EVOLUTION
OF SEX
According to the various research and surveys It is generally accepted that Isogamy ( Isogamous
reproduction is a kind of sexual reproduction in which both the gametes
involved in fertilisation have similar morphology. They can not be
distinguished as male or female )
was ancestral to Anisogamy ( when two
sexually reproduction parents produce gametes of different size and the
organism is anisogamous. The sexes of parents are defined on the basis of
gametes produced by them ) and
evolved several times independently in different group of Eukaryotes { any cell or organism that
possesses a clearly defined nucleus. The eukaryotic cell has a membrane that
surrounds the nucleus, in which the well defined chromosomes – ( Bodies containing
the hereditary material ) are located.}
including Protists ( any of a diverse taxonomic group and especially a kingdom
of eukaryotic organism that are unicellular and sometimes colonial or less
often multicellular and that typically
include the protozoans, most algae, and often some fungi ) algae, plants and animals. The evolution of
anisogamy is synonymous with the origin
of Male and the origin of Female. It is the first step towards dimorphism and
influenced the evolution of various sex differences.
The original form of sex was external fertilisation. Internal fertilisation or sex
as we know it, evolved later and became dominant for vertebrates after their
emergence on land.
If
we observe Evolution of sex is everywhere it means it can be found in birds,
bees, animals but sex is also in vegetation, plants, and its fungi and its
basically every kind of complex organism and sexual reproduction has been
around so long that the common ancestor of all complex life probably had sex of
some kind.
It
might be said which living thing was the
very first to arrive at the totally revolutionary process that is sexual reproduction , but we can follow the history
of how and why sex became a thing and some of the earliest animals that we all know did it .
Let’s discuss about the time before there ever was sex on earth – around 2 to 2.5
billion years ago the planet was home to simple, single celled organism like bacteria ( a member of a large group of unicellular
microorganism which have cell walls but lack of organelles and an organised
nucleus ) and archaea
( microorganism
which are similar to bacteria in size and simplicity of structure but radically
different in molecular organisation ) and their main mode of
reproduction was and still is to basically clone themselves .
They
duplicate their single chromosome
and then split it into with each offspring getting a copy of the original that
mean the offspring are always generally identical to their parents and for a
long time probably billions of years that worked out just fine, now bacteria do
have ways of swapping small amount of DNA among themselves and of picking up
DNA from their environment which changes their genetic makeup , But sexual reproduction
in the strictest sense where offspring get an equal share of two parents DNA –
that -- show up until well into the Proterzoic
Eon ( earlier
life ) and
its in there somewhere between 2 billion years ago , that a brand new kind of
thing evolved. Today it is known as the “Last
Eukaryotic common Ancestor” or LECA –
You
can think of it as the great – great, great grandparents of all the Eukaryotes
that are alive today , that includes
everything that has a nucleus in its cells so all the plants , all the animals,
all the fungi, all the Protists ( a single-celled organism of the kingdom protista . such as a
protozoan or simple alga ) – basically every living things that you have ever seen with
your naked eyes.
LECA
is not really a specific thing that have been found in the fossil record , we
don’t know exactly what it was but we can infer its existence because all
eukaryotes that are alive today are thought to have descendants from a single
eukaryotic species – so LECA not the
very first eukaryote- it’s the most distant common ancestor of all modern eukaryotes.
The
ones we know today and we can infer what characteristics LECA had based on what
all eukaryotes today have in common and one thing we all have in common is sex.
Now
what is the meaning of sex in this context. When the discussion is about sexual reproduction, It is about cells
that divide their chromosomes into matching sets, duplicate those sets and then
separate them out into many new cells those new cells with just one set of
chromosomes are gametes and they are looking for compatible gametes from
another parents that have their own set of chromosomes.
Since
each parent has a lightly different
combination of genes in its chromosomes,
when their gametes combing the offspring that they produce will be different,
every time this whole process probably took a lot of evolutionary time to master and it may or may not have been
perfected by LECA’s time. But nobody really know what LECA was.
So
where is the earliest evidence of sex ? We do have some pretty old fossils of
eukaryotes , including red algae that are about 1.6 billion year old but red
algae reproduce by using tiny spares and we have not detected any direct
evidence of those in fossils of that age .
Human
and animals however are a little more obvious about our
mating habits and the oldest fossil we
have that is interpreted as direct evidence of sex is of an animal actually
many animals they are known as funisia
is ( a genus
of animal containing the single species F. dorothea, a extinct sedentary animal
resembling an upright worm from the Ediacaran biota ) and their fossils don’t
look really scandalous or anything.
In
fact until scientists figured out that they were a new type of animals their fossils
were mistaken, they date to the Ediacaren period at the end of the proterozoic Eon
( The Proterozoic Eon is the most recent division of the Precambrian ) about 565 million years
ago . Funisia lived in huge colonies that looked like a tiny underwater bamboo forest but it
was neither plant nor algae, it seems to be most closely related to either
sponges or soft corals but we are not sure, so if we can barely tell this thing
is an animals, why do everyone think
that it had sex ?
When
it comes down to the size , age and arrangement of its fossils , fossils of
funisia are often found in groups of individuals that are all about the same
size and this kind of distribution is very similar to how some modern animals
are arranged, specifically Oysters.
Oysters reproduce by broadcasting their gambles into the ocean. The gambles
join up and start to develop while floating around in the water but as they
start to change into their adult forms, they settle to the sea floor and that
result in big groups of oysters that are all about the same age and size , a
lot like funisia but here is an interesting little wrinkle ,
we
think that funisia might have been able
to reproduce a sexually too, that is because some of them fossilized when they
were in the process of budding sprouting little buds off the main stem that would become clones of the
original, this is a technique that is still used today by fresh water animals
called Hydras. So because we have
found both budded offspring and synchronised groups.
We
think funisia could reproduce both sexually
and asexually
( in a way
that relates to reproduction without the fusion of gametes ) Which actually is
what Hydra so too . But why was the development of sex such a big deal in the
first place ? and if
sexual reproduction is so great , then why could funisia,
hydra and other animals still reproduce asexually?
Well
sexual reproduction creates new combination of
genes , which allows for new
variations in the offspring and some variations are more successful than others
that is the basic idea of natural selection and since the world is always
changing, it can help a lot if you can change too and quickly. But if your
environment is not changing much then there is not much selective pressure in
which case mixing up your genes
might not be such a great idea.
They are just keeping their option open and that is cool so for sex to have become a thing when it did actually makes sense , when you think about it for funisia , sex would have come in very handy in the Ediacaran, when ecosystems were suddenly becoming more complex than they ever had been before, so all of us eukaryotes living today owe LECA, FUNISIA and their descendants a debt of thanks for the evolutionary breakthrough that they discovered and perfected in the form of sex.
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https://www.sciencedirect.com
https://www.simplilearn.com
https://pbs.org
https://en.wikipedia.org
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This article / blog is for information purpose only, but by no means it is a complete and exhaustive explanation on the whole topic. This blog is intended for individual of 18 years and above. This blog/site never answer any personal question or provide any sex advice, nor it’s intended as a substitute for therapy.
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Informative.
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