Meaning: The quote you've provided is from Ernst Haeckel, a prominent German biologist, naturalist, philosopher, physician, professor, and artist who lived in the 19th and early 20th centuries. Haeckel is perhaps best known for his work in evolutionary biology and for coining the terms "ecology" and "stem cell." He was a staunch supporter of Charles Darwin's theory of evolution and made significant contributions to the fields of zoology and evolutionary theory.

In the quote, Haeckel touches upon two fundamental concepts in evolutionary science: heredity and adaptation. These concepts are central to the understanding of how species change over time and how new species emerge. Haeckel's assertion that these two branches of evolutionary science are closely connected reflects his belief in the interplay between genetic inheritance and the environment in shaping the characteristics of organisms.

Heredity refers to the passing on of traits from parents to offspring. This process is governed by the transmission of genetic information from one generation to the next. Through the mechanisms of genetic variation, mutation, and recombination, the genetic makeup of a population can change over time, leading to the emergence of new traits and characteristics within a species.

Adaptation, on the other hand, refers to the process by which organisms evolve traits that enhance their survival and reproductive success in a given environment. This can occur through natural selection, where individuals with advantageous traits are more likely to survive and pass on their genes to the next generation. Over time, this can lead to the accumulation of traits that are well-suited to the specific environmental conditions in which a species lives.

Haeckel's assertion that heredity and adaptation are in a "close causal connection" reflects his understanding of the reciprocal relationship between these two processes. As organisms inherit genetic material from their ancestors, they also inherit a set of potential traits that may be subject to natural selection in their environment. The traits that are most beneficial for survival and reproduction are more likely to be passed on to future generations, leading to a continual process of adaptation and evolution.

Haeckel's perspective on the close connection between heredity and adaptation aligns with the modern understanding of evolutionary biology, which emphasizes the complex interplay between genetic inheritance and environmental factors in shaping the diversity of life on Earth. This perspective has been supported by a wealth of empirical evidence from fields such as genetics, ecology, and paleontology, and continues to be a foundational concept in the study of evolution.

In conclusion, Ernst Haeckel's quote highlights the intertwined nature of heredity and adaptation in the evolutionary process. By recognizing the interplay between genetic inheritance and environmental pressures, Haeckel contributed to our understanding of how species change and diversify over time. His insights have continued to influence the field of evolutionary science and serve as a reminder of the intricate mechanisms that drive the evolution of life on our planet.

In summary, Haeckel's quote encapsulates the fundamental connection between heredity and adaptation in the process of evolution, reflecting his deep understanding of the reciprocal relationship between these two branches of evolutionary science.