Darwin lived in a time where natural selection was a strange theory among scientists and researchers. This was especially true when other researcher Lamarck argued that organisms passed on helpful traits to their offspring, that they magically could form a new trait to adapt to their environment and then pass it onto their offspring. For example, if a giraffe was too short to reach food, it would grow a larger neck in its lifetime and then pass that trait onto its offspring. Darwin argued that, through the process of survival of the fittest, that short giraffe would die off and never receive the chance to pass on its shortness to future populations. Thus, taller giraffes would survive— they can reach food, shorter giraffes can’t— and the short genes would disappear. The fact that Darwin was introducing a new theory that nobody was used to at the time was peculiar, so he had few people on his side until long after his observations.
Another problem Darwin had was the lack of technology. To travel, Darwin would have to use boats to reach far away places, and of course, this took time.
The final problem Darwin had was the extra time it took for evolution, a process that can take up to millions of years. Evolution didn’t occur over night— it took time for Darwin to conduct experiments, observe, conduct them again, come to a conclusion, and so on.
Hope this helped a little!
<span>Both of these show the distribution of phenotypes. In directional selection, the distribution of phenotypes forms a "bell curve." Selection against one of the extreme phenotypes causes the distribution to "move" in one direction or the other. An example might be plants whose flower color is determined by incomplete dominance: white, pink, or red. Pink flowers may be the average phenotype, but if we start to remove red flowers from the population, the "mean" phenotype will be shifted toward white flowers.
In disruptive selection, the average phenotype is selected against. This produces a "two-humped" bell-type curve, and the greater distribution is split between the two phenotype extremes. If we have the same type of incomplete dominance as mentioned in the previous paragraph, assume that the pink flowers are selected against. This means that the two "humps" shown in the distribution will be centered around the red and white phenotypes.</span>
