So what might be the cause of a population to split into two separate populations?
A population becomes separated by a geographic barrier, so when we say geographic barrier can be a
mountain range, a large canyon, a body of water, or large expanses of climatic differences.
And this might lead in reproductive isolation, resulting in two distinct species.
When a population is separated because of a geographic barrier those two subgroups of the
population are no longer able to reproduce together.
Why? Since the two groups are in their own unique ecosystems and each experience unique
pressures, they will adapt to their environment over time and can eventually become very
different from each other. This has the end result of speciation.
Ayan naexplain naman na kanina yung speciation.
The accumulation of differences between species or populations is called divergence.
For example, if snails slowly travel beyond a big canyon, the snails on one side will adapt to
that environment and the snails on the other side will do the same with their environment. On
one side, dark shells might hide them from predators. On the other side, bright coloring might
let them stay cool in strong sunlight. Over time, the two populations become more genetically
differentiated and might become two distinct species with independent geographic ranges.
environment presents challenges that only individuals with particular traits can meet.
Giraffes long neck is a perfect adaptation to the animal’s natural habitat. Clearly the giraffe
evolved this uncommon and helpful trait in order to reach those nourishing topmost leaves of
the trees and no other animal can reach them. That’s how natural selection works.
Gaya po ng sa giraffe kanina. The Traits possessed by organisms successful at
survival and reproduction are more likely to be transmitted to the next generation.
And these traits, will become more common in the next generation of giraffes
which would be long-necked.
Evidence from fossil record has led some scientist to propose that speciation need to occur gradually but
can occur in spurts. The theory of punctuated equilibrium states that evolutionary
change is characterised by short periods of rapid evolution followed by longer
periods of stasis in which no change occurs.
A species can evolve by only one of these, or by both. Scientists think that species
with a shorter evolution evolved mostly by punctuated equilibrium, and those with
a longer evolution evolved mostly by gradualism.
Gradualism is selection and variation that happens more gradually. Over a short
period of time it is hard to notice. Very gradually, over a long time, the population
changes. Change is slow, constant, and consistent.
species with more of the helpful trait survive, and a few more with less of the
helpful trait die.
change comes in spurts. There is a period of very little change, and then one or a
few huge changes occur, often through mutations in the genes of a few
individuals. Mutations are random changes in the DNA that are not inherited from
the previous generation, but are passed on to generations that follow. The species
changes very rapidly over a few generations, then settles down again to a period
of little change.
It is a state in which the frequency of an allele in a gene pool (such as a
population) does not change from generation to generation.
For a population to remain in genetic equilibrium natural selection must not occur. However, since
genetic equilibrium, is often disrupted, evolution occurs.
mutation, gene flow, small population, nonrandom mating, and natural selection
populations are usually not in genetic equilibrium. Instead, populations
tend to evolve: the allele frequencies of at least some of their genes
change from one generation to the next.
1. No mutation. No new alleles are generated by mutation, nor are genes duplicated or deleted.
2. Random mating. Organisms mate randomly with each other, with no preference for particular
genotypes.
3. No gene flow. Neither individuals nor their gametes (e.g., windborne pollen) enter or exit the
population.
4. Very large population size. The population should be effectively infinite in size.
5. No natural selection. All alleles confer equal fitness (make organisms equally likely to survive
and reproduce).
If any one of these assumptions is not met, the population will not be
in genetic equilibrium. Instead, it may evolve: allele frequencies may
change from one generation to the next.
Extinction of Species
Extinction of a particular animal or plant species occurs when there are no more individuals of that
species alive anywhere in the world - the species has died out. This is a natural part of evolution. It refers
to the normal extinction rate.
Mass extinction on the other hand is a widespread event that wipes out the majority (over 50%)
of living plants and animals.
What causes extinction?
an introduced species, pollution, population growth, and overconsumption. And the
destruction of natural habitats by human activities, such as cutting down forests and
converting land into fields for farming.
While mass extinctions were caused by extreme temperature changes, rising or falling sea
levels and catastrophic, one-off events like a huge volcano erupting.
Evolutionary adaptation, is the adjustment of organisms to their environment in order to
improve their chances at survival in that environment.
It can be a body part, body covering, body function, or behavior that increases an animal's
chances of survival in a particular place. Animals develop these adaptations over time to match
the environment where they live.
Classification and Evolution
Evolution and classification are two branches of biology. One deals with figuring out how
organisms evolve, how new species are born from old ones, and classification deals with
figuring out how closely related two species are.