From Discovering Intelligent Design: My How You've Changed
Excerpted from Discovering Intelligent Design, by Gary Kemper, Hallie Kemper, and Casey Luskin; Chapter 10, "Life Is Complicated":
One of the most amazing examples of animal complexity is insect growth and development. As they progress to maturity, insects undergo one of three processes: ametabolism, hemimetabolism, and holometabolism.
Ametabolism is the simplest of the three types of development and is only used by a few insects. In this process, young insects (called nymphs) have essentially the same body plan as the adult. After emerging from the egg, the insect undergoes only changes in size, but not shape, as it matures. Silverfish, for example, develop through ametabolism.
Ametabolous development: egg > miniature adult (nymph) > adult
The other two methods of development are more complex, in that they involve metamorphosis.
A process of pre-programmed development where an organism changes its body plan.
In hemimetabolism (partial metamorphosis) the insect undergoes gradual, progressive change in form. However in these insects, this change occurs through a process of instars (periods of growth and change) and molts (the shedding of skin).
After entering the nymph stage, the insect begins to feed. With each subsequent instar and molt, the nymph gradually changes into its adult form until it reaches maturity and is able to breed. Dragonflies, grasshoppers, and crickets develop through hemimetabolism.
Hemimetabolous development: egg > non-feeding larva > nymph > adult
Holometabolism (complete metamorphosis) is the most common and complicated form of insect maturation. The diverse group that undergoes this type of process includes butterflies, moths, beetles, fleas, bees, ants, and many kinds of flies.
A holometabolous insect emerges from the egg as a hungry larva -- consuming anything it can while going through multiple instars and molts. The larva may have a simplified body plan, with reduced legs and eyes, and little distinction between major body segments. Its job is to eat and grow. It molts to accommodate its increasing size, but does not change form nor develop adult structures.
At the right time, larval growth slows and stops, and the organism becomes a pupa.
- In butterfly species the exterior of the pupa forms a hardened shell called a chrysalis.
- Moths and many other holometabolous insects spin a silken case for their pupa called a cocoon.
- Other insects develop as a pupa inside the last larval skin.
Metamorphosis now occurs as the pupa undergoes a complete transformation of its body plan. Inside the pupa, the insect liquefies itself and restructures most of its body to emerge later as a fully formed adult, often with wings. By breaking down much of its body to supply the building materials for the adult form, the creature is then only alive in the form of a "soup."
The dissolved remnants of its tissues supply raw materials to build the adult form. Additionally, new tissues grow from cells set aside early in development.
After the transformation is complete, developmental hormones signal the insect to emerge from its confinement. For many insects, the force they must exert to emerge and pump fluids into their wings is essential for their development.
Holometabolous development: egg > feeding larva > pupa (metamorphosis) > adult
Without expending that effort, they would be deformed.
It is exceedingly difficult to understand the origin of holometabolism in Darwinian evolutionary terms. Neither the larval nor the pupal stage is capable of reproduction -- only the adult is. In particular, the pupal stage is an all-or-nothing proposition. It must complete the process and become an adult, or it will die without ever reproducing.
The liquefied organism must be completely rebuilt. For this to occur, large amounts of information -- encoding the larval body plan, the mechanisms of transformation during metamorphosis, and the adult body plan -- must exist before the larva enters this stage. An organism could not survive complete metamorphosis unless the entire process was fully programmed from the beginning. Such a large jump in complexity requires forethought and planning -- things that don't exist in Darwinian evolution. As one evolutionary entomologist acknowledges:
... the biggest head-scratcher in evolutionary biology would have to be the origin of the holometabolous insect larva.
But from an ID perspective, metamorphosis is easy to understand: it arose, evidently, by planning and foresight. An intelligent agent could produce the information to program the entire life cycle of such an organism, allowing it to undergo a radical transformation like this. Only a goal-oriented process like intelligent design can explain the mystery of holometabolism.
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