in the wold of biblical scholarship. To be truly scientific, Machen argued, modern Christians would have to heed the problematic findings of biblical scholars who had concluded that the Christ of the scriptures was altogether different from the Jesus of the modern church.
[…]
[p. 105] For him, the crucial difference between historic Christianity and liberalism had more to do with antagonistic ideas about Christ and the nature of salvation than with divergent accounts of creation. As Machen explained in his article in the New York Times, Christianity depended upon what Christ did at a definite point in history. By trying to shift debate from evolution to the historical Jesus, Machen hoped to make plainer to both conservatives and liberals what was at stake in the controversy over science.
Dr. John Byl, at the bylogos blog, has addressed Machen’s and B.B. Warfield’s acceptance of theistic evolution, which I discussed in a post here years ago. Hart and John Muether have said that Warfield’s and Machen’s views “offer a better opportunity for credibly engaging the scientific community and meaningfully defending the truth of Christianity than the one now promoted by scientific creationists.” But holding to what the Bible says requires us to take positions that will often mean the loss of credibility and even ridicule from non-Christians.
Years ago, I attended a lecture given by a professor of religion to senior economics students. Before launching into his main argument, which was that Christianity was inconsistent with a free-market position, the professor took a swipe at creationists. He argued that it is ignorant to interpret the Bible in a woodenly literal sense in every place, ignoring the use of literary devices. In principle, I agree that it is inappropriate to interpret the Bible literally at every point (e.g., Jesus said, “I am the vine” and “I am the door”). But this hermeneutical point was quickly followed by an argument appealing to the collective authority of the majority of mainstream scientists, and likening six-day creationists to several rednecks sitting around a cooler scoffing at educated folk. The well-known creationist Ken Ham didn’t meet the standard of formal schooling that the professor regarded as adequate for respectability, and this was taken as prima facie evidence of incompetence and error. Not only was this dismissive of the substantial amount of thought–theological and otherwise–that has gone into the six-day creation position, but there are problems with getting into a contest to see who can stack up the most Ph.D.s on his side. I commented to students later that Ph.D.s are frequently in error, and the heterodox position of one era becomes the mainstream opinion of another era. For example, in geology, plate tectonics as a theory was once greeted with ridicule.
But pointing out the transitory nature of science can be only a partial response. As Dr. Byl contended, “…waffling on the Bible to appease mainstream science is futile. The wiser strategy is to firmly uphold the Sola Scriptura of the Westminster Confession, proclaiming all that the Bible teaches. Christian faith is undermined not by biblical consistency but, rather, by unbiblical compromise.”
Byl concluded,
…one cannot argue that, since Warfield and Machen were orthodox, we should accept all their teaching. I think it fair to say that Warfield and Machen were generally soundly Reformed. They were great theologians from whom there is still much to learn. Nevertheless, regretfully, they did depart from Scripture in their treatment of evolution. Hence some of their teaching is non-Reformed.
The Machen Seminar 