LSAT 141, Section 1, RC Passage 1, Natural Selection

This is an explanation for passage 1 of LSAT preptest 73, the September 2014 LSAT. This passage is about natural selection. The author argues that strict contructionist Darwinians are wrong to say that natural selection is the only means of evolution.

This section has paragraph summaries and an analysis of the passage, links to the explanations for the questions are below.

Paragraph Summaries

1. Strict constructionist Darwinians contradict Darwin by saying that natural selection explains all evolution.
2. Strict constructionism implies that every attribute of every species is due to adaptation. But nature provides many counterexamples.
3. Many DNA mutations are random, and have no effect on survival. Nonetheless they persist and are passed down. This is a change in species which has nothing to do with natural selection.
4. Massive catastrophes let some species succeed even though they were not adapted to their original environments.

Analysis

The author’s opinion is very important on this passage. They think the strict constructionists are wrong. This is clear from the first paragraph. The author says strict constructionists contradict Darwin himself.

You may have noticed that the author doesn’t give any evidence supporting the strict constructionists. And after presenting the strict constructionist position, the author does nothing but criticize strict constructionism, by showing evidence against it. This is a strong sign. The author thinks the strict constructionists are really, really wrong.

The first two paragraphs are spent describing the strict constructionists views. The final two paragraphs provide examples that show why the strict constructionists are wrong.

How Natural Selection Works

It’s necessary to understand a little about natural selection. That’s the idea that individual members of a species will reproduce more if they are adapted to their environment. Their offspring will share their traits, and over time, those characteristics become more common in that species.

The standard example is a species of moth that was common during the industrial revolution in England. As pollution darkened the landscape, the moths became darker, because this allowed them to blend in with the landscape and avoided predators. As pollution diminished in the 20th century, the moths became lighter again.

Natural Selection is a Factor, But Not The Only Factor

The author agrees that natural selection is a factor in evolution (lines 1-4, lines 23-27), but their point is that it’s not the only factor.

Paragraph three shows how species can be changed by random, neutral mutations that are passed down and that change species over time. The mutations offer no reproductive advantage, so natural selection plays no role in their transmission.

The fourth paragraph gives the example of the mammals. We took over the world after the asteroid strike killed off the dinosaurs. But our takeover didn’t happen because we were particularly well adapted at the time of the asteroid strike. It was just dumb luck that we were small enough to survive.

We had a selection advantage after the asteroid strike, but natural selection doesn’t explain how we originally arrived in the position of being in the right place at the right time.

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