Practice Evolution and Natural Selection: Biology Unit 5.

A population of beetles has green and brown individuals living in brown leaf litter. Birds eat more green beetles. After several generations, the population is mostly brown beetles.

Brown coloration is a heritable variation that provides camouflage in the leaf-litter environment, giving brown beetles higher survival and reproductive rates. Green beetles are more visible to predators, so they reproduce less and their alleles decrease in frequency. Over generations, the brown allele becomes dominant in the population due to this selective pressure.

A student claims that giraffes developed long necks because they kept stretching to reach high leaves. Identify the error and provide the correct explanation.

The student is describing Lamarck's incorrect idea of inheritance of acquired characteristics—stretching the neck does not change DNA and cannot be passed to offspring. The correct explanation is that ancestral giraffes had variation in neck length; those with longer necks could reach more food, survived better, and reproduced more, passing the long-neck alleles to offspring. Over many generations, long necks became the norm through natural selection.

A whale's pelvic bones serve no locomotion function. What type of evidence of evolution do these bones represent, and what do they indicate about whale ancestry?

Whale pelvic bones are vestigial structures—remnants of bones that were fully functional in terrestrial ancestors. They indicate that whales share a common ancestor with four-limbed land mammals, from which the pelvic bones have been reduced over evolutionary time because they are no longer needed for walking. This supports the idea that whales evolved from land-dwelling mammals, a conclusion also supported by fossil evidence of transitional forms like Pakicetus.

A river forms and splits a population of squirrels into two groups. After thousands of years, scientists bring the two groups back together and find they no longer interbreed. Have new species formed? Explain.

Yes, new species have formed because reproductive isolation has been achieved. While the two groups were separated (allopatric), each accumulated different genetic mutations and experienced different selective pressures, causing their gene pools to diverge. Because they can no longer interbreed and exchange genes when reunited, they meet the biological species concept definition of separate species.