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We first have to accept that in multicellular organisms developmental changes from gametes through to the adult are obligatory. The modifications in body structure are gradual in many plants and animals, but in some, like amphibians and insects, they can be abrupt. Even though such gradual transformations occur in mammals, for example, metamorphosis is normally reserved to describe abrupt changes that occur after birth or hatching. A classical example is the monarch butterfly.
The monarch goes through four radically different stages:- the eggs, laid during spring and summer, hatch into worm-like larvae (caterpillars), which feed on milkweed leaves. They grow quickly, storing energy and nutrients for the non-feeding pupal stage. The caterpillar eventually builds a cocoon around itself to form the pupa (chrysalis). Under hormonal control its body mostly disintegrates and then reforms leading to the development of the butterfly, which emerges from the cocoon, flies away and migrates feeding on a variety of flowers (nectar).
Creationists claim that evolution cannot explain such transformations, arguing that metamorphosis couldn't evolve multiple stages since each organism must be able to reproduce and be superior, in some sense, to its ancestors.
Creationists miss, or perhaps intentionally avoid, important points. The first has already been stated: that development of multicellular body plans though various stages cannot be avoided, even if these 'morph' into one another, so it is likely that the original state for insects was gradual change and not metamorphosis. At some point, instead of developing in a steady fashion, they began to develop in bursts.
So it's likely that full metamorphosis arose because the first insects that evolved four life stages embryo, larva, pupa and imago outcompeted those that developed gradually through just three stages embryo, nymph, and adult without a pupal stage.
Another point creationists miss is that there are definite advantages to full metamorphosis: it allows for two life forms of the same organism to inhabit the same environment, yet to avoid competition with one another by exploiting different resources the caterpillar eats leaves and the butterfly consumes nectar. Each stage requires that the embryo or larval form has a source of food, and that explains why caterpillars are important as they can consume large amounts of leaves for very rapid growth. Also metamorphosis allows the organism, like the monarch butterfly, to migrate, mate, lay eggs and overwinter (for this, the larval form would be most inefficient!).
The Creation Science article asks why a larva should evolve in the first place, "because it cannot reproduce?". Of course, without the larval stage there would be insufficient food for rapid growth and ultimate formation of the butterfly. Moreover, even though the larvae can't reproduce, they are still subject to natural selection, not only ensuring that this essential developmental stage is free of less well performing individuals, but also providing raw material for evolution, such as the independent development of poisons and markings in the caterpillar.
The point is, perhaps contrary to popular belief, that evolution can occur at all levels of development right through to the reproducing adult. This is because natural selection and inherited genetic variation operate at every stage of development, even though it is only the adult that actually reproduces.
By switching on a certain set of genes, a particular metamorphic stage is produced, and because it is subject to natural selection (and genetic variation) it can evolve semi-independently of the other stages. Under the influence of hormones, another set of genes are then activated to produce a secondary phenotype, which in turn can evolve, depending on the success of the previous stages, of course. This explains how the various metamorphic stages can diversify to eventually look like completely different organisms.
There's nothing strange in this as gene switching is how our own bodies differentiate into various organs and tissues.
See The origins of insect metamorphosis
The monarch goes through four radically different stages:- the eggs, laid during spring and summer, hatch into worm-like larvae (caterpillars), which feed on milkweed leaves. They grow quickly, storing energy and nutrients for the non-feeding pupal stage. The caterpillar eventually builds a cocoon around itself to form the pupa (chrysalis). Under hormonal control its body mostly disintegrates and then reforms leading to the development of the butterfly, which emerges from the cocoon, flies away and migrates feeding on a variety of flowers (nectar).
Creationists claim that evolution cannot explain such transformations, arguing that metamorphosis couldn't evolve multiple stages since each organism must be able to reproduce and be superior, in some sense, to its ancestors.
What mutations could improve a larva? Certainly none that destroyed its nerves, muscles, eyes, brain, and most other organs, as occurs within a cocoon. So, even if a larva improved, it later ends up as "mush." From an evolutionary standpoint, liquefying complex organs is a giant step backwards. As Michael Pitman wryly noted,
Maggots will more or less dissolve themselves when developing into a fly. Was the process pre-programmed from the first production run? Or was the ancestral fly a dissolved maggot?
