Chapter 26, Problem 26.1CR

Humans and chimpanzees are sister species. Explain what this Statement means.

Summary Introduction

To explain: How humans and chimpanzees are sister species.

Introduction: The genome of an organism contains stored information about genetic changes that have occurred over time. A phylogenetic tree can be constructed from the sequence of genes of different organisms. Evolutionary history can be deduced from the branching pattern of a phylogenetic tree. The branching pattern indicates the relatedness among the organisms. The group that shares the immediate common ancestors are called sister species.

Explanation of Solution

Chimpanzees and humans are hominoids. They are together classified under the suborder: Anthropoidea. They branched off from a common ancestor. Chimpanzees and humans are the modern-day descendants of their lineage. Their lineage shows that they diverged 4 million years ago, but chimpanzees and humans did not exist at that time. Some undiscovered ancestors existed around 4 million years ago and it was a hominoid. It was neither a chimpanzee nor a human. It would have had a human-like and chimpanzee-like ancestor. Closely-related organisms resemble one another due to their common ancestry. However, it is not always possible if their lineage has evolved at different rates or has faced different circumstances. Phylogenetic analysis is helpful to infer the identity of species by analyzing the relatedness of DNA sequences. Humans and chimpanzees being sister species indicate that they both share an immediate common ancestor or that they have descendants from a common ancestor. Both the organisms are closely related to each other more than any other organisms.