The phylogenetic tree below represents the classification of species x, y, and z. Assuming this classification reflects evolutionary relatedness, explain how these species are related to each other.

Which type of neuron stimulates muscles to contract?

Which of the following must be true for a fossil organism to be useful as an index fossil? a. the fossil organism must be widespread geographically. b. the fossil organism must be abundant. c. the fossil organism must be limited to a short span of geologic time. d. all of the above.

What do genes contain the code for?