FROG "DESIGN"

There are more than 4,100 modern species of frogs. The evolutionary, creationism, and intelligent design models make different predictions about the types of variations that can be observed within the groups of frogs. Which is supported by the actual evidence?

EVOLUTIONARY MODEL

If evolution has occurred, populations can acquire new features as they adapt to their niche, at each level of classification. The same types of modifications which separate one group from another may be observed within a group.

CREATIONISM MODEL

While evolution may occur within a "kind", one "kind" cannot evolve from another. As a result, each "kind" has no relation by descent to any other "kind" and an examination should prove which organisms are completely unrelated to each other. The variations which occur within a "kind" should be minor compared to those which differ between "kinds".

INTELLIGENT DESIGN

If intelligent design has occurred, then some/substantial evolution could have taken place in frog lineages. However, each separate "design" should be impossible to develop over time. The variations on a specific "design" should not significantly alter the "design" or create a complex new "design".

 

VARIATION WITHIN A "KIND"

If creationists conclude that all frogs belong to the same "kind", this is problematic because it doesn't explain why fossil Proanurans would possess froglike features. Also, if creationists accept that the variation within frogs has evolved, this then means that creationists can reconcile an enormous amount of evolution with their religious faith (especially those that believe the earth is only a few thousand years old). Creationists would have difficulty claiming that a relatively small amount of change in one lineage could not occur, even given millions of years, if they accept a far greater amount of evolutionary change as occuring in a few thousand years.

For example, the methods of reproduction in frogs vary considerably. Egg clutches range from only 3 to more than 5, 000.  Most lay their eggs in water, some are laid in leaves and fall into water, some are laid in land which later becomes flooded, some tadpoles must try to reach water, some eggs hatch in a burrow and the female digs to help the hatchlings reach water, some tadpoles are carried to water by their parents after hatching, and parents may carry eggs or tadpoles.

TADPOLES

Some frogs cover their eggs in a protective foam. About 600 species undergo direct development, passing through the tadpole stage while in the egg and hatching as an adult.  This direct development is known in 9 different families of frogs (Mattison, 1998).

     Some species of frog (Nectophrynoides tornieri, N. viviparous, and Eleutherodactylus jasperi) give live birth to tadpoles after the eggs develop in the female‚Äôs oviduct.  Nectophrynoides liberiensis and N. occidentalis give birth to young toads after they are nourished by uterine secretions in the maternal uterus.   Some species carry the eggs with them until hatching, although the site of the body where the eggs are carried can vary: on the legs in Alytes; on the back in Hemiphractus, Stefania, Cryptobranchus, and Fritziana; in depressions on the back in Pipa, in pouches on the back Flectonotus and Gastrotheca; and in the oviduct in Nectophrynoides tornieri, N. viviparous, and Eleutherodactylus jasperi.  Some species carry their tadpoles.  Tadpoles are carried on the back of Sooglossus seychellensis, the groin pouches of Assa, the vocal sac of Rhinoderma darwini, and the stomach of Rheobatrachus (Mattison, 1998).

FROG WITH TADPOLEDARWIN'S FROG

MARSUPIAL FROG

If creationists equate the "kind" with the taxonomic rank of "family" (as many do), this creates an even greater hole in their nonexistent fossil record since each of these "kinds" should date to the first days of life on earth. If there are 27 frog families, then the fossil record should provide evidence that 27 "kinds" of frogs have always existed. The smaller the unit which is defined as a "kind", the more difficult it is to argue that frogs which seem to be very similar are as unrelated to each other as they are to trees and insects and people (given that all "kinds" are equally unrelated).

Even if the "kind" is equated with the level of family, an enormous amount of variation would have evolved since the creation of the "kind." Frogs can even vary significantly in size within a single family such as the two congeneric species of the family Hylidae pictured below.

Hyla faber and Hyla cerraclensis

TWO FROGS

Leptodactylus labyrinthicus, Leptodactylus laticeps, Leptodactylus mystacinus, Leptodactylus ocellatus

Body shape can vary among frogs, even within the same family.

FAMILY CERATOPHYDAE

Melanophryniscus atroluteus

FROG

Chacophrys pierotti

Ceratophrys ornata

FROG

THE "DESIGN" OF FAMILIES

How can a "design" be "irreducibly complex" if it is so frequently reworked? For example, how can one claim that the evolution of long legs is an essential aspect to frog design when so many frogs (especially toads) move more by hopping or walking than jumping? Is the variation in frog legs any more significant than differences in the length of legs across different dog breeds? Could the extensible tongues be an essential element of design if frogs of the family Pipidae lack them? Some frogs can only extend their tongues slowly (Rhinophrynidae). Could a voice be an essential element of frogs if the most primitive frogs (Ascaphidae, Leiopelmatidae) lack a voice and other primitive frogs (Discoglossidae, Bombinatoridae) possess a subdued voice? (Mattison, 1998).

