10.3 Phylogeny & Evidence For Evolution Flashcards
Phylogeny
Evolutionary relationships between organisms.
Phylogeny can happen without classification but many scientists use both.
Can display relationships using evolutionary/phylogenetic trees which show the common ancestor and were produced by looking at similarities and differences in organisms’ physical features and genetic makeup.
Advantages of Phylogeny
- produces a continuous tree whereas classification requires discrete taxonomical groups. Scientists are not forced yo put organisms into a specific group they don’t completely fit into.
- the hierarchical nature of Linnaean classification can be misleading as it implies different groups within the same rank are equivalent; For example, cats and orchids are both families but not comparable.
Evidence for Evolution
Evolution is the changes in a species over a long period of time because of changes in their environment. Advantageous characteristics are passed on to offspring.
Sources to study evolution:
- palaeontology
- comparative anatomy
- comparative biochemistry
Developing Theory of Evolution
Charles Darwin (born 1809).
Most people at that time believed in the Christian Bible and that God created all things.
In 1831 aboard the HMS Beagle, he read ‘Principles of Geology’. It suggested fossils were evidence of animals that lived millions of years ago.
Darwin carried out studies in the Galapagos on finches and mockingbirds. the finches had different shaped beaks depending on the food available on the island they inhabited.
He realised finches with a beak best suited to their environment meant they would survive and pass this characteristic on to their offspring.
Palaeontology
Fossils are formed when animal and plant remains are presented in rocks.
Over long periods of time, sediment is deposited on the earth to form layers of rock. These layers of rocks can be studied to find out when certain animals lived and you can see how they’ve evolved (forms a sequence of oldest to youngest) - this is a FOSSIL RECORD
Evidence for fossil records
1) fossils of the simplest organisms like bacteria and simple algae are found in the oldest rocks. Complex organisms like vertebrates are found in the more recent rocks, showing evolution has occurred.
2) the sequence in which the organisms are found matches their ecological links to each other. For example, plant fossils appear before animal fossils, which makes sense because we couldn’t have lived without plants.
3) by studying similarities in the anatomy, scientists can determine how closely related organisms are to other and their common ancestor.
4) fossils allow relationships between living and dead organisms to be investigated.
Comparative Anatomy
If a fossil record is incomplete, scientists can look for other sources of evidence to determine evolutionary links; CA is the study of similarities and differences in different organisms’ anatomies.
CA Study - Homologous Structures
A homologous structure is a structure that appears superficially different (and may perform different functions) in different organisms, but has the same underlying structure. For e.g. the pentadactyl limb of vertebrates.
Vertebrate limbs are used for a wide variety of functions such as running, jumping, swimming and flying. You would expect the bone structure to be very different however the basic structures are very similar. For example, a horse, mole, bat and human all have the same bones but they’ve adapted to be stacked differently based on the their function.
An explanation is that all vertebrates have evolved from a common ancestor.
Divergent Evolution
The presence of homologous structures provides evidence for DIVERGENT EVOLTION; this describes how, from a common ancestor, different species have evolved.
This type of evolution will occur when closely related species diversify to adapt to new habitats as a result of migration or loss of habitat.
Comparative Biochemistry
The study of similarities and differences in proteins and other molecules that control life processes.
Although these molecules can change over time, some important ones are highly conserved among species (almost unchanged). Slight changes can help identify evolutionary links.
2 of the most common molecules studied are cytochrome c (respiration protein) and ribosomal RNA (rRNA).
Hypothesis of NEUTRAL SELECTION states most variability in the structure of a molecule doesn’t affect its function; changes that don’t affect a a molecules’ function are ‘NEUTRAL’ and occur often.
How CB is conducted
To discover how closely 2 organisms are related, the molecular sequence of a particular molecule is compared (scientists look at order of amino acids and DNA base pairs).
The number of differences that exist are plotted against the rate the molecule undergoes neutral base pairing substitutions. From this we can see when they last shared a common ancestor.
