Arguments Against Evolution Pt. 5

Missing links and a look at the Romer’s gap

The term “missing link” was coined in Darwin’s time and was used to denote the “hypothetical organisms that linked different groups, and especially humans with anthropoid apes.” Perhaps the most famous “missing links” are those linking humans to our more ape-like ancestors. The term “missing link” is misleading, however, because it supposes that all creatures are linked in a hierarchy or Chain of Being when the case is rather that all creatures share common ancestors. The term also implies that there are certain links that are missing and thus disprove the theory of evolution. Modern scientists speak of transitional forms instead of “missing links.”

Cotner and Moore define a transitional form as: “An organism having anatomical features intermediate between those of two major groups of organisms in an evolutionary sequence. Transitional forms show evolutionary sequences between lineages by having characteristics of ancestral and newer lineages. Since all populations are in evolutionary transition, a transitional form represents a particular evolutionary stage that is recognized in hindsight.” Why don’t we find something halfway between a hippo and a whale, then? Miller explains that transitional fossils are retrospective: “For example, transitional forms are not to be found between living whales and their closest living relatives the hippos, but between whales and their common ancestors with the hippos. Such forms will be unlike anything living today. Transitional forms are found by moving down the tree of life into the past, not by trying to jump from limb to limb.”

Keith B. Miller addresses two errors with regard to the fossil record and missing links: “There are two opposite errors that need to be countered about the fossil record: (1) that it is so incomplete as to be of no value in interpreting patterns and trends in the history of life, and (2) that it is so good that we should expect a relatively complete record of the details of evolutionary transitions within most or all lineages.”

David H. Bailey states that many of the gaps pointed out by creationists have been filled over the past few decades. Dawkins states that “for a large number of fossils, a good cause can be made that every one of them is an intermediate between something and something else.” It is true that there are gaps in the fossil record, but that is exactly what one would expect if one takes into consideration the difficult process of fossilization and the amount of strata which have been excavated. A rare occurrence known as fossil Lagerstätten took place where one encounters thick layers of fossil-rich rock. These are very rare indeed. Organisms that lack hard parts (eg. Ediacaran organisms, sponges, plants) have very little hope to be fossilized and even when an organism has hard parts, dissolution and recrystallization could erase any traces of fossilization. Erosion and changes in the formation of rock can also destroy fossil evidence. Terrestrial organisms are less likely to be fossilized than those in aquatic environments, because sediments in water increase the chances of fossilization. Even when there are fossil-rich layers, these may be situated in inaccessible places, e.g. on the bottom of the sea or in the subsurface. Long-lived and abundant species stand a bigger chance of being preserved in the fossil record than short-lived or scarce species. For example, a fossil impala would be more probable than a fossil aardvark. As Charles Darwin stated: “The crust of the earth is a vast museum; but the natural collections have been imperfectly made, and only at long intervals of time.”

One famous gap in the fossil record is called Romer’s gap and spans from the end of the Devonian period (about 360 million years ago) and the early Carboniferous period (about 340 million years ago). This gap basically correlates to the evolution of fish into amphibians. Several of these transitional forms have been discovered:

  • Eusthenopteron foordi, discovered in 1881 in a collection of Canadian fossils, is an example from the late Devonian period. At the bases if its fins, this creature had bones which are analogous to those of terrestrial animals. Eusthenopteron looked like a fish and probably spent its life in water.
  • Panderichthys rhombolepis is another specimen from the Devonian. It had less fins and thicker ribs than fish. Thicker ribs are needed to support the body when the creature is out of the water, but Panderichthys probably lived mostly in water.
  • Ichthyostega stensioei and Acanthostega gunnari looked like fish with legs. Their cranial structure and skeletons resembled that of a fish, but their ribs were even thicker than those of Panderichthys. Both creatures could breathe air. Between the two, Ichthyostega probably spent more time on land than Acanthostega and moved like a seal does on land. Ictheostega would be the first known vertebrate that did not move like a fish. In fish, the hyomandibular bone serves to support the gills. This bone corresponds to the ear bone in mammals, also called the stapes. In Acanthostega the stapes resemble the hyomandibular bone of a fish and could not vibrate, thus rendering it useless for the purposes of hearing. Later, in the Carboniferous period, amphibians possessed a hyomandibular bone that could be used for hearing.
  • Tiktaalik roseae was discovered in 2004 and had amphibian-like skull, neck, ribs, elbows, wrists, and fingers, yet had fins, scales, and gills like a fish. It could probably prop itself up using the elbows, wrists, and fingers. Tiktaalik did not have gill plates and could thus move its head from side to side.

Also see: http://waitbutwhy.com/2013/12/your-ancestor-is-jellyfish.html for a cute family history

Sources:

Bailey, D H 2010. Creationism and intelligent design: Scientific and theological difficulties. Dialogue: A journal of Mormon Thought 43/3, 62-81.

Cotner, S & Moore, R 2011. Arguing for evolution: An encyclopedia for understanding science. Greenwood: Santa Barbara.