IF A SPECIFIC GROUP OF FROGS WAS DESIGNED TO REPRODUCE IN A CERTAIN WAY, WHY HAVE SO MANY FROGS HAD TO REWORK THE DESIGN?

It could be argued that there an animal's style of reproduction needs to be designed because of the complex interactions of anatomical structures, physiological mechanisms, and instincts. However, if such a complex "design" is indeed so "intelligent", then why did so many frogs rework their designs? In the evolutionary model, some modern frog groups have kept the ancestral system of reproduction (laying eggs in water to produce an aquatic larval stage) while other frogs, often closely related to those with aquatic tadpoles, have evolved a modified form of reproduction. Since much of this variation occurs within families (and even smaller taxonomic units), most modern creationists would permit this type of evolution in their model. If the original type of reproduction in frogs was created or designed by direct divine influence, why did it require subsequent evolutionary tinkering in order to fix it and make it workable?

For example, while some frogs/toads of the family Bufonidae lay eggs in water, others give live birth, and others undergo direct development. Some frogs of the family Myobatrachidae lay their eggs in the water, others provide foam nests, others lay their eggs on land and their larvae undergo direct development, some tadpoles feed while others do not, two frogs swallow their eggs so that they can develop in their stomachs, and the males of one species (Asa darlingtoni) possesses inguinal pouches for the eggs and larvae to develop. Most frogs of the family Hylidae lay eggs in water, some lay eggs on vegetation over water, some stages of development (eggs, tadpoles, and or juvenile frogs) can be carried on the back or in a dorsal pouch, some tadpoles feed while others do not, and some undergo direct development. Within the family Leptodactylidae, frogs vary on whether eggs are laid in water, whether foam is produced for the eggs to develop in, whether there is live birth, whether the larvae are aquatic or undergo direct development, and whether fertilization occurs inside the body of the female. Different forms of parental care have evolved separately in different groups of frogs (Mattison, 1998; Pough, 1998).

Chromosome number can vary withing a groups of closely related frogs and duplication of chromosomes (polyploidy) is a mechanisms through which speciation can come about. In the subfamily Xenopodinae (family Pipidae), the genus Silurana is composed of 1 diploid species (2n=20) and 1 tetraploid (2n=40) species while the genus Xenopus is composed of 10 tetraploid species (2n=36), 5 octoploid species (2n=72), and 2 dodecaploid species (2n=108) (Evans, 2004)

IF A SPECIFIC GROUP OF FROGS WAS DESIGNED FOR A CERTAIN HABITAT OR LIFESTYLE, WHY HAVE SO MANY ADAPTED TO DIFFERENT HABITATS AND LIFESTYLES?

It could be argued that an organism is "designed" to match its environment. However, these designs apparently needed reworking since significant variations occur within close relatives. It could be argued that an organism is "designed" to match its environment. However, these designs apparently needed reworking since significant variations occur within close relatives. For example, one could imagine that smooth-skinned, aquatic, leaping frogs might have a different "design" and represent a different "kind" than the warty-skinned, terrestrial, hopping toads. This is not true. All toads are not related to each other--the body form which is referred to with the word "toad" has evolved several times within separate frog families (such as Discoglossidae, Bufonidae, Myobatrachidae, Leptodactylidae). While most toads are predominantly terrestrial, the clawed and Surinam toads (family Pipidae) are almost entirely aquatic (Mattison, 1998).

Frogs which live in arid environments have evolved different ways of dealin with or preventing water loss. Some can tolerate water loss of up to 60%, others can coat their skin in wax, others can form a cocoon around themselves to store water, some store water in their enlarged bladder, some urinate uric acid in a powder form, some have modified their anatomy to limit water loss from the head, and others can fill enlarged lymphatic glands with water until water composes half the body weight. None of these can be considered an essential feature since there are other frogs living in arid areas which lack them. No frog has all these features.

Frogs which burrow have evolved different ways of adapting to this lifestyle.Some have dry skin, others have clawed digits, others have extra bony elements which adapt their feet for digging, gold frogs possess a bony plate on their backs, others have modified body shapes, and frogs vary in their instinctual burrowing behaviors (e.g. some burrow forwards and others backwards). None of these can be considered an essential design element since other burrowing frogs possess different adaptations.

Different adaptations to arboreal living have evolved in different groups such as flattened body shapes, adhesive disks on the tips of digits, membranes between digits which allow gliding from tree to tree, loose skin which can adhere to surfaces, and small hooks in the skin. Adaptations for arboreal life are most evident in the true tree frogs (Hylidae) and Old World tree frogs (Rhacophoridae) but can also occur in other families which are not primarily arboreal (Bufonidae, Hyperoliidae, Ranidae).

