Evolution the theory that organisms change over time
Natural Selection Charles Darwins idea that organisms with the best traits will live to reproduce and pass on their genetic information
Adaptation a trait that enables an organism to survive in the wild
Fossils are remains or traces of dead organisms buried and preserved in sedimentary rock.
Fossils present a vivid record of the earliest life on Earth and of a progression over time from simple to more-complex life forms.
4 Scientists have learned about prehistoric life by studying fossils of ancient insects such as this midge fly It was trapped in tree resin when it was alive. The resin eventually hardens and fossilizes into amber. Sometimes an entire organisms is preserved in this manner. 5 Although trilobites became extinct over 200 million years ago they left detailed casts in the rocks where they died. This silica shale formation shows several trilobites. Because these primitive arthropods were typical organisms of the Paleozoic era a paleontologist may use them to determine the relative age of the rock strata. 6 This fossil cast shows the remains of Archaeopteryx a birdlike dinosaur. It had teeth and a long reptile-like tail covered with feathers. Archaeopteryx lived between 163 million and 144 million years ago. 7 Distribution of Species
How different species of plants and animals are geographically distributed in nature and how they relate to their environment and to each other is evidence of change over time.
Populations that exist on islands provide living clues of patterns of evolution.
8 Darwin first observed the adaptive radiation of the Galapagos finches. Finches living on different islands changed over long periods of time due to the different habitats or living conditions. 9 The distribution of the worlds flightless birds reflects the shifting of continents (Plate Tectonics). These birds supposedly shifted with the continents too. Following this separation the flightless birds of each of these new continents gradually evolved into one or more distinct speciesthe ostrich of Africa (shown here) the rhea of South America and the cassowary and emu of Australia. 10 Anatomical Similarities
The study of the internal and external features of different living things is known as comparative anatomy.
It provides a wealth of information about evolution.
11 Structures that are similar due to evolutionary origin such as the forearm bones of humans birds porpoises and elephants are called homologous structures. 12 All vertebrate brains share the same basic three-part structure the cerebrum the cerebellum and the brain stem. Their size and development varies. In mammals the cerebrum dominates the brain. It is most developed among primates in whom cognitive ability is the highest. 13 Vestigial Structures
Some organisms have structures or organs that seem to serve no useful function. These are called vestigial organs or structures.
Human tailbone appendix body hair
Male nipples in mammals
Some snakes and whales tiny pelvic bones and limb bones
Some cave-dwelling salamanders have eyes even though members of the species are completely blind.
Vestigial organs are often homologous to organs that are useful in other species.
Comparison of the vertebrate development before birth.
Gill pouches in both the bird embryo and the human embryo.
A flexible notochord develops in the back.
Blocks of tissue called will become muscle vertebrae connective tissue and later the larger glands of the body.
Helps biologists identify like structures that are less apparent in adults.
15 DNA Amino Acid Chain Comparison
DNAs uniformity organisms have the same building blocks base pairing A w/T C w/ G.
Different combinations of these bases direct the assembly of amino acids into functional proteins.
DNA is thought to be a record of an organisms evolutionary history. Scientists gain insights into how different species are related by comparing the same proteins from different species.
In closely related species the proteins vary by only one to a few amino acids.
More distantly related organisms generally have proteins with fewer similarities.
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