This is a reading comprehension exercise for children. It is written by Susan Fineman, a reading specialist in the New Haven, Conn., school district.

One has no legs and swims in the ocean, and the other has four legs and lives in rivers, but a genetic study shows that the whale and the hippo are close relatives in evolutionary history.

The study--by researchers at the Tokyo Institute of Technology in Japan and Pennsylvania State University at University Park, Pa.--compared gene sequences from the minke whale, the sperm whale and the hippopotamus. It found that the diverse animals share a sequence of genes inherited from an ancient common ancestor.

A report of the study appeared in the Proceedings of the National Academy of Sciences.

The study found that the camel, pig, giraffe, sheep and cow share some gene sequences with the whale and hippo, indicating that far back in time all had a common ancestor, according to evolution theory.

The animals diverged genetically. A gene sequence found only in whales and the hippo show that they share a common ancestor that was not part of the evolutionary history of the other animals.

Until 1985, it was generally thought that pigs were more closely related to whales. Other genetic studies since then have suggested the whale-hippo link. The new study, researchers say, confirms that the hippo is the closest living relative to the whale.

The genetic analysis was conducted by Masato Nikaido and Norihiro Okada of the Tokyo Institute and by Alejandro Rooney of Penn State.

It has long been believed that the whale's ancient ancestor was a land animal.

It is thought that a lineage leading to the modern whale returned to the sea and evolved into a group of marine mammals called cetacean. Along the way, hind legs were lost and forelegs were replaced by flippers.

David Hillis of the University of Texas, in a Proceedings of the National Academy of Sciences commentary, said whales and hippos share several adaptations, including the lack of hair and oil-producing skin glands, and the ability to communicate and to nurse offspring under water.

Quiz

1. How did researchers discover that the whale and the hippopotamus are close relatives?

2. Where did the comparison of gene sequences take place?

3. What might be an advantage of having the same genetic analysis conducted at two different universities?

4. What animals were found to share a common ancient ancestor with the whale and hippo?

5. Until 1985, which animal was thought to be a close relative of the whale?

6. It is believed that far back in time, the whale was related to a land animal. What happened to that ancient creature's legs?

7. Name one feature that the whale and hippo have in common.

8. In what two ways do whales and hippos differ?

9. Do you find the results of the genetic study interesting? Explain.

10. Have you ever seen either of the two mammals in its natural habitat? Explain.

Answer key (wording may vary):

1. Scientists found the whale-hippo connection by studying gene sequences from both animals.

2. The genetic study was done at the Tokyo Institute of Technology and Pennsylvania State University.

3. Answers will vary.

4. Long ago, the camel, pig, giraffe, sheep and cow were believed to share a common ancestor with the whale.

5. Until recently, the whale was thought to be more closely related to the pig than to the hippopotamus.

6. It is believed that the land animal returned to the sea. Over time, it's back legs were lost and flippers took the place of its front legs.

7. Answers will vary.

8. Unlike hippos, whales do not have legs, and they live in the ocean.

9. Answers will vary.

10. Answers will vary.