Pop!ular: Stephen Jay Gould

Stephen Jay Gould

One of the most outspoken evolutionary biologists of the 20th Century

If you studied evolutionary biology seriously and never heard of Stephen Jay Gould, you haven’t really studied hard enough. This paleontologist and popular science writer often came up with novel ideas and wrote almost poetically about evolutionary biology. It’s a shame he died early in 2002. Let me just highlight a few of his many contributions to the field.

NOMA

In an effort to harmonise his thoughts of science and religion, he proposed NOMA (non-overlapping magisteria), arguing that both fields should cover different areas of human enquiry, and should not overlap. This was one of a rare attempts of a scientist to express his religious beliefs (he was agnostic), encouraging religious people not to be discouraged from studying science by the irreligious (Gould 1999).

Punctuated Equilibria

In the absence of expected number and type of transitional fossils, Gould suggested a phenonomen known as “Punctuated Equilibria”. This suggested that evolutionary changes occured at a faster and greater scale than once previously thought (Eldredge and Gould, 1972).

Evolution of form

He was also highly interested in the evolution of morphology (shape and size of an organism). Most of his empirical research on land snails was spent attemtping to account of the vast observable differences between land snails despite minimal genetic differences (Wolpert and Richards, 1998)

Conclusion

What makes Stephen Gould such a legend was not only the ideas he came up with, but also his colourful writing. If you have the chance, I recommend reading some of his landmark work in the further reading section.

References

Eldredge, N., Gould, S.J. (1972). “Punctuated equilibria: an alternative to phyletic gradualism.” In T.J.M. Schopf, ed., Models in Paleobiology

Gould, S.J. (1999). Rock of Ages

Wolpert, L., Richards, A. (1998). A Passion For Science.

Further reading

 

Gould, S.J. (1980) The Panda’s Thumb

Gould, S.J. (1989) Wonderful Life

Gould, S.J. (2002) The Structure of Evolutionary Theory

Huh what?: How are viruses classified?

seed of Convolvulus, looking oddly similar to the influenza virus

Living and non-living at the same time

Viruses are considered to be outside the traditional systems of biological classification. For one, there is a generally disagreement on whether they should even be considered ‘living’. This is because outside a host (the infected victim), the virus show no living features, such as reproduction and undergoing natural selection.

More related to the host than other viruses

One of the ways of affirm biological classifications is to compare the genetics of the biological organism. To be concise, more related organisms should be more genetically similar than their other counterparts. However, another problem with the classification lies with the fact that viruses are more genetically related to their host than other viruses.

This is because when replicating, the viruses inevitable incorporates some elements of the host genomes into its own. It has been argued that this feature allows it to avoid the host’s defence mechanism (by imitating the host genetic code) (Crawford, 2000). In other words, the H1N1 influenza virus would be more related than to humans and birds, than other viruses like AIDS.

ICTV

Yet attempts to classify them has been made. The International Committee on the Taxonomy of Viruses (ICTV) has worked on a classification system, similar to the Linnean system since 1971. The viruses are classified based on their phenotype (observable characteristics) rather than their genotype (genetics). Hence they are grouped according to their Orders, Families, Genera and Species based on their hosts, diseases they transmit and their replication strategy.

Baltimore

Another common classification strategy is the Baltimore System, named after virologist David Baltimore. This system classifies viruses according to the nature of the genome. To put it simply, this grouping is dependant on the (A) genetic material carried (i.e. DNA or RNA), (B) struture of genetic material carried (i.e. double-stranded or single-stranded) and (C) presence of reverse-transcriptase in the viral structure. The great adavantage of this method (although less pedantic than ICTV’s) is that it is a more practical way of identifying viruses and ignores the often tedious way of determining shape of the viruses.

Conclusion

Although classification via genetics have greatly helped taxonomy and evolutionary theory, we have to concede their are limits to this “genetics-only” approach. In this case, the classification of viruses.

References

Crawford, D. H. (2000) The Invisible Enemy

That can’t be true: The human appendix has a function!

Part of the digestive system

One of the predictions of evolution theory is the presence of vestigial organs. Evolutionary theory suggests as a result of common ancestry, some organs or features in organism would have lost its original function. Examples of vestigial organs would be the leg bones of snakes, the eyes of blind cavefish (Yamamoto and Jeffery, 2000) and of course, the human appendix.

Just those who are unfamiliar with anatomy, the appendix is a blind-end tube connected to the caecum (or cecum) 0f the large intestine. The narrowness of the appendix often leads to the appendix being inflamed. This condition is called appendicitis, and can be fatal if untreated (Hardin, 1999)

But the human appendix is functional!

Creationists are quick to point out that the human appendix still has an active function in the human body. Ham and Wiefield (1997) argue that since the appendix contributes to the human body, it cannot be regarded as vestigial, and therefore it is entirely possible that humans were created via creationism like a fully functional designed object.

