Which evidence supports the theory that fish and mammals involved from the same ancestor? Did they both produce egg and sperm cells that must join in fertilization?

Answer 1

The theory of fish and mammals evolving from a common ancestor is supported by several lines of evidence, including:

1. Fossil evidence: Paleontologists have discovered fossil records that exhibit transitional characteristics between fish and early mammalian ancestors. These fossils display features like intermediate limb structures and skeletal features that suggest a gradual transition from fish-like creatures to land-dwelling mammals.

2. Genetic evidence: The comparison of DNA and genetic sequences among different species provides insights into their evolutionary relationships. By analyzing the genetic code, researchers have found similarities in the genes responsible for embryonic development and body plan formation between fish and mammals. These similarities suggest a common ancestry.

3. Developmental evidence: The embryonic development of fish and mammals shows certain shared characteristics, further supporting their shared ancestry. Both fish and mammals undergo similar stages of embryonic development, such as the formation of a notochord, a dorsal nerve cord, and paired pharyngeal arches at early stages.

Regarding the production of egg and sperm cells, fish and mammals do produce these gametes that need to join in fertilization but with some variations:

- Fish: Most fish species lay eggs externally in the water, where they are subsequently fertilized by sperm released by male fish over the eggs.
- Mammals: Mammals, including humans, produce internal fertilization. In mammals, including aquatic mammals like dolphins and whales, both male and female individuals produce egg and sperm cells. The sperm cells are typically transferred into the female reproductive system, where fertilization occurs internally.

While there are differences in the reproductive strategies between fish and mammals, the fact that they both produce egg and sperm cells for fertilization supports the idea that they share a common ancestor with reproductive capabilities.