ArtsAutosBooksBusinessEducationEntertainmentFamilyFashionFoodGamesGenderHealthHolidaysHomeHubPagesPersonal FinancePetsPoliticsReligionSportsTechnologyTravel
  • »
  • Education and Science»
  • Life Sciences

Convergent Evolution Examples

Updated on April 30, 2013
The seed of the coffee cherry is one of the world's best natural sources of caffeine. It is also a wonderful example of convergent evolution.
The seed of the coffee cherry is one of the world's best natural sources of caffeine. It is also a wonderful example of convergent evolution. | Source

Throughout the 3.8 billion year history of life on Earth, plant and animal species from vastly different evolutionary backgrounds have come to possess very similar traits. This convergent evolution often results from these species living in ecosystems such as deserts, rain forests, and tundra that force these varied species to adapt to their climatic conditions in very similar ways. Modern genetic analysis is beginning to show that these adaptations not only have similar appearance and function, but have significant genetic similarities as well.

There are dozens of examples of convergent evolution in current species and in the fossil record. This article will examine three well-known ones in detail: evolution of the eye in vertebrates and cephalopods, evolution of caffeine production in coffee and tea plants, and evolution of echolocation in dolphins and bats.

Structure of the camera eye in vertebrates (left) and cephalopods (right).
Structure of the camera eye in vertebrates (left) and cephalopods (right). | Source

NCSE: Evolution of the Eye

Convergent Evolution Example One: The Eye

The independent evolution of the camera eye, which uses a lens to focus light on a retina, in at least two distinct groups of animals is perhaps one of the best examples of convergent evolution. Since the Precambrian approximately 500 million years ago, the eye has evolved separately multiple times in cephalopods (such as octopus and mollusks) and vertebrates (such as fish and humans) from the simple photoreceptor spot of our common ancestor to the complex camera structure of the modern eye.

The evidence for common ancestry of cephalopod and vertebrate eyes lies in the aspects they have in common. Though the exact structure of photoreceptor cells varies widely across the animal kingdom, they have the same basic operating procedure. At the heart of all photoreceptors contain a light-sensitive pigment bound to a protein called opsin. When hit by a photon, this bond is broken, and the opsin binds with another protein known as G-protein. This then sets off a complicated cascade of chemical reactions that ends with the production of a nerve signal. The presence of this basic procedure in all multicellular animals with vision suggests that it results from a common ancestry. This is further confirmed by genetic evidence

Though these eyes all evolved from a common ancestor, they developed quite differently. The camera eye of cephalopods, for example, fixes a major "design flaw" in vertebrate eyes by putting the photoreceptor layer of the retina above the nerve layer. Vertebrate eyes evolved with the nerve layer above the photoreceptor layer, producing a blind spot where the nerve fibers pass through to form the optic nerve.

The second key difference is in the types of photoreceptor cells lining the retina. There is a wide range in the structure of photoreceptors across different types of animals, but they can be categorized into two main types: ciliary and rhabdomeric. In addition to some major differences in the protein cascade sequence, the main structural difference is in the shape of the receptor area. Ciliary receptors are horizontal structures resembling a stack of discs. Rhabdomeric receptors are vertical structures resembling bristles on a paintbrush. While the eyes of cephalopods mostly use rhabdomeric receptors, the eyes of vertebrates contain only ciliary ones.

Camellia sinensis diagram from the 1897 edition of Köhler's Medicinal Plants
Camellia sinensis diagram from the 1897 edition of Köhler's Medicinal Plants | Source
Biosythesis of caffeine from xanthosine. (Click to enlarge.)
Biosythesis of caffeine from xanthosine. (Click to enlarge.) | Source

Convergent Evolution Example Two: Caffeine

A number of plant genera produce the chemical caffeine in their leaves and fruit seeds as a deterrent against pests - the coffee, tea, yerba maté, kola, and guarana plants being the most well-known examples. These plants tend to grow in similar tropical regions of Southeast Asia and South America, but are only distantly related. Their independent evolution of the complex, multi-step process needed to produce caffeine is a classic example of convergent evolution.

The tea plant (Camellia sinensis) belongs to the order Ericales, a large and diverse group of flowering plants that includes blueberries, brazil nuts, persimmons, and azaleas. The oldest fossil belonging to this order has been dated to approximately 90 million years ago, and researchers have estimated that this order diverged from its common ancestor with other plant orders between 92 and 109 million years ago.