And yes, I would agree the appendix has several functions. It has been suggested that the appendix acts a storage for gut flora (these gut flora bacteria aid in digestion of food). The appendix is also said to be involved in the body’s immune system, by producing hormones that regulates the production of antibodies (Zahid, 2004).

But it is also still vestigial!

Nevertheless, one still needs to note that a vestigial organ is one that has lost its original function. In other words, the fact that the appendix does not has the same function as the caecum (to absorb liquids from food) makes it vestigial regardless of what present functions it has. [The appendix is regarded an an evolutionarily ancient extention of the caecum, and therefore would have a similar function to it (Smith et al., 2009)].

Conclusion

A vestigial organ is not one that is functionless, but rather, one that has lost its original function. In the light of this, the human appendix is regarded to be vestigial, and can be used as evidence for common descent, and therefore evolutionary theory.

References

Ham, K., Wieland, C. (1997). Your appendix … It’s there for a reason. Creation Ex Nilhilo, 20, 41-43 (link)

Hardin, D. M. Jr. (1999). Acute appendicitis: review and update. American Family Physician, 60, 2027-2034.

Smith, H.F., Fisher, R.E., Everett, M.L., Thomas, M.D., Bollinger, R.R., Parker, W. (2009) Comparative anatomy and phylogenetic distribution of the mammalian cecal appendix. Journal of Evolutionary Biology, 22, 1984-1999

Yamamoto, Y.,  Jeffery., W.R. (2000). Central role for the lens in cave fish eye degeneration. Science, 289, 631-633

Zahid, A. (2004). The vermiform appendix: not a useless organ. J Coll Physicians Surg Pak 14, 256–8

Comparative anatomy and phylogenetic distribution of the mammalian cecal appendix

Huh what?: What do scientist mean when they say evolution is purposeless?

Kenneth R. Miller

Some scientists describe evolution as an unintelligent, unguided, undirected, random and purposeless process. Does that mean there is no role for God in the evolutionary process?

Yes, many scientists seemed to describe it that way. Even Professor Ken Miller (pictured), a Roman Catholic described that “natural selection operates in a manner similar to artificial selection, but … without goal or purpose”. (Miller and Levine, 2002). The famous biologist Richard Dawkins (1995) extends this view, arguing that the evolutionary theory shows that there is nothing but “blind, pitiless indifference.”

But wait!

However, it is not the job of science to detect purpose. In fact, science is limited in the sense that it detects methodology (i.e. how things came into being), rather that teleology (i.e. why things came into being) (Lennox, 2007). So briefly speaking, to comment on purpose (or the lack of) is not a scientific statement, but a philosophical one. In fact, Professor Miller has agreed that his writings were a “poor choice of words” and promised to update the future editions of his textbooks.

Furthermore, recent evidence has shown that the evolutionary process is not as random as thought, but as mentioned, this can be used for or against the existence of God.

So what do the scientists mean when they say evolution is purposeless?

Simply put, they are saying that the results of the evolutionary process is often unpredictable, and does not usually confirm to the results of artificial selection.

References

Dawkins, R. (1995) River out of Eden

Lennox, J. (2007) God’s Undertaker

Miller, K.R., Levine J. (2002) Biology: The Living Science

Pop!ular: Thomas Morgan

Thomas Hunt Morgan

A Nobel Prize winner? He deserves to be here!

Thomas Hunt Morgan (1866-1945) is one of the most influential evolutionary biologist ever. If Charles Darwin proposed evolution, and Gregor Mendel suggested genes were the carriers of inherited traits, then Thomas Morgan was the scientist who discovered the physical mechanism of inhertiance (i.e. chromosomes). This won him the Nobel Prize in Medicine in 1933.

He worked on flies?

Using Drosophilia melanogester (the fruit fly), he came up with several hypotheses. After noting differences in patterns of inherited traits among male and female flies, he proposed that some inherited traits were (A) sex-linked, (B) that inherited traits were carried on choromosomes (since the males and females differ in the Y and X choromomes) and (C) that the mechanism of inheritance involved physical crossing over of the chromosomes. Crossing over is the process in which duplicated chromosomes exchange genetic material before splitting into sex cells. This is one of the mechanisms (other mechanisms include mutation and fertilisation) explains why the offspring have different genetic material from their parents.

This significance?

In a time known as ‘the Eclipse of Darwinism’ (1875-1925) when natural selection was being criticised as a mechanism for evolution. (Everyone agreed that evolution happened; but not natural selection.) Morgan, in fact had been one of them. However, Morgan changed his stand based on his work. In 1916, he established that evolution will tend to retain characteristics benefical to “life and reproduction of the organism”.

Morgan had not only suggested a mechanism for inheritance to work, but gave demostratably evidence for natural selection. That’s why he deserves a worthy mention in the history of evolutionary theory.

