text: Since Darwin first proposed his ideas about biological evolution and natural selection, different lines of research from many different branches of science have produced evidence supporting his belief that biological evolution occurs in part because of natural selection.
  Because a great amount of data supports the idea of biological evolution through natural selection, and because no scientific evidence has yet been found to prove this idea false, this idea is considered a scientific theory. Because lots of evidence supports scientific theories, they are usually accepted as true by a majority of scientists.
  Here’s a brief summary of the evidence that supports the theory of evolution by natural selection:
  Biochemistry is the study of the basic chemistry and processes that occur in cells. The biochemistry of all living things on Earth is incredibly similar, showing that all of Earth’s organisms share a common ancestry.
  Comparative anatomy is the comparison of the structures of different living things. This figure compares the skeletons of humans, cats, whales, and bats, illustrating how similar they are even though these animals live unique lifestyles in very different environments. The best explanation for similarities like the ones among these skeletons is that the various species on Earth evolved from common ancestors.
  Credit: Illustration by Kathryn Born, M.AComparative anatomy of the bones in the front limbs of humans, cats, whales, and bats.Biogeography, the study of living things around the globe, helps solidify Darwin’s theory of biological evolution. Basically, if evolution is real, you’d expect groups of organisms that are related to one another to be clustered near one another because related organisms come from the same common ancestor.
  On the other hand, if evolution isn’t real, there’s no reason for related groups of organisms to be found near one another. When biogeographers compare the distribution of organisms living today or those that lived in the past (from fossils), they find that species are distributed around Earth in a pattern that reflects their genetic relationships to one another.
  Comparative embryology compares the embryos of different organisms. The embryos of many animals, from fish to humans, show similarities that suggest a common ancestor.
  Molecular biology focuses on the structure and function of the molecules that make up cells. Molecular biologists have compared gene sequences among species, revealing similarities among even very different organisms.
  Paleontology is the study of prehistoric life through fossil evidence. The fossil record (all the fossils ever found and the information gained from them) shows detailed evidence of the changes in living things through time.
  Modern examples of biological evolution can be measured by studying the results of scientific experiments that measure evolutionary changes in the populations of organisms that are alive today. In fact, you need only look in the newspaper or hop online to see evidence of evolution in action in the form of the increase in the number of antibiotic-resistant bacteria.
  Radioisotope dating estimates the age of fossils and other rocks by examining the ratio of isotopes in rocks. Isotopes are different forms of the atoms that make up matter on Earth. Some isotopes, called radioactive isotopes, discard particles over time and change into other elements.
  Scientists know the rate at which this radioactive decay occurs, so they can take rocks and analyze the elements within them. Radioisotope dating indicates that the Earth is 4.5 billion years old, which is plenty old enough to allow for the many changes in Earth’s species due to biological evolution.
  For the practice questions, use the terms that follow to identify the type of evidence that supports the theory of biological evolution.
  b. Comparative anatomy
  d. Comparative embryology
  e. Molecular biology
  g. Modern examples
  h. Radioisotope dating
  A fossil named Archaeopteryx has many features in common with reptiles but also, like birds, shows evidence of feathers.
  The genetic code of all life on Earth is written in the same chemical building blocks.
  Some genes from the bacterium E. coli have sequences that are similar to genes found in humans.
  In the 1940s, infections by the bacterium Staphylococcus aureus could be treated successfully with penicillin. Today, populations exist that are completely resistant to natural penicillin, as well as to partially modified penicillins like methicillin. These populations, called MRSA, are very challenging to modern medical professionals.
  Whales have tiny, useless bones inside the rear portion of their bodies that are very similar to the bones found in vertebrate legs.
  Human embryos have gill slits like those seen in fish embryos. (Developing fish retain their gill slits, whereas humans don’t.)
  Marsupial mammals (mammals like kangaroos that protect their young in a pouch) live in just a few places in the world today — Australia, South America, and part of North America. Although Australia is now thousands of miles away from the Americas, in the past the three continents were connected as one larger land mass.
  Fossils of the earliest life forms on Earth, which look like bacterial cells, occur in rocks that scientists estimate to be 3.5 billion years old.
  The following are the answers to the practice questions.
  The answer is f. Paleontology.
  The answer is a. Biochemistry.
  The answer is e. Molecular biology.
  The answer is g. Modern examples.
  The answer is b. Comparative anatomy.
  The answer is d. Comparative embryology.
  The answer is c. Biogeography.
  The answer is h. Radioisotope dating.