Our ancestors had much bigger jaws than we do, which helped them chew a tough diet, tear apart meat, etc. Their teeth also wore down quickly. Wisdom teeth (third molars) grew later in life, and helped our ancestors continue to eat. Today, ~35% of people are born without wisdom teeth. This is an example of:

Question

BlackTom AI · Accepted Answer

First, let’s restate the question and options to set the context: the passage describes ancestral jaws and teeth changing over time, with modern humans often lacking wisdom teeth. The question asks which concept this illustrates.

Option a: genetic drift. This is a random change in allele frequencies due to chance events, often in small populations. The wisdom-teeth example is not described as a random fluctuation or a chance event; it reflects a directional trend in trait usefulness over generations. Therefore, this option is not the best fit.

Option b: dominant alleles. This choice focuses on how dominant alleles determine phenotype. The scenario is not about a particular allele’s dominance pattern; it’s about a population-level change in a trait over time due to shifting selective pressures, not merely a dominance relationship. Hence, this is not correct.

Option c: convergent selection. The term most closely resembling a real concept would be convergent evolution, where different lineages independently evolve similar traits. The phrase “convergent selection” is not a standard or accurate label for this phenomenon. Moreover, the example involves changes within our own lineage over time, not convergence between separate lineages, so this is misleading.

Option d: evolution. This option captures the broad idea that species’ characteristics change over generations due to differential survival and reproduction. The reduction of jaw size and disappearance of many wisdom teeth in modern humans reflect evolutionary change in a population over time, driven by shifting dietary needs and wear patterns.

Option e: founder effect. This refers to a type of genetic drift where a new population is started by a small subset of individuals, leading to reduced genetic variation. The scenario given does not describe a new isolated population founded by a few individuals; it describes long-term trait changes in the species as a whole. Therefore, this is not the best match.

In summary, each incorrect choice either mislabels the mechanism (genetic drift, founder effect), relies on a nonstandard term (convergent selection), or focuses on a single allele concept (dominant alleles) rather than the broader population-level change over time. The most appropriate overall concept for a trait changing across generations due to selective pressures is evolution, which aligns with the described shift in jaw and wisdom-teeth traits across human history.

BIO 181 (001&002) FALL 2025 FA25: Cumulative Exam 4 covers the most important content from Units 1-4: You can do this!!! : ) [Grade is out of 150/900 pts, the same am't of pts for the active learning "easy points" classwork.]

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