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Convergent evolution

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"Convergent evolution" is the term evolutionists apply to the situation in which, they say, living things in different branches of the evolutionary 'family tree' have independently developed the same features.

In the theory of evolution, species acquire characteristics through adaptation to the environment, and these characteristics are passed on through inheritance. Any given feature that two species have in common, therefore, might be due to inheritance from a common ancestor, or due to adaptation to a common environment. "Difficult" changes, such as developing new types of organs (lungs, placenta), are thought to have happened only once, whereas more "superficial" changes, such as overall size or bodily proportions, may have have been "re-invented" several times.

Contents

Similarity due to common ancestry

Evolutionists believe that DNA, for example, must have arisen extremely early in the development of life, as all living things share the same DNA code. That is, all living things share the same DNA code because all living things have evolved from a common ancestor that used the DNA code.

In contrast to evolutionists, creationists explain similarity as being due to a common designer, who was free to re-use his designs in many different creatures. Creationists, therefore, do not expect to see a completely hierarchical pattern of features, although obviously similar creatures will have similar requirements and therefore have similar features.

The existence of common features is a vital factor in the study of evolution, as it is those common factors that are used to derive evolutionary 'family trees' (phylogenetic trees).

Like family trees, phylogenetic trees represent patterns of ancestry. However, while families have the opportunity to record their own history as it happens, evolutionary lineages do not — species in nature do not come with pieces of paper showing their family histories. Instead, biologists must reconstruct those histories by collecting and analyzing evidence, which they use to form a hypothesis about how the organisms are related — a phylogeny.

To build a phylogenetic tree ... biologists collect data about the characters of each organism they are interested in. Characters are heritable traits that can be compared across organisms, such as physical characteristics (morphology), genetic sequences, and behavioral traits.

...

Our goal is to find evidence that will help us group organisms into less and less inclusive clades. Specifically, we are interested in shared derived characters. A shared character is one that two lineages have in common, and a derived character is one that evolved in the lineage leading up to a clade and that sets members of that clade apart from other individuals.

Shared derived characters can be used to group organisms into clades. For example, amphibians, turtles, lizards, snakes, crocodiles, birds and mammals all have, or historically had, four limbs. If you look at a modern snake you might not see obvious limbs, but fossils show that ancient snakes did have limbs, and some modern snakes actually do retain rudimentary limbs. Four limbs is a shared derived character inherited from a common ancestor that helps set apart this particular clade of vertebrates.[1]

Similarity due to convergence

Equally vital in the study of evolution are features adapted to the environment. It is such adaptation that drives most evolutionary change. When two different species occupy similar environmental niches, the features the species use to exploit those niches might be expected to be similar, but this is not necessarily the case. There is no reason why, in principle, different species shouldn't come up with different features to exploit a similar environment, especially given that the environments will only be similar, not identical. An example of non-convergence despite occupying a similar ecological niche is kangaroos compared to cattle.

Also, if being in a similar ecological niche automatically generates similarities, why is the kangaroo not more like cattle, horses or deer—the kangaroo’s ecological counterparts on other continents?[2]

If an ecological niche is unoccupied, there may be several species that experience selection pressure to take over that niche. The first species that is successful will usually prevent other species from continuing to develop in that direction. For example, in the evolutionary scenario, there was once a time when all living things existed either in water (e.g. fish) or on the surface of the land (e.g. most reptiles). Every species of this latter group actually existed in an environment which was also at the base of the atmosphere. But while some creatures supposedly evolved features to exploit that part of their environment by developing the ability to fly, many others—in a "similar" environment—did not. This also illustrates that the physical environment is not decisive, but the ecological niche, that is, the combination of the environment and they way-of-life that exploits the environment.

Evolutionists consider parallel features to often, but not always, be the result of convergence, therefore they are not in and of themselves evidence for evolution. This means that invoking similar development due to similar environments therefore becomes an ad hoc explanation, invoked when necessary but ignored otherwise.

Creationists reject that parallel features of species in parallel environments is evidence for evolution at all:

‘Convergence’ is really just a grab bag to put similarities which cannot be explained through common ancestry (evolution). This is supposed to account for similarities which do not fit the evolutionary scheme of descent based on other similarities.[2]

Trivial cases of convergence

A simple example of convergence is the coloration of Arctic animals. Several genera, including bears, wolves, foxes, and hares, include some species that live in temperate climate zones and others that live in the arctic. The Arctic species generally have longer and lighter colored fur. It is generally agreed that these characteristics are an adaptation to the environment, the length of the fur to provide more warmth and the white coloration to provide camouflage in the snow.