References

Morgan, T.H. (1916) A Critique of the Theory of Evolution

Huh what?: How is the age of the earth calculated?

Fossil of an ammonite

How can we be so sure of the age of the earth?

The age of the earth, according to the current scientific consensus is 4.54 billion years old (Dalrymple, 2001). One of beauties of this conclusion is that it is reached via various lines of evidence. Just like the proverb “all roads lead to Rome”, different methods of dating still conclude the earth is billions of years old.

But what are these methods?

There are many, but I’ll classify them into two groups– radiometric and non-radiometric methods.

Radiometric

Radiometric dating is dependant on the idea of radioactive decay. It measures how the current proportions different elements in rocks differ from their initial ratios. For instance, Uranium-235 decays into Lead-207 at a fixed and measurable rate. Over time, we expect to have less uranium and more lead, and thus we can use the relative proportions of the two elements to determine the age of the earth (Dalrymple, 2001). This is the most common method of dating the age of the earth. Other methods of radiometric  dating using different elements (such as lead and argon) still date the age of the earth to be between 4.5 billion to 4.7 billion years old (Dalrymple, 2004).

Non-radiometric

Although non-radiometric methods can not be estimate the age of the earth as far back as radiometric methods (they only can provide an lower limit; there is no upper limit due to limtiations in such methods), they still show that the earth is very old indeed.

One non-radiometric method involves studying ice cores, or rather the variational in snow layers caused by the seasons. The differences in snow layers that appear during winter, spring, summer and fall allows us to date the age of ice formations. The differences include (i) increased bubbles and larger crystals of summer ice compared to winter ice, (ii) dust deposited during summer, (iii) nitric acid concentrations (measured via electrical conductivity), (iv) chemical containments and (v) relative amonts of heavy hydrogen (deuterium) and heavy oxygen (oxygen-18) in ice. Two ice cores drilled in 1990s in Greenland were dated to have been formed 123, 000 years ago (Andersen et al., 2004).

Another interesting method I would like to cover in this post involves studying calcium carbonate deposits in marine invertebrates. Similar to the banding patterns in trees (or ice cores as I earlier covered), it is possible to date fossils of clams and corals by looking at the carbon carbonate banding patterns. I’ll attempt to summarise how is it done.

Astronomical data has revealed that the speed of the Earth’s rotation is decreasing. This is due to friction of the moving tides on the earth’s surface (which are produced by the sun’s and moon’s gravitational field). This implies that the length of each day is getting longer since the formation of the earth-moon system. The average increased in day length is estimated to be .23 milliseconds per century. This means 1000 years ago, a day would be .23 seconds shorter than than a day now. If a direct estimate of day length is possible, we can use such information to date material.

And it turns out that we can obtain an estimate of day length from clam and corals fossils. Consider a clam living at the seashore. When the tide is in, the clam is open and respires aerobically. This incorporates calcium carbonate in the shells. When the tide is out, the clam shuts and respires anaerobically. This decalcifies the shells. Such differing patterns of deposition patterns allows us estimate the day length of the time fossiled organisms were alive.

As it turns out, some fossiled clams show a deposition patterns of a 21-hour day length , indicating that the fossils were about 465 million years old. What was more fascinating was that radiometric dating of the shells confirms this result (within a 99 percent accuracy) (Zhenyu et al., 2007).

Conclusion

So how old is the earth? Very old indeed.

References

Andersen, K.K. et al. (2004) High-resolution record of Northern Hemisphere climate extending into the last interglacial period. Nature 2004, 147-151

Dalrymple, G.B. (2001) “The age of the Earth in the twentieth century: a problem (mostly) solved”. Special Publications, Geological Society of London 190, 205–221

Dalrymple, G.B. (2004). Ancient Earth, Ancient Skies: The Age of the Earth and Its Cosmic Surroundings.

Stephenson, F.R. (2003). Historical Eclipses and Earth’s Rotation. Astronomy and Geophysics 44, 2.22-2.27.

Zhenyu, Z., Yaoqi, Z., Guosheng, J. (2007). The periodic growth increments of biological shells and the orbital parameters of Earth-Moon system. Environmental Geology 51, 1271–1277.

Personal Updates: My new job

A collection of insects, sorted by Order

Good and bad news

Hi everyone! I have some great news to share. I just started my new career at NIE (National Institute of Education) at Singapore. In other words, I attending a school that trains teachers.

I am delighted to have started, as this grants me a respite from academia, which I longed to have.

That said, my timetable looks pretty packed. As a result, the frequency of posts on this blog will drop. Nevertheless, this blog will still be running, and I will try to post some interesting articles. In fact, I am working on an interesting article on the age of the Earth coming in Feburary.

As for you my readers, have a good life, and always remember, God loves you.

God bless,

defensedefumer