Daintith, J & Martin, E (eds.) 2010. Oxford dictionary of science. Oxford: Oxford University Press.

Darwin, C 1909. Origin of species. New York: P F Collier and Son.

Dawkins, R 2009. The greatest show on earth: The evidence for evolution. London: Bantam Press.

Miller, K B 2003. Common descent, transitional forms, and the fossil record, in Miller, K B (ed.) Perspectives on an evolving creation. Grand Rapids: William B Eerdmans.152-181.

Rice, S A 2007. Encyclopedia of evolution. New York: Facts on File.

Darwin: A Friend of Theology? – Part 1

This is the first of a series of posts about evolution and theology. I am in part undertaking to write this series as a way to inspire myself and practise writing about this subject for my MTh thesis.

The Idea of Evolution

The idea of a progressive transformation of species is older than Darwin. The idea of some sort of evolution of species has been around in Europe before Charles Darwin. Darwin’s grandfather, Erasmus Darwin, speculated about evolution and published his proposals in Zoonomia, or, The Laws of Organic Life (PDF available from Project Gutenberg)in 1794. In 1844 Robert Chambers published a his views anonymously in the Vestiges of the Natural History of Creation (PDF available at archive.org). The French biologist Jean-Baptiste Lamarck proposed a mechanism of “transformation” almost sixty years before Darwin’s Origin of the Species. For Lamarck, the two components of evolution were the influence of the environment and the efforts of the animals themselves. For example, giraffes got long necks because generations of giraffes stretched their necks to reach high branches.

Image

Lamarck’s Giraffes

The work of August Weismann proved that only the sexual cells had hereditary powers and thus disproved Lamarck’s idea. Herbert Spencer proposed an evolutionary theory just prior to Darwin’s publication. Spencer was the first to use the term so often associated with Darwinian evolution: “survival of the fittest”. Charles Darwin coined the term “natural selection”, as opposed to artificial selection, which is the process whereby humans breed animals for their own needs. In 1900 the work of Mendel in genetics was rediscovered and paved the way for Darwinism and neo-Darwinism.

What is Evolution?

Let’s start with the basics. Evolution is a scientific theory of the history of biological life. The level at which evolution works is that of the population. A single individual cannot evolve, but a population of individuals can. Evolution can occur in a number of ways: mutations (random genetic changes, like a slightly longer tail), random changes in genetic frequencies (genetic drift, where by chance some individuals do not reproduce), migration (gene flow, when a population moves to a new habitat, taking their genetic information with them to the new environment). Individuals who reproduce take part in evolution. Survival is not enough, the individual must successfully reproduce.

Below are a couple of key words and definitions to start off with:

Extinction occurs when an entire species dies out. It is an essential part of the evolutionary process and facilitates the evolution of new species.

Adaptive radiation refers to the origin of new species from a common ancestor, e.g. as a result of migration or changes in habitat. A clue in adaptive radiation is the shared traits of the derived species, also called homologies. Examples of homologies are the flippers of whales and dolphins. Universal homologies are shared traits that occur in all life-forms. These universal homilies are the way cells are put together, the way ATP works at the cellular level and the way the genetic code works.

As opposed to homologies, analogies are similar structures that aren’t a result of shared ancestry.

Exaptations are features that were initially used for a certain purpose, but later became used for something else.

Vestigial traits or organs are features that no longer serve a function or serve only a very reduced function. Examples of vestigial organs are the human coccyx and the eyes of the blind cave-dwelling fish Astyanax mexicanus.

Transitional forms are organisms that are intermediate between two major groups, for example between fish and amphibians or reptiles and birds. Probably the most famous of these is archaeopteryx. In a sense all forms are transitional forms, because evolution is a dynamic process that is continually occurring.

Speciation is when a new species arises through evolution. A necessary factor for speciation is that the two or more forms that have become separate species cannot produce offspring that can reproduce (think of a mule).  Geographical or allopatric speciation happens when a population is divided by some natural barrier (e.g. glacier, arm of the sea, mountain) and continue to develop in different directions.  Sympatic speciation occurs in the same environment. This kind of speciation occurs when the first differences between the two species prevent them from breeding. The barriers of breeding might not always be because of sterility, but because of behavioural differences.

Bibliography:

Cotner, S & Moore, R 2011. Arguing for evolution: An encyclopedia for understanding science. Greenwood: Santa Barbara.

Durant, J (ed.) 1985. Darwinism and divinity: Essays on evolution and religious belief. Oxford: Basil Blackwell.

Montenat, C, Plateaux, L & Roux, P (eds.) 1985. How to read the world: Creation in evolution. London: SCM Press.

Pennock, R T 2002. Tower of Babel: The evidence against the new creationism. Cambridge: MIT Press.

Rice, S A 2007. Encyclopedia of evolution. New York: Facts on File.

Zimmerman, P A 2009. Darwin at 200. Concordia Theological Quarterly 73, 61-75.