For the creationist, the representatives of these species that were rescued from the Flood on Noah's ark, multiplied, and became established in different regions. The individuals living in Arctic regions lost the genes for shorter fur and darker coloration through recombination of existing genes (or, in some cases, the loss of genetic information by mutations) and natural selection, explaining the convergent development of their features.

Another example is that of Darwin's finches, a group of about 15 closely-related species found only on the Galápagos Islands. Many of the species prefer a particular source of food and have specialized beaks that help them to exploit their chosen source, whether leaves, fruits, insects, or grubs. Both creationists and evolutionists believe that a small number of these birds reached the islands by chance some time ago and multiplied to fill the islands. Under competition for food and natural selection different subpopulations specialized in the exploitation of different food resources. The end result was convergence of their beak forms to resemble the beaks of the species on the mainland that exploited similar types of food.

Non-trivial cases of convergence

However, there are more complex cases, and ones over which the opinions of creationists and evolutionists diverge. One of many such examples are the features of eyes. Most living things other than plants and single-celled creatures have eyes. (Some single-celled creatures such as euglenoids have a light-sensitive spot referred to as an "eyespot".)

While a few evolutionists hope to one day show that eyes essentially evolved only once,[3] most believe that they evolved independently dozens of times, even as many as 60 times.[4][5][6] One reason that the range of opinions can be so wide is that soft organs like eyes rarely leave any fossils, and biochemical pathways leave none at all. Another problem is that parts of the visual system, e.g. the photosensitive proteins (opsins) and regulatory genes (PAX6), may have appeared early in a common ancestor, while the morphology responsible for image formation, like the lens, could have come later and independently in several branches.

Other examples are:

  • Tree resin[7]
  • fovea and saccades[8]
  • Kleptoplasty (ingesting bacteria to make use of its plastids)[9]
  • Jet propulsion[6]
  • Flight[6]
  • Trichromatic vision in monkeys[6]
  • Echolocation[6][10] in creatures as different—in very different environments—as some birds, bats (mammals), and whales and dolphins.
  • The arrangement of rod cells in the eyes of oilbirds and deep-sea fish.[10]

Commonly found

Convergent evolution is not rare exception to the general rule. Instead, it is a common phenomenon.

Colin Patterson, then the senior palaeontologist at the British Museum of Natural History, said in a talk in 1981:

When I ask them [other evolutionists] about evolution the only answer I get from them is, "Convergence is everywhere."[11]

In 2013, a report in Nature News of a study to be published in Nature included the comment:

These results imply that convergent molecular evolution is much more widespread than previously recognized[12]

The Nature report itself said

…convergence is not a rare process restricted to several loci but is instead widespread, continuously distributed and commonly driven by natural selection acting on a small number of sites per locus.[13]

References

  1. Building the tree, Evolution 101, University of California Museum of Paleontology.
  2. 2.0 2.1 Batten, Don, Are look-alikes related?, Creation 19(2):39–41 March 1997.
  3. Eye-opening Gene: How many times did eyes arise?
  4. Squid Pax-6 and eye development
  5. Sarfati, Jonathan and Michael Matthews, Chapter 10 (Argument: ‘irreducible Complexity’), Refuting Evolution 2 Creation Book Publishers 1 May 2011, ISBN 978-0890513873.
  6. 6.0 6.1 6.2 6.3 6.4 Lael Weinberger, Long Tails, Tall Tales A Review of the Ancestor’s Tale: A Pilgrimage To the Dawn of Evolution By Richard Dawkins, Journal of Creation 22(1):37–40 April 2008.
  7. J. Oard, Michael, 320-million-yearold Amber Has Flowering Plant Chemistry, Journal of Creation 24(2):16 2010.
  8. Paula Weston and Wieland, Carl, The Mole, Creation 25(2):46–50 March 2003.
  9. Shaun Doyle, Photosynthetic sea slugs: an evolutionary enigma, Journal of Creation 24(3):10–12 December 2010.
  10. 10.0 10.1 Bell, Philip, The super-senses of oilbirds, Creation 28(1):38–41 December 2005.
  11. Patterson, Colin, address at the American Museum of Natural History, New York City, p.11, 1981.
  12. Erika Check Hayden, Convergent evolution seen in hundreds of genes, Nature News, Wed. 4th September, 2013Wed. September 4th, 2013.
  13. Joe Parker, Georgia Tsagkogeorga, James A. Cotton, Yuan Liu, Paolo Provero, Elia Stupka & Stephen J. Rossiter, Genome-wide signatures of convergent evolution in echolocating mammals, Nature, Fri. 18th January, 2013Fri. January 18th, 2013.
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