For a long time, people accepted the Geocentric Theory. Their observations seemed to show that the sun, stars, and planets revolved around the Earth.
Careful observations made by later scientists didn’t fit this model, and it was eventually scrapped in favor of the Heliocentric Theory.
Vestigial Structures Comparative Anatomy Convergent Evolution Fossil Record This is the Home Page From the Home Page, you can investigate several lines of evidence that support the Theory of Evolution. Click any box to enter that area. Fossil Record is a good place to start Embryological Development Molecular Comparisons Evidence of Evolution
Evidence of Evolution Molecular Comparisons Embryological Development Convergent Evolution Fossil Record Comparative Anatomy Vestigial Structures
The first mammals to evolve laid eggs, like their reptilian ancestors. (Only two species of egg-laying mammals are alive today.)
Marsupials, pouched mammals, give birth to underdeveloped young, who then complete development in their mother’s pouch. Nearly all of them are found in Australia/New Zealand.
Placental mammals keep their young inside of the mother’s uterus, connected to her through the placenta. Most of the world’s mammals are placental.
Still, because the same types of selective pressures exist in Australia and different habitats in other parts of the world, we would expect some convergence to evolve.
Examples of Marsupials/Placentals: Back Marsupial and placental species may look the same on the outside and occupy similar niches in their environment, but all of the placental mammals are more closely related to each other than to any marsupial, and vice versa. Marsupials Placentals (Click on animals to see videos.)
Sometimes, it is good to stand out. Dangerous animals like poison arrow frogs, bees, and nasty-tasting insects have markings that warn potential predators. Bright, high-contrast patterns are universal signals to stay away.
“ Leave us alone!” Next
Sometimes, it pays just to look tough. See if you can pick out the wannabes in the examples below. Click on the dangerous insects. or… or… Back
The monarch butterfly on the left is poisonous and will make a bird that eats it sick. The viceroy on the right is harmless, but the birds that have made the mistake of eating a monarch won’t touch it. Back
The yellow jacket on the right can afford to be aggressive because it has a stinger to back up its behavior. The hoverfly on the left is very tame. It flies from flower to flower eating nectar, confident that its colors will protect it from any nosy predators. Back
Mutations are always producing new body forms each generation. Sometimes, environmental changes and mutations combine to provide new opportunities for species.
As species evolve to fill different niches in their changing world, we would expect their bodies to change over many generations.
Vestigial structures are body parts that are reduced in size and function. Mutations that reduce the size of such structures are not harmful and may actually be of a benefit to the individuals that inherit them.
Click on one of the examples below to learn more.
Home Fossil whale legs Human coccyx Snake leg spurs Reduced eyes
They are thought to have evolved from 4-legged land animals that lived over 50 million years ago.
Paleontologists expected to find whale ancestors that showed reduced and vestigial legs by looking in sediments that were between 50 and 30 million years old. Sure enough, they did. Some examples of this transition are shown below.
Ambulocetus 49 million years ago Pakicetus 42 million years ago Basilosaurus 40 million years ago Back
Mutations that reduce or eliminate eyes in species that dwell in caves are not harmful, and may benefit the individuals that experience them.
Many different cave species show these same mutations.
Several examples of eyeless cave-dwelling animals The fish Astyanax comes in two varieties – the surface-dwelling varitey is on the left, the eyeless cave fish is on the right. The mutation that eliminates eyes also gives the fish a larger jaw and more taste buds. Back