Four Causes of Changes in Allele Frequency:
A mutation is the only way new alleles are created. Mutations can be harmful or helpful, and the mutation must affect the gametes of the mutated organism in order to be passed on to offspring. Genetic drift is a random change in allele frequency caused by the Founder Effect, a random sample of organisms in an isolated community, or the Bottleneck Effect, which is a random destruction of must allele populations, leaving one allele population still living and reproducing. Migration is also known as Gene Flow, which is when a group of individuals move from one place to another, causing a change in the allele frequency of the new location. Natural Selection is also known as Survival of the Fittest: those that are genetically best suited for their environment are able to survive and reproduce, producing offspring that are well suited for their environment. For natural selection to work, you need variation in a trait, the trait must be heritable, and the mutation has to help the organism survive.
Types of Natural Selection
There are three types of Natural Selection: stabilizing selection, directional selection, and disruptive selection. In stabilizing selection, the environment supports the medium allele of a trait. For example, in an environment, tall and short individuals in a species could be at risk in their habitat while medium-height individuals would be safe. In directional selection, the environment supports either extreme; for example, very short or very tall individuals could succeed while all others died out. Finally, in disruptive selection, the environment supports both extremes; both very short and very tall individuals would survive and reproduce while medium-height individuals would not.
Evidence of Evolution
One way to prove that evolution did happen is through fossil records. We can find fossils that resemble organisms we have today and figure out how old they are with relative dating, comparing placement of rocks throughout the centuries, and radiometric dating, using isotopes to measure the age of rocks. A second way is through geography: since the same fossils have been found on South America and Africa, where there are similar environments, similar species still exist because they come from a common ancestor. A third way is through comparative anatomy, consisting of 1) homologous structures: similar species have similar bones, suggesting that they share a common ancestor and have adapted to different environments 2) vestigial organs: due to evolution, some organisms have structures that are no longer serving a purpose 3) divergent evolution: similar species have a adapted to different environments and become more different 4) convergent evolution: species that aren't related show similar characteristics because they have adapted to similar environments and 5) molecular biology: using DNA, we can see what genes species have in common. A final way of proving evolution is through field studies using environmental pressure and forcing evolution.
One way to prove that evolution did happen is through fossil records. We can find fossils that resemble organisms we have today and figure out how old they are with relative dating, comparing placement of rocks throughout the centuries, and radiometric dating, using isotopes to measure the age of rocks. A second way is through geography: since the same fossils have been found on South America and Africa, where there are similar environments, similar species still exist because they come from a common ancestor. A third way is through comparative anatomy, consisting of 1) homologous structures: similar species have similar bones, suggesting that they share a common ancestor and have adapted to different environments 2) vestigial organs: due to evolution, some organisms have structures that are no longer serving a purpose 3) divergent evolution: similar species have a adapted to different environments and become more different 4) convergent evolution: species that aren't related show similar characteristics because they have adapted to similar environments and 5) molecular biology: using DNA, we can see what genes species have in common. A final way of proving evolution is through field studies using environmental pressure and forcing evolution.
Tiger Cowrie Evolution
Adaptations:
a. Cowries have a mantle (a fleshy material that covers the shell) that protects them from danger over their shell. The mantle has a different color and pattern than the shell, which confuses the predator. [1] When the cowrie is disturbed, it pulls its entire mantle inside its shell. [2]
b. They have little projections on their mantles called papillae. It is not completely clear what function these papillae perform, but they may camouflage the cowrie and help it absorb oxygen from the sea water. [3].
c. When female snails are ready to give birth, they go up onto the sand and they pull their foot over their entire body. Then cilia on the foot push sand all over the female, and stick it together with mucus, so the female is almost cement-like.
History:
Snails have existed for approximately 33.9-5.3 million years. The first snails lived in shallow water, feeding on algae. They had gills in their mantle cavity. As they evolved, their internal organs were twisted 180 degrees counterclockwise, causing the mantle cavity, gills, and anus to be on the front of the snail, allowing for the space needed for snails to withdraw their heads. Snail shells then became more spirally coiled and cone-shaped. [4]
a. Cowries have a mantle (a fleshy material that covers the shell) that protects them from danger over their shell. The mantle has a different color and pattern than the shell, which confuses the predator. [1] When the cowrie is disturbed, it pulls its entire mantle inside its shell. [2]
b. They have little projections on their mantles called papillae. It is not completely clear what function these papillae perform, but they may camouflage the cowrie and help it absorb oxygen from the sea water. [3].
c. When female snails are ready to give birth, they go up onto the sand and they pull their foot over their entire body. Then cilia on the foot push sand all over the female, and stick it together with mucus, so the female is almost cement-like.
History:
Snails have existed for approximately 33.9-5.3 million years. The first snails lived in shallow water, feeding on algae. They had gills in their mantle cavity. As they evolved, their internal organs were twisted 180 degrees counterclockwise, causing the mantle cavity, gills, and anus to be on the front of the snail, allowing for the space needed for snails to withdraw their heads. Snail shells then became more spirally coiled and cone-shaped. [4]