The loss of a 3 year old child 3 million years ago is giving new insight into the early development of evolutionary change that resulted in humans.
Although scientists have found bones and bone fragments of children from this and other species of human predecessors, and a few skeletons, the discovery represents one of the most complete individuals ever recovered and by far the oldest. Bones of young children are so small and soft that few survive.
Remains of children are especially valued by anthropologists because they give critical insight into development.
"We've never had anything so complete before," said Donald C. Johanson of Arizona State University, who discovered Lucy. "This is going to allow us to have extraordinary insight into the growth and development of this species."
...The discovery of a child also allows scientists to begin to study how the species developed. The child's brain size suggests that the species' brain matured relatively slowly.
"If the brain was developing slower, as in humans or similar to what you see in humans, here might have also been the beginnings of behavioral shifts towards being more human," Zeresenay said.
In this case, the find is especially exciting because this particular species is thought to be the mid point in the evolutionary change between ape and human.
The youngster's fossilized remains, the first to fully exhibit the mixed ape-human characteristics in a child, were found in the remote, harsh Dikika area of northeastern Ethiopia in 2000 when an expedition member spotted the face of the skull poking out from a steep dusty hillside....
Where the child's throat once was, Zeresenay found a hyoid bone, which is located in the voice box and supports muscles of the tongue and throat. It is the first time that bone has been discovered in such an old fossil of a human predecessor. It appears more primitive than a human hyoid and more like those in apes, suggesting that the 1 1/2 -foot toddler sounded more like a chimp than a human.
"If you imagine how this child would have sounded if it was crying out for its mother, its cry would appeal more to chimp ears than to human ears," said Fred Spoor of University College London, who is helping to study the remains. "Even though it's a very early human ancestor, she would sound more apelike than humanlike."
The child's lower limbs confirm earlier findings that the species walked upright like humans. But the shoulder blades resemble a young gorilla's. Along with the long arms, curved fingers and inner-ear cavity, the bones provide new evidence supporting those who believe the creatures may have still climbed trees as well.
"I see this species as foraging bipeds -- walking on two feet but climbing trees when necessary, such as to forage for food," Zeresenay said, adding that more research will be needed to be certain of that controversial conclusion.
The lower body that walks upright with an upper body that is suited for climbing trees along with the slow-brain development all indicate that we are looking at what appears to be a transitional species when viewed from our perspective.
But how does this happen specifically? One old idea has been revived and is gaining support as H. Allen Orr explains in his book review of Sean Carroll's “Endless Forms Most Beautiful” in the New Yorker
Evo devo, punk-band-inspired slang for “evolutionary developmental biology,” holds the promise of a radical new way to look at life’s evolution. Its central thesis is simple. Organisms show two kinds of change through time: during the lifetime of a single animal (you don’t look much like the egg you started as) and during the evolutionary history of a biological lineage (you don’t look much like your three-and-a-half-billion-year-old ancestor). Evo devo’s key claim is that the first kind of change can provide important insights into the second.
The notion that there’s a connection between evolution and development—the growth of an organism from a single cell, through an embryo, to an adult—is both natural and old. It was especially popular in the nineteenth century; Ernst Haeckel’s law of recapitulation—the proposition that “ontogeny recapitulates phylogeny”—captured the spirit of the age.
The theory holds that all the basic elements that make all creatures of a certain type exists within their DNA. And associated with each gene is a "switch" which either turns the gene on or off for that creature.
Not all our DNA is given over to genes, though; there are also long stretches of so-called noncoding DNA, which sit between genes. So as we move along a string of DNA, we might first come to a gene, and then to a stretch of noncoding DNA, and then to another gene, and so on. Despite the relative fame of genes and the relative obscurity of noncoding DNA, more than ninety-five per cent of our DNA is noncoding....
Evo devo’s first big finding is that all animals are built from essentially the same genes. In the past few decades, biologists collected thousands of genetic mutations that disrupt the normal course of an embryo’s development. (Most of this work involved the humble fruit fly.) By characterizing how particular mutations derail the growth of embryos, biologists were able to figure out which genes control key steps in animal development. In one of the biggest breakthroughs, biologists worked out how fruit-fly embryos decide which of their ends should be the head, which the tail, and what should go between. Part of the answer involves what are called Hox genes. Different Hox genes get expressed in different parts of a fly’s body, and each Hox gene tells that body part what appendage it should grow. A Hox gene expressed in the head, for example, might tell the head to grow antennae, while a Hox gene expressed in the body might tell the body to grow legs. If you tinker experimentally with Hox genes, you get the stuff of B movies: mutant flies, for example, that have legs, not antennae, growing out of their heads.
But the truly surprising thing about Hox genes turns out to be evolutionary. All animals have Hox genes, and nearly all animals use their Hox genes to determine which appendage should go where along the axis that runs from head to tail. Given that the major animal groups, among them arthropods (now including insects), mollusks (snails), annelids (worms), and chordates (human beings), were in place at the start of the Cambrian period, Hox genes must be at least half a billion years old.
What’s more, plenty of important genes turn out to be this old.
Hox genes along with other genes have been dubbed "took-kit" genes because together these genes are necessary to lay out the basic design of an animal. But many of these "tool-kit" genes are generic
The same gene, for example, that triggers eye development in fruit flies also triggers eye development in mice. Indeed, genetically engineered flies will happily build eyes if supplied only with the mouse gene. (They build fly eyes, not mouse eyes.)
Proponents of Evo Devo say that because of all this, evolution's primary mechanism is the switch configurations; which is how you can see something like an animal with the upper body of a gorilla that also walks upright.
Evo devo’s emphasis on switch-throwing represents a profound departure from evolutionary biology’s long obsession with genes. Animal evolution works not so much by changing genes, Carroll maintains, but by changing when and where a conserved set of genes is expressed. In the lingo, evolution is regulatory (involving patterns of gene expression), not structural (involving the precise proteins coded by genes). You can think of this distinction in terms of those light switches. Imagine two houses that were built from the same blueprint and that were initially identical. But now, years later, we notice that they look different at night. In one, the first floor is bright and the second floor dim; in the other, the opposite is true. This difference could have arisen in two ways. Maybe the houses now feature different lights; the owners of the first house might, for instance, have replaced bulbs on the first floor with brighter ones; the other owners might have done the same thing on the second floor. But maybe—and this is the evo-devo picture—the owners of the first house have switched on most first-floor lights and switched off most second-floor lights; the owners of the second house might have done the reverse. Evo devo tells us that animal species look different not because their structural bits and pieces have changed but because they switch on and off the same old bits and pieces in different combinations. Roughly speaking, then, penguins and people differ for the same reason your pancreas and eye differ: they’re expressing different genes.
In the evo-devo view, animals still adapt to their environments by Darwin’s natural selection, but adaptation involves a different kind of genetic change from what biologists used to assume. As a result, evolutionists may need to abandon what Carroll calls their “protein-centric perspective” and look instead to the poorly understood noncoding DNA that sits between genes. Evo devo’s advocates argue that switch-throwing also makes good evolutionary sense. If a gene itself were to change, its altered protein would show up in every tissue that expresses the gene, and the new protein probably wouldn’t work well in some tissue. If a switch were to change, though, the same old protein would show up in all the usual tissues except one. This kind of “modular” change is far less likely to wreak havoc on an organism and so is much more likely to be used by evolution. Indeed, evolution likes modular change for the same reason engineers do: while changing all the metal in an airplane to some new alloy would be asking for trouble, switching the metal in the bathroom door handle to the new alloy would probably go fine.
Perhaps the discovery of "baby Lucy" will help to prove or disprove the theories put forth by the Evo Devo group.
