Evidence of evolution: embryology | Evolution | Middle school biology | Khan Academy

Summary

This script explores the fascinating world of embryonic development, revealing that humans, like many vertebrates, once possessed a tail during our early stages as embryos. As we grow, these structures transform into the tailbone, part of our spine. The script delves into homologous features, such as pharyngeal arches, which are present in all vertebrate embryos and demonstrate our evolutionary connections. It highlights how studying these features in embryos can reveal similarities and relationships among species, even when they are not apparent in adulthood.

Takeaways

• 🤔 Humans once had a tail-like structure during the early stages of embryonic development, which eventually forms the tailbone.
• 🍰 The concept of a tail is humorously introduced as a helpful appendage for various tasks like swinging to school or holding an umbrella.
• 👶 The tail structure in human embryos is not unique and is shared by the embryos of many vertebrates, indicating a common evolutionary origin.
• 🔍 Scientists refer to such shared embryonic features as 'homologous features', which can help determine the relatedness of different species.
• 🧬 Studying embryos is crucial for identifying similarities among species that may not be apparent in their adult forms.
• 🐘 The physical development of an elephant embryo is highlighted, showing the significant changes from a tiny weight to its birth weight of about 100 kilograms.
• 🐠 Pharyngeal arches, also known as gill arches, are present in all vertebrate embryos and transform into different structures like ears and jaws as they develop.
• 🧬 The presence of pharyngeal arches in vertebrate embryos provides evidence of a shared common ancestor among all vertebrates.
• 🦜 In more distantly related species, homologous features are fewer and less apparent, both during embryonic development and after birth.
• 🦓 Closely related species tend to share more homologous features during their development and into adulthood.
• 🧐 The study of homologous features in embryos is a key method for scientists to understand the evolutionary relationships between different species.

Q & A

What is an embryo?

An embryo is an organism in the earliest stages of development before it is born or hatched.

Why might someone wish for a tail?

One might wish for a tail to swing their way to school, bake pies more efficiently, or carry an umbrella while keeping their hands free.

Do humans have a tail at any point in their development?

Yes, early in the growth of a human embryo, there is a tail-like structure that eventually forms the tailbone, which is part of the spine.

At what stage of development does the human tail-like structure disappear?

The tail-like structure in a human embryo is not visible at all by the time the embryo is eight weeks old.

Which other vertebrates share the trait of having tails as embryos?

Vertebrates such as monkeys, mice, turtles, and chickens also have tails as embryos, indicating a common evolutionary trait.

What are homologous features in the context of embryonic development?

Homologous features are structurally similar anatomical features that two species share, indicating that they share a common ancestor.

How do scientists use homologous features to understand species relationships?

Identifying homologous features helps scientists figure out how different species are related to each other and how they evolved.

Why is studying embryos important for finding similarities between species?

Studying embryos is helpful because it allows scientists to find similarities that might not be visible once the animals are born and grow up.

What changes do embryos undergo during their development?

During development, embryos undergo physical changes where some structures become visible and others disappear, such as the tail-like structure and pharyngeal arches.

What are pharyngeal arches, and why are they significant in embryonic development?

Pharyngeal arches, also known as gill arches, are structures found in all vertebrate embryos early in development. They change structure and help form ears and jaws in elephants and other mammals, providing evidence of a common ancestor.

How does the development of pharyngeal arches differ between fish and mammals?

In fish, pharyngeal arches develop into gill structures, while in humans and other mammals, they develop into ear and jaw structures.

What does the study of homologous features in embryos reveal about human evolution?

Studying homologous features in embryos reveals that humans are related to many tail-using creatures because of shared evolutionary history.