Identifying stem cells
As early as 1961, scientists knew that adult bone marrow contained cells that could make all of the blood cell types. But it wasn’t until 1988 that those stem cells were isolated as pure populations. Why did it take so long? The techniques for identifying stem cells have only recently been developed. Partly, this is because adult stem cells are, by their very nature, inconspicuous in shape, size and function. They also tend to hide deep in tissue and are present only in very low numbers, making their identification and isolation like finding a needle in a haystack.