Topics:
Macroevolution and related topics
Macroevolution refers to large-scale evolution like rise of a new species or death of another. Only in the fossil record can we watch evolution for long enough to be able to detect large-scale patterns. But there are quite a few wrong ideas about rise of species.Humans evolved from monkeys but not from the monkeys we see at the zoo. They evolved from a different species of monkeys now extinct.
How do we know when a new species came into existence?
The answer to this lies in the DNA of every species. A certain number of genes can be taken to study this. First of all, we must learn what a certain species branched out into. The split into plants and animals can be taken as an example. Then by comparing the position of genes and using advanced interpretation techniques, the biologists give us the approximate date. So that's about the dating system which is used to find when a new species came about.
Now let us see what the mechanisms of macroevolution are. Basically, it is known as speciation.There are two widely known theories for this:
The rise of species in this case is due to geographical separation. For example, if a part of a population wandered far away and got stranded, they would have to adapt to that environment, and over time, they evolve into a new species due to natural selection and other related phenomena.
At any point the geographic ranges of the populations may again change. The geographically separated populations may move together, and their individual members mingle and meet. What will happen now probably depends on how much the two populations have evolved apart. If they are still much the same, their members may mate together and the two populations simply fuse to become a single population again. But if they have become very different, they might not be able to interbreed; the two populations would then have become two species. This is in short, allopatric speciation.
2) Sympatric speciation -It is a rather confusing form of natural selection applied on a population or some factor that leads to them becoming reproductively different. When they become reproductively different, they cannot mate with each other and thus will gradually diverge into two species. The first stage is for natural selection to favour the evolution of two forms within the continuous range of a species. If the force of natural selection is strong enough, two forms could evolve. If the process continued far enough the two forms might diverge sufficiently to look like different species.
If the offspring of crosses between individuals of the same form survived better than the offspring of crosses between the different forms, natural selection would favour a reduction of interbreeding between the two forms. Speciation would then result from divergence followed by selection to reduce interbreeding. Quite a handful don't you think?
But not much has been found out about this, and nobody can be sure even now about how speciation occurs. But the two theories discussed above are very common. Allopatric speciation seems to be more sensible than the other, but there are cases which might make one reconsider their views. That was about the birth of species, but what about extinction?
It is the final and ultimate end of a species. There is no specific way by which this can occur. The destruction of the habitat where a species lives could finish it off. Killing of individuals of the species could also trigger off such extinction or even the rise of a dominant species might lead to the extinction of another. There are also events known as mass extinctions. The wipeout of a number of major animal or plant groups is known as mass extinction. The death of dinosaurs is an example.
Humans are responsible for endangering many species and nearly destroying them by clearing forests and polluting the environment. Hunting and poaching have not helped the cause. Creatures like the dodo have become extinct due to our foolishness. The extinction of creatures upsets the food chain and night lead to extinction of others as well. We must try and protect our environment as it is our only hope.
Let us round off our discussion about the fundamentals of evolution by discussing the rates of evolution.
How fast does evolutionary change occur? Like most other things in evolution, there are many theories to explain this concept. One is the punctuated equilibrium theory and the other theory says that evolution takesplace gradually.
The punctuated equilibrium theory says that species remain unchanged for long stretches of time and then are quickly replaced by new species. Gould and Eldredge proposed it.
For
example, in Jurassic brachiopods of the genus Kutchithyris, K. acutiplicata
appears below another species, K. euryptycha. Both species were common and covered
a wide geographical area. In just one small locality an approximately 1.25m
sedimentary layer with these fossils is found. In the narrow layer that separates
the two species, both species are found along with transitional forms. In other
localities there is a sharp transition.This debate continues to rage on and
each new fossil find seems to add fuel to the fire.
After reading through all these pages, you finally have a good idea about evolutionary theories and concepts.
