The incidents surrounding the first Australopithecus ever found illustrate some of the strengths and weakness of science.
While Dart, who had handled and subsequently described the specimens, had full access to the materials others did not. What also clouded the picture is that the then existent majority consensus was that "Piltdown man" was ancestral to modern humans.
This scientific consensus position entertained that the ancestors of modern humans must have had large brains and then evolved tool use and upright posture.
The Taung child challenged this consensus. Here was a small brained upright walker.
Scientists were initially reluctant to accept that the Taung Child and the new genus Australopithecus were ancestral to modern humans. In the issue of Nature immediately following the one in which Dart's paper was published, several authorities in British paleoanthropology criticized Dart's conclusion. Three of the four scholars were members of the Piltdown Man committee: Sir Arthur Keith, Grafton Elliot Smith, and Sir Arthur Smith Woodward.
By John Cooke - http://blog.geolsoc.org.uk/2012/12/13/a-tale-of-three-meetings/geological/, Public Domain, Link
The discoveries from Piltdown were barely a decade old by the time the Taung child made its appearance. It would still be a few decades more before modern methods of dating could conclusively prove that the Piltdown material was recent and almost a full century to prove the methods of forgery and the full extent of the elaborate hoax.
But a hoax it was, and a convincing one at that, stir into the mix imperial bias towards the colonies and science did not come of looking so good.
Between Dart's rampant speculation with too little material and the British scientist eagerness to dismiss the matter because it didn't confirm to the currently fashionable wisdom of the time, hasty lines were drawn in the sand.
Wikipedia sums up the situation quite nicely:
There were several reasons that it took decades for the field to accept Dart's claim that Australopithecus africanus was in the human line of descent. First, the British scientific establishment had been fooled by the hoax of the Piltdown Man, which had a large brain and ape-like teeth. Expecting human ancestors to have evolved a large brain very early, they found that the Taung Child's small brain and human-like teeth made it an unlikely ancestor to modern humans.
Second, until the 1940s, most anthropologists believed that humans had evolved in Asia, not in Africa.
Third, despite accepting that modern humans had emerged by evolution, many anthropologists believed that the genus Homo had split from the great apes as long as 30 million years ago and so felt uneasy about accepting that humans had a small-brained, ape-like ancestor, like Australopithecus africanus, only two million years ago.
Last, many people disputed the role of this fossil because of their religious affiliation. When Taung was first announced in February 1925, many anti-evolutionists began to rise up in protest of this fossil. Dart began receiving many threats from members of various religious communities that threatened his imminent damnation. Some were able to reconcile the science with the religious theology through the lens of "creation science", but there was still significant opposition.
In spite of this, the scientific method ensures that early faults may be corrected in time if new material and evidence becomes available for scrutiny.
Such was the case with the Australopithecenes and Dart's initial vilification was reversed and he is now lauded for his discoveries and pioneering efforts.
The valuable lesson we learn from all of this is that scientific understanding and knowledge is a moving target. It is refined with time and that discoveries on the fringe should not be rejected or embraced too emphatically when the substantiating evidence is sparse and in its early stages.