The majority of frogs possess some level of poison in their skin. Within some families, the amount of poison has been greatly augmented in some species, such as the poison arrow frogs (Dendrobatidae). While many frogs of the family Bufonidae posses large parotid glands which produce toxins which deter their predators, others do not. The toxins which are produced in these frogs vary with different species. Were poison-producing glands part of the original design for this group? If so, why don't all members have them? Since parotid glands would have been present in the ancestors of the group, why couldn't natural selection operating over millions of years simply make them bigger in some species and vary their content?

Most of the frogs of the Family Bufonidae have adapted to terrestrial habitats but some inhabit aquatic environments and others have adapted to life in trees. These species include the true toads and the very colorful (but poisonous) harlequin frogs. While most species of Hylidae live in trees, some are burrowing. Burrowing species living in arid areas may form a cocoon around themselves to protect themselves from drying out. Some frogs of the family Dendrobatidae are poisonous, one is foul smelling, and many are not toxic.

 

IF ANATOMICAL STRUCTURES WERE DIVINELY DESIGNED, WHY HAVE SO MANY FROGS CHANGED THEM?

It could be argued that a reworking of an anatomical structure requires design. Some frogs of the families Leiopelmatidae and Pipidae possess cartilaginous rods known as the postpubis. In most frogs, this structure fuses with the hips and is not visible as a discreet structure. In the frog Ascaphus of the family Ascaphidae, these rods support a tail-like structure developing from the cloaca which males use as an intromittent organ. While it could be argued that a complex structure that allows internal fertilization is designed, why does it appear as a modification of structures that other frogs use for other purposes? Since some experts combine the families Leiopelmatidae and Ascaphidae, the evolution of this structure could have occurred within a family (Mattison, 1998; Pugh 1998).

The shape of the shoulder girdle often varies within frog families. The shape of vertebrae varies between and within frog families. The calcaneus and astragalus are fused in the two species of the family Pelodytidae. Frogs of the family Pipidae lack tongues and most (except Pipa) possess clawlike structures at the tips of their digits. Frogs of the family Bufonidae lack teeth and possess a ovarian remnant which develops on one end of the laval male testes. Adults of the family Myobatrachidae retain their notochords as adults. Within the family Hylidae, frogs can vary in the formation of elaborate bony projections from skull bones, the presence of teeth on the mandible (absent in all except the species Gastrotheca guentheri), some move by walking slowly unlike the strong jumping ability displayed by most, some have poison glands, and some possess the only lipid glands known in amphibians whose products are spread over the body to prevent dessication. The absence of a sternum is known in two frog families and another frog genus. In the family Anthroleptidae, males develop long integumentary filaments superficially resembling hairs to give them enhanced respiratory abilities while they care for the eggs (Pough, 1998).

IS INTELLIGENT DESIGN DESCRIBE A DESIGN WHICH IS ACTUALLY INTELLIGENT?

Most of the variations given above occur within families, a taxonomic group that many to most modern creationists would equate with their term "kind". Creationists accept that evolution can occur within a "kind". If this variation can evolve (and, as the previous paragraphs have illustrated, variation within a frog family can be significant) then what aspects of the organism are so complex that they could not evolve? If they are designed, then why didn't the original designs work? Why are so many designs necessary? Why did different groups have to alter the original design in similar ways? For example, if it were "intelligent" to design terrestrial frogs and arboreal frogs, frogs with tadpoles and frogs which undergo direct development, why aren't there discrete groups of frogs which only have those qualities? Would it be intelligent to require direct divine action to fix an aspect of frog design, only to have to repeat the same repair in additional frog groups?

In Newton's day, there was a philosophical question about design that went something like this: Which type of watch gives evidence of a more Intelligent Designer--one which can run on its own, or one that requires that the Designer continually turns the gears and pushes the hands to the correct position?

BEAUTY AND THE CHOICE YOU DON'T HAVE TO MAKE

If evolution is the natural process through which the natural world changes, you are free to believe that these changes fulfill the will of God, whatever you perceive God to be. The majority of believers in the world feel that God can work through weather, earthquakes, astronomical events, disease, normal physiology, etc. even though they accept that there are natural processes which are the immediate determinants of these events (low pressure systems, bacteria, a comet's orbit, pressure between plates of the earth's crust, etc.) In the Dark Ages, many believers were told that they had to choose between a divine miracle and a godless natural processs to explain an event in the natural world. Modern creationists and design advocates approach the natural world in a similar way.

Here's a problem however. If creationists and design advocates feel that the differences between related species can evolve through natural mechanisms, then evolution is responsible for the variations in color and song that we fight so beautiful in frogs. Do creationists feel that evolution is responsible for the beauty of this world?

yellow frogtreefrog

I think that most modern believers feel that God can work through natural processes, including evolution. In approaching the evolution/creationism/design debate, you do not have to choose between religion and science, only ignorance and understanding. One and only one of these models is supported by the evidence by those who actually study frogs.