Thus, over successive years, the researchers have observed an oscillation of measurable traits. The hereditability of the trait is estimated by the slope of the function, which can vary between zero and one. This technique enabled us to estimate the hereditability of beak depth in the medium ground finch population as 0.74. Natural selection effects, therefore, are measurable in these finch populations. This research is rightly regarded as a significant contribution to ecology and biological variation.
Selection pressures act on characters of organisms which have relevance to survival.
These characters may be hereditable. In a relatively stable environment, changes in characters will oscillate about a mean. It is possible that, with selection pressures acting in a consistent direction, the population characters will shift so far that eventually a new sub-species or a new species will be formed. Natural selection is not a creative influence on organisms. It can only act on and mould what is already there.