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Answers to Exploration Questions: Human evolution

1. What were some general some physical changes seen in hominid evolution?
Answer: As hominids evolved, their bodies became larger, their skulls became larger, and their bone structure became better adapted for walking upright. For example, their big toes became smaller and pointed forward — more for propulsion (upright walking) rather than climbing. Also, their faces became flatter and their brow ridges smaller.
2. Why would paleontologists studying ancient primates be interested in fossils of other organisms discovered at the same site? What did paleontologists on Rusinga Island in Kenya learn about the ancient primate Proconsul by identifying fossils in two separate sites? How does this discovery apply to human evolution?
Answer: Paleontologists studying an ancient primate would be interested in other fossils discovered at the same site in order to recreate and understand the primate’s environment. On Rusinga Island, paleontologists learned that the ancient primate Proconsul lived in two distinct environments: a watering hole in a dry region, and a forest. This discovery revealed that Proconsul, like modern humans, were able to adapt to different environmental conditions.
3. Explain the difference between DNA in the nucleus, mitochondrial DNA, and Y-chromosome DNA. Where is each found? How is it passed down? Why are scientists who study evolution interested in mitochondrial DNA and Y-chromosome DNA?
Left: Liver cell cross-section, revealing DNA
Right: Illustration of cell
Answer: Most of our DNA is in the nucleus, but there is some in the mitochondria, the cell’s energy generators. There is also DNA in the Y chromosome in males. Half of the DNA in the nucleus comes from your mother and half from your father. Mitochondrial DNA passes only from a mother to her children. Since only males have a Y chromosome, Y-chromosome DNA passes from father to son. Scientists who study evolution are interested in Y-chromosome DNA and mitochondrial DNA because they come from only one parent — they don’t get “shuffled” like DNA in the nucleus. Since this type of DNA remains unchanged from generation to generation, scientists can use them to look millions of years into the past and reconstruct events in human evolution and human migrations.

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