There are three main species of coffee plant used to produce most of the world's coffee supply: Coffea arabica, Coffea canephora, and Coffea liberica. These belong to the order of flowering plants known as Gentianales, which also includes gardenias and milkweeds. Researchers have estimated that this order first emerged between 83 and 89 million years ago.

Given the ages of the orders containing both coffee and tea plants, their last common ancestor must date back to at least 100 million years ago, probably much older. As caffeine production is not common among other plants in either order - there are no caffeinated gardenias or blueberries, after all - this appears to be a relatively recent trait.

Caffeine production is a rather complex five-step process converting the organic compound xanthosine into the 1,3,7 trimethylxanthine we know as caffeine. The last step in the process is accomplished by the production of an enzyme known as caffeine synthase that enables the chemical reactions to produce caffeine from the predecessor chemical theobromine.

Recently, scientists have isolated the genes CCS1 in coffee plants and TCS1 in tea plants that produce the caffeine synthase enzyme, and found both genes to have a 40% agreement in the amino acid sequences they code for. Thought these genes aren't exactly the same, they have enough in common that they can produce the same result - caffeine - even though they evolved via vastly different genetic pathways.

Big brown bat
Big brown bat | Source
Dolphin playing in the wake of a boat
Dolphin playing in the wake of a boat | Source

Poll Time!

Is echolocation too complex to have evolved by natural processes?

See results

Convergent Evolution Example Three: Echolocation

Bats and dolphins use echolocation for similar purposes - navigating and catching prey. These distant mammal families both evolved these powers at different times and in different ways, but with some interesting commonalities, making echolocation a fascinating example of convergent evolution.

The earliest bats evolved around 52-54 million years ago, in the late Eocene. Although for a time there was some disagreement among paleobiologists whether flight or echolocation evolved first, the emerging consensus is that flight indeed evolved first in the common ancestor of all bats, and that echolocation evolved twice - once in the common ancestor of all yangochiropteran microbats using a vocal ultrasound chirp, and then re-evolved in the Egyptian Rousettus bat using tongue clicks.

Microbats use a variety of vocal strategies for echolocation, depending on their environment. In open environments, they will use constant frequencies as a form of sonar ping for distant objects. In confined cave environments, they will use frequency modulation, changing pitch to keep the echos from overlapping each other.

Dolphins are part of the odontoceti , or "toothed whale" suborder of whales. This suborder includes sperm whales, orcas, porpoises, and beaked whales. Nearly all of the toothed whales are capable of echolocation, indicating that this is a trait that evolved at or just prior to the time of their split from the baleen whale branch some 34-36 million years ago.

Toothed whales produce a beam of high-pitched clicks using a structure in their skulls known as the bony nars and the phonic lips. These sounds are then amplified and pitch-shifted by a structure known as the melon. The melon is a round fatty protrusion from the cetacean's head, giving dolphins, orcas, and sperm whales their distinctive forehead shape. Echoed sounds are received through fatty structures in the lower jaw that transfer the sound vibrations to the inner ear. Like many species of bats, dolphins and other toothed whales can modulate the frequencies of their clicks depending on the situation.

Although dolphins and bats evolved at different times and under vastly different conditions, there are some very similar strategies of producing sound and mechanisms for receiving it. There are also similarities at the molecular level. The protein prestin is a critical component of the hair cells in the cochlea of the mammalian inner ear. In both dolphins and echolocating bats, the gene that codes for prestin has undergone a very similar series of mutational changes, altering the amino acids used in the protein. This seems to indicate that prestin is critical to the sensitive hearing required for echolocation. Though this relationship is still being studied, if demonstrated to be valid it would represent one of the best examples of molecular convergent evolution.

But Wait, There's More...

The examples above are just a few of the many examples of convergent evolution that abound in modern plants and animals and in the fossil record. Though at first glance the phenomenon of convergent evolution can seem like evidence of a designer, upon inspection of the details it confirms the haphazard and very organic nature of natural evolution.


Comments

    0 of 8192 characters used
    Post Comment

    • nicomp profile image

      nicomp really 2 years ago from Ohio, USA

      "... - there is no evidence of design or purpose in anything in the natural world. "

      My car was designed on purpose.

    • profile image

      whowas 4 years ago

      Hi there, scottcgruber - a really good hub on the phenomenon of convergent evolution. Great job.

      Nice to see you trying to reason with creationists - I gave up a long time ago. After all, if you could reason with creationists there would be no creationists!

