Which of the following is a key observation that must be explained in a unifying theory about life?

• A. All living things require oxygen to survive.
• B. Evolution is based on descent with modification.
• C. Earth is very old.
• D. Organisms are rarely well suited to their environments.
• E. Many basic characteristics are shared by all living things.

Answer: (E)

Verified step by step guidance

1. Identify the key observation that a unifying theory about life must explain. This involves understanding the fundamental principles that apply to all living organisms.
2. Consider the options provided: the requirement of oxygen, the concept of evolution, the age of Earth, the suitability of organisms to their environments, and shared characteristics among living things.
3. Evaluate each option in terms of its universality and relevance to all forms of life. A unifying theory should address a characteristic that is common across all living organisms.
4. Recognize that while not all living things require oxygen, and not all organisms are perfectly suited to their environments, there are basic characteristics shared by all life forms, such as cellular structure, genetic material, and metabolic processes.
5. Conclude that the observation 'Many basic characteristics are shared by all living things' is the key observation that a unifying theory about life must explain, as it encompasses the fundamental similarities that define life.