Evidence for Evolution Embryology – Histology – Morphology Fossil Records – Natural and Artificial Selection

What is Evolution? The theory that all living organisms have developed and diversified from earlier forms during the history of the Earth

What Evidence Do We Have to Support the Theory of Evolution?

Embryology Ernst Haeckel created some of the first drawings of embryological development showing similarities within the first developmental stages (arm buds from different species, for example, are virtually indistinguishable when they first form on the embryo, yet they may develop into a wing, an arm, or a flipper) Embryos of different vertebrates look alike in their early stages but as each organism grows, it diverges according to its species’ way of life

Embryology Continued… Combined morphological evidence (see example on hand out and next slide) and histological evidence (DNA) provide validation for this theory

Examples of Fetal Growth and Similarities:

Histological Evidence Living things on earth are primarily similar in the way that their basic anatomical structures develop (think back to embryology and try to relate to homologous structures coming up) and in their chemical compositions.  No matter whether they are single-celled or complex multi-cellular organisms, they all begin as single cells that reproduce themselves by similar division processes.  Also after a limited life span, they all grow old and die. 

Histology Continued… Our closest relatives, chimpanzees, gorillas and orangutans, possess 48 chromosomes, or 24 pairs, while humans possess 46 chromosomes, or 23 pairs Evidence shows chromosome fusion - human chromosome 2 is now accepted by scientists as having resulted from the fusion of two ancestral chromosomes still found in apes The original chromosomes are now called 2A and 2B

All chromosomes have a distinct telomeres (at the ends of the chromosomes) centromeres (center of the chromosomes) By looking at the DNA mentioned (human chromosome 2) we see that it appears to be longer than others and looks as though it is two chromosomes fused together as the theory states – it also matches the DNA of the two ape chromosomes This large chromosome has evidence of a telomere in the center and we also see evidence of two centromeres – sufficient evidence to assume a connection of the identical ape chromosomes 2A and 2B

Morphology: Homologous and Analogous Features Homologous structures/features are observed when different organisms have body parts that serve for different functions but have similar structure and developmental patterns Analogous structures/features are observed when different organisms have body parts that serve similar functions but have very different development and structural patterns

Homologous Structures In this example you can see the similar joints and digit patterns between The different species

Homologous Bones

Morphology Continued… Interactive link showing homologous bones: http://evolution.berkeley.edu/evolibrary/article/0_0_0/similarity_hs_03

This evolutionary tree shows the relationships between different species, all of which evolved from a single common ancestor. This common ancestor, an animal millions of years old, had limbs with one long bone (the humerus) attached to two other long bones (the radius and ulna)

(Hummingbird/Flower Example) Analogous Structures Often, two species face a similar problem or challenge, evolution may then shape both of them in similar ways — resulting in analogous structures http://evolution.berkeley.edu/evolibrary/article/0_0_0/similarity_hs_08 (Hummingbird/Flower Example)

Evidence Supporting Morphological Evolution Vestigial features (example: dew claws on dogs, pigs etc.) Homologous bones (example: see diagrams) Analogous structures (example: plants and animals adapting to overcome obstacles in environment) DNA evidence, embryological evidence, fossil evidence all show results that support the relationships between organisms and back up the morphological evidence we have found

Fossil Records Organisms have changed significantly over time, in rocks more than 1 billion years old, only fossils of single-celled organisms are found - If we look ahead to rocks that are about 550 million years old, fossils of simple, multicellular animals can be found Gradually, new animals appear: From 350 million years ago we can see fossil evidence of the first amphibians, reptiles at around 300 million years ago, mammals are found to emerge about 230 million years ago, birds at 150 million years As the rocks become more and more recent, the fossils look increasingly like the animals we observe today.

Chronology of Fossils Relative dating places fossils in a sequence based on their positions in layers of rocks, known as strata. Fossils found in lower strata were deposited first and are viewed to be older. Numerical dating is based on dating volcanic ash layers both above and below a fossil layer, as shown in the diagram, you can determine what is older or younger. This is how we can tell where and when new species emerge in the evolutionary chain.

Fossil Record Continued… The fossil record provides snapshots of the past that, when assembled, illustrate a panorama of evolutionary change over the past four billion years. The picture may have bits missing, but fossil evidence clearly shows that life is old and has changed over time.

Natural and Artificial Selection Natural selection in most simple terms can be described by “survival of the fittest.” It is the process whereby organisms that are better suited to their environment tend to survive and those that are not, die off. Natural selection can lead to evolutionary change in the expression of the trait in the population because the “fittest” pass on their genetic info creating new, stronger offspring. Artificial selection is essentially this same process, except that favored traits are those that for one reason or another are preferred by humans, rather than those that enhance the organism's fit to its environment.

Example: Natural Selection Natural selection resulting in evolution of a population can be easily demonstrated in a laboratory petri dish with bacteria.  When a lethal dose of antibiotic is added, many of the bacteria will die but a few of the bacteria usually are immune and survive.  The next generation is mostly immune because they have inherited immunity from the parent generation. The bacteria have evolved.

In Conclusion… When presented with research in embryology, histology, morphology and fossil records in relation to evolution, it is clear that there is much scientific evidence to support of the theory of evolution. Although there is much more to know, our current knowledge is enough to keep us on the right path to knowing more about the way organisms develop and thrive.