      Thanks for this excellent summary of the fundamentals of this important aspect of evolutionary biology. :)

    • TrahnTheMan profile image

      TrahnTheMan 5 years ago from Asia, Oceania & between

      I remember from my college days when a geography lecturer told us about a principle called equifinality, where two similar forms can exist but having been created from completely different processes: for example, two sand dunes can exist, one being the result of erosive processes, the other the result of depositional processes. t seems to be a similar concept to convergent evolution in the life sciences??

    • f_hruz profile image

      f_hruz 5 years ago from Toronto, Ontario, Canada

      Nature is simply amazing ... and since all intelligent life on earth evolved from natural sources, the problem solving capacity of learning from undesirable results may have its natural source in the old saying that necessity in itself is the mother of invention.

      Just like science will only come up with good discoveries by first asking smart questions, it's hard to see how silly ID ideas or creationist myth can advance intelligent minds to new insights ...

    • scottcgruber profile image
      Author

      scottcgruber 5 years ago from USA

      Good question! I haven't read enough on cetacean evolution, but I imagine the predecessor mammals to the whale family were something like our seals and sea lions - coastal land mammals that were really well-adapted for swimming. Eventually they transitioned to living entirely marine lifestyles.

    • scottcgruber profile image
      Author

      scottcgruber 5 years ago from USA

      Well said, f_hruz. The entire design argument is based on a false premise: design cannot not be proven, therefore design. It's bad rhetoric, bad science, and bad theology all in one.

      The burden of proof is not on science to disprove the design philosophy. Science is by definition naturalistic - it cannot accept supernatural explanations for natural phenomena.

      Nor does it need to - there is no evidence of design or purpose in anything in the natural world. These are human philosophical concepts we apply onto nature, they do not exist in nature itself.

      If someone needs to have a personal belief that some "intelligent designer" designed life to look exactly like it happened by random chance and natural selection, I can't argue with that. But if they want to assert this as fact, the burden of proof is on them.

      If the cdesign proponents can demonstrate evidence of the hand of some unseen force deliberately mutating genes or manipulating gene expression, I will accept design as legitimate science and will advocate for it as strongly as I advocate for the theory of evolution.

      Of course, once that happens, it ceases to be a supernatural force and becomes a natural force that can be measured and explained through testing of falsifiable hypotheses. So the IDers lose again.

    • f_hruz profile image

      f_hruz 5 years ago from Toronto, Ontario, Canada

      Hey parster, what you just said is really just educated sounding ID BS ... it's brain dead from the start!

      Trying to create a Creator for everything natural adaptation or natural selection explains so much better than any of these 1/2 cooked ID and creationist BS, simply shows ever so clearly, how intellectually unsubstantiated all of these religion based arguments really are!

      It's the same irrational religioniods who keep raising these silly non-issues.

      Nature is the basis to all forms of life. Nature, just like reality, has no use for any gods or man made creators - the idea of a creator is about as irrational and artificially constructed as the myths in all the holy books combined!

    • parrster profile image

      Richard Parr 5 years ago from Oz

      Sub-optimality, the modern evolutionary argument against the necessity of design demanding a designer is full of holes.

      Firstly, For the evolutionist to produce an example of something which, to him, evinces either non-design, or poor design, does not somehow magically negate all the other evidences of obvious design!

      Secondly, it is possible that an object possesses purposeful design, but that it is not recognised by the observer; we may not presently know why an organism is designed the way it is.

      Third, one of the most serious flaws with the sub-optimality argument is this: those who claim that something is “suboptimal” must, by definition, set themselves up as the sole judge of what is, and what is not, “optimal.” In other words, those who would claim non-design in nature must somehow “know” two things: (1) they must know that the item under discussion positively evinces no design; and (2) they must know what the absolute standard is in the first place (i.e., “the optimal”) in order to claim that something has become “suboptimal.”

      The evolutionist looks at the creation, sees that it does not fit what he would do if he were the Creator, and then suggests on that basis that evolution is true. And all of this is from someone who does not even believe in a Creator in the first place! Such thinking makes for an extremely weak argument.

      Further refutations of sub-optimality can be found in the links below.

      http://www.apologeticspress.org/APContent.aspx?cat...

      http://www.apologeticspress.org/APContent.aspx?cat...

    • f_hruz profile image

      f_hruz 5 years ago from Toronto, Ontario, Canada

      What a great hub - thanks!

      The video about the eye is very good.

      So we know dolphins aren't fish, what was it in the evolutionary process that drove them from living on land to becoming sea creatures?

    • profile image

      jenubouka 5 years ago

      Interesting information Scott. Granted I had to have wiki in the next window to understand some of it, but none the less I really enjoy articles that are packed with great info.