What evolved first—a dexterous hand or an agile foot?

What evolved first--a dexterous hand or an agile foot?
Both monkey (Macaca fuscata, left) and human (Homo sapiens, right) have five physically independent fingers (top) and five toes (bottom), although the human foot is irregular in shape - human toe I is larger than the other toes, whereas monkey toes are similar in size. The fingers are represented independently (colour coded) in the primate somatosensory cortex (SI): I, red; II, orange; III, yellow; IV, green and V, blue. By contrast, the representations of the toes are fused, with the exception of the big toe in humans.

Resolving a long-standing mystery in human evolution, new research from the RIKEN Brain Science Institute indicates that early hominids developed finger dexterity and tool use ability before the development of bipedal locomotion.

Combining monkey and human behavior, brain imaging, and fossil evidence, a research team led by neurobiologist Dr. Atsushi Iriki and including Dr. Gen Suwa, an anthropologist from the University of Tokyo Museum, have overturned the common assumption that manual dexterity evolved after the development of bipedal locomotion freed hominid hands to use fingers for tool manipulation.

In a study published today in Philosophical Transactions of the Royal Society B, the researchers employed in humans and electrical recording from monkeys to locate the brain areas responsible for touch awareness in individual fingers and toes, called somatotopic maps. With these maps, the researchers confirmed previous studies showing that single digits in the hand and foot have discrete neural locations in both humans and monkeys.

However, the researchers found new evidence that monkey toes are combined into a single map, while human toes are also fused into a single map, but with the prominent exception of the big toe, which has its own map not seen in monkeys. These findings suggest that evolved dexterous fingers when they were still quadrupeds. Manual dexterity was not further expanded in , but humans gained fine finger control and a big toe to aid bipedal locomotion.

"In early quadruped hominids, finger control and tool use were feasible, while an independent adaptation involving the use of the big toe for functions like balance and walking occurred with bipedality," the authors explained.

The brain study was supported by analysis of the well-preserved hand and feet bones of a 4.4 million year-old skeleton of the quadruped hominid Ardipithecus ramidus, a species with hand dexterity that preceded the human-monkey lineage split.

The findings suggest that the parallel evolution of two-legged locomotion and in hands and in the human lineage were a consequence of adaptive pressures on ancestral quadrupeds for balance control by foot digits while retaining the critical capability for fine finger specialization.

"Evolution is not usually thought of as being accessible to study in the laboratory", stated Dr. Iriki, "but our new method of using comparative physiology to decipher ancestral traces of adaptation may allow us to re-examine Darwin's theories".

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Feet may be the key to hand evolution

More information: T. Hashimoto et al. Hand Before Foot? cortical somatotopy suggests manual dexterity is primitive and evolved independently of bipedalism, Philosophical Transactions of the Royal Society B, 2013. DOI: 10.1098/rstb.2012.0417
Provided by RIKEN
Citation: What evolved first—a dexterous hand or an agile foot? (2013, October 7) retrieved 23 October 2019 from https://phys.org/news/2013-10-evolved-firsta-dexterous-agile-foot.html
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User comments

Oct 07, 2013
Evidently, you need to study the mountain of evidence in support of natual selection by means of natural selection. Wanting to believe there is a supernatural force behind evolutionary processes does not make it so. "Believe" what you like, but don't mistake evidence supported by the scientific method with your belief system.

Oct 07, 2013
Belief in a Creator makes a lot more sense

No it doesn't. Unless you've been deluded. In which case it makes perfect sense that you think it makes perfect sense.

than believing in the failed non-scientific theory of evolution.

First, since evolution is based on fact, belief isn't a requirement.
Second, it's pathetic how you attempt to denounce the theory of evolution using colourful adjectives rather than reason.

Evolution is not science, no matter how many atheist scientists want to call it that. It is simply a try at doing away with the necessity of acknowledging God in nature and in all of science.

You may not realise this but there is no need to "try do away with god". He's simply not there. Not in nature or all of science is there this hint of god.

All of you atheists out there, please give me a "1".

At least the 1s are out of pity not hate...

Oct 07, 2013
Humans born without hands can use their feet for almost all tasks for which hands are normally used indicating that cognitive ability or predisposition can guide evolution of physical traits.
For example (women easily threading needle with feet)

Oct 07, 2013
Lol Verkle... It's all Magic!

Oct 08, 2013
Please show me this "mountain of evidence". I have not seen any real evidence supporting true evolution. Just theories that have never been reproduced as required by the scientific method. By the way, natural selection is not evolution.


Oct 08, 2013
The article pdf is free (ie not behind the usual Royal Society paywall)

Oct 08, 2013
God is simply not there. Not in nature or all of science is there this hint of God.

What a pity! Open your eyes to nature. There are comparatively few people in this world that believe like you.
Have you ever heard of the contemporary song "Look at the World" by John Sutter? The first lines are:

"Look at the world, everything all around us
Look at the world and marvel every day.
Look at the world: so many joys and wonders,
So many miracles along our way...."

Song lyrics. What a compelling argument. I have now accepted Jesus Christ as my lord and savior.

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