The millions of changes inside the thick liquid never produce something survivable or advantageous in the outside world until the adult completely forms. How did the genetic material for both larva and adult develop? Which came first, larva or adult? What mutations could transform a crawling larva into a flying monarch butterfly that can accurately navigate 3,000 miles using antennae and a tiny brain? Indeed, why should a larva evolve in the first place, because it cannot reproduce?
Based on metamorphosis alone, evolution "breaks down." In the Beginning: Compelling Evidence for Creation and the Flood - 37. Metamorphosis
Maggots will more or less dissolve themselves when developing into a fly. Was the process pre-programmed from the first production run? Or was the ancestral fly a dissolved maggot?
The millions of changes inside the thick liquid never produce something survivable or advantageous in the outside world until the adult completely forms. How did the genetic material for both larva and adult develop? Which came first, larva or adult? What mutations could transform a crawling larva into a flying monarch butterfly that can accurately navigate 3,000 miles using antennae and a tiny brain? Indeed, why should a larva evolve in the first place, because it cannot reproduce?
Based on metamorphosis alone, evolution "breaks down." In the Beginning: Compelling Evidence for Creation and the Flood - 37. Metamorphosis
Creationists miss, or perhaps intentionally avoid, important points. The first has already been stated: that development of multicellular body plans though various stages cannot be avoided, even if these 'morph' into one another, so it is likely that the original state for insects was gradual change and not metamorphosis. At some point, instead of developing in a steady fashion, they began to develop in bursts.
Growth patterns intermediate to full metamorphosis already exist, ranging from growth with no metamorphosis (such as with silverfish) to partial metamorphosis (as with true bugs and mayflies) complete metamorphosis with relatively little change in form (as with rove beetles), and the metamorphosis seen in butterflies. It is surely possible that similar intermediate stages could have developed over time to produce butterfly metamorphosis from an ancestor without metamorphosis. In fact, an explanation exists for the evolution of metamorphosis based largely on changes in the endocrinology of development. CB311: Butterfly metamorphosis
So it's likely that full metamorphosis arose because the first insects that evolved four life stages embryo, larva, pupa and imago outcompeted those that developed gradually through just three stages embryo, nymph, and adult without a pupal stage.
Another point creationists miss is that there are definite advantages to full metamorphosis: it allows for two life forms of the same organism to inhabit the same environment, yet to avoid competition with one another by exploiting different resources the caterpillar eats leaves and the butterfly consumes nectar. Each stage requires that the embryo or larval form has a source of food, and that explains why caterpillars are important as they can consume large amounts of leaves for very rapid growth. Also metamorphosis allows the organism, like the monarch butterfly, to migrate, mate, lay eggs and overwinter (for this, the larval form would be most inefficient!).
The Creation Science article asks why a larva should evolve in the first place, "because it cannot reproduce?". Of course, without the larval stage there would be insufficient food for rapid growth and ultimate formation of the butterfly. Moreover, even though the larvae can't reproduce, they are still subject to natural selection, not only ensuring that this essential developmental stage is free of less well performing individuals, but also providing raw material for evolution, such as the independent development of poisons and markings in the caterpillar.
The point is, perhaps contrary to popular belief, that evolution can occur at all levels of development right through to the reproducing adult. This is because natural selection and inherited genetic variation operate at every stage of development, even though it is only the adult that actually reproduces.
By switching on a certain set of genes, a particular metamorphic stage is produced, and because it is subject to natural selection (and genetic variation) it can evolve semi-independently of the other stages. Under the influence of hormones, another set of genes are then activated to produce a secondary phenotype, which in turn can evolve, depending on the success of the previous stages, of course. This explains how the various metamorphic stages can diversify to eventually look like completely different organisms.
There's nothing strange in this as gene switching is how our own bodies differentiate into various organs and tissues.
See The origins of insect metamorphosis
"Which came first, larva or adult?" Weeeell, as anyone with a cursory knowledge of insect biology knows, insects with complete metamorphosis are generally considered more derived. Do grasshoppers and bugs look like caterpillars? No? Go figure...![[serious]](/data/avatars/m/160/160873.jpg?1431539545){kind=avatar}
