Mẫu descriptive essay cause and effect

Đề bài: Why Our Ancestors Started to Walk on Two Feet
Around six million years ago, our ancestors began to walk on two feet
instead of traveling on four feet. Bipedalism, the act of moving about on two
rear limbs or legs, has been seen in various species throughout evolution. Did it
make those species smarter? Apparently not. However, in this essay, the task
will be exploring the various reasons why our ancestors started being bipedal
beings instead of the usual four-limbed walkers. The most accepted theory is
that climate change prompted our early selves to stand up to see beyond the tall
grass of the savanna for predators, to run away faster from attackers, and also to
walk further distances easier. Another theory suggests that we initiated the
process of being bipedal in order to walk between trees easier and to collect
food in treetops with greater ease, such as orangutans sometimes do. And yet
other theories suggest that walking on two legs came about because new
hunting strategies, and also an evolutionary adaptation to dealing with African
heat.
Going into detail about the dominant theory of why we became bipedal,
climate seems like the most reasonable factor at this point. According to the
BBC, “Bipedalism made more sense in an environment where trees were rare.
Standing up allows you to see over long grass to scan for predators and prey.
The ancestral humans who were best at standing would have been more likely
to survive and pass on their genes, so it is easy to imagine how natural selection
could have resulted in a gradual shift from simply standing up briefly to
permanently moving around in an upright posture” (Gray, Richard). However,
this theory has issues, as the climate changed dramatically in Africa over the
course of eons. Though savannas were created, they sometimes reverted back
into forested areas. It is possible that our ancestors started to walk on two legs
and never looked back, despite climate change transforming the landscape over
time again into a lush forest and back into a savanna.


Another theory posits that we started to walk on two legs in trees, much like

our cousins, the orangutan. According to a report called Origin of Human
Bipedalism As an Adaptation for Locomotion on Flexible Branches,
“Orangutans react to branch flexibility like humans running on springy tracks,
by increasing knee and hip extension, whereas all other primatesdothe reverse.
Human bipedalism is thus less an innovation than an exploitation of a locomotor
behavior retained from the common great ape ancestor” (Thorpe, S. K. S., et
al.). So, this theory says that being bipedal is a much more ancient practice than
we commonly think, and that its use started due to our ancestors vying for more
ways to gather food and to traverse the forest canopy.
Though our ancestors did not start hunting with weapons until much
after we started to walk on two feet, some researchers say that is one of the
main reasons we took to being bipedal more readily. Though this theory was
adopted by Charles Darwin initially, it has been proved to be a probable part of
the process of humans becoming bipedal. For sure, standing and walking on two
feet lends itself to more flexibility and ability to throw weapons at predators or
prey (Gray, Richard).
Finally, some theories point to adapting to heat as one of the reasons we
started to walk on our hind legs. Stated by a report named Human locomotion
and heat loss: an evolutionary perspective, “…because bipedal hominins are
necessarily slow runners, early hominins in open habitats likely benefited from
improved abilities to dump heat in order to forage safely during times of peak
heat when predators were unable to hunt them. Endurance running capabilities
evolved later, probably as adaptations for scavenging and then hunting. If so,
then there would have been strong selection for heat-loss mechanisms,
especially sweating, to persistence hunt, in which hunters combine endurance
running and tracking to drive their prey into hyperthermia” (Lieberman, D.E.).


Thus, our ancient ancestors developed mechanisms to reduce physical heat to
survive and perform tasks more efficiently.

Looking at all of these reasons, it is not difficult to assume that it was
perhaps a combination of these factors that made our prehistoric selves stand
upright. Besides climate change, wanting to traverse treetops with greater ease,
new hunting strategies, and heat adaptation, there might be numerous other
major reasons to consider. We may never know for sure, but we do know that
becoming bipedal aided us in evolving into who we are today
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