Scientific reasoning
GradualismGradualism is a model used to explain evolution given the fossil record. The fossil record shows large changes, such as speciation, which seem to appear suddenly. The thing about fossils is they are a glimpse into the past, they don't show everything. It is like reading pages 5, 10 and 35 of a book and then trying to write a book report. Gradualism suggests that speciation happens slowly and is just not captured in the fossil record. It happened on page 30 and we didn't read that page! The model is shown above.
Punctuated equilibrium is a model that suggests that change in fact happens abruptly and so we see it as such in the fossil record. It suggests that species have long periods of equilibrium with no change. For now, most scientists assume that both models have some validity, but new discoveries may someday disprove one or both models. ![]() Alright folks, this is a commonly misunderstood process. Here is my best attempt at dispelling myths about natural selection. Myth - Organisms somehow develop a favourable characteristic. Giraffes' necks grow longer as they stretch to reach food. Pesticide applications cause weeds to develop a trait that makes them resistant. This was Lamarck's hypothesis that was disproven by discovery of genes and inheritance. Fact - Organisms are born/reproduced with inherent characteristics! If reaching for things on a high shelf made me taller, I would be at least 5'5" by now. But alas, I am 5'2". Why? Because my DNA does not change through the course of my life! Neither does a weed's or a giraffe's. However, a population has inherent variation. There are some tall people and some people are short. If the tall people kept hitting their heads on door frames and getting concussions and brain injuries, they would be less likely to reproduce (due to injury or death). So the small people genes would get passed on because they are making babies. As time passes, the short gene becomes more prevalent and there are fewer tall people. Yes, this is a silly oversimplification, but this is how natural selection works. Myth - Natural selection can be observed easily. You will observe the changes in an organism as it changes over time. Fact - Of course not! Firstly, an individual organism does not change! A population changes. Over many, many generations! The only way a person would be able to get a front row seat to natural selection is if they watch a population (NOT organism) over many generations. We can do this with organisms that have a short reproductive cycle (i.e. fruit flies, moths, some plants). For organisms with longer reproductive cycles, scientists need to rely on historical data to make observations about natural selection. Sooooo. Change in a population occurs over many generations when an inherent trait provides an organism a reproductive advantage (like surviving long enough to make babies). |
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