Homologous StructuresDo similar forelimbs mean we all came from the same ancestor?

Homologous Structures – Evidence?Diagram showing the difference in developmental patterns of frog and human digits.

In humans, programmed cell death (apoptosis) divides the ridge into five regions that then develop into digits (fingers and toes) [after Sadler, T.W., ed., Langman’s Medical Embryology, 7th Ed., Williams and Wilkins, Baltimore, Maryland, USA, pp. 154–157, 1995].

In frogs, the digits grow outwards from buds as cells divide [after Tyler, M.J., Australian Frogs: a natural history, Reed New Holland, Sydney, Australia, p. 80, 1999].

The DNA code for how to build these structures is completely different!

Embryology• Embryology is the study of

embryos.• Do fish, reptile, bird, and

humans all have similarly-shaped embryos during the first few weeks of life?

• If they do, does that mean they all have the same ancestor?

• p254 in our Life Science Text• p303 in our Biology Text

Ernst Haeckel's Sketches…Ernst Heinrich Philipp August Haeckel (February 16, 1834 – August 9, 1919),[1] also written von Haeckel, was an eminent German biologist, naturalist, philosopher, physician, professor and artist who discovered, described and named thousands of new species, mapped a genealogical tree relating all life forms, and coined many terms in biology, including anthropogeny, ecology, phylum, phylogeny, stem cell, and the kingdom Protista. Haeckel promoted and popularized Charles Darwin's work in Germany. http://en.wikipedia.org/wiki/Ernst_Haeckel

He was an incredible artist, and was very interested in embryology – the study of pre-born animals. He made some drawings of animals that were not yet born at different stages, and compared them to the unborn human embryos at the same stages. They closely resembled each other – which reinforced the idea that all living things came from the same ancestor.

Embryology – Evidence for Evolution?

Embryology – Evidence for Evolution?

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• Vestigial Structures have no function in their present-day form, but once served some function in an ancestor.

• Example: Whale’s pelvis used to be attached to hind legs when its ancestors walked on land. Now it has no use.

Vestigial Structures – Evidence for Evolution?

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The pelvic bone in whales serves as an important anchor for muscles of the

reproductive organs.

Tailbone? Leftover from Apes?

http://en.wikipedia.org/wiki/Coccyx

[The coccyx] is an important attachment for various muscles, tendons and ligaments—which makes it necessary for physicians and patients to pay special attention to these attachments when considering surgical removal of the coccyx.[2] Additionally, it is also a part of the weight-bearing tripod structure which acts as a support for a sitting person. When a person sits leaning forward, the ischial tuberosities and inferior rami of the ischium take most of the weight, but as the sitting person leans backward, more weight is transferred to the coccyx.[2]

The anterior side of the coccyx serves for the attachment of a group of muscles important for many functions of the pelvic floor (i.e., defecation, continence, etc.): The levator ani muscle, which include coccygeus, iliococcygeus, and pubococcygeus. Through the anococcygeal raphé, the coccyx supports the position of the anus. Attached to the posterior side is gluteus maximus which extend the thigh during ambulation.[2]

Many important ligaments attach to the coccyx: The anterior and posterior sacrococcygeal ligaments are the continuations of the anterior and posterior longitudinal ligaments that stretches along the entire spine.[2] Additionally, the lateral sacrococcygeal ligaments complete the foramina for the last sacral nerve.[7] And, lastly, some fibers of the sacrospinous and sacrotuberous ligaments also attach to the coccyx.[2]

• Example: The human appendix was considered a perfect example of a vestigial structure until recently. It’s an example in my College textbook on Evolution. Scientists thought it was a shrunken left-over second intestine that could digest tough leaves and grass. Monkeys, Cows and other grazers have this.

• The story goes that as humans ate more easily digested food, its usefulness went away, and so it shrank in size and stopped working.

• Appendix Rescued From Biology's Junk Heap

• The appendix, a narrow tube that hangs off one end of the colon, is probably the most famous "junk" organ. But it's turned out to be important even today—in certain circumstances.

• "It's hard to figure out what the appendix does when you're studying superclean animals and people," said Bill Parker, assistant professor of surgery at Duke University Medical Center and one of the researchers who exposed the appendix's secrets in a 2007 Journal of Theoretical Biology study.

• “Far from useless, the appendix is actually a storehouse of beneficial bacteria that help us digest food.”

http://news.nationalgeographic.com/news/2009/07/090730-spleen-vestigial-organs_2.html

Vestigial Structures – Evidence for Evolution?

The spleen heals the heart

Cytochrome c similarities?• Look at page 255 in your textbook.• Human Cytochrome c is most like monkeys’.• Evolutionary theory says this is because we’re more

closely related to monkeys.

Cytochrome-c is a molecule that is VITAL for all life: plants, animals, bacteria. It helps cells change food into ATP energy inside the mitochondria.

Different animals and plants have different kinds of cytochrome-c. Its shape is more different between some animals than others.

The chart on page 255 in your textbook shows that the cytochrome-c for humans is similar to that of monkeys, and less similar to that of other animals and plants.

However, the cytochrome-c molecule is just ONE of thousands of DNA differences between humans and monkeys. Telomeres in chimps and humans are drastically different. 1

"Apart from the single gene controlling the constitution of cytochrome-c, humans and chimps differ in many thousands of other genes."

Dr. Allan is a former senior lecturer in genetics at the University of Stellenbosch in South Africa. He holds a Ph.D. in genetics from the University of Edinburgh, Scotland.

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Molecular Biology – Evidence?• Chimps and Humans share 98.5% of the same

DNA – Does this show that we came from a common ancestor?

• 98.5% similarity in DNA was based on an older study from 2005. Other studies disagree with this number because of the way it was done. 2

• Another type of study (2012) shows that the way human and chimp DNA is USED is extremely different. Epigenetics is a new field of genetics that is discovering new ways DNA is read and used – chimps and humans read it and use it differently. 3,4

Molecular Biology – Evidence?

Molecular Biology – Evidence?

• Because DNA is the code for how to build structures - it makes sense that the organisms that look most similar would have the most similar DNA. Apes and humans have similar shapes, so both have similar DNA.

• This doesn't necessarily mean we have a common ancestor - it only proves that we have similar shapes.

References

1. Kakuo, S., Asaoka, K. and Ide, T. 1999. 'Human is a unique species among primates in terms of telomere length.' Biochem Biophys Res Commun 263:308-314.

2. Britten, R.J. 2002. 'Divergence between samples of chimpanzee and human DNA sequences is 5% counting indels.' Proceedings National Academy Science 99:13633-13635

3. Polavarapu et al. ‘Characterization and potential functionalsignificance of human-chimpanzee large INDELvariation.’ Mobile DNA 2011, 2:13http://www.mobilednajournal.com/content/2/1/13

4. Zeng, J, et al. 2012. 'Divergent Whole-Genome Methylation Maps of Human and Chimpanzee Brains Reveal Epigenetic Basis of Human Regulatory Evolution.' American Journal of Human Genetics. 91 (3): 455-465.